choose, install, test & service brakes. Disc- & drum-brake sign. Brake materials for racing or street. Air cooling & water ceding. Proportioning valves & balance bar Practical da'ta & formulas.
Fred Puhn
HPBooks@
11ArlDBOOK Fred Puhn Registered Professional Fred Puhn Engineer Registered Professional Engineer
I
3
3 4 1. 2. 1. 2. 3. 4.
Corvette rotor-ano-caliper assembly by Girlock, modified·for racing by Tilton Engineering. Neal Products brake-pedal , balance-bar, bracket & dual master-cylinder assembly ; Airheart master Corvette rotor-and-caliper for racing Engineering. cylinders shown. ·' . _ _assembly _ . . by - Girlock, 'modifled . - by Tilton -Neal Products brake-pedal, balance-bar, & dual master-cylinder assembly; Airheart master Tempilaq temperature-sensing paintfrornbracket Big"Three Industries; cylinders shown. Alston proportioning valve. .... 3. Tempilaq temperature-sensing paint from Big-Three Industries. 4. Alston proportioning valve.
Contents 11 2 3 3 4 5 6 6 7 7 8 8 9 9 10 10 11 11 11 22
Introduction ............................................ 33 Introduction ............................................ Basics................................................. Basics ................................................. 44 Drum Drum Brakes Brakes .......................................... .......................................... 1155 ........................................... 23 Disc Disc Brakes Brakes ........................................... 23 Friction Friction Material Material ....................................... ....................................... 34 34 Hydraulic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 42 Hydraulic Systems Systems .... ..................................... 42 Brake Brake Pedals Pedals & & Linkages Linkages ............................... ............................... 66 66 Power Assist .......................................... .......................................... 77 77 Other Types Types of Brakes Brakes ................................. ................................. 82 82 HighPerformance Brakes High-Performance Brakes .............................. .............................. 88 88 Testing Testing ............................................. ............................................. 104 104 ........................................ 1121 Maintenance Maintenance ........................................ 21 Modifications........................................ Modifications ........................................ 1 37 37 Trouble-Shooting Guide .............................. .............................. 166 1 66 Suppliers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 Suppliers List. List ........................................ 169 69 Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 71 Reference Tables ..................................... 71 Index ............................................... 174 174
...............................................
THANKS Thanks to the many brake brake suppliers and and experts experts who helped helped with technical information and Tilton Engineering, Bill Bill Neal Neal of Neal Neal and photographs. photographs. Special Special thanks to Mac Tilton of Tilton Products, and John Moore of AP Racing Racing for their personal contributions. Products, cohtributions. Thanks also to Carroll Smith Carroll Smith of Carroll Carroll Smith Consulting for helpful helpful suggestions given given after reading reading the finished manuscript. Special thanks to Garrett Van Camp, Camp, Van Camp Racing Racing Enterprises, Inc., 25192 Maplebrooke, Southfield, MI MI 48034. His His heroic efforts and and great technical knowledge gained Ford Motor brake-design engineer and and race-car brake-design gained over the years as a Ford made a significant contribution to the content and completeness of this book. consultant made book. It could could not have been been this quality without him. Thanks Garrett.
NOTICE: in this book is true and complete to the best of our knowledge. All NOTICE: The information contained in guarantees on the part of the author or recommendations on parts and procedures procedures are made without any guaranteeson the quality of parts, materials and methods are beyond control, author and HPBooks. Because thequality beyond our control, publisher disclaim all liability incurred in connection with the use of this information. information. SAE.; Senior Publisher: Rick Bailey; Editor: Randy Summerlin; Editorial Editorial Director: Monroe, P.E., Publisher: Bailey; Executive Editor: Director: Tom Monroe, P.E., S.A.E.; Editor: Don Burton; Editor: Ron Ron Sessions, Sessions, A.S.A.E.; A.S.A.E.; Art Director: Director: Don Burton; Book Design: Design: Paul Fitzgerald; Fitzgerald; Production Production Coordinator: Coordinator: B. Narducci; Coatsworth; Typography: Typography: Michelle Michelle Carter; Carter; Director of Manufacturing: Manufacturing: Anthony B. Narducci; Photos: Photos: Fred Fred Cindy J. Coatsworth; Puhn, Bill Keller Puhn, others noted; noted; Cover Photo: Photo: Bill
Published by HPBooks A Division of HPBooks, Inc. P.O. 50 P.O. Box 5367, 5367, Tucson, A2 AZ 85703 6021888-21 602/888-2150 0-89586-232-8 Library of Congress Catalog Number 84-62610 84-62610 ISBN 0-89586-232-8 Inc. Printed in U.S.A. U.S.A. ©1985 HPBooks, HPBooks, Inc. 01985 2nd Printing Printing 2
Introduction
When driving down a long hill on a crowded freeway, a situation can occur that demands good brakes. Many of the cars in this photo are going over 55 mph . If an emergency were to happen, the resulting chain-reaction braking would result in some drivers locking the wheels.
When driving down a long hill on a crowded freeway, a situation can occur that demands good brakes. Many of the cars in this photo are Most of55usmph. onlyIf an think about were brakes problems, too. chain-reaction braking would result in some drivers locking the wheels. going over emergency to happen, the resulting
when a panic stop occurs ahead in trafof we us only think about brakes ficMost and all see are brakelights and when a panic stop occurs ahead trafthe undersides of cars. Theseinnearfic and all weillustrate see are brakelights and emergencies how important the undersides of safety. cars. These brakes are to our Brakesnearare emergencies illustrate important, also a vital part of highhow performance brakes are can to our safety. Brakes are as any racer tell you . also a vital part of high performance, Because everyone wants higher peras any racerand cansafety, tell you. formance brakes deserve a Because wants pergreat deal everyone of attention. Wehigher not only formance and safety, brakes deserve want our car to go fast , but it shoulda great dealquickly of attention. We not also stop and safely. Anyonly car want powerful our car toand go fast, but it should with consistent brakes also stopconfidence quickly andin safely. Any car instills the driver. It with powerful and consistent brakes also increases driving pleasure. Bad instills confidence brakes are terrifying. in the driver. It also increases driving If racing is your game,pleasure. you needBad to brakes are terrifying. know more about brakes than the If racing is your game, what you need to casual driver. No matter type of know more about brakes than the racing you do, brake performance is casual driver.racing NO matter type of vital. Road is mostwhat demanding racing you do, brake drag performance is on brakes, although racing and vital. Road racing is most demanding oval-track events have special
on brakes, although drag racing and oval-track events have special
I talk about brakes as a system. This
problems, too. lines, pedals, levers includes fluid, I talk about a system. This and linkages, brakes as wellas as the brake includes fluid, lines, pedals, levers units. Wheels, bodywork and even and linkages, as well as the brake the frame structure become a part of units. Wheels, bodywork and affect even the brake system when they the frame structure This become a part of brake performance. book covers the brake system when they affect each part of the system and how it rebraketoperformance. book covers lates overall brakeThis performance. It each help part of andofhow it rewill in the the system selection compolates braketo performance. It nents toif overall you prefer design a brake will help in the selection of composystem. nents yousection prefer of to the design a brake The iffirst book deals system.particular parts of a brake with The first the book deals system. Thesection secondofsection, starting with particular parts of a brake with Chapter 9, describes how to system. second starting design , The install, test,section, maintain and with 9, system describesfor how to modifyChapter a brake racing design, install, test, maintain and applications. Race-car concepts also modify toa brake system for racing apply high-performance road concepts applications. vehiCles. I alsoace-bar note where there also are apply to differences high-performance road important between racing vehicles. I also note where t'here are and road use . important differences between racing and road use.
Braking is essential in winning races. These stock cars are competing on a road course-the severe for automoBraking is most essential in duty winning races. tive brakes. cars Notice thea right aresmoke from On road front tire on most car that's braking hard in the course-the severe duty for automocorner. tive brakes. Notice smoke from the right
front tire on car that's braking hard in the corner.
3
Basics
I
Good brakes are essential to overall vehicle performance. Even though engine performance, suspension and body aerodynamics approach perfection, race cars, such as this GTP Corvette, will not be competitive without good brakes. Photo by Tom Monroe.
Good brakes are essential to overall vehicle performance. Even though engine performance, suspension and body aerodynamics approach perfection, race cars, such as this GTP Corvette, will not be competitive goodtobrakes. by Tomthe Monroe. Brake systems are without designed do Photo brakes, friction materials rub
Most production sedans have drum brakes on the rear and disc brakes on the front. Drum brakes are sedans preferred on drum rear wheels Most ~roduction have brakes because a parking brake is easily adapted on the rear and disc brakes on the front,. This drum on the rear of awheels 2-ton Drumlarge brakes are ispreferred on rear sedan. a parking brake is easily adapted. because ~
-
- -
This large drum is on the rear of a 2-ton sedan.
4
one thing-stop the vehicle. Sounds Brake designed to do easy, but systems problemsare start when brakes one the from vehicle. mustthing-stop stop a vehicle highSounds speed easy, but problems startdowhen brakes in a short distance, and it over and must stop a vehicle from high speed over again . We expect no failures or in distance,All andbrake do it over and lossa short of control. systems over again. expectThe no failures or should stop We a vehicle. difference loss of control. All brake systems between a good system and a bad one should stop ita vehicle. The difference is how well will perform under the between a good system and a bad one most adverse conditions. is All howvehicles well it will the haveperform brakes, under and they most adverse conditions. always did . Ever since m an discovered vehicles have itbrakes, and they theAll wheel , stopping was a problem. always did. Ever since discovered Carts, wagons and man carriages had the wheel, stopping it was a problem. brakes, usually simple blocks rubbing Carts, wagons carriagesa basic had on a wheel. This and established brakes, usually simple blocks rubbing that has yet to change, even with the on a wheel. This established a basic most sophisticated brake system: All that hasuse yetfriction to change, with the brakes to stopeven the vehicle.
most sophisticated brake system: All brakes usefiiction BRAKE TYPES to stop the vehicle.
When two parts rub together, the
BRAKE resulting TYPES friction generates heat. In When two parts rub together, the resulting friction generates heat. In
against metal surfaces . Different types brakes, friction materials of brakes the are arranged differently,rub or against metal surfaces. Different use different methods of forcing types rubof brakes are together. arranged There differently, or are also bing surfaces use different methods of forcing rubdifferences in dissipating heat once it bing surfaces together. There are also is generated. differences in dissipating heat once or it Either drum brakes or disc brakes, generated. of the two, are used on ais combination Either drum brakes disc brakes, most vehicles. Theseorterms refer or to ahow combination of the two, are usedand on friction surfaces are designed most vehicles. These terms refer to configured. how friction surfaces are and Drum Brakes-All eadesigned rly vehicles configured. used drum bra kes ; many of today's Drum early vehicles vehicles Brakes-All still do . The rubbing surface used drum brakes;called many of today's drum , is a metal cylinder a brake vehiclesmade still do. Theiron rubbing surface usually of cast . is aEarly metal drum cylinderbrakes called awere brake drum, exterusually made ofsurface cast iron. nal-rubbing was outside of brakes internal were extertheEarly drum.drum More modern drum nal-rubbing surface was outside of brakes have the rubbing surface inside the drum. More modern internal drum the drum. There are shoes inside the brakes with have frict the ion rubbing surface inside. drum material attached the drum. are isshoes inside This frictionThere material called lining.the It
drum with friction material attached. This friction material is called lining. It
..
Honda disc brake is typical of front brakes on small sedans. Exposed rubbing I surface of disc brake aids cooling. Honda disc brake is typical of front brakes
Iused
used on small sedans. Exposed rubbing surface of disc brake aids cooling.
is designed to rub against the drum without burning, melting or wearing is designed rub are against theagainst drum The to shoes forced rapidly. without burning, melting or wearing the inside surface of the drum when rapidly. Thepushes shoes are the driver the forced brake against pedal, the insidefriction surfacebetween of the drum when the lining creating the driver pushes the brake pedal, and the drum surface . Drum brakes creating friction between in Chapter 2. the lining are covered and the drum surface. Drum brakes Disc Brakes - A modern brake are covered in Chapter 2. design is the disc brake. The drum is Disc modern replacedBrakes-A by a flat metal disc, or brake roto;; design is the disc brake. The drum is with a rubbing surface on each side. replaced by a flat metal disc, or rotot; The rotor is usually made of cast iron. with a rubbing surface on each side. Friction materials are inside a caliper, The rotor is usually made of cast iron. which surrounds the rotor. Disc-brake Friction materials are inside caliper, friction material-one on eacha side of which surrounds the rotor. Disc-brake the rotor- is called a brake pad, puck friction each side of or lining.material-one This caliper on is designed to the rotor-is a brake pad,ofpuck clamp the padscalled against the sides the or lining. This caliper designed to rotor to create friction.is Disc brakes clamp the pads against 3. the sides of the are covered in Chapter
Earliest automotive brakes were drum type with the rubbing surface on the outside of the drum. Because brakes frictionwere material surEarliest automotive drum type rounds outside of theon drum, coolwith thethe rubbing surface the little outside of ing air contacts the friction hot rubbing surface. the drum. Because material surExternalthe drum brakes are drum, simplelittle and cooleasy rounds outside of the to but have coolingsurface. ability. ingservice, air contacts thehorrible hot rubbing
External drum brakes are simple and easy to service, but have horrible cooling ability.
Finned aluminum drums give better cooling than plain cast iron. Caliper P = Clamping Force on Rotor
p
P
=
Clamping Force on Rotor
Caliper Mounting Bolt -
-
- Axle Centerline
Axle Centerline
rotor to create friction. Disc brakes are covered in Chapter 3.SYSTEM BRAKE-ACTUATING
Wheel Stud
Between the driver's foot and the BRAKE-ACTUATING SYSTEMthat wheel brakes are components Betweenforce the from driver'sthefoot and into the translate driver wheel brakes are components that friction force at the brake-rubbing translate force into surfaces. I callfrom this the thedriver actuating friction force at the brake-rubbing system. This system can be mechanisurfaces. I call this theor aactuating cal, hydraulic , pneumatic combisystem. This system canvehicles be mechanination of these . Future could cal, pneumatic or a combiWhatever the use hydraulic, electric systems. nation these. Future vehicles could type ofof actuating system, the result is use electricWhen systems. Whatever the the same: the driver operates typesystem, of actuating the .result is the brakessystem, are applied the same: When the driver operates Brake Pedal & Linkage-Brake the system, brakes areare applied. pedals and linkages integral parts Brake Pedal & Linkage-Brake
Stud
pedals and linkages are integral parts
Prewar MG used mechanical brakes. Front brakes are operated by cables that flex as the wheels steer mechanical and move up and down. Prewar MG used brakes. Front Finned aluminum drums better brakes are operated by give cables that cooling flex as thanwheels plain cast iron.and move up and down. the steer
~Rotor
-\
Rotor Disc brake operates by clamping rotor between two stationary pads. Rotor turns with the wheel; caliper is mounted to a fixed part of the suspension, usually the spindle or upright. I I
Disc brake operates by clamping rotor between two stationary pads. Rotor turns with the wheel; caliper is mounted t o a fixed part of the suspension, usually the spindle or upright.
of a brake system. The pedal is the familiar lever that the driver pushes of a brake system. pedal the fawith his foot to The apply the is brakes. miliar lever that the driver pushes Regardless of the type of brakewith his system foot toused, apply the applicabrakes. actuating system Regardless the with type the of braketion always ofbegins driver actuating used, system operating system a pedal-or lever applicain rare tion always beginsdesign with determines the driver cases. Brake-pedal operating a pedal-or in rare the leg force required tolever stop the car.
cases. Brake-pedal design determines the leg force required to stop the car.
It is also a factor in determining how solid the brakes feel to the driver. It Trade-offs is also a factor in determining how when designing are made solid brakesLong feel to the driver. brakethe pedals. pedals reduce the Trade-offs are madetowhen pedal force required stop adesigning vehicle. brake pedals. Longpedals pedals have reducelong the However, long pedal force required to stop a vehicle. travel. They can also feel spongy to the However, long pedals long driver. Brake-pedal design have is detailed travel. They6. can also feel spongy to the in Chapter
driver. Brake-pedal design is detailed in Chapter 6 .
5
Although most mechanically actuated brakes are found on antique cars, some are still being used. by APactuated Racing Although most Developed mechanically for useare onfound competition brakes on antiquerally cars,cars, somethis are modern caliper mechanically actuated. still being used. isDeveloped by AP Racing Independent the hydraulically actuated for use on of competition rally cars, this brakes, calipers are used onactuated. the rear modern these caliper is mechanically for high-speed on slick surfaces. Independent of control the hydraulically actuated Photo courtesy AP Racing. brakes, these calipers are used on the rear
for high-speed control on slick surfaces. Photo courtesy AP Racing.
Early race cars had no front brakes. Although this Peugeot was a winner with its advanced high-speed dual-overhead-cam engine, it used cable-operated rear-wheel brakes.
Early race cars had no front brakes. Although this Peugeot was a winner with its advanced high-speed dual-overhead-cam engine, it used cable-operated rear-wheel brakes.
In the '20s, Duesenberg introduced hydraulic brakes with large finned drums . This was probably the firstintroduced road car with In the '209, Duesenberg hyenough horsepower required great draulic brakes with that large finned adrums. improvement in braking. It didroad not car use with flex This was probably the first hoses, but instead ranthat fluidrequired through internal enough horsepower a great passages in the improvement in suspension. braking. I t did not use flex
hoses, but instead ran fluid through internal passages in the suspension.
The brake pedal is connected to a linkage that transfers force to the acThe brake pedal connected to asa tuating system. Thisislinkage can be linkage asthat transfers force to the ac-a simple a push/pull rod operating tuating hydraulic system. This linkage can beOr, as single master cylinder. simple as a push/pull rod operating the linkage may be a complicated, ad-a single master cylinder. Or, justablehydraulic balance-bar system for changthe linkage maybetween be a complicated, ading the balance front and rear justable balance-bar system for changbrakes. Early-design, mechanicaling the balance between front actuating linkage extends all and the rear way brakes. Early-design, mechanicalto the brakes themselves. Brakeactuating linkageis extends all inthemore way linkage design discussed to the brakes themselves. Brakedetail in Chapter 6. linkage designBrakes-The is discussed in more Mechanical simplest detail in Chapter 6. brake-actuating system is a mechaniMechanical Brakes-The simplest cal system. The brake pedal operates brake-actuating system is a mechanicables or rods that apply the brakes cal system. The isbrake pedal operates when the pedal pushed . Early sys-
cables or rods that apply the brakes when the pedal is pushed. Early sys-
6
tems were mechanical and are still used for parking brakes on presenttemsvehicles. were mechanical and are still day The mechanical linkage used fortheparking brakes onin presentmoves shoes outward a drum day vehicles. The mechanical linkagea brake, or clamps the pads against moves the shoes outward in a drum disc-brake rotor. brake, or clamps the pads against Hydraulic Brakes-Modern cars usea disc-brakebrakes. rotor. In a hydraulically achydraulic Hydraulic Brakes-Modern tuated system, the cables or cars rodsuse of hydraulic brakes. In a hydraulically the mechanical system are replaced acby tuated system, or rods of fluid-filled lines the and cables hoses. The brake'the mechanical system are replacedinbya pedal linkage operates a piston fluid-filled linestoand hoses. The master cylinder pressurize thebrake: fluid pedal linkage operates a piston in a inside the lines and hoses. Fluid presmaster cylinder to pressurize the fluid sure in each wheel cylinder forces the inside the lines and hoses.the Fluid presfriction material against drum or sure eachChapter wheel cylinder the rotor.inSee 5 for aforces detailed friction material against the drum or explanation of how a hydraulic system rotor. See Chapter 5 for a detailed works. explanation of how a hydraulic system, Pneumatic Brakes-In a pneumatic works. or air-brake, system the brakes are Pneumatic by Brakes-In a pneumatic, controlled compressed air. Air or air-brake, system the are brakes are generally usedbrakes on large controlled compressed air. Air commercial by vehicles and trucks. An brakes are of generally used on brake large advantage the pneumatic commercial vehicles and trucks. An system is safety. Small leaks cannot advantage of the pneumatic brake cause a total loss of braking because system is safety. supplied Small leaks air is constantly by acannot comcause total stored loss ofinbraking because pressora and large volume. air is constantly suppliedoperation by a comPneumatic brake-system is pressor and stored in large described briefly in Chapter 8. volume.
Pneumatic brake-system operation is described briefly in Chapter 8. BRAKE HISTORY
The earliest brakes were derived BRAKE HISTORY from those used on horse-drawn The earliest derived wagons. As carsbrakes becamewere heavier and from those used on horse-drawn more powerful, these primitive
wagons. As cars became heavier and more powerful, these primitive
brakes soon were improved to the early external- type drum brakes, all brakes soon were improved to the mechanical-actuating systems. with early external-type drum all Early brakes were on brakes, the rear with mechanical-actuating systems. wheels only. The major reason for this Early brakes were on thean rear was the difficulty in designing acwheels only. The major reason for this tuating system on wheels that are was the difficulty designing acsteered. Engineersinavoided the an probtuating system on wheels that are. lem by omitting front-wheel brakes steered. the probAnother Engineers reason foravoided not using front lem by omitting front-wheel brakes was concern that the carbrakes. might Another reason for not usingbrakes front tip over on its nose if front brakesapplied was concern were hard! that the car might tipEarly over external-type on its nose if drum front brakes brakes were applied hard! used a band of friction material outEarly external-type brakes side the drum. This typedrum of brake was used to a band of but friction materialmateouteasy design, the friction side the drum. thehisdrum typefrom of brake was rial prevented cooling. easy to design, but the friction mateAlso, exposed friction materials were rial prevented the drum su bject to dirt, oil from and cooling. water Also, exposed friction materials were contamination. When the brake shoes subject to dirt, oil and water were relocated inside the drum, a contamination. Whenwas the born. brake These shoes modern drum brake were relocated theRenault. drum, a were first used oninside the 1902 modern drumfour-wheel brake was braking born. These Although was were first used on the 1902 Renault. tried early in the 20th century, most Although was early cars hadfour-wheel rear brakes braking only. Then, triedtheearly in the 20thdiscovered century, most in 1920s it was that early hadadded rear brakes front cars brakes greatlyonly. to aThen, car's in the 1920s it was discovered that stopping a bility, and they were judged front brakes added greatly to a car's safe. Four-wheel brake systems soon stopping ability, and they were judged became universal. safe. Four-wheel brake systems systems soon were Mechanicalac tuating became universal. still used on most cars until the late Mechanical-actuating systems came were '20s when hydraulic systems still most cars until late into used use . onMechanical brakesthewere '20s when hydraulic systems came used for auto rac ing long after hydrau-
into use. Mechanical brakes were used for auto racing long after hydrau-
Internal details of early Duesenberg hydraulic drum brake: Notice fluid passages through axle, kingpin and spindle. Sealing was a problem solved by use of flexible hydraulic lines. I
Ieventually
Internal details of early Duesenberg hydraulic drum brake: Notice fluid passages through axle, kingpin and spindle. Sealing was a problem eventually solved by use of flexible hydraulic lines.
.
This little disc brake started it all-first disc brake used on a mass-produced car. Goodyeardiscstarted brakesit were ofThis little Hawley disc brake all-first fered on Crosley Hotshot and Supersports disc brake used on a mass-produced car. roadsters in the early '50s. A were Crosley Goodyear-Hawley disc brakes ofHotshot won theHotshot first Sebring 12-hour fered on Crosley and Supersports endurance in race with these brakes. In later roadsters the early '50s. A Crosley years, they were for small 12-hour sportsHotshot won thepopular first Sebring racing cars.race with these brakes. In later endurance
years, they were popular for small sportsracing cars. were developed for passenlic systems ger cars. The simple mechanical brake lic systems developed system waswere reliable, easy for to passenunderger cars. The simple mechanical brake stand and maintain, and not subject to system was easy that to undersudden loss reliable, of braking could stand not subject happenandto maintain, a hydrau and lic system with toa sudden loss of braking that could failed line or seal. happen to a hydraulic system with After World War II, disc brakesa failed or seal. The first production began line to appear. War 11,wasdisc carAfter with World disc brakes thebrakes 1949 began to appear. The first production Crosley Supersport. Disc brakes were car disc brakes on was the the 1949 usedwithsuccessfully 24Crosley Supersport. Disc brakes hours-of-LeMans-winning Jaguarwere in
used successfully on the 24hours-of-LeMans-winning Jaguar in
Since the mid-'50s, disc brakes have been highly developed for both racing and road use. Companies such as JFZ Engineered Products have taken brake development far beyond the early concept. Rotors, brake-mounting haveand all benefited Since thedisc-brake mid-'50s, disc brakes havepads beenand highly developed forhardware both racing road use. from rigors of faster Photo courtesy Engineered Products. JFZ cars. Engineered Products.IFZ have taken brake development far beyond Companies such as race
the early disc-brake concept. Rotors, pads and brake-mounting hardware have all benefited from fasterbrakes race cars. Photo courtesy JFZ Engineered the rigors '50s. ofDisc soon became design, there Products. have been many impor-
popular on many race cars. Indianathe '50s. Disc used brakes became polis 500 cars discsoon brakes early popular on many race cars. Indianatoo, but they had little effect on the polis 500 of carsraces usedondisc early outcome thisbrakes fast track. too, but had little effect the Only at they LeMans, where carsonmust outcome of races on this fast track. decelerate from 180 to 30 mph every Only at do LeMans, lap, and it for 24where hours,cars weremust disc to limit. 30 mph every decelerate fromto 180 brakes tested their Even in lap, anddrum do it brakes for 24 hours, racing, are stillwere useddisc in brakes classes, tested tobut their Evenrace in certain mostlimit. modern racing, brakes are still used in cars use drum disc brakes. certain classes, but most modern race the basic changes in brake Beyond
cars use disc brakes. Beyond the basic changes in brake
tant improvements. Brake systems
design, there havesafe; beenand many importoday are very complete tant improvements. Brake systems system failure occurs rarely. Modern today are brakes can very go forsafe; yearsand withcomplete little or system failure in occurs rarely.use Modern no attention highway , but brakes years with or therein can lies go a for problem: Whenlittle really no attention in highway use, but needed , performance may be marginal therein a problem: When because lies of inattention . This bookreally will needed, may be marginal help you performance keep that from happening. because of inattention. This book will help you keep& that from happening. FRICTION ENERGY Friction is resistance to sliding . Any FRICTION & ENERGY Friction is resistance to sliding. Any 7
Type of Energy
..
Friction Force Friction Friction between the box and floor is what Force makes the box difficult to slide. If box weight frictionthe between floor and Friction or between box andthe floor is what box increases, sodifficult must theto force to slide it. makes the box slide. If box Heat is or developed on slidingthe surfaces as weight friction between floor and box is moved. so must the force to slide it. increases, Heat is developed on sliding surfaces as two isobjects box moved. in contact with and trying
to move relative to each other have two objects in contact and trying friction. It can be high with or low dependto move each other have ing on therelative types ofto surfaces in contact. friction. It can be high or low dependFriction helps keep your feet from ing o n the in contact. sliding outtypes fromof surfaces under you. When Friction helps keep your feet isfrom you are standing on ice, friction low sliding fromto prevent under you. When and it is out difficult slipping. you standing on ice, If are two surfaces in friction contactis low are and it is difficult to prevent sliding, the friction createsslipping. heat. You two surfaces contact your are canIf confirm this byin rubbing
sliding, the friction creates heat. You can confirm this by rubbing your KINETIC ENERGY OF ROTATION
KINETIC ENERGYan object with Strictly speaking, OF ROTATION kinetic energy can be either moving Strictly speaking, an object with in a straight line or rotating about its kinetic energyofcan be either own center gravity (CG).moving In a in a straightcar, line or rotating about its speeding kinetic energy is own gravity a mostlycenter in the of moving car. (CG). UnlessInthe speeding car, down kinetic is car is spinning the energy road, less mostly in the moving Unless the than 10% of the total car. kinetic energy car is spinning downparts the of road, is stored in rotating the less car. than 10%parts of theinclude total kinetic energy Rotating tires, wheels, is storedengine in rotating parts line. of the car. brakes, and drive Addi~ Rotating partsenergy include tires, in wheels, tional kinetic stored these brakes, engine and drive line. Addirotating parts must be absorbed in tional kinetic energy stored these the brakes. However, to makeincalcurotating simpler, parts must be absorbed in lations I ignore the small the brakes. However, to make calcuamount of kinetic energy stored in lations simpler, I ignore the small rotating parts. amount of kinetic in At high speed, energy kineticstored energy rotatinginparts. stored the rotating tire-and-wheel At high speed, kinetic energy assemblies increases significantly. stored If you in hitthe therotating brakestire-and-wheel hard at high assemblies increases significantly. speed, the rotating parts must be If you hitbefore the brakes hardcan at high stopped the wheel lock speed, the Itrotating partsand must be and slide. takes time pedal stopped the rotating wheel can lock effort to before stop this weight, and slide. takes time slow and at pedal even if the Itcar doesn't all. effort to stop this rotating weight, Consequently, it is more difficult to even if the car doesn't slow at all. lock the wheels when traveling at Consequently, it is Ironically, more difficultthis to higher speeds. lock the wheels traveling makes a car saferwhen at high speed at if higher speeds. the driver panics Ironically, and hits this the makes a safer at highinspeed brakes toocar hard. However, racing,if the driver panics it increases pedal and effort hits as the brakestries too hard. However, in racing, driver to reach the traction limit it the increases pedal effort as the of tires. driver tries to reach the traction limit of the tires. 8
Example
Heat Energy stored ina hot brake rotor. Type of Energy Example Sound Noise from exhaust. Heat Energy stored in a hot brake rotor. Ught Light from headlights. Sound Noise exhaust. Stored Mechanical Energyfrom stored in a compressed coil spring. Light Light from headlights. Energy in agallon of gasoline. Chemical Stored Mechanical Energy stored a compressed spring. Electrical Current from a in battery turning a coil starter. Chemical Energy in a energy gallon of Radiation Microwave in gasoline. a microwave oven. Electrical Current from a ina battery turning a starter. Kinetic Energy stored speeding bullet. Radiation Microwave energy in a microwave oven. Kinetic Energy stored initacan't speeding bullet. Energy can be changed from one form to another, but be created or destroyed. Here are some different forms of energy. Most forms are transformed into heat after energy does itscan useful work. Energy be changed from one form to another, but it can't be created or destroyed. Here are some different forms of energy. Most forms are transformed into heat after energy does useful work. handsitstogether rapidly back and forth. varies as the square of speed. To calcu-
You can feel the warmth. This friction hands together back and can help warm rapidly your hands on aforth. cold You can feel the warmth. This friction day. In brakes, friction is used to can help warm handsofo ncreating a cold create heat. Theyour process day. In brakes, heat stops the car. friction is used to create heat. T h eofprocess creating The amount frictionof between heat stops the car. two rubbing surfaces depends on the T h e amount of friction between materials and their roughness. The two rubbing surfacesis depends amount of friction describedo nbythea materials called and their e number the roughness. coefficient T hof amount of friction is described by a friction. A high number means a large number ofcalled the a coefficient of amount friction; low number A high number means a large .friction. means a small amount of friction. amount of about friction; a low Read more friction at thenumber beginmeans a small amount of friction. ning of Chapter 4. Read moreisabout frictionto atdothe beginEnergy the ability work. A ning of Chapter 4. moving car develops energy. The Energy is the ability to doenergy work. A faster it moves, the more it moving car energy. The develops. Thisdevelops type of energy is called faster moves, thespeed moreis energy kinetic it energy. When doubled,it develops. This type of energy is called four times the kinetic energy is kinetic energy. W h e n speed is doubled, developed. That is, kinetic energy
four times the kinetic energy is developed. That is, kinetic energy TEMPERATURE & HEAT
The difference between temperature TEMPERATURE & HEAT We all and heat may be confusing. The familiar difference between temperature are with temperature, meaand heat confusing. We all sured in may eitherbedegrees Farenheit are familiar with temperature, (F) or degrees centigrade (Cl. measured Farenheit Heat inis either a formdegrees of energy. When (F) or isdegrees (C).itstemheat added centigrade to a material, Heat is arises; form of energy. When perature when heat is heat is added a material, its temremoved, its totemperature drops. perature rises; when heat of is Thus, temperature is the effect removed, its temperature drops. adding or subtracting heat energy. Thus, ,Itemperature is the effect When say something heats up, ofI addingheat or subtracting mean is added. heat Whenenergy. I say When I say something heats up, InI cools off, I mean heat is removed. mean case, heat is When of I say either theadded. temperature the cools off, I mean heat is removed. In object changes. either case, the temperature the I measure kinetic energy inoffootobject changes. pounds (It-I b). However, it could be I measure footmeasured in kinetic British energy ThermalinUnits pounds it could be (BTU's), (ft-lb). just asHowever, engineers do .. One measured British Units BTU is the in amount of Thermal heat it takes to (BTU's), as engineers One raise the just temperature of onedo. pound BTU IS theby amount of heat Farenheit. it takes to of water one degree raise BTU the temperature oneIt-Ib pound One is equal to of778 of of waterorbyone oneft-Ib degree Farenheit. energy, equals 0.0013 One is equal to 778 offt-lb of BTU. BTU Although one pound water energy, or one ft-lb equals 0.0013 BTU. Although one pound of water
late kinetic energy of a car, use the folvaries as the square of speed. To calculowing formula:
late kinetic energy ofS2a car, use the folWc lowing Kinetic formula: energy = - -
29.9 W,S2 = Kinetic energy in foot-pounds (It-Ib) 29.9 W = Weight of Car in pounds (Ib) in c= foot-pounds S Speed of(ft-lb) car in miles per hour = Weight of Car in pounds (Ib) W, (mph) S = Speed of car in miles per hour Converting Energy-The first law of (mph)
thermodynamics says: Energy can Converting law of never be Energy-The created nor first destroyed. thermodynamics can However, energy says: can beEnergy converted neveronebeform created nor destroyed. from to another. However, canenergy be converted Differentenergy forms of are heat, from o n e form to another. sound, light, stored mechanical, Different electrical forms of energy heat, chemical, and are radiated. sound, electrical light, stored mechanical, Stored energy in a battery chemical, will convert electrical energy intoand heatradiated. or light Stored electrical energy by connecting the batteryin toa battery a light will into heat or light bulb.convert Stored energy mechanical energy in a by connecting battery to to kinetic a light spring can be the converted
bulb. Stored mechanical energy in a spring can be converted to kinetic changes temperature one degree F when one BTU of heat is added, F changes temperature one react degree other materials do not the when of heat change is added, sallle. one TheirBTU temperature is other materials do BTU not of react different when one heatthe is same. Their temperature change is added. different when one BTU of heat is The relationship between temadded. perature change and heat-energy The relationship temchange is governed between by a property perature change andEach heat-energy ca ll1ed specific heat. material change is governed by aasproperty has its own specific heat shown called specific heat. in Each for typical materials the material accomhas its own specific heatheat as shown panying table. Specific is the for typical materials thepound accomtemperature rise for in one of panying table. is the material when Specific one BTU heat of heat is temperature rise forspecific one pound added. A material's heat of is material when one of heat is very important to aBTU brake-design added. A material's spec~ficheat is engineer for calculating brakevery important to a temperature change for brake-design each stop. engineer for calculating Ideally, brakes should be brakemade temperature change eachspecific stop. from materials with for a high Ideally, should inbea made heat. This brakes would result small from materials high specific temperature r isewith for aa given amount heat.kinetic This would a small of energyresult put ininto the temperature rise for a given amount brakes. A small temperatur e rise of kinetic energywouput intofewer the means the brakes l1d have brakes. A small temperature rise problems. means the brakes would have fewer problems.
MELTING TEMPERATURE Material
Degrees F Degrees C MELTING TE'MPERATURE
Water Material Beryllium - pure Water Beryllium-QMV Beryllium-pure Magnesium-AZ 31 B-H24 Beryllium-QMV Aluminum-6061- T6 Magnesium-AZ 31 6-H24 Aluminum -2024-T3 Aluminum-6061 -T6 Carbon-pure Aluminum-2024-T3 Titanium-pure Carbonpure120VCA Titanium-B Titanium-pure Magnesium-HK 31 A-H24 Titanium-B 120VCA Stainless Steel-304 Magnesium-HK 31A-H24 Cast Iron Stainless Steel-304 Steel-C1020 Cast Iron Copper-pure
Degrees F
32 2340 32 2340 2340 1100 2340 1080 1100 940 1080 6700 940 3070 6700 3100 3070 1100 31 00 2600 1100 2750 2600 2750 2750 1980
Steel-C1020
0 1282 0 1282 1282 593 1282 582 593 504 582 3704 504 1688 3704 1704 1688 593 1704 1427 593 1510 1427 1510 151 0 1082
2750
1510
Degrees C
SPECIFIC HEAT SPECIFIC BTU/1 b/F
HEAT 1.00 BTU/l b/F
0.52 1.oo 045 0.52 0.25 0.45 0 .23 0.25 0.23 0.23 0 .16 0.23 0.14 0.1 6 0 .13 0.1 4 0 .13 0.1 3 0 .12 0.1 3 0.10 0.1 2 0.10 0.10 0 .09
0.10
Specific heats of various materials are1980 listed from the highest heat is Copper-pure 1082 to lowest. Specific 0.09 amount of heat energy required to raise one pound of material by one degree Fahrenheit . Material heats with highest specific heat are is not necessarily besttoforlowest. brakes. To be a good Specific of various materials listed from the the highest Specific heat is brake material, must withstand temperature, conduct heat and have a good amount of heat it energy required tohigh raise one pound of material by rapidly one degree Fahrenheit. rubbing surface. Material with highest specific heat is not necessarily the best for brakes. To be a good
brake material, it must withstand high temperature, conduct heat rapidly and have a good rubbing surface. energy when a wind-up toy car is released. Chemical energy stored in energy whenis converted a wind-up int toy car is gunpowder o sound, released. Chemical energy heat and kinetic energy when stored ignited in . gunpowder is converted intoroad sound, down the has A car moving heat andenergy. kinetic energy kinetic To stopwhen the ignited. car, you A car moving downkinetic the road has must dispose of this energy. kinetic stop bethedestroyed, car, you Becauseenergy. energy To cannot must of thistokinetic it mustdispose be converted anotherenergy. form. Because energy cannot be be destroyed, This kinetic energy could convertit be converted to another edmust into any of the forms listed onform. page This kinetic energy could convert8, but conversion to heat isbe easiest. By ed into anyfriction of the forms listed on page forcing material against 8, but conversion heatis iscreated easiest.and By drums or rotors , to heat forcing friction material against the car slows . If the brakes or tires drums, orsome rotors, heat energy is created and squeal sound is also the car slows. If the brakes or tires produced, but the amount of kinetic squeal, some sound energy isis small also energy converted to sound produced, tobut theenergy. amount of kinetic compared heat energy soundcaris using small If youconverted had an to electric compared to heat energy. batteries, you could brake the car by If you had electric car inusing converting the an electric motor to a batteries, you brake car by generator. Thiscould could be the done by converting the motor into switching the electric connections. Thea generator. could be done by motion of This the car would turn the switching putting the connections. generator, electric energy The into motion of the the the batteries. Thecarcarwould would turn s low begenerator, putting electric energy into cause power- kinetic energy in this the batteries. The car would slowelecbegenerator. Some case - turns the cause this tric carspower-kinetic maintain their energy battery in charge case-turns generator. Somecalled elecby using thistheform of braking tric cars maintain their battery charge regenerative braking. byItusing of braking wouldthis be form wonderful if fuel called could regeneralive braking. be put in the gas tank by hitting the It would be 'twonderful fuelallcould brakes. It can , however,if so that be put in the gas tank by hitting the kinetic energy is lost. On the other brakes.if Ityou can't, so allor that hand, drivehowever, more slowly ankinetic every energystop, is lost. theuseother ticipate you On could the hand, if you drive more slowly anbrakes less and, th us , conserveorfuel. ticipate every stop, you could use the Try this while driving to work. The brakes less and, conserve fuel. fuel energy used thus, to move the car is Try in thisheat while driving work. lost energy eachtotime youThe hit
fuel energy used to move the car is lost in heat energy each time you hit
the brakes. By minimizing braking , you increase mileage. theIf brakes. By the minimizing braking, you slow car without using you mileage. the increase brakes, the kinetic energy can be If you into slow two the different car without using changed forms. If the brakes, the kinetic energy can be you are driving on a flat road and take changed twothrottle, differenttheforms. If your foot into off the car will you driving on a flat road take slow.are Kinetic energy is lost in and air drag, your foot(heat) off the throttle, theand cardrive will friction in the engine slow. Kinetic energy is lost in air drag, line, and rolling resistance of the tires. friction (heat) in items the engine andkinetic drive Because these get hot, line, and rolling resistance of the tires. energy is converted into heat. Because these items slowing get hot, kinetic However, because takes energy longer andis theconverted items beinginto heatedheat. are However, slowing takes much larger,because drive-line components longer anddon't the items area nd tires reachbeing the heated high tem" much larger, drive-line components peratures achieved by the brakes. But, and tires isdon't the heat therereach . Put the yourhigh handtemon peratures by run the on brakes. But, your tires achieved after a fast the highthe heat is there. Put feel your hand the on way and see how they . Touch your tires after a fast run on the highrear-axle housing and the transway and. see how they feel. Touch mission A portion of the power of the the rear-axle and the transengine washousing lost supplying the energy mission. A portion to heat those parts. of the power of the engine was lost The other waysupplying yo u can the slowenergy a car to heat those parts. without the brakes is by coasting up a The other way you can toslow car hill. The car loses energy draga the without the brakes is by coasting up same as on a fl at road , but it slowsa hill. TheThe car kinetic loses energy drag the quicker. energyto is convertsame as on a flat road, but ed into potential energy as ittheslows car quicker.the The kinetic energy is convertclimbs hill. as another the car edPotential into potetltiol energyetiel,gy is just climbs the hill. form of stored mechanical energy. It Potential when energy is justis raised another a weight to is increased of stored greater height.mechanical As the carenergy. climbs Ita aform is increased a weight is raised to hill, some ofwhen its kinetic energy is conaverted greater height. As the car climbs to potential energy. This pote n-a hill, energy some ofcan its be kinetic energy is contial changed back into verted potential energy. kine tic to energy by all ow in gThis the potencar to tial energy back coast down can the be hillchanged with the e nginto ine kinetic energy by allowing the car of to shut off. The speed at the bottom coasthilldown hill than with the the original engine the will the be less
shut off. The speed at the bottom of the hill will be less than the original
Car parked at top of hill has zero kinetic energy. However, its position at top of the hill gives it potential Car parked at top ofenergy" hill hasThis zeropotential kinetic energy is changeditsinto kinetic as energy. However, position at energy top of the car gives coastsit down hill. energy. This potential hill potential
energy is changed into kinetic energy as car coasts down hill.
After coasting half way down the hill, car has lost half of its potential energy, but has gainedcoasting kinetic half energy. energy inAfter way Kinetic down the hill, car creases as car increases. has lost half of speed its potential energy, but has
gained kinetic energy. Kinetic energy increases as car speed increases.
All potential energy of coasting car is converted into kinetic energy at bottom of the hill where carenergy reaches speed and All potential of maximum coasting car is conkinetic verted energy. into kinetic energy at bottom of the
hill where car reaches maximum speed and
speed kinetic when energy.you began to coast up the hill because some energy is lost in fricspeed when yougoing beganuptothe coast the tion and drag hill,upplus hill energy becauselost some energy losthill. in fricthe going downisthe
tion and drag going up the hill, plus the energy lost going down the hill. 9
Tempera ture (OF)
Rubbing Surface
Temperature (" F)
Brakes Re leased
/
Temper at ure of Brakes Released
Rubbing Surface of Drum or Rotor Temperature of
Rubbing Surface
Interior of Rotor _ Materi al
Interior of Rotor Material
,/ '\.. "
Te mpe rature of I nterior of Drum or Rotorof Temperature Mater ia of l Interior
In te rior of Drum Material Interior
~
Cross Section
of Drum
Drum or Rotor T s L---__~-------------------------Time of Stop
Rotor Cross Section Rotor
%
Rubbing Surface
Drum Cross Section Drum
Cross T m = Maximum temper ature reached at r ubbing surface . Section T a = Average temperature after stop. temperatur e before stop.at rubbing surface. T, s == Starting Maximum temperature reached T, = Average temperature after stop. T, = Starting temperature before stop. During a stop, brake rubbing-surface temperature increases more rapidly than interior temperature of a drum or rotor. Eventually, temperatures equalize after brake is released . Aver-I age brake temperature occurs at a point betweenincreases rubbing - more surface and than interior temperaDuring a stop, brake rubbing-surface temperature rapidly interior temtures before place. temperatures equalize after brake is released. Averperature of amuch drum cooling or rotor.takes Eventually, age brake temperature occurs at a point between rubbing-surface and interior temperatures before much cooling place. in a brake. The problem is that heat is Potential energy is takes measured
units of foot-pounds (ft-Ib). PotentialPotential energy measured in e nergy change equalsis the weight of units of foot-pounds by the Potentialchange in the object mUltiplied (ft-lb). energy equals thecoasts weightup ofa height. change If a 3000-1 b car the objectghmultiplied by the change in 100-ft-hi hill , it gains 300,000 ft-lb height. If a energy. 3000-lbIf al car coasts up isa l this energy of potential 100-ft-high back hill, itinto gains 300,000 ft-lb converted kinetic energy, of potential energy. If all this energy is the speed of the car can be calc ul ated converted back into kinetic 8. Byenergy, changfrom the formula on page the of the carusing can bealgebra, calculatedit ing speed the formula from the formula on page 8. By changcomes out as follows: ing the formula using algebra, it comes outf29.9E: as follows: Speed ~---p in miles per hour We (mph) in miles per hour Ep = Potential energy of car in foot-pounds (ft-Ib) Ep = of car in (Ib) We = Potential Weight ofenergy car in pounds foot-pounds (ft-lb) W, Weight of le car Fo r=our examp , in pounds (Ib) ,.,.."..~";"-~.....,.....,...-,.Speed (29.9)(300 ,000) = 55 h For our=example. 3000 mp . Speed = is much faster th an Obviously, this3000 would happen if you tri ed it with a real this is much faster than car.Obviously, The difference between this would happen if you tried it sample problem and a real with test isa real the car. The difference this and friction. kinetic energy lost in dragbetween samplehot problem and aget realduring test is one the do brakes How kinetic energy lost in drag and friction. stop? -Because the brake-rubbing How hotaredoheated brakes get during it is one imsurfaces by friction, stop? -Because the thebrake-rubbing portant to know what temperature surfaces are stop heated friction, it istemimsurface is after one . P.byhigh portant to know what the temperature perature can cause fade or damage to is after one stop. P. high surface temperature can cause fade or damage to 10
=y
constantly being transferred from the afriction brake.surface The problem is that heat to is of the drum or rotor constantly being transferred from the air and cooler interior metal. This friction surface of surface the drumtemperature or rotor to makes the exact air and to cooler interior metal. This calculate. However, it is difficult makes exact surface temperature ate the average temperaeasy to the calcul difficult calculate. it is ture of a to drum or rotor However, after one stop'. easy to calculate the average temperaThe difference between surface temture of a and drum orrage rotor after one stop. perature ave temperature of a The between surface temn above. drumdifference or rotor is show perature and average temperature of a In calculating the average temperadrum or rotor is shown above. tu re of a drum or rotor, you must In calculating theptions. average temperamake so me ass um This makes ture caoflcualatidrum or rotor, youanswer must on easier and the the make some assumptions. This makes more accurate. Tests have shown that the fo calculation easier and are thevalid: answer llowing assumptions the more accurate. haveenergy shownfrom that • Assume that Tests all heat the following assumptions are valid: the stop fl ows into the drum or rotor. heatteenergy from is anall accura assum ption In Assume fact this that the stop flows into the drum or rotor. because th e frict ion material insulates In is an accurate assumption thefact rest this of the brake from heat and the because the friction material insulates metal drum or rotor is a very good the of the brake from heat and the heatrest conductor. metal drumdrag or rotor is car a very • Assume on the fromgood all heat conductor. sources is zero, including the effects on the car fromand all of Assume air drag,drag rolling resistance sourcesbraking. is zero,This including theassumpeffects is a good engine of rolling100resistance and mph because tionair for drag, stops below engine braking. This is a good assumpair drag is small compared to braking tion for stops below 100 mph because forces. air drag is kinetic small compared braking in • Ignore energy to stored forces. rotating parts of the car. This assumpIgnore kinetic energyof stored in tion and the assumption zero drag rotating parts of the car. This assumption and the assumption of zero drag
The heavier a drum or rotor, the lower its temperature rise during a single stop. Designed for a a3000-lb car lower powered The heavier drum or sports rotor, the its by a 300-HP large temperature rise engine, during a this single stop.drum Deweighs for 22 lb. signed a 3000-lb sports car powered
by a 3 0 0 - H P engine, this large drum weighs 2 2 Ib.
cause errors in opposi te directions. Thus, the error in the brakecause errorscalculation in opposite directions. is sma ll. temperature Thus, error ofinbrakes the during brake• Ignorethecooling temperature calculation is small. stop. Heat flo w into rotor or drum Ignore iscooling of brakes during to coo ling material rapid compared stop. time. Heat flow into rotor or drum material is step rapidiscompared cooling The first to calculatetothe temtime. perature change of the drum or rotor. Theincrease first step to calculate isthe temin istemperature known Any perature change of the drum or rotor. ture rise. Temperatures are as tempera Any increase in temperature is known to energy by always related as tetnperature Temperatures change -not byrise. the absolute valuesare of always or related to . It energy byt is importan energy temperature change-not by the values of to think of this as aabsolute change in energy energy or temperature. It is important in temperature. Temcausing a change change inused energy to think of this as abrake in the is ca by perat ure rise causing a change in temperature. a kinetic-energy reduction inTemthe peraturecar. rise in the brake is caused by moving a For kinetic-energy in the a particular reduction stop, figure the moving car. change in kinetic energy using th e For a onparticular stop,results figurein the the formula page 8. This change kinetic energy using the followinginrelationship: formula on page 8. This results in the = Kinetic energy change in footKe following relationship: pounds = Ks - KAin foot-pounds K c == Kinetic Kinetic energy energybefore change footKs the instop in K, - K, in foot-pounds pounds = foot-pou nds K, = the stop stop in in KA = Kinetic Kinetic energy energy before after the foot-pounds foot-pou nds K, = Kinetic energy after the stop in Obviously, if the car comes to a foot-pounds complete halt , KA is zero . The change if the car comes in Obviously, kinetic energy is used to comptoutea A is of zero. change complete halt, K rise the temperature theThe brake. For in kinetic used use to compute the weight energy of the is brake, only the the temperature rise of and/ the brake. For weight of the drums or rotors. the weight of the brake, use only the The temperature rise must be added weight of the drums and/or of the brake rotors. before to the temperature The rise must the temperature stop to obtain finabe l added brake to the temperature of the brake before temperature . the stop to obtain final brake temperature.
The temperature rise of the brakes is calculated as follows:
The temperature rise of the brakes is calculated as follows:Kc Temperature rise = - - 77.8 KcW B Temperature rise = (F) in degrees Fahrenheit 77.8the W, rotors and W B = Weight of all in degrees Fahrenheit (F) drums in pounds W, = Weight of all the rotors and For inexample, drums pounds let 's compare the
temperature rise in the brakes of a For example, let's compare the 3500-lb sedan stopping from 60 mph temperature rise in rise the of brakes of a to the temperature a 3500-lb 3500-lb sedan stopping fromfrom 60 rnph stock-car's brakes slowing 120 to the temperature rise of a 3500-lb mph to 60 mph. stock-car's from 120 First let'sbrakes figure slowing the temperature rnph to 60 rise for themph. sedan. Assume the brakes First 5let's figure forthea temperature weigh Ib each, total brake rise for the sedan. Assume the the change brakes weight of 20 lb. Calculate weigh 5 Ib each, for a total brake in kinetic energy slowing from 60 weight 20 From Ib. Calculate mph to of stop. page 8, the the change kinetic in kinetic energy car slowing from 60 energy of a moving is: rnph to stop. From page 8, the kinetic W S2
KinetiC energy = _ ccar _ is: energy of a moving 29.9 W,S2 - at 60 mph: Kinetic energy For our sedan= traveling 29.9 KB = (3500 Ib)(60 mph)2/29.9 For our sedan traveling at 60 mph: = 421,000 ft-Ib . K , = (3500 1nph)~/29.9 KB = Kineticlb)(60 energy before stop = 421,000 ft-lb. Kinetic energy after thestop stop = 0, K, = Kinetic energy before
because car now has zero speed. Kineticin energy the =stop = 0, Change kinetic after energy 421,000 because car now has zero speed. ft-Ib. From the above formula temChange perature in risekinetic of the energy brakes is:= 421,000
ft-lb. From the above formula tem. _ (421,000 ft-Ib) perature rise rise of the is: Ib) Temperature - brakes (77.8)(20
Tires on this car have reached their maximum coefficient of friction. Although a car stops faster if the wheels are not locked, most drivers hit the brakes too hard during a panic stop. This being at Goodyear's San Angelo, Texas, test track, is to see howstops tires Tirestest, on this carconducted have reached their maximum coefficient of friction. Although a car react during a paniC are stop.not Photo courtesy Goodyear. faster if the wheels locked, most drivers hit the brakes too hard during a panic stop.
This test, being conducted at Goodyear's San Angelo, Texas, test track, is to see how tires react during a panic stop. Photo courtesy Goodyear.
time, racing on a medium-speed track with short straights might result in time, racing a medium-speed tracka higher brakeon temperatu res than with short straights might result in high-speed track with long straights. higher brake temperatures than Both temperature rise per stop anda high-speed track long to straights. cooling time arewith critical brake Both temperature riseweighing per stopmore and performance. Rotors cooling time are critical to brake than 5 Ib would normally be used on a performance. weighing rotors more 3500-lb race Rotors car. Heavier than 5 Ib normallyrisebeper used on a reduce thewould temperature stop.
3500-lb race car. Heavier rotors
reduce the temperature rise per stop. DECELERATION Deceleration is a measure of how
DECELERATION quickly a car slows. Deceleration (77,i)(20 Decele~.a/ion is a measure of how
(421 000 ft-lb) Temperature rise = = 270F (132C)
For stock car slowing from 120 to 60 mph, change in kinetic energy is:
For stock car slowing from 120 to 60 K = (3500 Ib)(1 20 mph)2 mph, B change 29.9in kinetic energy is: (3500 IbI(l20 = 1,686,000 ft-IbmphI2 K, = 29.9 K = (3500 Ib)(60 mph)2 A = 1,686,000 29.9 ft-lb (3500 lb)(60 = 421,000 ft-Ib rnphI2 K, = 29.9 Kc = KB - KA = 421,000 ft-lb Kc = (1,686,000) - (421,000) Kc = 1,265,000 ft-Ib. KA energy K, == Kinetic 1,265,000 ft-lb.after stop KB = Kinetic energy before stop energy after stop K, = Kc = Kinetic Kinetic-energy change K, Notice = Kinetic energy before stop how much greater this change Kc = Kinetic-energy change in kinetic energy is compared
howEven much greater this to Notice the sedan. though the speed change in was kinetic is compared reduction the energy same 60 mph, the to the reduction sedan. Even thoughatthe speed speed occurring a higher reduction was the same 60 mph, the initial speed resulted in much greater speed reduction occurring a higher energy put into the brakes at . The teminitial speed in much perature rise resulted for the stock car greater in the energy put into the brakes. The temrace is: perature rise for the stock car in the Temperature rise = (1,265,000 ftrace is: Ib)/(77.8)(20Ib) = 813F (434C). Temperature rise = of (1,265,000 ftHowever, because less cooling lb)/(77.8)(20Ib) = 81 3F (434C).
However, because of less cooling
means slowing the car-acceleration
quickly a car itslows. Deceleration means speeding up. means the car-acceleration Both slowing acceleration and deceleration means speedinginit units up. of gravity-g's. are measured Both acceleration and deceleration One g is the force exerted by an object are in units gravity-g's. due measured to gravity at ofthe Earth ' s One g is the exerted by anweighs object surfacehowforce much an object due to gravity at the Earth's while at rest. One g is also a measure surface-how object weighs of accelerationmuch or an deceleration - 22 while at rest. One Zero g is also a measure mph per second. g occurs in a of acceleration or deceleration-22 weightless environment. Acceleration rnph per second. Zero isg negative. occurs in a is positive; deceleration weightless environment. Acceleration Once the brakes are applied, a car is is positive; negative. stopped by deceleration the friction is force between the brakes are applied, a car is theOnce tires and the road. During stopped by the friction force between braking, friction acts on the tires in a the tiresopposite and the road. During direction to movement. The braking,the friction acts on the in a higher deceleration, thetires greater direction opposite to movement. The this friction force becomes . Maximum higher the deceleration, the greater possible deceleration occurs at the this friction force becomes. Maximum maximum coefficient of /riction bepossible occursThis at hapthe tween the deceleration tires and the road. maximum fiiction bepens just as coeflicient the tires areofabout to skid. tween the tires and the road. This hapOnce tires lose traction and skid, pens just as the tires are about deceleration drops. Read on to forskid. an Once tires of losecoefficient traction ofand skid, explanation friction, deceleration drops. Read on for an or si mply friction coefftcient. explanation of coefficient of friction, or simply ,f,.ictiot7 coeJficient.
INERTIA FORCES
More than 200 years ago, Sir Isaac INERTIA FORCES Newton wrote the basic law relating a More 200 years Sir Isaac force on than an object to itsago, acceleration. Newton wrote Newton's the basic Law law relating a Simply stated, is:
force on an object to its acceleration. Acceleration of an object = ~ in g's Simply stated, Newton's Law is:
F of an object in g's in Acceleration force = on object F = Unbalanced pounds F == Weight Unbalanced force on object in W of object in pounds pounds In this formula, the force F causes W = Weight of object in pounds
acceleration. If a car weighing 3000 Ib formula, causes hasIna this braking forcethe of force -1500F lb, the acceleration. weighing 3000 Ib Ib stopping forceIf isa car -1500 Ib -7- 3000 has a braking force of 1500 Ib, the = -0.5 g. stopping force pushes is - 1500 + 3000 to Ib If the force in aIbdirection = -0.5theg.object to speed up , the force cause the force in a direction to is If positive andpushes acceleration is a posicause the object to speed up, the force tive number. If the force causes the is positive and acceleration a posiobject to slow, the force is isnegative tive number. If the force causes the and acceleration is negative. We call object to slow, the force is negative the negative acceleration deceleration . and acceleration is negative. We call The force referred to in Newton's the acceleration Lawnegative is unbalanced force. decele~.arion. That means Theforce forceis referred to inby Newton's if the not resisted opposing unbalanced force. That means Law is force, the object is free to move, or if the force is not resisted by opposing accelerate. If I push on a tree with a force, freewill to not move, or force ofthe 100object Ib, theistree move. accelerate. I push on a tree with The 100-lb If force is resisted by the treea force 100a Ib, the tree will so notthere move. roots of with 100-lb force, is The 100-lb force is resisted by the no unbalanced force on the tree.tree To roots with a 100-lb either force, positive so there or is cause acceleration, no unbalanced force tree. To negative, the force on on the the object must cause acceleration, either positive or be unbalanced. negative, the force on the object must To understand how unbalanced be unbalanced. forces work on a car, assume you are To understand how strip. unbalanced driving a car on a drag At the forces work on a car, assume youpush are start, you let out the clutch and drivingona the car accelerator, on a drag strip. At fricthe down and the start, you let out thetheclutch tion force between tires and and push road down on the accelerator, and thestart, fricpushes the car forward . At the
tion force between the tires and road pushes the car forward. At the start, 11
air drag is zero, so the forward force is not resisted by anything but drive-line friction and tire drag, or rolling resistance. The forward force is almost unbalanced. Consequently, acstart. celeration is maximum at the start. As the car gains speed, air drag increases. It opposes the forward force on the tires that is trying to accelerate the car. The unbalanced force is the forward force minus the rearward force. As speed increases, the unbalanced force becomes smaller because of air drag. Consequently, acceleration also gets smaller. Near the end of the drag strip, the car is moving so fast that the air-drag force approaches the forward force of the tires against the road. Assuming engine rpm and track length aren't limiting factors, factors, speed will increase until no force unbalance exists and acceleration becomes zero. The car has reached its maximum speed. The only way to accelerate the car to a higher speed would be to increase the forward force (more engine power), or reduce (Jess air drag). the rearward force (less drag). Every race-car designer knows that more power or less drag will increase car speed. speed. In addition to the basic relationship between force force and acceleration, Newton came up with other important laws of of nature. nature. He t l e discovered that every moving object has inertia. That is, an object always always moves at the same same speed and in the same same direction until acted on by an unbalanced force. force. Inertia is is what keeps the Earth moving around the Sun and keeps satellites in orbit. orbit. There is no air drag in outer space, space, so so once an an object is is at speed, it keeps moving forever. forever. Only a force force can change its speed or direction. direction. A car also acts acts according to Newton's laws. laws. Once Once it is moving, a car wants to continue in a straight line line at the the same same speed. speed. Every part of the the car and its passengers also want to keep moving. moving. When the brakes are applied, applied, a force force is is applied to to the the car by the tires, causing deceleration. deceleration. Because Because passengers passengers tend to to continue at the the same same speed, speed, they will will move forward forward in in the seat seat and strike strike the the instrument panel unless held by restraint devices, devices, legs or friction friction against the the seat. seat. This This forward forward force force that tends tends to to "throw" "throw" a passenger forforward during during braking is is called called inertia force. ,force. Inertia force force acts acts on on everything in in aa car as as its its speed speed changes. changes. 12
--
. . Inertia Force
Friction Forces ForCes on Tires Friction
-
-
Tire friction forces are external forces that cause deceleration. deceleration. The road road pushes pushes on the opposite direction direction of motion. tires in in the opposite motion. Inertia lnertia force of the car acts in the same direction as motion equals friction friction force. force. motion and equals
Therefore, if a car accelerates, the inertia force acts toward the rear; if it decelerates, the inertia force acts forward. forward. Inertia force in g's is equal to car's car's acceleration or deceleration. deceleration. Inertia forces are easy to calculate in pounds if you know the acceleration. acceleration. W object in W == Weight of the theobject in pounds a= = Acceleration of the object in in g's
Inertia force is measured in pounds. If the car is decelerating, decelerating, the inertia force is negative-it negative-it acts in a forward direction. direction. Try visualizing visualizing what happens when a car decelerates. decelerates. It is easier to visualize the forces if you imagine a driver trying to stop stop so so quickly that he locks the wheels. wheels. Imagine a car skidding with all all four wheels locked and smoke smoke pouring off the the tires. tires. Assume the the car weighs 3000 lb Ib and the coefficient of friction friction between the tires and road is is 0.7. The The friction friction force force on all all four tires 0.7. is: is: Friction p FN FN Friction force == f.L p = = Coefficient Coefficient of friction friction between between two f.L
Inertia lnertia forces forces act on on every every part of a car. car. This passenger resists resists inertia inertia force on on his his This body with his his arms arms against the the dash, dash, feet body against the floor, floor, and and seat belt around around his his against waist. waist. Inertia lnertia force force on on his his hat is is not not resisted by by anything, anything, so so it it flies flies forward forward into into the ed windshield. windshield.
Acceleration of car == F F/Wc IW c F == Unbalanced Unbalanced force forceon in pounds ~ounds F on car in We Wc == Weight of car in in pounds pounds
Acceleration of of car Acceleration Ib) == -0.7 -0.7 g. g. Ib)
= =
00 Ib)/(3000 lb)/(3000 (-2100
Friction Friction force force = = (0.7)(3000 (0.7)(3000 Ib) Ib) = = 2100 lb. Ib.
The unbalanced force force has a minus minus The sign because it acts acts in in a direction direction sign car. Remember: Remember: Negaopposite to the car. tive acceleration means deceleration; deceleration; tive car to to slow. slow. itit causes the car deceleration is is 0.7 0.7 g, E., every everv Because deceleration part of the car has an inertia force force on it g. The inertia force force on a 200-lb of 0.7 g. passenger is: is: passenger
This This friction friction force force on the the tires tries tries to to decelerate decelerate the the car. car. The The deceleration deceleration is is easy to calculate calculate from from Newton's law, law, easy page 11: 11:
Inertia lnertia force force == Wa Wa w == Weight Weight of of the the passenger passenger in in W pounds pounds Acceleration of the the passenger passenger in in aa == Acceleration g's g's
sliding surfaces sliding FN F, == Force Force pushing pushing the the two surfaces together in nds in pou pounds
In this this example, example, p == 0.7 0.7 and and FN FN== 3000lb 3000 Ib f.L
-
- - -
~
~-~
If there were some way to support a car at its center of gravity (CG), it would be balanced. Rotate the tocar to another If there were some way support a car at position, as on a (CG), side, and it would its centersuch of gravity i t would be remain balanced. CGcar is the supbalanced. RotateThe the to only another port pointsuch where exists regardless position, asbalance on a side, and it would of position. remain balanced. The CG is the only sup-
port point where balance exists regardless of position. I nertia force = (200 Ib) (-0. 7 g) =-140Ib.
Inertia force = (200 Ib)(-0.7g) The minus = sign the force is -1 40means Ib. forward. If there is little friction beThe sign means the seat, forcethe is tweenminus the passenger and the forward. If there is little friction be140-lb inerti a force acts on his seat tween belt or the legs.passenger and the seat, the 140-lb forcetheacts his seat In thisinertia example, car on decelerates belt or legs. at only 0.7 g. With the wheels locked In sliding, this example, the car decelerates and the coefficient of friction at g. With the wheelspossible locked is only lower0.7 th an its maximum and sliding, the coefficient of friction value. Maximum deceleration of a car is determined lower than by itsmany maximum lis factors,possible includvalue. Maximum deceleration car aerodynamic forces,of aroad ing tires, pis determined by many factors, includcondition and brake-system design. ing tires, forces, road Most cars aerodynamic on street tires can reach condition and deceleration brake-system on design. about 0.8-g dry Most cars Race on street tires can reach pavement. cars can decelerate at about well over0.8-g 1 g. deceleration on dry pavement. Race cars can decelerate at well over 1 g. WEIGHT TRANSFER A car's inertia force acts at its center
WEIGHT TRANSFER of gravity, or CG, of the whole cal'. The
forcewhich acts atthe its entire center CGA iscar's the inertia point about of graviry, or CG, of the whole car, car is balanced. If you could hang The the CG by is the pointattached about which car a cable a t itsthe CGentire , the car would is balanced. you hang the car balanceIf in anycould position. carThe by aCG cable at its is attached the center ofCG, all the the car would balance in any position. weight. All the inertia forces on the inof togethall the The CG dividual partsis ofthe the center car added weight. inertia on the iner are All the the same as forces a single inertia dividual parts of the car added togethforce for the whole car acting at its er the same as a CO single inertia CG.areBecause a car's is always force for whole car acting its above thethe road, inertia force at from CG. Because car'sto CG braking always atries load isthealways front above theliftroad, inertia force from tires and the rears . This effect is brakingweight always tries to load the front transfer. called tires and lift the rears. This that effectthe is Weight transfer means called weightare transfer. front tires loaded more during a Weight transfer means that the stop, and the rear tires are unloaded.
front tires are loaded more during a stop, and the rear tires are unloaded.
A front-wheel-drive car, such as this VW, has majority of weight at front. When brakes are applied hard, more weight is transferred to the front. The nose drops and tail rises during braking due to weightcar, transfer. A front-wheel-drive such as this VW, has majority of weight at front. When brakes are
applied hard, more weight is transferred to the front. The nose drops and tail rises during braking due to weight transfer.
t
~I F, = vertical force on front tires Ob) F, = vertical force on rear tires (Ib) Xeg horizontal Ff ==vertical forcedistance on frontfrom tiresfront (Ib) axle to CG .) F, =(in vertical force on rear tires (Ib) I = wheelbase length (in.) from front axle to Xcg = horizontal distance Y CG height (in.) CG (in.) eg = (Ib) (in.) We Car weight I = =wheelbase length fJ. == Coefficient friction Ycg CG heightof(in.) Wc = Car weight (Ib)
F
,
=
W _F e
,
+ We fJ.I Y cg
wc P YYCg I eg F =WcXCg·_W c fJ.Y 'I I wc xc;WC P Ycg F, = I I Yea Weight transfer = W efJ.
Ff=Wc-F,+-
I
Weight transfer
= Wcfi
Ycq
p. = Coefficient of friction I Ignoring aerodynamic forces, these forces act on a car during hard braking. Maximum weight transfer can be calculated if tire coefficient of friction is known.
Ignoring aerodynamic forces, these forces act on a car during hard braking. Maximum weight transfer can be calculated if tire coefficient of friction is known.
The weight of the whole car does not change. Weight added to the front The of the whole car rear doestires not tires weight is subtracted from the change. Weight added to the front during weight transfer. The forces tires is on subtracted from the rear tires acting a car during braking are during transfer. Thedrawing forces. shown inweight the accompanying acting on a car during aerodynambraking are In this simple illustration, shown in the accompanying drawing. ic forces are not shown. Aerodynamic In this simple aerodynamforces changeillustration, the amount of the ic forcesbut arenot not the shown. forces, basicAerodynamic principle of forces change the amount of the weight transfer. forces, but weight not thetransfer basic principle of Because loads the weight transfer. front tires, additional friction force weight transfer loads tires the canBecause be developed by the front
front tires, additional friction force can be developed by the front tires
before they skid. To produce this extra friction force, front brakes have before skid. produce to work they harder thanToif there was this no extra force, front brakes weightfriction transfer. At the same time,have the to hardercan than do if there no rearwork brakes less was work. weight transfer. At the same time, the Typically, front brakes supply about rear brakes less force work. two-thirds of thecan totaldo braking in Typically, front about Thebrakes ratio issupply even higher a hard stop. two-thirds of the total braking car. forceBein on an extremely nose-heavy acause hard the stop. T h e ratio is even higher front brakes do most of the on an they extremely car. rear Bework, need tonose-heavy be larger than cause front brakes most higher of the brakes.the The forces are do usually work, they need to larger than rear on front brakes, so be they must absorb brakes. The forces are usually higher more heat energy.
on front brakes, so they must absorb more heat energy. 13
BRAKE FADE Brake fade is loss of braking due to overheating. It can cause lo'nger pedal travel as the brakes get hotter-maybe to the paint where the pedal goes to the floor. Pedal effort may also increase as heat bu'ilds up, even to the point where pushing with maximum force won't lock the wheels! Many times, fade causes a combination of both longer pedal travel and increased pedal effort. Whatever fade is, the driver is faced with a panic situation. Brake fade typically occurs at the worst posSible moment-going down a long hill pulling a trailer, at the end of a long race, or during a panic stop from freeway speed in heavy traffic. This is when you need your brakes the most. Consequently, brake fade is always scary, and often dangerous.
Geoff Brabham is at the traction limit of his Toyota Celica in this turn. Combination of braking and cornering forces causes tires to slip and pOint at extreme angles to the direction of travel. When carisisatat tractionlimit limit, attempt to corner, or brakeofharder Geoff Brabham theitstraction of any his Toyota Celica in thisaccelerate turn. Combination brakwill throw it into a forces skid. causes tires to slip and point at extreme angles to the direction of ing and cornering
travel. When car is at its traction limit, any attempt to corner, accelerate or brake harder will throw it into a skid.
BRAKING LIMITS With a modern brake system, how BRAKING LIMITS good can brakes be? What determines a modern brakeperformance? system, how theWith limits to brake good can brakes be? What determines What makes your car stop quicker the limits than the nextto car,brake or vice performance? versa? What quicker Theremakes are your limits car thatstop determine than the next car, or vice versa? how quick a car can stop. Some of There arecanlimits that determine these limits be altered by design how quick a car can Somelaws of or maintenance, so onlystop. the basic these limits cana car be ' altered by ability. design of nature limit s stopping or maintenance, so only Brake-performance limitsthe are:basic laws of l.nature limit a car's stopping ability. Force Brake-performance limits are: 2. Deflection 1. Wear Force 3. 2. Deflection 4. Temperature 3. Wear 5. Tire traction
4. Temperature 5. A Tire braketraction system should be designed
and maintained so that tire traction A brake system should your be designed determines how quickly car can and maintained so other that tire stop. If any of the fourtraction limits determines howstopping quickly quicker, your caryour can keep you from stop. any the other four limits brakesIfare notofadequate. keep you from your Force limit stopping means quicker, the driver brakes are not adequate. pushes as hard as possible with his Force means foot and limit the car can't the stopdriver any pushes as possible with his quicker. In hard otheraswords, if the driver foot carthecan't stop stop any could and push the harder, car would quicker. This In other the driver quicker. limitwords, can beif altered by
could push harder, the car would stop quicker. This limit can be altered by
14
reducing master-cylinder size, putting on different lining, using power-assist reducing size,I putting brakes, ormaster-cylinder other methods. discuss on different lining, using power-assist how to reduce the force a driver has to brakes,later or inother methods. I discuss exert the book. In some cases, to reduce the force a driver has to ahow force limit occurs when the brakes exert later in the book. In some get hot . This is called brake fade.cases, The a force limit occurs when the answer here is dissipating heat.brakes Perget brake fade. The hapshot. theThis forceis called limit you've encounanswer is dissipating heat. limit. Pertered is here really a temperature haps to the forceexcess limit heat you've encounHow handle is discussed tered is really a temperature limit. in Chapters 10 and 12. How to handlelimit excess is discussed Deflection is heat reached as the in Chapters andat12. brake pedal 10 stops the floor or stop. Deflection limit is reached as the This means the pedal is moving too brake pedal stops at the floor or stop. far to get maximum efficiency from This means Athedeflection pedal is limit moving the brakes. can too be far to get maximum efficiency from eliminated by design changes such as deflection limit can be the brakes.theA pedal-support stiffening structure, eliminated design changessize, such inas increasing by master-cylinder stiffeningstiffer the pedal-support stalling brake hoses , structure, changing increasing master-cylinder size, into stiffer calipers, or other modistalling stiffer brake hoses, changing fications. Maintenance can eliminate stiffer calipers, other modiato deflection limit if or air is trapped in fications. Maintenance can eliminate the brake lines. a deflection limit if airhappen is trapped in Wear limit won't when the brake lines. brakes are new. However, if friction Wear limit happen it when material is wornwon't excessively, may brakes friction be wornare outnew. just However, when you ifneed the material is worn excessively, it may brakes most-such as at the end of a
be worn out just when you need the brakes most-such as a t the end of a
long race. Wear limits can be eliminated or reduced by changing linings, long Wear limitsorcanbybedissipating eliminatusingrace. larger brakes, ed reduced changing inlinings, heat.orBrake wear by is discussed Chapusing larger ters 4 and 12. brakes, or by dissipating heat. Brake wearlimit: is discussed ChapTemperature Brakesincannot ters 4 and absorb the12.full power of an engine Temperaturewithout limit: some Brakes time cannot continuously to absorb the full power of an engine cool. When the temperature limit is continuously without time to reached , you can reachsome a force limit, cool. Whenlimit, the temperature limit is deflection or greatly increase reached, you can reach a force limit, the wear at the same time. Other deflection limit, or greatly increase things can happen , too , such as comthe at theofsame time. orOther pletewear destruction the brakes total things can too,part. suchExcessive as comcollapse of ahappen, structural plete destruction. the brakescause or total temperature is aofcommon of collapse of a structural part. Excessive brake problems. temperature is a Ifcommon of Traction limit: brakes arecause properbrake problems. ly designed and maintained, and don't If brakes are propergetTraction too hot,limit: the only stopping limit is ly maintained, and don't tiredesigned traction.and If you try to stop quicker get hot,traction the onlylimit stopping limitthe is thantoothe allows, tjre traction. If you try to stop quicker wheels lock up and the tires skid. The than thelimit traction limittheallows, the traction is always limit with wheelsbrakes, lock upbut andit the The good cantires be skid. increased the limit with traction is always through limit correct adjustment of brake good brakes, but it can be increased balance. Adjusting brake balance is through correct adjustment of brake discussed in Chapter 10. Modificabrake balance is balance. tions to Adjusting allow brake-balance adjustdiscussed in Chapter 10. Modificament are described in Chapter 12.
tions to allow brake-balance adjustment are described in Chapter 1 2 .
2
DrumBrakes
Drum Brakes Backing
~~
PI"e~ Hole Covers
~
!;
Wheel Cylinder Assembly
&(
)
Anchor-Pin Plate
~Secondary
fJ
a ~
Hold-Down Pin or Rod
Adjusting Lever
Return Spring
rr;;
r
Cup
Spring Retainer
Retainer
hoe Hold-Down
Modern drum brake automatically adjusts shoes outward as friction material wears. Drum is not shown. Drawing courtesy Chrysler Corporation. Modern drum brake automatically adjusts shoes outward as friction material wears. Drum is not shown. Drawing courtesy Chrysler Most cars have used internal drum Corporation.
brakes over the years. They continue carson have to Most be used theused rear internal of most drum road brakes over the years. They continue cars. to Even be used on thedrum rear brakes of most share road though cars. common features, details may differ. Even Each hasthough a metaldrum drum,brakes usuallyshare cast common iron. Thefeatures, drum details rotates may withdjffer. the Each a metalthedrum, cast wheel.has Within drumusually are brake iron. The with drum rotates with This the shoes lined friction material. wheel. Within the drum are brake material, consisting of various organic lined with friction material. This shoesmetallic and compounds, is the brake material, consisting of various organic lining. The brake shoes are moved and metallic compounds, is thebybrake against the inside of the drum pis*The brake shoes are moved lining. tons inside the wheel cylinders. Hyagainst the of the drum by draulic fluidinside under pressure in pisthe Hytons inside the wheel wheel cylinders moves cylinders. the pistons. draulic fluid under in the Wheel cylinders and pressure brake shoes are wheel cylinders moves the pistons. mounted on a metal backing plate. Wheelbacking cylinders and isbrake shoes are This plate bolted to the plate. mounted a metal orbacking car's axleonhousing suspension This backing plate is bolted to the upright.
car's axle housing or suspension upright.
Cable Guide
~ Adjuster cable!
Cable Guide ""
Adjuster-Lever Spring
I
rgIiUli€l4S---' Pa ingBrake Strut " t" Ad JUS 109 Shoe Hold-down Parts
Nt/~~ u
Pivot
Adjusting Screw
Automatic-Adjuster Parts
Shoe Hold-down Parts Automatic-Adjuster Parts Bendix duo-servo rear brake is typical of drum brakes found on American cars. Brake features automatic adjuster and high servo action. Included is linkage to operate shoes from the parking-brake Drawing courtesy Bendix Corp.found on American cars. Brake feaBendix duo-servo cable. rear brake is typical of drum brakes tures automatic adjuster and high servo action. Included is linkage t o operate shoes from the parking-brake cable. Drawing courtesy Bendix Corp.
15
r
Trailing Shoe
Leading Shoe
Wheei Cylinder Hydraulic Force
\Trailing
Shoe
Pressurized Hydraulic on Leading Shoe Fluid r Hvdraulic~Leading Force ~ Shoe
Friction Force on Friction Trailing Force Shoe on
Trailing Shoe Pivots Away From Drum
Friction Force on Leading Shoe
Trailing Shoe
-
1//
'Leading Shoe Pivots Toward Drum
~Friction Force on Shoe
~ Drum Rotation
I
L ~ h o Pivots e Single leading-shoe drum brake-sometimes called a lea dingand-trailing-shoe brake-has one leading and one trailing shoe. As drum clockwise, friction force on leading shoea forces it Singlerotates leading-shoe drum brake-sometimes called leadingagainst drum, creating servo one action, or force multiplication. Drum and-trailing-shoe brake-has leading and one trailing shoe. As rotation tends clockwise, to reduce shoe-to-drum of trailing shoe. drum rotates friction forceforce on leading shoe forces it
I
against drum, creating servo action, or force multiplication. Drum rotation tends to reduce shoe-to-drum force of trailing shoe.
Drum
Shoes in this single leading-shoe brake both pivot toward the right Rotation when acted on by friction forces. Although wheel-cylinder force keeps both the drum, friction forces modify Shoes in thisshoes singleagainst leading-shoe brake both pivot toward thepresright sure shoe. Leading-shoe pressure increases; when exerted acted onbybyeach friction forces. Although wheel-cylinder force trailing-shoe pressure decreases. is forces little overall keeps both shoes against the drum,There friction modify servo presaction with thisbytype of shoe. brake, Leading-shoe as friction-force effectsincreases; on shoes sure exerted each pressure cancel out each other. decreases. There is little overall servo trailing-shoe pressure
action with this type of brake, as friction-force effects on shoes cancel out each other.
SERVO ACTION There are many varIatIOns of SERVO ACTION design. Designs simple drum-brake There variations of differ in are the many amount of forcesimple drum-brake design. Designs multiplication, or servo action . Imagine forcediffer amount of brakes driving in one the car with standard servo action. multiplication, and another or equipped with Imagine powerdriving one car withamount standardofbrakes assist brakes . The pedal and another equipped force is greatly reduced with with powerpowerassist brakes. Servo The amount of much pedal assist brakes. action acts force is greatly reduced withthepowerlike power assist-it reduces force assist brakes. Servobrake actionpedal acts much required on the for a reducesHowever, the force like power assistof- itbraking. given amount required on the brake pedal for a servo action occurs within the brake given itself. amount of braking. However, servo action occurs withinhelp theunderbrake Leading or Trailing-To itself. stand servo action, let's look at how or Trailing-To under-a Leading brake shoes are mounted.help Imagine stand look howa brake servo shoe piaction, voting let's at one endatand brake shoes are mounted. Imagine wheel cylinder pushing on the other.a brake shoe pivoting at mount one enda brake and a There are two ways to wheel ascylinder the other. shoe, leading pushing shoe or ason/railing shoe. Theredepends are two ways to mount This on which end aofbrake the shoe, aspivots leaditillginshoe or as trailing shoe. shoe relation to drum This depends whichdrum end rotates of the rotation . If theonbrake shoe pivots in relation to end drum from the free (wheel-cylinder) of rotation. If the brake drum rotates the shoe toward the pivoted end, it is from the free (wheel-cylinder) of a leading shoe. If the brake end drum the shoeistoward the pivot pivoted it is motion from the endend, toward atheleading shoe. If the brake drum free end, the shoe is trailing. motion is from the pivot end applied toward Now let's look at the forces the free end, the shoe is trailing. to each type of brake-shoe arNow let's The look at the forces rangement. friction forceapplied on a to eachshoe type arleading tendsof to brake-shoe rotate the shoe rangement. The friction force on around its pivot and against the drum.a leading shoethe tends to rotate theinshoe This assists wheel cylinder ap-
around its pivot and against the drum. This assists the wheel cylinder in ap16
Single leading-shoe found on rear wheels has low leading-shoe servo action, Single in bothon directions. found rear wheels
brake is generally only. Although brake itbrake works is equally well generally
only. Although brake has low servo action, it works equally well in both directions.
plying the brake shoe. A trailing shoe is just the opposite-the friction force plying shoe.from A trailing shoe moves the the brake shoe away the drum, is just the opposite-the friction force thus counteracting the force of the moves the shoe away from the drum, wheel cylinder. thus counteracting the drum forcerotation of the With a leading shoe, wheel cylinder. increases pressure between the shoe With a leading drum rotation and drum, givingshoe, increased friction increases pressure between theaction. shoe and braking force. This is servo and driver drum, doesn't giving increased friction The have to push the and force. Thisa isleading-shoe servo action. pedalbraking as hard with The have the to push the drumdriver brake.doesn't It is just opposite pedal as hard with a leading-shoe with a trailing-shoe brake. The driver drum brake. It hard. is just the opposite has to push very with a trailing-shoe brake.leading-shoe The driver When car with has to push very hard. brakes on all wheels is backed up, the
a
When a car with leading-shoe brakes on all wheels is backed up, the
reversed direction of the wheel rotation changes all the leading shoes into reversed direction the wheel trailing shoes. The of driver noticesrotathis tiona changes all the leading as huge increase in pedalshoes forceinto retrailing toshoes. Thecar. driver this quired stop the For notices this reason, as a huge increase in pedal of force redrum brakes have a mixture leading quired to stop the -car. For this reason, and trailing shoes two leading shoes drum a mixture of leading leading on thebrakes front have wheels and one and trailing shoes-two leading and one trailing shoe on eachshoes rear on the front wheelssome and one leading wheel. This gives amount of and one trailing shoe on one eachsetrear servo action and still allows of wheel. toThis some shoes amount of shoes workgives as leading when servo action and still allows one set of braking in reverse. shoes to work as leading when Duo-Servo-Another typeshoes of brake, braking in reverse. which differs from leading- or trailingDuo-Servotype of brake, shoe types, Another is the duo-servo drum which differs from leadingbrake. Its features are shownorintrailingthe acshoe types, drawing. is the duo-servo drum companying brake. featuresbrake are shown acThe Its duo-servo does in notthe have companying drawing. a simple pivot on its brake shoes. The The are duo-servo brake have shoes connected to does each not other at athe simple on its shoes. The end pivot opposite thebrake wheel cylinder shoes are connected to link eachtransmits other at by a floating link. This the end opposite the wheel the force and motion of one cylinder shoe to by floating link. linkpin transmits the aother shoe. AnThis anchor next to the motionkeeps of one to the force wheeland cylinder theshoe shoes the shoe.with An anchor pin next to fromother rotating the brake drum. the wheel cylinder keeps the shoes The two shoes are called the primary from rotating with the shoe. brakeThe drum. the secondaty prishoe and primary The shoes are called mary two shoe pushes on thethe secondary shoe and the secondary The prishoe through the link; shoe. the secondary mary shoe pushes on the secondary shoe pushes on the anchor pin. When shoe through the link; the secondary braking in reverse, the action reverses shoethe pushes onchange the anchor When and shoes roles.pin. The pribraking in reverse, the action reverses mary shoe then becomes a secondary and the shoes shoe in the way change it works.roles. The pri-
mary shoe then becomes a secondary shoe in the way it works.
Anchor Pin
Anchor Pin
Anchor Pin
Anchor Pin rimaf hoe
Forward Braking Typical duo-servo front brake used on large front-engine, rear-drive American cars; pin is front above brake wheel used cylinder. Typicalanchor duo-servo on Adjuster joins lower rear-drive ends of shoes. Only large front-engine, American .cars; rigid connection between backing plate anchor pin is above wheel cylinder, and shoesjoins is at anchor pin. of shoes. Only Adjuster lower ends
rigid connection between backing plate and shoes is at anchor pin.
Duo-servo brakes have servo action regardless of rotation. The Duo-servo brakes have forward servo brake is designed for mostly action regardless of rotation. motion or rotation. Lining wearThe is brake is designed forward equalized betweenforthemostly primary and motion or shoes rotation.by Lining is secondary puttingwear more equalized between the primary and lining on .the face of the secondary secondary shoes the by driver puttingcanmore shoe. However, feel liningdifference on .the face of theaction secondary when little in servo shoe. driver can feel brakingHowever, in reversethe . Duo-servo brakes little difference in servo action when were used on most American cars brakingrear-wheel in reverse. drive Duo-servo with and brakes drum were onthe most cars brakesused before use American of disc brakes. with rear-wheel duo-servo drive brakesand havedrum the Because brakes before the use disc well brakes. most servo action, theyofwork on Because brakes have the heavy carsduo-servo . most action, they work well the on Pedal servo Effort-Let' s compare heavy three cars. types of brake-shoe arrangePedal Effort-Let's compare ments and see how the servo action the afthree types of brake-shoe fects pedal effort. Pedal effortarrangeis the mentsthe anddriver see how the servo action afforce applies to the pedal. fects effort. Pedal effort the accompanying ch art , it is isobviIn thepedal forcethat thethe driver appliesbrake to thehaspedal. ous duo-servo less In the accompanying chart, is obvipedal effort for a given it rate of ous that the duo-servo brake has less deceleration. pedal for bad a given rate of Now effort comes the part-we never deceleration. get something for nothing. Let 's see Nowhappens comes the bad brakes part-we getnever what when too get nothing. Let's see brake-lining material, hot. something With most for what happens when with brakesincreasing get too friction decreases hot. With most brake-lining material, temperature. As an example, assume friction decreases withbetween increasing the friction coefficient the temperature. As lining an example, assume brake drum and drops from 0.5 the between the gets hot. The comparito 0.4friction when itcoefficient brakeisdrum andinlining from 0.5 son shown the drops accompanying to 0.4 when it gets hot. The comparitable for each type of drum brake . The son is shown the loses accompanying duo-servo druminbrake the most table for force. each type of ,drum brake. The braking Thus the brake that duo-servo drum brake servo loses actiontheis most also has the greatest braking Thus, the one force. affected the the mostbrake by a that dehas thein greatest crease friction . servo action is also
the one affected the most by a decrease in friction.
Primary Shoe
Reverse Braking
Forward Braking Duo-servo drum-brake operation: Notice that primary shoe Reverse is pushedBraking away from anchor pin in forward braking. It moves until it is stopped against the drum. When backing up, rotation reverses and other shoeoperation: acts as primary courtesy Bendix Corp. Duo-servo drum-brake Noticeshoe. that Drawing primary shoe is pushed away from anchor pin in forward braking. I t moves until i t is stopped against the drum. When backing up, rotation reverses and other shoe acts as primary shoe. Drawing courtesy Bendix Corp. 160 Single Leading-Shoe or Leading-and- TrailingShoe Brake SingleDrum Leading-Shoe or
140
Leading-and-TrailingShoe Drum Brake 120
Two Leading-Shoe Drum Brake
Two Leading-Shoe
100 Pedal Effort
80
(I b)
60
40 40 -
20
20 .2
.3
.4
I
I
I Lining Coefficient of Friction
.5 I I
.4 .5 Duo-servo drum brake gives lowest pedal effort for all practical friction coefficients. Lining Coefficient of Friction .2
.3
Duo-servo drum brake gives lowest pedal effort for all practical friction coefficients.
Pedal Effort at
Pedal Effort at
Percent Increase
CF=O.5 CF=O.4 in Pedal Effort Pedal Effort at Pedal Effort at Percent Increase Duo-servo 107.61b 115.2% 50lb Brake Type CF = 0.5 CF = 0.4 in Pedal Effort 50lb 99.81b Two-leading shoe 99.8% 176.0% 15.2% 50 1b 107.6 Ib Duo-servo Leading-trailing 50lb 88.01b 50 Ib 99.8 Ib 99.8% Two-leading Disc brake shoe 50lb 62.51b 25.0% 88.0 1b 76.0% 50 Ib Leading-trailing 25.0% 50 could Ib 62.5 fade. 1b Pedal effort brake 0.1Disc friction-coefficient drop occur from brake more than doubles Brake Type
A with duo-servo drum brakes. Disc brakes have no servo action, so effect of fade is considA 0.1 friction-coefficient drop could occur from brake fade. Pedal effort more than doubles erably less.
with duo-servo drum brakes. Disc brakes have no servo action, so effect of fade is considerably less.
17
I
Cast-iron brake drum is large and heavy compared to disc-brake rotor of equal effectiveness. Many '60s and '70s Cast-iron brake drum is large and Ameriheavy can cars have drums of this This compared to disc-brake rotortype. of equal front-brake drum has'60s integral wheel hub effectiveness. Many and '70s Ameriand can bearings. cars have drums of this type. This
During later days of race-car drum-brake development, a great deal of work was spent cooling-fin design. This type of Duringon later days of race-car drum-brake radial-finned drum pumps air was bedevelopment, a great dealcooling of work tween wheel and drum. spent the on cooling-fin design. This type of
front-brake drum has integral wheel hub Duo-servo and bearings. brakes are most sus-
ceptible to the type of brake fade Duo-servo brakes are most suswhere a force limit is reached. Thus , if ceptible to the brake fade they are ever usedtype in a of racing or highwhere a force limit is reached. Thus, if performance application, care must they are ever used in a racing or highbe taken to use linings that do not performance carewith must have a drastic application, drop in friction inbe takentemperature. to use linings do with not creasing Carsthat fitted have a drastic in friction induo-servo frontdrop brakes have a with tendencreasing temperature. Cars fitted with cy to pull to the right or left if the fricduo-servo front brakes have a tendention in one brake is slightly higher cy to the pullother. to the right or left if the fricthan tion in one slightlyin higher More is saidbrake aboutis linings Chapthan the other. ter 4.
More is said about linings in Chapter 4. BRAKE DRUMS The brake drum is a large, critical
BRAKE brake system. If the drum is part of a DRUMS brake is athe large, critical tooThe small or drum flexible, brake will part of a poorly brake system. If the drum is perform under severe use, no too small flexible, the brake matter howorgood the system may will be. perform severe ause, no Let ' s seepoorly what under constitutes good matter how good the system may be. brake drum. The important properties Let's see what constitutes a good are: brake drum. properties • Must haveThe a important hard wear-resistant are: rubbing surface and the surface finish Must a the hardlining. wear-resistant must not have damage rubbing surface the surface finish strongand enough to withstand • Must be must not damage the lining. the hardest braking, while at high Must be strong enough to withstand temperatures . the hardest braking, while toatdistorhigh • Must be stiff and resistant temperatures. tion and warping. Must bedissipate stiff and heat resistant to distorrapidly and • Must tion and warping. withstand excessive temperatures. Must dissipate rapidlyof grey and Most brake drumsheat are made withstand excessive cast iron, because it temperatures. is hard and wearMost brake are madecarbon, of grey resistant. Castdrums iron contains cast iron, because it is hard and wearwhich prevents galling and seizing resistant. Cast iron contains carbon, when hot. It's also a good d,y rubbing which without preventslubrication. galling and seizing surface when also arigid good dry rubbing Casthot. ironIt's is very , compared to surface without lubrication. most metals. Therefore, the drum reCastdistortion iron is very rigid,load compared to sists under . Because most metals. Therefore, the drum re-, the drum is cast at high temperature sists distortion under load. Because the drum is cast at high temperature, 18
Racers soon discovered that bigger brakes are better. This old Talbot Grand Prix car used wheels-brake drums are Racers18-in. soon discovered that bigger brakes bigger! Fitting into wheel its are better. Thisdrum old Talbot Grandlimits Prix car size. used 1 8-in. wheels- brake drums are
bigger! Fitting drum into wheel limits its size.
it resists warpage when repeatedly heated and cooled. it However, resists warpage whenis repeatedly cast iron not the heated andmetal cooled. strongest in the world; it tends cast iron Tois avoid not this, the to However, crack if overstressed. strongest metal in the world; it tends thick sections are used in a drum . to crack if overstressed. Tostrengthens avoid this, This extra metal not only thickdrum, sections used the in astiffness drum. the but itare increases This extra metal not only strengthens of the drum. It also reduces temperathe but during it increases turedrum, buildup hard the use.stiffness When of thearedrum. also help reduces temperafins used,It they reduce tem'ture buildup duringby hard use. When peratures quickly exposing more fins used, tothey help reduce temmetalare surface the cooling air. When peratures quicklyarebyused, exposing all design tricks a drummore will metal surface to strength. the cooling When have adequate In air. addition, all tricks are used, a drum heatdesign dissipation is improved with will the have adequate strength. In addition, fins and extra metal. heat dissipation is improved with the Drum Cooling-High-performance fins anddrums extra metal. brake must be BIG; bigger the Drum Cooling-High-performance befter is the key for reducing temperathe brake drums must be BIG; tures and eliminating fade. bigger A large the key has for reducing temperabetter is drum diameter the added advantures ofand eliminating fade. A large tage reducing pedal effort because drum diameter has the added advanof the increased "leverage" of the tage of reducing pedal effort friction material-similar to abecause longer of increased "leverage" the pry the bar. Racing drum brakes are of usualfriction material-similar to a longer ly the largest possible diameter that pry bar. Racing brakes are usualwill fit inside thedrum wheel. ly The the largest possible that size and weightdiameter of a brake will fit inside the wheel.in determining drum are important Themuch size heat and energy weightit of brake how can aabsorb. drum are important in determining Brake drums are measured by the how much heat of energy it can inside diameter the drum andabsorb. width Brake drums The are drum measured by surthe of the linings. rubbing inside diameter of the drum and width face is slightly wider than the lining to of the linings. The Don drum allow clearance. ' t rubbing measuresur-a face istoslightly widerlining than width. the lining to drum determine
allow clearance. Don't measure a drum to determine lining width.
radial-finned drum pumps cooling air between the wheel and drum.
Swept Area-The brake-drum inside circumference multiplied by lining Swept inside width isArea-The the brake brake-drum swept area, an imcircumference multiplied by lininga portant measure of how effective width is. the brakea car's sweptbrake area, specifian imbrake is Usually portant measurea ratio of how effective cation includes of brake swepta brake tois. the Usually a car's brake specificar weight. A figure of area cation ratioin.)of brake swept square includes inches a(sq per ton is figurearea of area to Athecarcar weight. typical. with a highAswept square in.) per ton is per ton inches will have(sqlong-wearing, fadecar with a high swept area typical. Abrakes, resistant with all other factors per tonequ will long-wearing, being al. have A typical road carfadehas resistant brakes, with all other about 200 sq in. per ton of sweptfactors area; equal. typical car has abeing race car may A have twice road this amount. about 200 sqdrum-brake in. per ton of swept area; Calculate swept area by athis race car may have twice this amount. formula:
Calculate drum-brake swept area by
Swept area = 3.14 DL in square inches this formula: D = Brake-drum inside diameter in Swept inches area = 3.14 DL in square inches D Brake-drum inside diameter in L = =Lining width in inches inches ToLining calculate area per ton, L= width swept in inches
divide swept area of all four brakes by calculate swept theTo car's weight in tons. area per ton, divide swept area of all four by To help remove heat andbrakes cool the the car's weight in tons. drum, fins are necessary. If the fins Towheel help remove heat and and are designed as acool unitthe to drum, are necessary. If as theanfins promotefins airflow, they can act air and wheel are designed as a unit to pump. Some older race-car drum promote airflow, they can act as an air brakes were highly sophisticated in pump. air Some older race-car drum forcing around the hot parts, as the brakes show. were highly sophisticated in photos forcing air around the hot further parts, as imthe Bimetallic Drums-To photos show. prove cooling, a high heat-conducting Bimetallic Drums-To further immaterial is used outside the cast-iron prove cooling, a highThis heat-conducting rubbing surface. is usually material is used outside the has cast-iron aluminum, although copper been rubbing surface. This is usually tried. Such drums are called bimetaflic. aluminum, although copper Aluminum carries heat from has the been rubtried. Such drums called fins bimetallic. to theare cooling more bing surface Aluminum heat from thebenerubrapidly than carries iron. An additional
bing surface to the cooling fins more rapidly than iron. An additional bene-
Drum
l +
A
Bellmouthing, which results from overheating and hard use, createsBrake angle Shoe A between drum and shoe. This angle causes shoe distortion, extra pedal movement, and faster lining wear on inside edges.
Airflow
Vintage sports car is powered by fuel-injected Chrysler hemi. Because of its high weight and a top speed of over 160 mph, it needed all the brakes it could get. Buick aluminum/cast-iron bimetallic drums were some of the best ever produced for passengercar use.
Bellmouthing, which results from overheating and hard use, creates angle A between drum and shoe. This angle causes shoe distortion, extra pedal movement, and faster lining wear on inside edges.
Airflow Vintage sports car is powered by fuel-injected Chrysler hemi. Because of its high weight and a top speed of over 160 mph, it needed all the brakes it could get. Buick aluminum/cast-iron bimetallic drums were some of the best ever produced for passengercar use.
A
Plate
lron Sheet Steel
.
Cast- lron Drum
Composite Drum Cast Iron
'
Sheet Steel
y
Composite Drum
Aluminum
Cast-Iron Drum
cast 1.0"
Bimetallic Drum
Cast Aluminum
Centrifugally Cast Composite Drum
Of commonly used designs, bimetallic drums cool best due to high heat transfer of aluminum. Bimetallic drums are also the lightest. Bimetallic is lighter. Centrifugally minum around the iron, known as the fit is that aluminum Cast Composite A /-fin process. For an Drum aluminum/iron drum to There Drum are four basic types of brakework properly, the aluminum must be drum construction. The simplest is attached tightly to the iron. The drum Of commonly used designs, bimetallic drums cool best due to high heat transfer of cast in one piece from iron. Another, will not cool sufficiently if there are aluminum. Bimetallic drums are also the lightest. lighter drum style, is the composite air gaps between the two metals. A drum. This type uses a sheet-steel once-popular type of bimetallic drum fitused is that aluminum is lighter. around therim iron, the h u b with an iron castknown to it. Aasvariaa special process for casting alu- minum
For an aluminumliron drum to work properly, the aluminum must be attached tightly to the iron . The drum will not cool sufficiently if there are air gaps between the two metals. A once-popular type of bimetallic drum used a special process for casting alu-
A I-fin process. There are four basic types of brakedrum construction. The simplest is cast in one piece from iron. Another, lighter drum style, is the composite drum. This type uses a sheet-steel hub with an iron rim cast to it. A varia-
Wheel Rim
Angled lip on drum can help cooling. If lip has fins, drum rotation can pump air between the wheel and drum. If lip extends inboard past wheel and backing plate, additional cooling is realized.
tion of the composite drum uses a stamped sheet-steel drum with a castAngled lip on drum can inside help cooling. lipa iron rubbing surface it. LastIf is has fins, drum rotation can pump air bebimetallic drum, made of aluminum tween the wheel and drum. If lip extends inand cast board pastiron. wheel and backing plate, addiDrum Design-The tional cooling is realized. design of the open edge of the brake drum is critical tion of the performance. composite drum uses a to a drum's The stiffness stamped sheet-steel drumwill withkeep a castof the lip at the edge the rubbing it. Last (egg is a iron drum from surface going inside out-of-round bimetallic , made of aluminum bellmouthing (diameter inshaped) ordrum and cast iron creasing at . open end) under severe Drum Design-The design of Also, the loads and high temperatures. open edge ofofthethe brake is critical the shape lip drum can determine tohow a drum's stiffness well aperformance. drum cools. The An angled lip of lip promote at the edge will around keep the canthehelp airflow the drum going out-oj-round (egg drum.from Because airflow around a drum shaped) or bel/mouthing (diameter inis complicated and affected by other creasing at open end) under severe parts on the car, drum cooling can loads and high temperatures. Also, only be determined by tests. the Besides shape of the lip and can cooling determine stiffening the how wellthe a lip drum lip drum, alsocools. matesAn withangled the backcan airflow around ing help plate.promote This helps keep dirt the and drum. around a drum water Because out of airflow the drum. The usual isdesign complicated and affected by other has a groove at the edge of the parts the car, brakeondrum. T h e drum outer cooling edge ofcan the only be determined by tests. Besides stiffening and cooling the drum , the lip also mates with the backing plate. This helps keep dirt and water out of the drum. The usual design has a groove at the edge of the brake drum . The outer edge of the
19
Fins on Alfa-Romeo aluminum/cast-iron drum are designed to pump air between drum and Alfa-Romeo tight-fitting aluminum/cast-iron wheel. Drum goes Fins on with brake assemblyto pictured on page 22. drum are designed pump air between Photo and by Ron Sessions. wheel. Drum goes drum tight-fitting with brake assembly pictured on page 22. Photo by Ron Sessions.
backing plate is flanged. This flange fits into the groove, but does not backing is This flanged. Thisfor flange touch theplate drum. is a seal dirt fits water, into the groove, but does not and making it difficult for fortouch the drum. This is a seal for dirt eign matter to blow or splash into the and water, it difficult for fordrum. The making brake-lining surfaces are eign to from blow contamination. or splash into the thus matter protected A drum. are problemThe withbrake-lining this seal is surfaces it also prethus protected contamination. A vents cooling from air from entering the problem with this seal is i t also preinterior of the brake.
vents cooling air from entering the
interior of the brake. BACKING PLATE The backing plate is a bracket on BACKING which the PLATE brake shoes and wheel The backing is serves a bracket on cylinders mount.plate It also to prowhich brake ofshoes and wheel tect thetheinterior the drum from cylinders mount. as It also serves to procontamination, just discussed. tect the interior of the drum from Braking torque is transmitted from contamination, as just discussed. the shoes to the suspension of the car Braking is transmitted from through torque the backing plate. A good the shoes to the suspension of the car backing plate must be stiff and strong through the backing plate. A good so the shoes stay in alignment with backing plate musta be stiff and strong the drum. When backing plate deso the excessively shoes stay inunder alignment flects load, with the the drum. driver feels When this asa abacking spongy plate pedaldeor flects excessively under load, the as excessive pedal travel. driver this asplates a spongy pedal or Mostfeels backing are stamped as excessive pedal travel. from heavy sheet steel. Ridges, Most and backing plates are stamped bumps edge lip stamped into the from heavy sheet steel. Ridges, backing plate increase its strength and bumps andCritical edge lipareas stamped into the stiffness. for strength backing increase its strength and are the plate brake-shoe-pivot and wheelstiffness. Critical areas for strength cylinder mounting points. Any cracks areother the brake-shoe-pivot wheelor weakness in thoseand areas can cylinder mountingsituation. points. Any cracks cause a dangerous or Some other backing weaknessplates in those areas race can on older cause a dangerous situation. cars are cast aluminum or magnesium backingThese plates are on older race forSome lightness. not good cars are cast or magnesium materials for aluminum this application because for These are not good they lightness. lack sufficient stiffness and materials for this application because strength. By the time an aluminum or they lack sufficient stiffness and strength. By the time an aluminum or
20
Early race-car drum brake has finned backing plate to help cooling. Unfortunately, the designer neglected usehas vents. And, beEarly race-car drum to brake finned backcause thetobacking plate Unfortunately, doesn't get very ing plate help cooling. the hot, theseneglected cooling fins help much. designer to don't use vents. And, because the backing plate doesn't get very hot, these cooling fins don't help much.
magnesium casting is sufficiently beefed up to equal the strength of a magnesium castingit will is be sufficiently steel backing plate, nearly as beefed up to equal the strength of a heavy. steel plate, it will nearly as Thebacking backing plate is be a precision heavy. part. Brake-shoe mounting points Thebebacking is brake a precision must aligned plate with the drum part.proper Brake-shoe points for operation.mounting A bent or twisted must be aligned the brake drum backing plate is with useless, so inspect for proper operation. A bent or twisted each one carefully for damage when backing plate is useless, so inspect working on your car. You should each one for damage when never pry carefully on a backing plate to working a on your car.This Youwillshould remove brake drum. bend neverbacking pry onplate a backing plate the to the and misalign remove a brake drum. This will bend brake shoes. theA backing plate isand misalign backing plate usually boltedthe to shoes. upright or axle flange abrake suspension A backing plate high-strength is usually bolted to with tight-fitting, bolts. aIt suspension upright or axle flange is important that this joint is tight with tight-fitting, and cannot shift high-strength under load. bolts. This It is important that this joint tight brings up an important point. isWhen and cannot working on shift brakes,under makeload. sure This the brings up an important point. bolts are the correct lengthWhen and working for on the brakes, make sure the strength application. bolts are theCooling-The correct length and Drum-Brake backing strength for the application. plate has little brake-cooling effect. It Drum-Brake never gets as Cooling-The hot as the otherbacking brake plate has little brake-cooling It parts. Therefore, fins or air effect. blowing never as hot other brake on the gets backing plateasisthe ineffective. Efparts. to Therefore, fins orbrake air blowing forts cool a drum should on the backing plate is ineffective. Efalways be directed to the drum. forts to backing cool a drum brake should Some plates are vented or always be directed to theon drum. have scoops mounted them. The Some backing plates are vented or purpose is to direct cooling air into have scoops mounted on them. The the interior of the brake drum. This purpose is to direct cooling into setup is found on most drumair brakes the interior of the brake drum. This used for racing, if the rules allow it. setupproblem is found with on most drumbacking brakes The ventilated used for racing, if the rules allow it.
The problem with ventilated backing
Large forward-facing scoop was used on 520-HP Auto Union Grand Prix cars from the mid-'30s. These cars usedwas huge drums Large forward-facing scoop used on and butPrix brake cooling 5 2 0 -hydraulic H P Auto actuation, Union Grand cars from withmid-'30s. that muchThese powercars was used a realhuge problem. the drums and hydraulic actuation, but brake cooling with that much power was a real problem.
Although most brake shoes are made of steel plate, cast aluminum has been used. Aluminum most is lighter, weakens at exAlthough brakebut shoes are made of treme temperatures. If youhas arebeen building a steel plate, cast aluminum used. car with aluminum make sure Aluminum is lighter,shoes, but weakens at they exwon't temperatures. be subjected Iftoyouextremely high treme are building a temperatures. Never use metallic racingcar with aluminum shoes, make sure they brake linings on aluminum won't be subjected to shoes. extremely high temperatures. Never use metallic racingbrake linings on aluminum shoes.
plates is that the venting may allow entry of water, dirt or other plates is that the venting maybraking allow contamination. This creates entry of particularly water, dirt or side other problems, if one of contamination. This more createsthan braking the car is affected the problems, particularly if one sideside of other. Grabbing or pulling to the the car is affected more than the while braking can result. other. Grabbing to the side A scoop shouldorbepulling designed to keep while braking can result. out contamination. To do this, some A scoop should be designed to keep people place a screen flush with the out contamination. To do this, some scoop intake. This restricts airflow to people place a screen flush the the brake, thus defeating the with purpose scoop intake. AThis to of the scoop. goodrestricts solutionairflow is to use the brake, thus defeating the purpose a long air duct with a coarse screen re-
of the scoop. A good solution is to use a long air duct with a coarse screen re-
Adjuster Cab le
Hold -
Return springs and hold-downs have been removed from these brake shoes. Springloaded hold-downs the shoes against Return springs and keep hold-downs have been flats on the backing shoeSpringedges removed from these plate. brakeThe shoes. rub against these flats asthe they moveagainst in and loaded hold-downs keep shoes out. on the backing plate. The shoe edges flats rub against they Thus move ,inonly and cessed intothese the flats duct asinlet. out.
Adjuster Levers
1
~) ~
.,-
fine partic les are likely to reach the
cessed ductwill inlet. Thus, only brake . into The the screen tend to repel fine particles are likely to reach the stones and other large objects entering brake. Thebut screen tendairflow to repel the duct, won'twill block as stones other large objectsthat entering much . and However, be aware dust the but brake won't and block as will duct, enter the mayairflow increase much. However, be aware that dust lining wear and drum-surface scoring. will enter the brake and may increase lining wear and drum-surface scoring. BRAKE SHOES Brake shoes are rigid metal assem-
BRAKE blies to SHOES which friction material is Brake shoes are rigid metalorassemattached. Friction material, brake blies material is lining, tois which ri veted friction or bonded to the brake attached. Friction material, or brake shoe. Brake shoes are usually or basis bonded to can the lining, sold on isan riveted exchange so they brake shoe.by Brake shoes usually be rebuilt installing newarelining on sold on an exchange so they the old shoes. Brakebasis shoes can can be be rebuiltandby used installing new lining on relined repeatedly unless the Brake shoes can be they old haveshoes. been damaged. relined and used unless Most brake shoesrepeatedly are fabricated of they have been damaged. sheet steel with a tee-shaped cross Most brake fabricated of section. Someshoes are are made of cast sheet steel. The with shoe a tee-shaped cross is shaped to aluminum section. Some made ofof cast match the insidearediameter the aluminum. shoe is shaped to drum , with The new full-thickness lining match the inside diameter of the installed . Accurate fit between the drum, and withdrum newisfull-thickness lining lining assured by machininstalled. Accurate fit between the ing the lining after it is attached to the lining This and drum is assured by machinshoe. machining process is called it is exact attached to the ing thethe lining afterThe arcing lining. radius of shoe. This machining process is called the arc is determined by the inside arcing the lining. TheIfexact radiushas of radius of the drum. the drum the arc is determined by the inside been turned to an oversize diameter, drum has radius of the drum. the lining-arc radius Ifis the increased to been turned to an oversize diameter, match. theBrake lining-arc increased to shoes radius have is rubbing points match. that are contacted by wheel-cylinder Brake shoesand havebrake rubbing points mechanisms adjusters. that are contacted by wheel-cylinder Also, there's a mechanical linkage mechanisms andparking brakebrake adjusters. connected to the , which Also, there's a mechanical operates the rear brake shoes. linkage These connected to the which rubbing points areparking subjectbrake, to wear and operates the rear brake shoes. These rubbing points are subject to wear and
Adjusting-Hole Cover
Adjusting-Screw Spring
~~ ~ Adjust in g-Screw Assemb ly
Assembly in the typical drum brake. This is a duo-servo rear brake Various types of springs are usedAdjusting-Screw with an automatic adjuster. Drawing courtesy Bendix Corp. Various types of springs are used in the typical drum brake. This is a duo-servo rear brake with an automatic adjuster. should be lubricated withDrawing specialcourtesy high- Bendix Corp.
temperature grease for maximum life .
should lubricated with special highBrakebeshoes have holes in them for temperature grease for maximum life. locating pins and return springs. Brakebuying shoes new have shoes, holes inmake themsure for When locating pins and ones return springs. the holes in the new match those. When new shoes, in the buying old shoes. Shoes make often sure get the holes in the new ones match those., mixed up when relining is performed in carefully the old comparing shoes. Shoes so old ofter! to newget is mixed up when relining is performed, worthwhile. When installing the new so carefully oldwhere to newthe is shoes, pay comparing attention to worthwhile. When installing the new return springs connect. Some shoes shoes, pay attention the have extra holes toforwhere various return springs applications. If aconnect. spring isSome placedshoes in a have hole, extra poor holes various wrong brake for performance applications. a spring is grabbing placed inora can result, in Ifthe form of wrong hole, poor brake performance dragging brakes. canBrake result, in grabbing or shoesthe getform very ofhot in racing dragging brakes. use, but not nearly as hot as the drum . Brake shoes hot the in racing If the shoe gets get too very hot and lining use, butworking, not nearly as hotofasthe the liningdrum. is still failure If the shoe gets toocould hot and the lining to-shoe bonding occur. Foris still working, failure of the tunately, most heat generatedliningby a to-shoebrake bonding occur. drum goes tocould the drum andFornot tunately, heat generated the shoes,most so overheated shoesbyarea drumBrakes brake goes theed drum and linnot rare. using to bond metallic the shoes, so overheated shoes are ings are the type for which bonding rare. Brakes using bonded metallic linstrength is extremely important. ings are the type design for which bonding Lining-material is more imstrength is extremely important. portant than brake-shoe design . See Lining-material design is discussion more imChapter 4 for an in-depth portant than brake-shoe design. See of brake linings. Chapter for anshoes in-depth discussion Usually4, brake are held to the of brake linings. Usually, brake shoes are held to the
Girlock of Australia manufactures this lightweight mechanically-operated brake for use asofa parking brake on '84-and-later Girlock Australia manufactures this Chevrolet It has all the features lightweightCorvettes. mechanically-operated brake of standard drum brake, including an adforause as a parking brake on '84-and-later juster and Corvettes. return springs. in Chevrolet It hasDrum all theinstalls features the hat. including Photo courtesy of a disc-brake-rotor standard drum brake, an adGirlockand Ltd.return springs. Drum installs in juster the disc-brake-rotor hat. Photo courtesy backing plate with a spring clip or Girlock Ltd.
spring-loaded pin. This pin lightly backing platebrake with shoe a spring clip the or presses the against spring-loaded pin. This pin lightly backing plate. Flats are provided on presses brakeforshoe against the the backithe ng plate the edge of the backing plate.against. Flats are provided on shoe to rest Pressure of the the backing plate for the edge of the shoe hold-down springs is low, so fricshoe rest against. Pressure of the tion isto minimal.
shoe hold-down springs is low, so friction is minimal. RETURN SPRINGS Drum-brake shoes are pulled away
RETURN SPRINGS Drum-brake shoes are pulled away 21
Brake adjuster is operated by turning star wheels. This type adjuster is used between the on byaturning leadingBrake brake adjuster shoes is operated star and-trailingdrum brake. Adjuster wheels. This shoe type adjuster is used between housing is mounted to backing plate.leadingthe brake shoes on a
and-trailing-shoe drum brake. Adjuster housing is mounted to backing plate.
from the drum-retracted-after application by a set of return springs. Befrom the apcause the drum-retracted-after force exerted by these plicationisbyhigh, a set of return springs. springs a special tool is Berecause to theinstall forcethem. exerted quired Thereby are these varisprings is high, a and special tool for is the reous arrangements mounts quired install them. There are return tosprings, depending on varithe ous arrangements and mounts for the specific design. return on thea If the springs, brake hasdepending any servo action, specific design. loss of return-spring force can cause the brake hasorany theIf brake to lock grabservo . Thisaction, may bea lossdangerous of return-spring can cause as as a lossforce of braking. For the brake if to only lock or grab. Thisloses may be instance, one wheel its as dangerous as a loss of side braking. For return-spring force , that can lock instance, if only one swerve wheel or loses up and cause a sudden skidits . return-spring force, that side can lock Some manufacturers provide difup and return cause a springs sudden swerve or skid. ferent that give a difSome manufacturers provide different force when installed. Springs ferent return springs by thatcolor. give Check a difare usually identified ferent force when installed. Springs with your parts supplier to be sure you are usually identified by color. Check have the correct ones on your vehicle. with your parts supplier to be if sure This is particularly important theyou car have the correct ones on yourorvehicle. is fitted with heavy-duty racing This is particularly important if the car brakes.
is fitted with heavy-duty or racing brakes. BRAKE ADJUSTERS
The return springs pull the brake BRAKE ADJUSTERS shoes away from the drum a minimum The return springs pulldistance the brake specified distance . If the the shoes away from the drum a minimum shoes must travel before contacting specified If theexcess distance the the drum distance. is too great, brakeshoes must results. travel before pedal travel Thus , contacting some adthe drum must is toobegreat, excessto brakejustment provided minipedal travel results. Thus, admize shoe clearance and to some compenjustment mustwear. be provided to minisate for lining mize shoeare clearance and to of compenThere two types brake sate for lining wear. adjusters, ma nua I and a uloma lie. There are two and types automaticof brake Both manualadjusters,designs man~/aland adjuster use aautomatic. cam or screw-
Both manual- and automaticadjuster designs use a cam or screw-
22
Prior to disc brakes, some drum-brake designs got pretty exotic. This three-leading-shoe drum brake was used on some Alfa Romeo sports cars. Although they did a good job of stopping the little sports cars, they weredesigns heavy and Notice that each shoe has its Prior to disc brakes, some drum-brake got complex. pretty exotic. This three-leading-shoe own drumwheel brakecylinder. was used on some Alfa Romeo sports cars. Although they did a good job of
stopping the little sports cars, they were heavy and complex. Notice that each shoe has its own wheel cylinder.
thread mechanism to move the brake shoes toward or away from the drum. thread mechanism move the brakea The duo-servo tobrake uses shoes toward or away from the drum. turnbuckle-like threaded link between The duo-servo brake uses the primary and secondary shoes.a turnbuckle-like threaded link between There are right-hand threads on one the primary and secondary shoes. end and left-hand threads on the There are right-hand threads on other. A star-shaped wheel, whichone is end and left-hand on thea rotated manually withthreads a tool through star-shaped wheel, is other. hole inA the brake drum or which backing rotated manually with a tool through plate, turns the threaded link. This ro-a hole the brake or backing tation in makes the drum link shorter or plate, the threaded link. This rolonger,turns increasing or decreasing shoetation makes the link shorter or to-drum clearance. longer, increasing or decreasing shoeAutomatic adjusters have a linkage to-drum clearance. that rotates the star wheel as the vehihave a linkage cleAutomatic is backedadjusters up and brakes are that rotates the star wheel as the vehiapplied. This is a ratchet-type cle is backed only up and brakes are mechanism-it works in one applied. . Automatic This is adjusters a ratchet-type direction are not mechanism-it only worksThere in one actuated in forward driving. is a direction. Automatic adjusters are not limit to the stroke of the actuating in forward driving. There the is a actuated linkage. When clearance between limit and to the of the actuating shoe the stroke drum reaches a certain linkage.the When clearance between the value, actuating linkage jumps shoe and the drum reaches a certain over the next tooth on the star wheel. value,feature the actuating jumps That prevents linkage the automatic over the next tooth on the star wheel. adjusters from overtightening the That brakes.feature prevents the automatic adjusters from overtightening thea Other types of brake adjusters use brakes. cam or an eccentric bolt for adjusting
Other types of brake adjusters use a cam or an eccentric bolt for adjusting
the shoes. These are actuated manually by turning a bolt that protrudes the shoes.the These are actuated manualthrough backing plate or by using ly by turning a bolt that protrudes a screwdriver through a hole in the through the backing plate or by using brake drum. a screwdriver throughisa covered hole in the Adjusting brakes in brake drum. Chapter 11 .
Adjusting brakes is covered in Chapter 1. WHEEL1CYLINDERS Brakes are applied by hydraulic WHEEL CYLINDERS fluid inside wheel cylinders. One or two Brakesin are pistons eachapplied cylinderbyarehydraulic moved fluid inside cylinders. One orwhen two outward by wheel brake-fluid pressure pistons in each cylinder are moved the driver pushes on the brake pedal. outward by brake-fluid pressure when Piston movement is transmitted to the pushes onthe thebrake brakeshoe pedal. the driver movable end of by movement is transmitted to aPiston pushrod or other linkage. theThere movable of the brakeofshoe by are end many types wheel acylinders. pushrod or other linkage. Cylinders are made from There are types are of singlewheel aluminum or many iron. There cylinders. Cylinders are made from or dual-piston cylinders, depending aluminum or iron. Duo-servo There are singleon brake design. brakes or cylinders, depending havedual-piston one cylinder operating two on brake brakes shoestwodesign. pistons Duo-servo are used with this have cylinder operating design. one Others have one cylinder two on shoes-two pistons are used with this each shoe-one-piston cylinders are design. used. Others have one cylinder on each shoe-one-piston cylinders are Wheel cylinders and other hydraulic used. components are discussed in more Wheel cylinders5. and other hydraulic detail in Chapter
components are discussed in more detail in Chapter 5.
Disc Brakes
3
Racing-brake setup on this March Indy Car uses four-wheel disc brakes with dual master cylinders pressurized by remotely adjustable balance bar. Brake cooling is critical at Phoenix International's one-mile oval. Photo by Tom Monroe.
Racing-brake setup on this March lndy Car uses four-wheel disc brakes with dual master cylinders pressurized by remotely adjustable balance bar. Brake cooling is critical at Phoenix International's one-mile oval. Photo by Tom Monroe.
Rotor
Caliper
Shield
Transfer Tube
Splash Shield
Major parts of disc brake are caliper, rotor and splash shield. A transfer tube connects hydraulic cylinders on opposite sides of Major parts of disc brake are caliper, rotor this fixed caliper. othertube fixedconnects calipers and splash shield. Many A transfer have internal fluid passages. Photosides courtehydraulic cylinders on opposite of sy Bendix Corp. Many other fixed calipers this fixed caliper.
have internal fluid passages. Photo courtesy Bendix Corp.
Disc brakes are used on the front of most modern road cars, and on all Disc brakesofaremost usedrace on the front of four wheels cars. Disc most modern road cars, and on all brakes were first introduced on cars in four wheels race cars. the late '40s. ofBymost the early '70s, Disc disc brakes first introduced on carson in brakes were had replaced drum brakes the late '40s. By the early '70s, disc the front. brakes had replaced brakes on Two common typesdrum of disc brakes the front. are single and multiple disc, both with Two common of disc brakes rotating discs or types rotors. Single-disc are single and multiple disc, both with types have a rotor, which is clamped rotating discs or rotors. Single-disc on by friction material called brake types Multiple-disc have a rotor, which clamped pads. types, is commonly brake on byonfriction used aircraft,material have acalled number of Multiple-disc types, commonly pads. rotating discs separated by stators, or used on aircraft, have a number stationary discs. Operation is by ofa stators, or rotating discs separated by large-diameter hydraulic piston in the stationary discs. Operation by a backing plate moving outward,isclamplarge-diameter piston in the ing the rotors hydraulic and stators together. backing plate moving outward, clampMultiple-disc brakes are 100% ing the , rotors stators types together. metallic while and single-disc use Multiple-disc brakes are 1000/o organic/metallic friction material.
metallic, while single-disc types use organic/metallic friction material.
ADVANTAGES OF DISC BRAKES The auto industry changed from ADVANTAGES DISC BRAKES drum brakes toOF disc brakes for a The auto industry changed from number of reasons: drum brakes to disc brakes for a • More resistant to brake fade. number reasons: • Better of cooling. More resistant to brake fade. and dirt resistant. • Water Better cooling. • Less maintenance. Water andsurface dirt resistant. • Greater area for a given Less of maintenance. weight brake. Greater surface area for given The main advantage disc a brakes weight of brake. have over drum brakes is their inThe main advantage disc reasons brakes creased resistance to fade . The havethisover for are : drum brakes is their increased resistance to fade. Theexposed reasons • Friction surfaces directly for this are: to cooling air. surfacesis directly exposed Drum deflection eliminated. • Friction to cooling air. have no servo action. • Disc brakes Drum deflection eliminated. The lack of servoisaction is a disadDisc brakes have no action. vantage with a heavy servo car. Resulting The lack of servo action is disadpedal effort is too high. As aa result, vantage with almost a heavyalways car. Resulting brakes require disc pedal effort is too high. As a result,
disc brakes almost always require
23
AHeatlnput
Air Cooling
Heat Input
" I_\J" ~
Drum
Drum
Heat lnput Drum Brake
Drum Brake
Rotor Disc Brake
Rotor
Why a disc brake has superior cooling is illustrated here. Heat generated by brake drum Disc Brake must flow through drum before air can cool the brake. On a disc brake, hot rubbing surfaces are directly exposed to cooling air; heat-to-air transfer begins immediately Why a disc brake has superior cooling is illustrated here. Heat generated by upon brakebrake drum application. must flow through drum before air can cool the brake. On a disc brake, hot rubbing surfaces
are directly exposed t o cooling air; heat-to-air transfer begins immediately upon brake application. Expansion
Adapted to a hot rod, early Chrysler Imperial disc brake looks like a drum brake and works like Adapted toaaclutch. hor rod,Although early ~ nneat r y s llooking, e Imper it worklooks as well a modern rialdoesn't disc brake like as a drum brakedisc and brake. like Rubbing surfaces on brake are on works a clutch. Although neat looking, inside of finned i t doesn't work housing. as well as a modern disc
brake. Rubbing surfaces on brake are on inside of finned housing.
Direction
Expansion Direction
Expansion Direction
Expansion Direction Pad
Drum
Drum
_
d$$ ... -..._. .. . _ . ..__-_.... , . Drum Brake
&pad ... ..,.. 8 .
... ..I
Shoe
Drum Brake
Rotor
Disc Brake
Disc Expansion of hot brake drum is away from brake shoes. This requires extra pedal travel. A Brake disc-brake rotor expands slightly toward the pads. Therefore, extra pedal travel due to heat expansion is brake not a problem hot disc brake. Expansion of hot drum is with awaya from brake shoes. This requires extra pedal travel. A
disc-brake rotor expands slightly toward the pads. Therefore, extra pedal travel due to heat expansion is not a problem with a hot disc brake.
SPOT BRAKES & -, DISC BRAKES SPOT BRAKE9 & first called a The disc brake was
Disc brakes were used on many race cars in the mid-'50s. This car, built in 1955, is powered by were a 300-HP Chevy. Disc brakes used on many Tiny race solid cars rotors would never becar, used today on such in the mid-'50s. This built in 1955, is a powerfulby car.a 300-HP Chevy. Tiny solid powered
rotors would never be used today on such assist, apower powerful car. while drum brakes with
high servo action may not. On race power assist, while drumless, brakes cars , weight is much so with disc high servo action may not. On race brakes usually do not require power cars, weight is much less, so disc assist. brakes usually part do not The hottest of arequire brake power is the assist. metal surface contacted by the friction The hottest a brake the On a part drumofbrake, thisis surmaterial. metal surface contacted by the friction face is inside the drum; on a disc material. Onthe a drum brake, thisrotor. surexterior of the brake, it is face is inside the drum; on a disc For a drum brake to cool, the tembrake, it is the exterior of the rotor. perature of the entire drum must first For aThen drumthebrake theattemdrumto iscool, cooled the rise.
perature of the entire drum must first rise. Then the drum is cooled at the 24
DISC BRAKES spot brake or spot disc brake. The dlsc brake was first acalled a This distinguished it from type of spot brake brake that or spot brake. disc has adisc clutch-like a type of This dlstlnguished full circle of frictionIt from material. This disc brake thatof has ctufcblike unusual type disca brake was full of frlction material. This Chrysler Imperial in usedcircle on the unusual was the early type '50s, of butdisc was brake discOritintheofChryder Imperial in used ued i'non favor the traditional drum the early '50s, but was discolltln-brake. ued In favor ofmultidisc the traditional Full-circle brakesdrum are brake. Full-circle multidisc brakes are
exterior by surrounding air. A disc brake is cooled immediately by air exterior A disc the disc'sair. rubbing blowing byonsurrounding brake is cooled immediately by air surfaces. blowing on the disc's rubbing drum expands-ID A brake surfaces. increases-when it gets hot, increasbrake expands-ID ingA pedal travel.drum The drum can also increases-when it gets warp from temperature hot, or increasbraking ing travel. The deflection drum can also deforce.pedalBrake-drum warp temperature or braking creasesfrom performance and causes fade. force. Brake-drum derotor is essenHowever, a disc-brake deflection creases performance and causes fade. tially a flat plate. Temperature expanHowever, disc-brake rotortheisfriction essension of thearotor is toward
tially a flat plate. Temperature expansion of the rotor is toward the friction
used on large aircraft. Light aircraft typically use more conventional used on large Light alrcraft spot-type discaircraft. brakes. There's a typlcelb use more convent~onal brief discussion of aircraft brakes spot-type disc brakes. There's a in Chapter 9. brief discussion aircraft brakes To keep things of simple, I call the in Chapter automotive 9. standard disc ', brake -simply To keep th'inggsimple, I call the a disc brake because the standard brake brake is nodisc longer in term spot automotive simply a use. disc And, brake I beaause the common call aircraft term spotbrakes brake simply Is no longer in multidisc multidisc cbrakes. m m n use. And, I oall aircraft
multidisc brakes simply multidiso brakes.
material rather than away from it. Squeezing a disc cannot cause suffimaterial rather tothan from it. cient deflection affectaway performance. Squeezing a disc cannot cause The lack of servo action meanssuffithat cient deflection performance. a disc brake to is affect affected little by The lack servo action that changes in of friction. As I means mentioned aearlier, disc drum brake brakes is affected little by with maximum changes in friction. As I mentioned servo action are also affected the most earlier, drum brakes maximum by friction changes. Awith slight drop in servo action most friction, suchare as also thataffected caused the by heat, by friction changes. A slight drop in is magnified by the servo action . The friction, such as that caused by heat, driver senses this as fade. Disc brakes is magnified by the servo action. The as sensitive as drum are simply not
driver senses this as fade. Disc brakes are simply not as sensitive as drum
JFZ disc brake is designed to stop a oval-track race car. Four-piston, I lightweight caliper is is massive to reduce JFZ disc brake designed to stopde-a flections minimize temperature. Photo powerful and oval-track race car. Four-piston, courtesy JFZ Engineered Products. lightweight caliper is massive to reduce de-
Changing brake pads on most disc brakes is easy. Pads are sometimes retained with quick-release pins. New being inChanging brake pads on pads mostare disc brakes stalled thisare transaxle-mounted caliper is easy. in Pads sometimes retained with for bedding in. pins. New pads are being inquick-release
flections and minimize temperature. Photo courtesy JFZ Engineered Products.
stalled in this transaxle-mounted caliper for bedding in.
Ipowerful
Rotor bolts to lightweight aluminum hat. Assembly then bolts to wheel hub or axle . . Deep flexes when rotor aluminum expands from Rotor hat bolts to lightweight hat. high temperature and to minimizes brake heat Assembly then bolts wheel hub or axle. transferred to thewhen wheelrotor hub expands and bearings. Deep hat flexes from Photo courtesy JFZ Engineered high temperature and minimizesProducts. brake heat
transferred to the wheel hub and bearings. Photo courtesy JFZ Engineered Products.
brakes to changes in friction. The shape of a drum brake also conbrakes in friction. tributestotochanges fade. Many organic brake The shape of a drum con-. linings expel gases brake when also heated tributesgases to fade. Many brake These can act as aorganic lubricant belinings expel when causing heated. tween the lininggases and drum, These as a lubricant befrictiongases loss can andact severe brake fade. tween the lining and drum, causing The cylindrical surface of a brake friction and severe brake infade. drum is loss similar to bearings an The cylindrical surfacehigh-pressure of a brake engine. For example, drum is similar bearings in an oil between a main tobearing and crankengine. For example, high-pressure shaft journal keeps the surfaces apart oil between bearing and and friction atomain a minimum. A crankbrake shaft journal keeps the surfaces drum and shoes act much like an apart oiled and friction to a minimum. A gas brake bearing and journal when hot is drum and shoes act much an oiled expelled between them.like They are bearing when hot gas is pushed and apartjournal by the high-pressure expelled between them.andThey are gas , reducing friction causing pushed apart by the high-pressure brake fade. gas, frictionarea andof causing Thereducing small surface a discbrake brake fade. pad and the flat face of the rotor surface area of a discdoThe not small simulate a bearing container. brake pad and the flat face of the There may be some gas coming rotor from do simulate a bearing the not lining, but because it iscontainer. not conThere someisgas coming tained may well,bethere little effect.from To the lining, it is on nota conrepeat, any but dropbecause in friction disc tained well, there littleon effect. To it lessis than a drum brake affects repeat, any drop in friction on a disc brake because the disc brake has no brake action affects. it less than on a drum servo brake because cooling the discisbrake no Disc-brake betterhasthan servo action. drum-brake cooling because the rotorDisc-brake cooling is better than contact surfaces are directly exposed drum-brake cooling becausethis themakes rotorto cooling air. However, contact surfaces are directly exposed the contact surfaces "potentially" to cooling air. However, this makes more vulnerable to damage from corthe contact surfaces "potentially" rosive dirt or water contamination. more vulnerable corFortunately, theto damage constantfrom wiping
rosive dirt or water contamination. Fortunately, the constant wiping
action of the pads against the rotor keeps the surfaces clean. Also, cenaction the tends pads to against rotor trifugal of force throwthe material keeps the surfaces clean. Also, cenoff the rotor. Because water is wiped trifugaltheforce tends throw material from rotor, discto brakes are less off the rotor. Because water is wiped sensitive to this contamination than from the rotor, disc brakes less drum brakes. On the otherarehand, sensitive to this contamination than water lubricates a drum brake well. drum more brakes. On action the other And, servo meanshand, less water lubricates a drum brake well. braking. And, more servo action less Disc-brake pads are easymeans to change braking. on most cars. Usually, disc pads can padsremoving are easy the to change beDisc-brake changed after wheel on most cars.locking Usually, disc Some pads 'can and a simple device. inbe changed after removing the wheel stallations requires removing the and a simple locking device. Some incaliper. stallations requires removing the Another advantage of disc brakes caliper.drums is adjustment. Drum over Another of disc brakes brakes mustadvantage be manually adjusted or over drums is adjustment. must have the added complexityDrum of an brakes must be manually adjusted or automatic-adjusting system . Disc must added to complexity an brakeshave are the designed run with of little automatic-adjusting system. each Disc clearance, and are self-adjusting brakes are designed to run with little time they are applied . clearance, and are rotor self-adjusting each The disc-brake has a contact time they are applied. surface on each side; the brake drum rotor has contact hasThe a disc-brake contact surface onlya on the surface on each side; thearea brake drum inside. Disc-brake swept is larger has contact surface only brake on the whena compared to a drum of inside. Disc-brake swept area is the same diameter and weight. larger More when compared a drum brake of swept area means to better cooling.
the same diameter and weight. More swept area & means better cooling. ROTORS HATS
The rotor, usually made of cast ROTORS HATSand heaviest part of iron, is the&largest The rotor, of disc cast a disc brake. Itusually is a flatmade circular iron, is the largest and heaviest part of with a contact surface on each side.
a disc brake. It is a flat circular disc with a contact surface on each side.
The rotor may either be solid or it can be vented with cooling passages The rotorit.may either be solid or i t can through be vented with iscooling passages HatsThe rotor usually attached through to a hat, it. which in turn is attached to a Hats-The rotor is flange. usually The attached wheel hub or axle hat to a hat, which in turn is attached to a gives a long path for heat to travel wheelthe hub or rubbing axle flange. The hat from brake surface to the gives long pathThis for heat travel wheel a bearings. keepsto wheelfrom thetemperature brake rubbingdown. surface to the bearing The hat wheel bearings. This keeps wheelsometimes is cast integral with the bearing temperature hat rotor, and sometimes down. it is a The separate sometimes is cast integral with the part. rotor, it is aorseparate Hatsand are sometimes made of iron lighter part. material, such as aluminum. ProHats are hats madeareof usually iron oriron lighter duction-car and material, such aluminum. Prointegral with the as rotor. Most race-car duction-car hats are iron and hats are separate and usually made of alumiintegral with the rotor. Most race-car num alloy. hats are non-integral separate and rotors, made ofthe alumiWith hatnum alloy.attachment can be either of to-rotor With rotors, the hattwo typesnon-integral , bolted or dog-drive. A dogto-rotor attachment can be either of drive is a series of radial slots in the two types, bolted or dog-drive. A dogrotor with metal driving dogs attached drive seriesact of asradial slots the to the is hat.a They a spline to in transrotor with metal driving dogs and attached mit torque between brake hat. to the hat. actthe as arotor splinetotoexpand transThese dogsThey allow mit torque between brake and hat. freely while keeping the rotor cenThese dogsthe allow rotorfreedom to expand tered on hat.theThis to freely keeping cenexpand while eliminates loadsthe therotor hat would tered on get thewhen hat. the This freedom otherwise rotor gets hot.to expand loadstothe would If the eliminates hat is bolted thehat rotor, it otherwise get when the rotor rotor gets must expand with the as it hot. gets If the hathat is bolted to the thin rotor,andi t hot. If the is relatively must expand with the rotor as i t gets flexible, it works without breaking. hot. Ifbolted the hat is relatively thin and The connection between the
flexible, it works without breaking. The bolted connection between the
25
Slots on Surface
Slots on Surface
,
Rotor Rotation Direction Curved Vent Holes Curved
Vent Holes Racing rotor from AP Racing uses a dogdrive rather than bolts to transfer braking action the from hat. Dogs on hatuses fit ina slots Racing to rotor AP Racing dogmachined in than edge bolts of rotor 10. Slightbraking cleardrive rather t o transfer ance between hatDogs dogsonand action t o the hat. hat rotor fit in slots allow rotorintoedge expand uniformly, but remain machined of rotor ID. Slight clearcentered. Cleverhat mounting arrangement is ance between dogs and rotor slots called rotor castel/a ted drive by AP allow t o expand uniformly, but Racing. remain Photo courtesy APmounting Racing. arrangement is centered. Clever
called castellated drive by AP Racing. Photo courtesy AP Racing.
On this racing rotor, metal is removed at outer edge to reduce weight and slots are cut in rotor faces to reduce of On this racing rotor, metal ispossibility removed at fade. Photo courtesy Racing. outer edge to reduceAP weight and slots are
cut in rotor faces to reduce possibility of fade. Photo courtesy AP Racing.
Highly developed AP Racing Sphericone rotor-notice projections cast inside ventJ holes-transmits cooling air more Highly developedheat AP to Racing Sphericone efficiently standardcast vented rotor-noticethan projections insiderotor. vent Design is used onheat Grand Prix cars, holes-transmits t o cooling airwhere more every ouncethan of rotor weight vented counts. Photo efficiently standard rotor. courtesy Racing. Design isAP used on Grand Prix cars, where
every ounce of rotor weight counts. Photo courtesy AP Racing. two items must use high-strength
bol ts wi th close-fitting, un threaded two items mustbolts use are high-strength shanks . Aircraft often used boltsthiswith close-fitting, for purpose, because unthreaded they come
shanks. Aircraft bolts are often used for this purpose, because they come 26
A rotor that has curved vent holes or angled slots must rotate in a particular direction be has effective. rotation A rotor tothat curvedCorrect vent holes or relative slots to vents and slots in is ashown. angled must rotate particular di-
rection to be effective. Correct rotation relative t o vents and slots is shown.
Here's what eventually happens to a rotor when thermal stresses are high. Because race-car rotors undergo such atobeating, Here's what eventually happens a rotor they should inspected and when thermalbestresses are frequently high. Because replaced ifrotors cracksundergo are detected. race-car such a beating,
they should be inspected frequently and replaced if cracks are detected.
with accurately machined unthreaded shanks. with accuratelyhats machined Aluminum reduce unthreaded weight and shanks. thermal stress on the rotor. Because Aluminum hatse xpands reduce atweight and aluminum alloy a gre ater thermal the to rotor. Because rate thanstress iron , itontends equalize the aluminum alloy expands at a greater expansion difference caused by exrate thantemperature iron, i t tends of to equalize ther. treme the roto expansion difference caused by exAdditionally , aluminum alloy is about treme temperature of the rotor. one-third as rigid as iron, so there is Additionally, aluminum alloy is about much less force put on the rotor fo r a one-third as rigid as iron, .so there is given amount of e xpansion The lightmuch less force put on the rotor for er aluminum hat aids the car ' s per-a given amount of expansion. lightformance and handling . One The disadvaner aluminum hat aids the car's tage of the aluminum-alloy hat is perthal formance handling. One iron. disadvanit conductsand heat better than This tage of the causes the aluminum-alloy wheel bearingshattois that* run ithotter. conducts heat better than iron. This causes the wheel bearings run Rotor Design-A disc-braketo rotor hotter. has many features common with that Rotor Design-A rotor of a brake drum. The disc-brake material is usualhas many that ly grey castfeatures iron forcommon the samewith reasons of a brake drum. The material is usualit is popular for brake drums. Cast ly greyhas cast good iron for the same iron wear and reasons friction itproperties, is popularis rigid for brake drums. and strong at Cast high iron has good and friction temperatures, and wear is inexpensive and properties, is rigid and strong at high easy to machine. temperatures, and is inexpensive and A rotor is measured by its outside easy to machine. diameter and its total thickness across rotorcontact is measured by its theA two surfaces. A outside vented diameter and its total thickness rotor is always thicker than aacross solid the two surfaces. A vented rotor. Thecontact diameter of the rotor is usurotorlimited is always than a solid ally by thethicker wheel size. rotor. Thearea diameter of theisrotor is usuSwept of a brake an imporally by of theitswheel size. tant limited measure effectiveness. The Swept area a brake imporswept area of of a disc brakeis isanthe total tant measure effectiveness. The area contactedofbyitsboth the brake pads swept of a disc brake is the total in one area revolution. area contacted by both thearea brakeofpads The combined swept a ll in one revolution. brakes divided by the weight of the combined swept area all carThe is one way of indicating how of effecbrakes by the the tive its divided brakes are likelyweight to be.ofWith
car is one way of indicating how effective' its brakes are likely to be. With
Tiny cracks on race-car-rotor surface are caused by thermal stresses. Rotor should be replaced before larger cracks form. Tiny cracks on race-car-rotor surface are Small cracksstresses. can oftenRotor be removed caised surface by thermal should by be grinding. replaced before larger cracks form.
Small surface cracks can often be removed by grinding. good brake design, high swept area
per ton indicates a high-performance
good design, swept brake brake system. Brake high swept area area for per ton cars indicates a on high-performance various is given page 28 . brake Brakeslots swept area mafor Somesystem. rotors have or holes various cars is given on page 28. chined in their contact surfaces . Some rotorshot-gas have slots holes maThese reduce and or dust-particle chined in their pad contact surfaces. buildup between and rotor. AlThese reduce hot-gas and dust-particle though fade caused by gas buildup is buildup padthan and for rotor. Alless for abetween disc brake a drum though fade caused by gas buildup is brake , some fade can still occur. This lessmore for a prevalant disc brakewith than large for a brake drum is brake, some fade stillhas occur. This pads , because the can hot gas a harder is more prevalant with large brake time escaping than with small pads. pads, because theorhot gas have has a greater harder Therefore, slots holes time escaping withpads small effect in racing,than where are pads. large Therefore, slots orareholes and temperatures veryhave high.greater Holes effect in racing, where pads large increase the tendency for are cast-iron and temperatures are very high. Holes rotors to crack, so they should be increase used only the whentendency required. for cast-iron rotors crack, so they be Vented to Rotors-Many rotoshould rs are cast used only when required. with radial cooling passages in them. Ventedact Rotors-Many rotors are cast These as an air pump to circulate withfrom radial passages in them. air thecooling rotor center through the These act as an air pump to circulate air from the rotor center through the
Tension Tenslon
1m I Compression Compression
Shear
Three ways stress act on a material: Tension pulls; compression crushes; and and shear rips rips Each stress occurs simultaneously in in a hot brake component, particularly particularly if one sideways. Each area area of the part is hot and and another is cool.
.' THEflMALSTRESS
Lightweight race-car rotor has has no hat. Rotor heat flows directly from rotor to t o aluminum minum hUb. hub. Such a design design should only be be used used on light cars with small small engines, where little heat is generated. Wheel bearings ings in in this hub hub have to t o be be replaced replaced several times a season.
'Stress is a measure of the internal force' inasolio material, usually giVen. in pounds per square inch (psj).:.,..the same units for measuring 'l1y<;lraulic pressure. Stress acts in compressIon, tension orin a sliding. dfrectioti '.. called ,shear. Typically, . only 'tension stress-pulling..:.causes cast ironto crack., The stress at wl1ich. a material breaks, in tension is called.its fensiJes.trengt1:), . Tl1e tensile 'strength of g(eyca~t ,jrortJs apout 25,000 psI. . ,". Wh~m . a metal is heated, it;· expands. If the metal is' restrained" so it can't expand freely, it,r:lI:essss ., against its restraint with atorce:.·· The restraining force ,causes,ao', additional stress in the: metaLt'hi.S" ' streS$ caused by a changeinlem,,;. " peratl,Jre is called a thermalsfr.ess,'.~'· Thermal stress occurs.' .WR,el'] , metal is hotter in one area.l(acqlo brake rotor is suddenlyusedfcir' a
Rp Rp == radius to outside of pad pad RR RR == radius to the outside of the rotor wp wp == pad pad width
passages to the outside of the rotor. This type of rotor is referred to as a vented rotor. rotor. Vented rotors are used on most heavy cars requiring the larglargest possible rotors. rotors. Lighter cars usually use solid rotors. Powerful race cars use vented Sometimes there is a difference rotors. Sometimes sidewalls. in the thickness of the rotor sidewalls. On many race-car brakes, the rotor side closest to the wheel is thicker than the side away from the wheel. This is done to try to equalize the temperature on each side of the rotor. The wheel tends to prevent cooling air from reaching the outboard rubbing surface of the rotor, making it run hotter than the inboard surface. The extra thickness next to the poorly cooled outboard surface tends to equalize temperatures.
Racing rotors often have curved cooling passages, which increase airpumping efficiency. efficiency. Because these vents are curved, there are different rotors for the right and left sides of the car. car. If your brakes use curved-vent up! rotors, don't get them mixed up! A problem with vented rotors used in severe service is cracking. cracking. This is caused by thermal stresses and by brake-pad pressure against the unsupported metal at each cooling passage. passage. Thermal stresses on a rotor with a cast- or bolted-on hat are caused by the contact portion of the rotor being hotter than the hat portion. Because heat causes expansion, the outer portion of the rotor expands more than the cooler hat. This distorts and bends the rotor into a conical shape. shape. Repeated expansion and contraction cause
If Rp R, nearly equals RR. RR, use the following following formula formula to find swept area of brake: brake: Disc-brake swept area
= =
6.28 wp wp) w, (2RR (2RR-- w ),
Disc-brake swept area is area on both both sides of rotor rubbed rubbed by pads. pads. It I t is more more accurate to use use Rp R, instead instead of RR' R,. However, However, because the two radii radii are nearly equal in R, is used used for convenin most brakes, RR ience. RR R, is easier to t o measure than Rp. R,.
cracks to appear. appear. Even though crackcracking may not occur, coning causes uneven lining wear. Rotor cracking is greatly reduced for two reasons with curved vents: First, curved vents provide better support for the sides. sides. And, because curved-vent rotors cool better, therless. mal stresses are less. Rotors-The Composite RotorsThe latest rotor material was developed for heavy aircraft brakes and is being 27
TYPICAL SWEPT AREAS PER TON OF VEHICLE WEIGHT Swept Area· TYPICAL Sq SWEPT AREAS PER TONCar OFMake VEHICLE WEIGHT Car Make and Model In.lTon and Model Swept Area Alta Romeo Spyder Veloce Mercury Lynx RS 259 Car Make Model S q In./Ton Car Make and Model Audi 5000 and Turbo 245 Mitsubishi Cordia LS R S Turbo Alfa Romeo Spyder Veloce 259 Mercury Lynx Audi Quatro 254 Mitsubishi Starion Audi 245 Mitsubishi Cordia LS BMW5000 528eTurbo Nissan Sentra 259 Audi 254 Mitsubishi Starion Turbo 745i Nissan Stanza BMWQuatro 302 BMW 528eCamaro Z28 259 Nissan Sentra Peugeot 505 STI Chevrolet 176 BMW 7451Citation X11 HO 302 Nissan Stanza Chevrolet Pontiac Firebird Trans-Am 180 Chevrolet Corvette Camaro 228 176 PeugeotGrand 505 ST1 Pontiac National Racer Chevrolet 284 Chevrolet Citation X 1 1 HO 180 Pontiac J2000 Firebird Trans-Am Pontiac Datsun 200SX 266 Chevrolet 284 Pontiac Grand Porsche 944 National Racer Delorean Corvette 346 266 Pontiac J2000 DatsunAries 200SX Dodge Wagon Renault Alliance 145 346 Porsche Fuego 944 Turbo Delorean Renault Dodge Challenger 230 145 Renault Alliance Dodge Aries Wagon Charger 2.2 161 Renault LeCar ISMA GTU Turbo Dodge Challenger 230 Renault 5Fuego Ferrari 308GTSi Renault TurboTurbo 263 Dodge Charger 2.2 161 Renault LeCar I S M A GTU Turbo Renault 18i Fiat Brava 154 Ferrari 308GTSi 5 Turbo 263 Renault Spyder Saab 900 Fiat Turbo 221 Fiat Brava 154 Renault GL 18i Ford Mustang GT 5.0 162 Subaru Fiat Turbo Spyder 221 Saab Honda Accord Toyota900 Celica 177 162 SubaruCelica GL Supra Ford Mustang Honda Civic GT 5.0 Toyota 171 HondaI-mark AccordLS 177 Toyota Starlet Celica Isuzu 209 Toyota Honda Civic 171 Toyota CelicaQuantum Supra Jaguar XJ-S 219 Volkswagen S 209 Toyota Starlet lsuzu I-mark LJalpa Lamborghini 227 Volkswagen Rabbit GTI 21 9 Volkswagen Quantum Jaguar XJ-S Carlo GP.5 Turbo Lancia Monte 537* Volkswagen Sci rocco Larnborghini 227 Volkswagen Rabbit GTISCCA GT3 Mazda GLC Jalpa 174 Volkswagen Sci rocco Lancia Monte Carlo GP.5 Turbo 537* Volkswagen Scirocco Volvo GLT Turbo Mercedes-Benz 380SL 237 Mazda GLC 174 Volkswagen Scirocco Mercury LN7 173 *Indicates race car. SCCA GT3
Swept Area Sq In.lTon Swept Area 188 S196 q In./Ton 188 236 196 272 236 174 272 269 174 277 269 236* 277 173 236* 303 173 190 303 185 190 348* 185 175 348' 189 175 275 18 9 169 275 208 169 224 208 196 224 183 196 216 183 198 21 6 304* 198 242
304* Volvo GLT Turbo 242 and '82 cars as published in Road & Track magazine. Notice that high-performance 'Indicates race car. economy sedans. Those for race cars are indicated by asterisks. Race-car brakes are
237 Mercedes-Benz 380SL ListedMercury are brake swept areas per ton for typical 1981 LN7 173
cars tend to have higher swept areas per ton than larger and race cars are generally lighter. The 537 sq-in./per ton area for the Lancia Monte Carlo GP 5 Turbo long-distance racer indicates long-wearing powerful brakes. cars tend to have higher swept areas per ton than economy sedans. Those for race cars are indicated by asterisks. Race-car brakes are larger and race cars are generally lighter. The 537 sq-in./per ton area for the Lancia Monte Carlo GP 5 Turbo long-distance racer indicates
long-wearing powerful brakes.
Curved-vent AP Racing rotor has slots angled so rotor rotation will tend to throw off dust. As viewed, rotorrotor should inCurved-vent AP Racing hasbeslots stalled sorotor it rotates angled so rotation counterclockwise. will tend to throw Photo courtesy AP Racing. Off dust. As rotor be in-
stalled so it rotates counterclockwise. Photo courtesy AP Racing.
used on Grand Prix cars. These new rotors are made of carbon-graphite, used Grand Prix These rotor new borononcomposite. A cars. composite rotors are made of carbon-graphite, is lighter than a cast-iron rotorA composite boron 30-lb composite. about less total weight onrotor the is lighter F-l than a cast-iron rotorBrabham car-and it can operate about 30-lb less temperatures. total weight onTemthe at much higher Brabham F-1 car-and it can operate peratures up to 1700F (927C) have at muchobserved higher temperatures. Tembeen without damage. peratures up to 1700F 7 0 have Graphite-composite pads( 9 2are used been composite observed rotors without with due damage. to high Graphite-composite pads are used operating temperatures. with composite rotorsrotors due to Because composite are high exoperating perimentaltemperatures. for racing use, there is no Becausethey composite are way excertainty will everrotors find their perimental for racing use, there is no into production cars. However, if the certainty they will ever find their way car manufacturers continue to work
into production cars. However, if the car manufacturers continue to work
Brabham Grand Prix car is fitted with graphite-composite brake rotors. Exotic material from the aerospace industry can operate at extreme temperature. Brakes work while rotors glow red! Grand Prix car is fitted with graphite-composite brake rotors. Exotic material Brabham
from the aerospace industry can operate a t extreme temperature. Brakes work while rotors glow red!
28
on weight reduction and the cost of composites become reasonable, there on reduction and on theyour cost car of mayweight be composite brakes composites become reasonable, there some day. The problem is that commay be composite brakes on your car posite brakes experience extreme some day.toThe problem is that comwear due road-dirt contamination.
posite brakes experience extreme wear due to road-dirt contamination. CALIPERS Disc-brake calipers contain brake
CALIPERS pads and hydraulic pistons that move calipers contain brake theDisc-brake pads against the rotor surfaces. pads and hydraulic pistons that move There are many types of calipers. the pads against the rotor structural surfaces. They differ in material, There are types arrangement. of calipers. design andmany piston They differ all in material, Regardless, disc-brake structural calipers design and piston arrangement. operate on the same principle-when Regardless, all disc-brake the driver pushes the brake calipers pedal, operate on the same brake fluid forces theprinciple-when pistons against the driverpads pushes the them braketo pedal. the brake , causing clamp brake fluid forces the pistons against the rotor. theCalipers brake pads, them to clamp usedcausing on most production the rotor. cars are made of high-strength nodular Calipers used low-cost on most material productionis cast iron. This cars are made of high-strength suited to mass production, andnodular makes cast This low-costcast-iron materialcaliis a rigidiron. caliper. However, suited to mass and cars makes pers tend to beproduction, heavy. Race or ahigh-performance rigid caliper. However, cars cast-iron usually caliuse pers tend to be heavy. cars or aluminum-alloy brake Race calipers. A high-performance carscaliper usuallyweighs use light aluminum-alloy aluminum-alloy calipers. A about half as muchbrake as cast-iron caliper light aluminum-alloy caliper weighs of the same size. about much as cast-ironarecaliper Fixed half & as Floating-There two of the same size. Fixed & Floating-There are two
I
Rotor on dragster rear axle has been given the swiss-cheese look by cross-drilling. Care must be exercised when Rotor on dragster rear axle has beendrilling given rotors to avoid weakening or ruining the swiss-cheese look bythem cross-drilling. their Drilling reduceswhen rotor drilling weight Care balance. must be exercised and, therefore, the heat it can absorb. This weakening them Or ruining is no balance. problem Drilling for a dragster the their reduces because rotor weight brakes are coolthe for heat each itstop. drilling and, therefore, can Such absorb, This is more critical oval- or because road-racing is no problem foron a dragster the cars. Beare careful! brakes cool for each stop. Such drilling
JFZ racing caliper is typical fixed-caliper design; caliper is fixed and only pistons move. Two pistons on each side are housed in cylinders bored in caliper body. Caliper assembly is bolted to axle housing or suspension upright through ears at Fluid-transfer is LFZ racing caliper is typical fixed-caliper design; caliper is bottom. fixed and only pistonstube move.! sometimes prevent fluid boil. Photo courtesy Engineered Products. TWO pistonsinsulated on each to side are housed in cylinders bored inJFZ caliper body. Caliper assembly is
bolted to axle housing or suspension upright through ears at bottom. Fluid-transfer tube is sometimes insulated t o prevent fluid boil. Photo courtesy JFZ Engineered Products.
is more critical on oval- or road-racing cars. Be careful!
~
Guide-Pin Boot
.; " I
, 1984 Corvette floating caliper uses finned-aluminum caliper housing with one piston inboard floating side of rotor. Mounting 1984 on Corvette caliper uses bracket is darker caliper portiol housing to right of finned finned-aluminum with one housing. on rotor. two guide pins piston onHousing inboardslides side of Mounting are applied rotor bewhen brakes bracket is darker portiol to t oclamp right of finned tween pads. See separate in followhousing. Housing slides on parts two guide pins ing drawing. courtesy Girlock Ltd .bewhen brakesPhoto are applied t o clamp rotor
tween pads. See separate parts in following drawing. basic typesPhoto of courtesy calipers:Girlock fixedLtd.and
floating. The difference is obvious basic types calipers: fixedcaliper and when you lookofat them. A fixed floating. The obvious twodifference pistons on isboth sides has one or A fixed usually caliper when looka at them. caliper of the you rotor; floating has one or two pistons on both has one piston on only one side ofsides the of theThe rotor; a floating usually rotor. housing of a caliper fixed caliper is has onerigidly piston to on the onlyspindle one sideorofaxle the bolted rotor. TheAhousing a fixed caliper is is mounted housing. floating of caliper bolted rigidly to the spindle or axle so it moves in the di recti on opposite housing. floating caliper is mounted the pistonA(s). Because a floating caliso moves direction per itonly has in thethe piston (s) onopposite the inthe piston(s). Because caliboard side of the rotor, athefloating entire caliper only has the piston(s) on the inper must shift inward for the outboard board of the pad to side contact the rotor, rotor. the entire cali-
per must shift inward for the outboard pad to contact the rotor.
Outer Pad & Spring Assembly
I
Blowup of '84 Corvette floating caliper. Guide pins are retained in close-fitting holes in anchor plate. Pins are in line with piston to minimize twisting of housing as it slides. Drawing courtesy Ltd. Blowup ofGirlock '84 Corvette floating caliper. Guide pins are retained in close-fitting holes in
anchor plate. Pins are in line with piston t o minimize twisting of housing as it slides. Drawing courtesy Girlock Ltd.
Floating-caliper mountings vary. Some are mounted on guide pins and mountingssurfaces vary. areFloating-caliper held between machined Some are mounted on guide pins anda to take braking torque. Others have are held between machined surfaces flexible mount or are mounted on a to take braking torque. have a linkage. Depending on Others their mountflexible mount or are mounted ing, they are also called slidingonora linkage. Depending on their mounthinged calipers. ing, they also are called or Floating are calipers usedsliding on most hinged calipers. production cars; fixed calipers are preFloating are used on most ferred for calipers racing applications. This production cars; fixed calipers are predoes not mean one type is good and ferred foris bad-each racing applications. This the other has advantages. does mean one has typemore is good and Thenot fixed caliper pistons the other is bad-each has advantages. (two or four) and is bigger and heavier
The fixed caliper has more pistons (two or four) and is bigger and heavier
than a floating caliper. In severe use, it will take more hard stops to make than a floating caliper. In severe use,a the fixed caliper overheat. And, it will take more hard stops to make fixed caliper generally will flex less the fixed caliper overheat. And, a than a floating caliper. fixed calipera generally will flex less However, floating caliper is more than a floating compact, thuscaliper. packages better in a However, floating is more wheel. With athe pistoncaliper an d fluid on compact, thus packages better in a the inboard side of the rotor, a floating wheel. With better. the piston fluidcalion caliper cools The and floating the side of the parts rotor, and a floating per inboard has fewer moving seals, caliper cools better. The floating so is less likely to leak or wear out.caliOn per fewerside, moving andfeature seals, the has negative the parts floating is cause less likely to leak or wear out. On so may the pads to wear at an angle the negative side, the floating feature due to caliper motion. One advantage
may cause the pads to wear at an angle due to caliper motion. One advantage 29
Anti-Rattle Clip
ffiJ
Dust Boot-
~ ~
Seal Piston
Seal
Steel Balls
/
~
Operating Shaft
Th'''' Be,,,o, End Retainer
@
~.
•
a)~
/~~"W
'o't·Ro"tioo Pto Pad and Plates Thrust Screw
B"'eLe,.,
Seal
Pad and Plates Thrust Screw Floating caliper used on rear of some larger Ford cars features an integral parking-brake mechanism. As parking-brake shaft rotates, steel balls roll up ramps and push on piston to apply brake. Drawing courtesy Bendix Corp. r l u a i l l l y CiaIIper useu UII rear UI aume laryer roru cars raarures an lnregral parnlng-urane meclnanlsm. n s parnlng-urane snarr roiares, ateel balls roll up ramps and push on piston t o apply brake. Drawing courtesy Bendix Corp.
Bridge 0-._
\1
Deflection DuetoP Caliper
I
I Rotor
One-piece AP RaCing caliper is used on race cars using 10-in.-diameter,I small I 0.375-in.-thick solid rotors. Caliper is One-piece AP Racing caliper is used on available withcars 1.625 or 1.750-in. pistons. small race using 10-in.-diameter, Photo courtesy AP Racing. 0.375-in.-thick solid rotors. Caliper is
available with 1.625 or 1.750-in. pistons. Photo courtesy AP Racing.
of the floating caliper on road cars is the ease of using a mechanical parking of the floating caliper on road cars is The single-piston design is brake. the easeoperated of using abymechanical parking easily a parking-brake brake. while T h e asingle-piston is cable, fixed caliper design with piseasily a parking-brake tons onoperated both sidesbyof the rotor is more cable, while a fixed caliper with pisdifficult. tons bothbody sidescan of the is more A on caliper be rotor one piece of difficult. metal or it can be several pieces A caliper body Boiled can be one pieceuse of bolted together. designs metal or it can be pieces only high-strength, highseveral torque-value bolted together. Boltedmust designs use bolts because a caliper not flex only high-strength, high torque-value during heavy brake application. Bebolts because caliper must flex rotor, thenot caliper cause it spansa the during heavy brake application. by body acts as a curved beam loadedBecause spanseach the pad rotor, forces it against . If the the caliper caliper body acts a curved beam by theasdriver senses thisloaded as a soft flexes, forces againstIteach thetocaliper brake pedal. will pad. also If tend cock flexes, the driver senses this as aconsoft the pistons. This reduces braking brake pedal. It will the alsopads tendwear to cock sistency and makes in a the pistons. This reduces braking contaper.
sistency and makes the pads wear in a taper. 30
Two-piece caliper is for small race cars 10.5- in.-diameter, 0.44- in.-thickI solid rotors.caliper Caliperisuses pistons. Two-piece for 2.00-in. small race cars Photo courtesy AP RaCing. 0.44-in.-thick using 10.5-in.-diameter,
Iusing
solid rotors. Caliper uses 2.00-in. pistons. Photo courtesy AP Racing.
You can visualize caliper flex using a C-clamp. The frame of the C-clamp You cantovisualize caliper flex body. using is similar a disc-brake-caliper aAsC-clamp. The frame of the C-clamp the C-clamp is tightened , it simuis similar a disc-brake-caliper lates the to clamping action of a body. discAs the caliper. C-clampAfter is tightened, it simubrake the C-clamp is lates clamping action of ahandle disctight, the continued turning of the brakedistort caliper. the This C-clamp is will the After C-frame. is what tight, continued turning of the handle happens to a flimsy caliper when the will distort the C-frame. brakes are applied hard. This is what happens to a flimsy the The portion of the caliper caliper when body that brakes are applied hard. spans the outside of the rotor is called portion of the caliperdetermines body that theThe bridge. Bridge stiffness spans outside of the Bridge-design rotor is called overallthe caliper stiffness. bridge. Bridge determines the requirements call stiffness for stiffness, which overall caliper stiffness. Bridge-design requires a thick cross section and requirements call the for caliper stiffness, which weight. Because must fit requires cross side section between athethick outboard of and the fit weight. the wheel caliperrim, must rotor andBecause inside the space between the dictate outboard side ofcross the requirements a thinner rotor and inside the wheel rim, section. Unfortunately, this space may
requirements dictate a thinner cross section. Unfortunately, this may
Fluid pressure in disc-brake-caliper body exerts a force P on each side of caliper and tries bend caliper bridge. Caliper-bridge Fluid to pressure in disc-brake-caliper body stiffness is critical caliper design. If exerts a force P onpart eachofside of caliper and caliper is too bridge. thick, wheel may not tries to bridge bend caliper Caliper-bridge fit over it. is On the inside, of most car deSigners stiffness criticalpart caliper design. If want largest rotorwheel diameter, so caliper bridge possible is too thick, may not bridge limited. fit overthickness it. On the is inside, most car designers
want largest possible rotor diameter, so bridge thickness is limited.
allow caliper flexing. Because bridge design is a allow caliper flexing. compromise, most calipers have Because bridge about the same bridge design thickness.is Buta compromise, most calipers havea racing calipers are designed with about the same bridge thickness. But wider bridge to gain additional racing calipers are designed with a stiffness. wider bridge piston to gain additional is installed in a A disc-brake stiffness. machined bore in the caliper body. A disc-brake is have installed in a Usually, floatingpiston calipers a single machined boreside in of thethecaliper body. on one rotor. Fixed piston Usually, have floating calipers a single calipers one or twohave pistons on piston on one side of the rotor. Fixed each side of the rotor. calipers one or are tworequired pistons on on When have big calipers each side of the rotor. heavy, powerful cars, a single piston big the calipers areis required not do job. It difficult on to willWhen
heavy, powerful cars, a single piston will not do the job. It is difficult to
caliPer Pad ;;
.. .
-
'
Brakes Applied
.. , .
'
,'
,
. *
.
Seal
.
... .
Brakes Applied Piston
Piston
,
Piston Frank Airheart, working for Alston Industries, designed this racing caliper with noncircular pistons. Kidney-shaped pistons closely match the pads, resulting in more even pad-to-rotor clamping Frank Airheart, working for Alston Industries, designed this racing pressure. Drawing courtesy Alston Kidney-shaped Industries. caliper with noncircular pistons. pistons closely
match the pads, resulting in more even pad-to-rotor clamping pressure. Drawing courtesy Alston Industries.
Cross section through caliper-piston seal shows position of seal brakes applied and released. When brakes are released, seal I retracts piston through from rotor. As pad wears, slides on piston to Cross section caliper-piston seal seal shows position of seal compensate. with brakes applied and released. When brakes are released, seal
Iwith
retracts piston from rotor. As pad wears, seal slides on piston to compensate.
Flu id Pressure
Fluid Pressure
Fluid Pressure
Fluid Pressure
Piston
Piston
Y'
Pad
Pad
Pad
. .-:. -:-; ,. .
Single-Piston Caliper
Single-Piston Caliper
Pressure of Lini ng on Rotor
Pressure of Lining on Rotor
-.;:: :::,.'
11113-1 Dual- Piston Caliper
Dual-Piston
Pressure of Lining on Rotor
Pressure of Lining on Rotor
Caliper
Wide brake pad used with large single piston results in uneven pressure on rotor. Unsupported ends of pad deflect and apply little pressure. Wide pads should be used with multiple-piston calipers. More-even pad-to-rotor pressure resulting from two smaller pistons gives improved braking. Wide brake pad used with large single piston results in uneven pressure on rotor. Unsupported ends of pad deflect and apply little pressure.
Wide pads should be used with multiple-piston calipers. More-even pad-to-rotor pressure resulting from two smaller pistons gives improved braking.
make a large single-piston caliper that fits inside a wheel. As the caliper gets make caliper that larger, aitlarge gets single-piston wider. If a single piston fits the caliper gets wereinside useda wheel. with a As wide rectangular larger, getssurface wider. would If a single piston pad, theit pad not contact were used with a wide rectangular the rotor evenly. If the pad overhangs pad, pad surface contact the the piston, it will would bend not when the the rotor If Only the pad brakes areevenly. applied. thatoverhangs pad porthe will bend tion piston, directly it behind the when piston the is brakes are applied. Only that pad porloaded aga inst the disc. Multiple pistion directly this. behind the piston is tons minimize loaded thespread disc. caliper-piston Multiple pisIn anagainst effort to tons minimizethis. load evenly against the pad and In an effort to spread caliper-piston achieve maximum piston area for a load evenly against pad and given-size caliper, FranktheAirheart deachieve maximum piston area veloped a racing caliper with a for non-a given-size caliper, decircular piston for Frank AlstonAirheart Industries. veloped a racingkidney-shaped caliper with apiston nonThis unusual circular for the Alston Industries. roughly piston matches shape of the This unusual kidney-shaped piston brake lining . Consequently, there is roughly matches the and shape of disthe little piston overhang lining
brake lining. Consequently, there is little piston overhang and lining dis-
tortion with this design . Multiple-piston calipers are used on tortion with this most large and design. powerful cars. Most Multiple-piston calipers are used on race cars with over lS0-HP engines most large and powerful cars. Most use multiple-piston calipers. These race carshave with four over or150-HP usually more engines pistons . use These The multiple-piston largest calipers calipers. are found on usually haveand fourGTorcars. more pistons. racing stock These caliThe largest calipers arerotor. found on pers cover nearly half the Usualracing stock and G T cars. These calily larger, multiple-piston calipers use pers cover nearlyFloating half thecalipers rotor. Usuala fixed mount. using ly larger, pistons multiple-piston multiple are rare incalipers racing,use alathough fixed mount. calipers BMW Floating uses a big ATE using twomultiple pistons aluminum are rare in caliper racing, alpiston f10ating on though BMW uses a big ATE twothe M 1 coupe. piston Most floating caliper aluminum pistons arecaliper made on of the M1 coupe. steel, aluminum or cast iron. MoldedMost caliper are made of phenolic plastic pistons is becoming popular steel, aluminum or cast iron. Moldedon road cars because of its low cost phenolic is becoming popular and lowplastic thermal conductivity. on road cars becausehasn't of its found low cost However, phenolic its
and low thermal conductivity. However, phenolic hasn't found its
way into many racing app lica tions yet, even though it should work quite well way into many applications yet, where f1uid boilracing is a problem. even it should workisquite well A though disc- brake piston usually where is a problem. sealed fluid with boil a square cross-section 0A This disc-brake piston as istheusually ring. seal stretches piston 0sealed a square cross-section moves with toward the rotor. When the ring. stretchesthe as the piston brakesThis areseal released, stretched moves toward the rotor. Whenelimthe rubber seal retracts the piston, brakes are need released, the stretched inating the for return springs. rubber elimBecauseseal the retracts pad and the rotorpiston, surfaces are inating the need for return springs. flat, only a slight movement is needed Because the pad and rotor surfaces are to obtain pad-to-rotor clearance. flat, only a slight movement is needed Consequently, disc brakes never need to obtain The pad-to-rotor clearance. adjusting. piston moves to take Consequently, disc brakes never need up wear. adjusting. The piston to with take Some calipers are moves designed up wear.springs on the pistons. Airheart return Somecalipers calipershave are this designed with racing mechanical return springs on theto pistons. Airheart retraction feature make sure the racing calipers mechanical pad never dragshave on this the rotor. With
retraction feature to make sure the pad never drags on the rotor. With 31
Caliper
r------1 -
-
~FF - - - _ - .. - - - 1- --"'--------,
-
Rotor
- - - - - - -FF- R
T
. - , - - - Caliper Mounting y Caliper ~ Bracket Mounting Bracket Bolt
Bolt
Forces on brake pads, indicated by FF' are resisted by a force R at caliper bracket. Because force R is not in line with the rotor, twisting torque T is pads, also applied toby the Effect twisting Forces on brake indicated Ffibracket. are resisted by aofforce R at torque on the bracket shown If mounting R isinnotlower in linedrawing. with the rotor, twistcaliper bracket. Becauseisforce bracket is not sufficiently rigid,tocaliper cocks against causing torque T is also applied the bracket. Effect rotor, of twisting ing uneven wear, is spongy pedal, excessive pedal torque on thepad bracket shown in lowerand drawing. If mounting movement. Usesufficiently a stiff caliper bracket and this will not happen. bracket is not rigid, caliper cocks against rotor, caus-
Husky bracket attaches caliper to spindle on this sprint car. Because spindle was not designed to mount a disc-brake caliper, mounting bolts attaches are too far from to caliper. Risk twisting Husky bracket caliper splnale on of tnlsbracket sprlnr car. Beexcessively is reduced heavy plate. cause spindle was notbydesigned t o mount a disc-brake caliper,
mounting bolts are too far from caliper. Risk of bracket twisting excessively isreducedby heavy plate.
ing uneven pad wear, spongy pedal, and excessive pedal movement. Use a stiff caliper bracket and this will not happen.
Racing stock cars use the largest calipers. This is the popular Hurst! Airheart caliper with twostock pistons onuse each side of rotor. Racing cars the largest calipers.
This is the popular Hurst/Airheart caliper with two pistons on each side of rotor.
Tilton Engineering sells sturdy calipermounting brackets for popular race-car applications. Bracket adapts caliper to " four-bolt normally used to mounting pattern brackets for popular racemount :;& drum-brake plate. Disc brakes applications.backing Bracket adapts caliper can to be fitted pattern in place normally of drum used brakes a four-bolt t o with mount bracket suchbacking as this. plate. Disc brakes can drum-brake -<
be fitted in place of drum brakes with a bracket such as this.
mechanical-retraction calipers such as this, a slightly different mastermechanical-retraction calipers as cylinder design is used. This such is disthis, ain Chapter slightly 5.different mastercussed cylinder design is used. This is disCaliper Mounting-It is essential 5. cussed in Chapter that a caliper not move or flex as the Caliper Mounting-It brakes are applied-other is thanessential the latthat movement a caliper not or flex as the eral ofmove a floating caliper. If brakescaliper-mounting are applied-other structure than the latthe is eral movement of a floating caliper. If flexible, the caliper can twist on its the caliper-mounting structure is mount. This causes uneven pad wear, caliper twist on its and can excessive pedal aflexible, spongy the pedal mount. This causes uneven pad wear, movement. a spongy pedalrace-car and excessive pedal A common design error is movement. using thin, flexible brackets to mount common race-car design errorthe is theA caliper to the spindle. Because
using thin, flexible brackets to mount the caliper to the spindle. Because the 32
rotor and caliper-mounting bracket lie in two different planes, the caliper rotor andhas caliper-mounting bracket lie bracket a twisting force on it when in different planes,If the the bracket caliper the two brakes are applied. bracket has aittwisting forcecocking on it when is too thin, will twist, the the brakes are applied. If the bracketa caliper against the rotor. Generally, is too thin, bracket it will twist, cocking the mounting at least I/2-in. caliper againstbethe rotor. Generally,ona thick should used, particularly mounting bracket least large race cars such asatstock cars 112-in. .
thick should be used, particularly on large race cars such as stock cars. SPLASH SHIELDS
The inboard side of the rotor on SPLASH SHIELDS most production cars is shielded by a The inboard the rotor on steel plate that side looksof similar to the most production cars is shielded by backing plate on a drum brake. This isa steel plateshield. that looks similar to prethe the splash This shield only
backing plate on a drum brake. This is the splash shield. This shield only pre-
vents mud, dirt and water from being thrown up against the inboard surface vents and water from being of the mud, rotor. dirt It does not have a structhrown up against the inboard . If splash shields surface are not tural function of the road rotor. debris It doesmay not have strucused, cause a excess tural function. If splash shields are not scoring and wear on the inboard side used, road debris may cause excess of the rotor. scoring and wear on the shields inboard tend side Unfortunately, splash of the rotor. to block cooling air from reaching the Unfortunately, rotor. This is why splash splash shields shields tend norto block cooling air from reaching the mally are not used on race cars. Racerotor. This usually is why need splashallshields norcar brakes the cooling mally are get. not Road-debris used on race contaminacars. Racethey can car brakes usually need all the tion is a secondary problem. cooling Therethey get. Road-debris fore, can deleting the splash contaminashield is a tion is a secondary Therecompromise betweenproblem. brake cooling fore, deleting the splash shield is a and rotor protection.
compromise between brake cooling and rotor protecti.on.
BRAKE PADS Disc-brake
friction
material
is
BRAKE mounted PADS on a brake-pad backing plare, Disc-brake material is which is usuallyfriction a steel plate . This asa brake-pad plare, mountedis on sembly called a brake backirlg pad. Friction which steel plate. This asmateri aisl isusually usu allya bonded to the backsembly is called a brake pad. Friction ing plate during the lining-molding material usually bondedit to the backbut sometimes is joined in process, is plate during the with lining-molding operation rivets and aingseparate process, but sometimes it is joined in conventional bonding adhesives. a separate operation with rivets and Brake pads are sold with friction conventional bonding adhesives. material attached as are brake shoes. Brakedrum-brake pads are sold withpadfriction Unlike shoes, backmaterial attached as are shoes. reused. To ing plates usually are notbrake Unlike drum-brake shoes,your pad partsbackmake sure, check with ing plates usually are discarding not reused.used To house before supply make sure, check with your partsdisc-brake pads. supply used The house piston before in thediscarding brake caliper disc-brake often doespads. not bear directly against piston in many the brake caliper theThe brake pad . On cars, there is often does not bear directly against the brake pad. On many cars, there is
an anti-squeal shim between the piston and brake pad. This sheet-metal an anti-squesl between the shim is supposed shim to reduce the noise piston and brake pad. This Sheet-metal caused when the pad chatters against shimrotor. is supposed reduce the noise the Follow to manufacturer's incaused when the pad chatters structions when servicing the against brake the Follow inpads.rotor. These shimsmanufacturer's may require restructions when with servicing the brake placement along the pads. pads. Theserace shims requirehave recars,may insulators On some placement along with the pads. been used between the brake pads Oncaliper some race cars,This insulators have is done to and pistons. been used between the brake pads reduce brake-fluid and piston-seal and caliper pistons. Thistemperature is done to temperature. Excessive reduce brake-fluid and piston-seal can cause seal failure or fluid boiling. temperature. Excessive temperature If an insulator is used, it must be stiff, can cause or fluid boiling. andseal notfailure too large. These constrong, If an insulator is used,make it must stiff, flicting requirements thebedesign strong, not toovery large. These conofa goodand insulator difficult. flicting requirements make the design in Friction materials are covered of a good insulator verychapter. difficult. detail in the following
Friction materials are covered in detail in the following chapter.
•• 1984 Corvette rear brake less rotor shows splash shield. Thin circular plate mounted behind rotor protects it from and 1984 Corvette rear brake lessroad rotordirt shows water. cars usecircular splash plate shields to prosplash Road shield. Thin mounted vide good braking in ait dirty environment. behind rotor protects from road dirt and bettershields off without Most race aresplash water. Road cars use t o prosplash shields because cooling vide good braking in a they dirty block environment. air. Photo courtesy Girlock Ltd. off without Most race cars are better splash shields because they block cooling air. Photo courtesy Girlock Ltd.
Racing brake pads look similar to those for road use. Pads come with lining bonded to a steel brake backing plate. are deRacing pads lookThese similarpads to those for signed forPads JFZ come racingwith calipers use on road use. liningfor bonded to dragsters. Photoplate. courtesy JFZpads Engineered a steel backing These are deProducts. signed for JFZ racing calipers for use on dragsters. Photo courtesy JFZ Engineered Products.
33
Friction Matarial
Friction Matefzl
4
Stock car running on road course is hard on brakes. Stock cars are the heaviest road-racing vehicles, and are powerful. Brake ducts and heavy-duty linings are a must on hot day at Riverside Raceway.
Stock car running on road course is hard on brakes. Stock cars are the heaviest road-racing vehicles, and are powerful. Brake ducts and heavy-duty linings are a must on hot day at Riverside Raceway.
The material that rubs on a brake drum or rotor is called friction material material rubs on afriction brake or The brake lining. that Drumbrake drum or rotor is called friction material is attached to thematerial brake or brake Drum-brake friction shoes. In alining. disc brake, friction material material is to attached to the plates. brake is attached steel backing shoes. a disc brake, friction material composition is simiFrictionInmaterial is to steel backing lar attached in both types of brakes, but itplates. is deFriction material composition disc signed for higher temperaturesisinsimilar in both types of brakes, but it is debrakes.
signed for higher temperatures in disc brakes. WHAT IS FRICTION?
Friction exists when two contacting WHAT ISeither FRICTION? surfaces try to or do slide Friction exists whenThere two contacting each other. is always against surfaces either try to do slide resistance to sliding. This or resistance is againstfriction each force. other. The There is always friction force called resistance to sliding. resistance is on the sliding This surfaces at their acts called friction force. The friction force point of contact in a direction opposite acts on the sliding surfaces at their to movement. point contact in aisdirection In aofbrake, there friction opposite between to movement. the friction material and the drum or
In a brake, there is friction between the friction material and the drum or
34
rotor rubbing surface. The problem is controlling the amount of friction rotor and rubbing The is usingsurface. it to stop theproblem car. force controlling theforce amount of friction The friction depends on two force usingof it tosurfaces stop theincar.contact things:andtypes The friction force depends the on surtwo and amount of force pressing things:together. types of surfaces in contact faces andEach amount of force surof these haspressing its ownthe name. faces together. The force pressing the two surfaces Each ofis called these normal has its force own, or name. together perThe force force. pressing the two surfaces pendicular Because only engitogether is called or perneers use the normal word force, normal for Because only engipendiclrlar force. pelpendiculal; I'll use perpendicular to neers confusion. use the Itword for avoid should normal be obvious perpendicular, 1'11 perpendicular use perpendicular to that a higher force avoid confusion. It should be obvious causes a higher friction force. Ifsliding that a are higher perpendicular force surfaces slippery, friction force is causes higher friction force. If sliding low. If athe surfaces resist sliding, fricsurfaces force is "slipperiness" tion forceare is slippery, high . Thefriction low. If the surfaces resist sliding, fricof a surface is described by a number tion force high. Theof"slipperiness" called its iscoefficient friction. The of a surface is described a number value of this friction by coefficient
called its coefficient of jiction. The value of this friction coefficient
varies, usually between 0 and 1. The friction coefficient for surfaces trying varies, between 0 and 1. The to slideusually is given by the following friction :coefficient for surfaces trying formula
to slide is given by the following Friction Force formula: f.1. = Perpendicular Force Friction Force If Perpendicular the coefficientForce of friction is low ) =
'the surfaces are slippery - the friction
If the coefficient of friction is low, If the friction coefficient force is low. the surfaces are slippery-the friction is high, the surfaces grip each other force is the low. If the friction betterfriction force coefficient is high. is high, griphave eacha other Tires on the dry surfaces pavement high better-the friction but force on is ice high. they friction coefficient, Tires n dry pavement have a high have a olow friction coefficient. friction coefficient, but on ice life complicated, the they fricTo make have a low friction coefficient. tion coefficient has two different To make complicated, fricvalues. It is life somewhat higher the if there tion coefficient has two different is no sliding. As soon as the surfaces values. is somewhat there start to Itmove relative higher to eachif other, is nofriction sliding. coefficient As soon as drops the surfaces the to a start move relative other, lower to value . This is whytoit each is harder to the friction coefficient drops to a lower value. This is why it is harder to
W = Weight FF = Friction Force W = Weight W = Perpendicular Force FF = Friction Force Coefficient of Friction =~ W = Perpendicular Force
IL Coefficient Friction To slide box, tractorofhas to pull= with W a force equal to friction force Fp Friction force is related perpendicular force two To slideto box, tractor has to pull pushing with a force sliding this example, equal t osurfaces friction together. force F, In Friction force is the perpendicular force force is boxpushing weighttwo W. related perpendicular Frictionsurfaces coefficient is friction force divided sliding together. In this example, by force, theperpendicular perpendicular forceorisFF/W. box weight W' Friction coefficient is friction force divided by perpendicular force, or F,/W. start something sliding than It IS to keep it sliding. The friction coefficient start slidingis than is to calledit static beforesomething sliding occurs keep it sliding. The friction coefficient coefficien t of friction. After sliding static before it's sliding occurs is called called dynamic coefficient starts, coefficient of friction. of friction. After sliding dynamic coefficient starts, called Eitherit'stype of friction coefficient is of friction. calculated by the previously given Either type friction coefficient is Justof remember that the formula. calculated previously value drops by oncethe sliding starts. given formula. Justweremember thatabout the In a brake, are concerned value drops once sliding starts. the coefficient of friction between the In a brake, we are about friction material andconcerned the drum or the coefficient between the For most brake rotor surface.of friction friction and the drum or rna terials,material the friction coefficient is rotor surface. For most about 0.3. I'll discuss later howbrake the materials, the friction affects coefficient is coefficient of friction brakeabout 0.3. I'll discuss later how the pedal effort. coefficient of Friction-The friction affects friction brakeTire-to-Road pedal effort. coefficient between the tires and road Tire-to-Roadhow Friction-The determines fast a car canfriction stop. coefficient between the tires This value varies from less and thanroad 0.1 determines how0.5fast car can roads stop. on wet ice and on arain-slick This value varies less than than l.0 from for racing tires 0.1 on to more on wet ice and 0.5 on rain-slick roads dry pavement. The friction coefficient to more 1.0 for racing tires for on for tires than on pavement is critical dry pavement.under The friction coefficient all conditions. It performance for tires onhow pavement critical for determines fast a caris can accelerperformance all as conditions. as well how fast It it ate and cornerunder determines how fast a car can accelercan stop.
ate and corner as well as how fast it can stop. FRICTION-MATERIAL CHARACTERISTICS FRICTION-MATERIAL A good friction material must have CHARACTERISTICS these characteristics: A good friction material must have these characteristics:
As first car brakes in turn, inside front wheel locks. Tire smokes as it slides on pavement due to heat from friction. Following car can slow quicker because its wheels aren't locked. Static-nonsliding-coefficient of front friction is higher dynamic-sliding-coefficient of As first car brakes in turn, inside wheel locks. than Tire smokes as i t slides on pavement friction. due t o heat from friction. Following car can slow quicker because its wheels aren't locked. Static-nonsliding-coefficient of friction is higher than dynamic-sliding-coefficient of friction.
• Friction coefficient must be high. • Friction coefficient must not Friction be high. change withcoefficient increasingmust temperature. Frictionnot coefficient • Should wear rapidly. must not change with increasing • Should not damage temperature. surface it rubs Should not wear rapidly. against. not damage it rubs Must withstand highsurface temperature • Should against. failing. without Must withstand high when temperature not be noisy brakes • Should without failing. are applied. Should not be there noisy iswhen brakes Unfortunately, no perfect are applied. friction material. Instead, there are Unfortunately, thereeach is no many different types, oneperfect made
friction material. Instead, there are many different types, each one made FRICTION & SURFACE AREA For sliding surfaces, the friction FRICTION & SURFACE AREA force depends only on the coeffiFor sliding surfaces, the friction cientot friction and perpendicular force only the or coeffiforce. depends The amount of on sliding rubcient of friction anddoes perpendicular bing surface area not affect force. The amount of sliding rubfriction. This holds true for all or condibing surface does not affect tions of s lidingarea where matertal isn't friction. true for all condiremovedThis fromholds the sliding surface. tions sliding where material Skidofmarks result from lockingisn't up surface. removed from the brakes onthe drysliding pavement. Each Skid marks up skid mark is result rubberfrom thatlocking was torn the brakes on and dry deposited pavement.onEach the tires the from skid mark Because is rubber material that wasistorn pavement. refrom the tires deposited on the theand tires during sliding, moved from pavement. material is resurface ar eaBecause does affect the friction movedConsequently, from the tires the during sliding, force. greater the surface area does thethe friction area in contact, theaffect greater fricforce.force. Consequently, greater the tion To makethethe friction area in contact, greater the fricwork forthe tires on pavement, formula tion force. To make the friction formula work for tires on pavement,
to emphasize a particular characteristic or several of them. The ideal friction to emphasize a particular characteristic material for severe or racing use is not or friction theseveral same ofasthem. that The for ideal lowest-cost material for severe or racing use is not passenger-car use. thePopular same friction as thatmaterials for lowest-cost fall into passenger-car use.categories: one of these basic Popular friction fall into • Organic material materials held together by one of these basic categories: resin binders. Contains asbestos, glass together by or Organic syntheticmaterial fibers, held and may contain resin binders. Contains asbestos, glass metallic particles. or syntheticmaterial fibers, fused and may • Metallic or contain sintered metallic particles. together. Almost entirely made of @ Metallic material fused or sintered
together. Almost entirely made of engineers choose to change the coefficient of friction rather than the engineers choose to change the fric t ion formula. coefficient friction rather than the with all but width being For tires of friction formula. coefficient of friction inequal, the For tires but widthThis being creases as with widthallincreases. is equal, coefficient of friction infactor that makes the friction a majorthe creases as greater width increases. This is coefficient than 1.0 for wide a majortires. factorSo, thatthe makes the friction racing friction coefficoefficient greater than 1.0than for wide cientcannot be greater 1.0 racing So,isthe frictionfrom coeffiunless tires. material removed the cient slidingcannot surface.be greater than 1.0 unless is removed from the discussing handling, I call Whenmaterial sliding surface.of friction of a tire its the coefficient When discussing handling, call This differentiates grip I from grip. the coefficient of friction of a tirebeits ordinary coefficient of friction, grip. This differentiates grip from cause tire area affects "coefficient ordinary coefficient of friction, beof friction."lf the subject of tires and cause tire area affects "coefficient grip interests you, read my HPBook of friction." If the subject of tires and "How to Make Your Car Handle." grip interests you, read my HPBook "How to Make Your Car Handle."
35
Metallic linings for 1962 Corvette drum brakes were highly successful for racing. Prior to the use of disc brakes, drum brakes with these werefor relatively brakes were highly linings successful racing. fade-free, even 3000-lb, 300-HP Prior to the useonof a disc brakes, drum sports brakescar. with these linings were relatively
fade-free, even on a 3000-lb, 300-HP sports car.
metal particles. • Semi-metallic material held together metal particles. by resin binders. Contains steel fibers Semi-metallic material held together and metallic particles.
by resin binders. Contains steel fibers and metallic MATERIALS particles. ORGANIC Most brake friction material on the
ORGANIC MATERIALS market is organiC. This means that the Most brake friction on the friction material, suchmaterial as petroleummarket is organic. meanswas thatonce the based products andThis plastics, friction material, such as petroleuma living plant or animal. Early friction based products plastics,leather was once materials wereandwood, or a living impregnated plant or animal. friction cotton withEarly asphalt or materialsThese were old-fashioned wood, leather or rubber. linings cotton impregnated with asphalt or did not have many desirable rubber. These Ifold-fashioned characteristics. used severely,linings they did have many desirable tendednot to catch on fi re! characteristics. If used severely, Superior friction material was they obtended to catch on fire! tained by weaving asbestosSuperior friction was with obimpregnated fibers material together tained by weaving organic material to glueasbestosthem impregnated fibers together with together. Today, asbestos is still used organic material to glue them in most brake linings, along with varitogether. Today, still used ous binders andasbestos frictionis modifiers. in most brake along with holds variBinder, usuallylinings, a plastic resin, binders and friction modifiers. ous the friction material together. The Binder, provide usually astrength plastic resin, fibers and holds resist the friction material together. wear. Glass and synthetic fibers The are fibers provide strength andin some resist beginning to replace asbestos wear. Glass and synthetic fibers are organic-lining material. Friction modibeginning to replace asbestos in some fiers tune the friction of the material organic-lining material. Friction modito the desired level. fiers tune the friction the first material Molded brake liningsofwere proto the desired level. duced in the '30s. Woven lining matebrake fibers linings was were manufacfirst prorialMolded with small duced in the a'30s. Woventechnique. lining matetured using molding In rial fibers was manufacof friction material, the this with type small tured using a molding In binder, modifiers andtechnique. fibers are this type of friction material, the pressed together in a mold under heat binder, modifiers and fibers are and pressure to produce a curved pressed together in a mold under heat brake-shoe lining. and pressure to produce a curved brake-shoe lining. 36
In a molded lining, other materials such as mineral or metallic particles In aadded molded lining, the other materials were to change characterissuch as mineral or metallic Later, tics of the friction material.particles were added change were the characterispads for discto brakes developed tics of the friction from molded material,material. as well as Later, semipads for disc brakes were developed metallic high-temperature friction from moldedWoven material, as wellgradually as semimaterials. linings metallic high-temperature friction became less popular because the materials. Woven was linings gradually range of materials limited. Today, became material less popular because the woven is found in clutch range of materials was limited. Today, discs, but not in brakes. woven material found has in a clutch Organic friction is material variediscs. but not in brakes. ty of ingredients. Manufacturers keep material has varietheOrganic 'exact friction specifications a asecret. ty of ingredients. Manufacturers keep Generally, a typical organic brake the specifications a secref. lining.exact contains these components: • Asbestos fia bers for friction andbrake heat lining contains thesematerial components: resistance. Friction is usually Asbestos fibers for friction and heat more than 50% asbestos. resistance. Friction material such is as usually oil of • Friction modifiers, more than 50% asbestos. cashew-nut shells, give the desired Friction modifiers, such as oil of friction coeffici~nt. cashew-nut shells, give the desired • Fillers, such friction coefficient.as rubber chips, reduce noise. Fillers, such as rubber chips, • Powdered lead, brass or aluminum reduce noise. improves braking performance. Powdered lead, as brass or aluminum • Binders, such phenolic resin, improves braking together. performance. hold the material Binders, agents such as provide phenolic proper resin, • Curing hold the material together. chemical reactions in the mixture Curing agents provide proper during manufacturing. chemical reactions in the mixture The friction coefficient and wear during manufacturing. properties of friction material can be The friction coefficient and wear modified by changing the components properties of friction material can be in this magic brew. When you change modified by changing theprobably components lining material , you are getin this magic brew. WhenWhat you ischange ting a different mixture. actuliningin material, you are probably getThe actual perally it is a secret. ting a different is actuformance of themixture. materialWhat is also diffially in determine. it is a secret. actual percult to YouThe must resort to formance of the material is also diffia trial-and-error method based on excult to determine. resort to perience to find the You best must friction matearialtrial-and-error based on exfor a particularmethod car. to find theorganic best friction mateperience Conventional materials rial for a particular car. work well at low temperatures, but Conventional organic their friction coefficient tendsmaterials to drop work well low also temperatures, but when hot. atThey usually wear their friction coefficient tends to drop rapidly at high temperature. Above when hot. They usually wear 400F (204C), mostalso organic materials rapidly at highandtemperature. Above have fade wear problems. 400F (204C), mostoforganic materials their good wear However, because have fade and wear problems. properties when cool, low noise and However, because linings of theiraregood low cost, organic usedwear on properties when most road cars . cool, low noise and low cost, organic linings are Friction used on HighTemperature Organic most road cars. Material-A special organic lining, High-Temperature Organic called high-temperature organiCFriction materMaterial-A special organic lining, ial, has improved wear properties at called high-temperature organic mate/high temperatures. However, it has improved wearfriction properties at ial, has wear poorer and low at low high temperatures. However, it has temperatures. It is also harder on the poorer and wearrotors and than low low-temperature friction at low drums
organic materials. High-temperature organic materials usually have a high organic materials. High-temperature concentration of metai particles in a high organic materials usually have coeffithem to increase the friction concentration metaiMost particles in cient and resistof heat. popular them increase friction coeffihigh-temperature racing tolinings are the cient resist heat. Most popular organicand materials. The best ones work racing linings high-temperature well up to 1250Fare (677C). organic materials. Theorganic best ones work High-temperature material well up to (677C). is stiff and1250F brittle compared to lowHigh-temperature organic material. material temperature organic friction is and itbrittle compared As stiff a result, is harder to attachtoitlowto a temperature friction material. shoe or pad. organic The old-fashioned rivetAs result, itwon't is harder attach it to a worktowell because ing amethod shoe or pad. tends The old-fashioned the material to crack at therivetrivet ing method workbonding well because holes. And won't ordinary techthe material to crack at the rivet niques have tends too low a temperature holes. And ordinary bonding techlimit. Therefore , great care must be niques too low a temperature used inhave attaching high-temperature limit. great care mustonly be organicTherefore, friction material. Trust used in attaching high-temperature an expert. The best attachment is one organic material. Trust only in whichfriction the friction material is mold an expert. is one bonded to The the best metalattachment backing during mold in which the friction materialofisbondmanufacture. A combination to the metal backing during bonded ing and riveting also works well. manufacture. A combination High-temperature organicof bondlining ing and riveting also works well. operamay require a special finishing High-temperature organic on the drums or rotors. lining The tion may require a special finishing operamanufacturer of the lining material tion specify on the what drumsshould or rotors. The will be done. manufacturer of the lining material Always follow his instructions, or you will should be done. won'tspecify achievewhat the superior performAlways follow instructions, or you ance of this ma his terial.
won't achieve the superior performance of this material. METALLIC MATERIALS In the mid- '50s, Chevrolet was METALLIC MATERIALS competing in road races with its new In the mid-'50s, Chevrolet V8 Corvette. Using drum brakeswas to competing in road its new stop a 3000-lb car races with with its 300-HP V8 Corvette. drum brakes to engine was a Using big technical problem, stop a 3000-lb car with its 300-HP particularly in the 12-hour endurance engine a big To technical problem, race at was Sebring. make the Corparticularly in the with 12-hour endurance vettes competitive the lighter forTo make the Cor-a race cars, at Sebring. eign the company developed vettes competitive with the lighter forceramic-metallic brake-lining material eign cars, the company developed that could operate at extremely higha ceramic-metallic brake-lining material temperatures. that couldcerametallic operate at extremely high These linings worked temperatures. well, but at the brutal Sebring 12-hour These linings worked race they cerametallic tended to wear through the well, at the brutal brakebutdrums! AfterSebring these12-hour early race they tendedless-harsh to wear through the experiments, materials brake drums! After these early were developed, using an iron base experiments, less-harsh materials rather than abrasive ceramic. Ironusing an offered iron base were developed, base metallic linings were by rather thanforabrasive ceramic. Chevrolet street use prior toIronthe base metallic of linings offered by introduction disc were brakes on the Chevrolet The for street use metallic prior to linthe Corvette. Chevrolet introduction of disc onOnly the for brakes the time. ings were excellent Corvette. The Chevrolet metallic linthe superior characteristics of the disc ings excellent the time. Only brakewere has made themfor obsolete. theMetallic superior linings characteristics of the disc are designed to brake has made them obsolete. operate at higher temperatures than
Metallic linings are designed to temperatures. It is also harder on the drums and rotors than low-temperaf~rre operate at higher temperatures than
Organic friction material attached by bonding only didn't stay attached long under racing conditions. Organic friction material attached by bonding only didn't stay attached long under racing conditions.
Grand Prix cars frequently run on courses with long straights and tight turns, which is extremely hard on brakes. Friction-material hardness is selected to match the course. "Hard" linings are required when running race likewith this one the streets Long Beach. Grand Prix cars frequently run ona courses longon straights and of tight turns, which is extremely hard on brakes. Friction-material hardness is selected to match the course. "Hard" linings are requiredmaterials. when running race like this one on the streets of Long Beach. organic friction Alla organic
materials, such as plastic resin, disinorganic friction materials. All reached organic tegrate at high temperatures materials, such as plastic resin, disinin severe braking conditions. The astegrate at high temperatures reached bestos fiber in organic linings can in severe braking conditions. but Thewith aswithstand high temperature, bestos fiber in organic linings no binder to hold it together it hascan no withstand. The highmetallic temperature, but solve with strength materials no to . hold it together it has no thisbinder problem strength. The metallic materials solve Sintering-Metallic linings are manuthis problem. factured using a sintering process . A Sintering-Metallic linings are manumetal-powder mixture is compressed factured using a sintering process. A in a mold at high temperature and metal-powder is compressed pressure. The mixture metal partially fuses in a mold high material. temperature and together intoata solid pressure. The metal partially fuses Sintered friction material can be attogether solid or material. tached tointo the ashoe pad by brazing, can sinterbe ator Sintered it can be friction fused onmaterial during the tached to the shoe or pad by brazing, ing process . Sometimes, the material or i t can be to fused onplate during is sintered a thin andthe thesinterplate ingthen process. Sometimes, the material is riveted to the shoe or pad . is sintered to a eliminates thin plate and plate This processes the the ne~d for is then riveted to the shoe or pad. organic adhesive. This processes eliminates the need Metallic friction material that for is organicon adhesive. glued loses some of its highMetallic friction material is temperature capability. This that is beglued on loses some of its highcause the organic adhesive will fail at temperature that capability. Thismaterial is betemperatures the friction cause the organicWhen adhesive will failure fail at can withstand. such temperatures that the frictioncomes material occurs, the friction m aterial off can withstand. failure its backing, and When brakingsuch is severely occurs, the affected . friction material comes off itsMetallic backing,friction and braking severely materialis does not affected. fade at high temperature, but it does Metallic material does not have otherfriction bad properties. It costs fade at high temperature, but it does more than organic material, works have other It costs worse when bad cold, properties. wears the drum or more than and organic material, works rotor more, is harder to attach to
worse when cold, wears the drum or rotor more, and is harder to attach to
the shoe or pad . Many metallic racing linings are dangerous if not warmed the pad. Many up. shoe Whenorcold, some metallic metallic racing matelinings are dangerous if nothave warmed rials either grab viciously or very up. When matelow friction.cold, In some racing,metallic warming up rials either prior grab viciously or have very the brakes to using them may be low friction.butInnotracing, warming acceptable, for street usage . up theSintered-metallic brakes prior to using themmaterial may be friction acceptable, but not for street usage. is used extensively in heavy aircraft Sintered-metallic friction material brakes, and some high-performance is used clutches extensively heavy aircraft racing andin brakes. Some brakes, and some high-performance motorcycle disc brakes use st ainlessracingrotors clutches and brakes. steel and sintered linings. Some
motorcycle disc brakes use stainlesssteel rotors and sintered linings. SEMIMETALLIC MATERIALS
To solve some of the problems with SEMIMETALLIC MATERIALS organic and sintered-metallic maTo ,solve some of the problems with terial semimetallic friction material organic and sintered-metallic mawas developed. Semimetallic linings terial, semimetallic friction material contain no asbestos. This material is was Semimetallic linings madedeveloped. of steel fibers bonded together contain no asbestos. This characterismaterial is wi th organic resins to give made steel fibers together tics ofof both organicbonded and sinteredwith organic resins to give characterismetallic materials. Semi metallic lintics both well organic and sinteredings of operate at temperatures of metallic materials. linup to lOOOF (538C).Semimetallic The steel fibers ingstheoperate at totemperatures of in materialwell tend melt and weld up to lOOOF (538C). The steel fibers to the rotor when operated at higher in the material tend to melt and weld temperatures.
to the rotor when operated at higher temperatures. FRICTION-MATERIAL HARDNESS
FRICTION-MATERIAL Racers often talk about hard or SO/I HARDNESS brake pads. This is slang for how high often talk about hard or soft theRacers coefficient of friction is. "Soft" brake pads. This is slang for how high friction material has a high friction the coefficient of friction coefficient; "hard" materialis.has"Soft" a low friction coefficient. material has a high friction friction coefficient; "hard" material has a low friction coefficient.
Why does a racer want to use a "harder " friction material ? The Why isdoes racer to use a reason wear aand fadewant characteristics "harder" friction material? The of the material. Unfortunately, " soft" reason ismaterial wear and fadetocharacteristics friction tends wear rapidly ; of the material. Unfortunately, "soft"is it also fades easier. "Soft" material friction material tends to wear rapidly; usuaJly organic. "Hard" material may it alsoa fades "Soft" ofmaterial is have highereasier. percentage metallics. usually may A racer organic. usually "Hard" chooses material soft material haveshort a higher of metallics. for racespercentage or on tracks that are A racer usually chooses soft material easy on brakes. Hard materials are for races or is on high, tracksorthat are usedshort where wear where easy on brakes. Hardlittle materials are very hard braking and brake coolused where wear is high, or where ing occurs.
very hard braking and little brake cool-
ing occurs. FRICTION-MATERIAL ATTACHMENT FRICTION-MATERI Friction m aterial is AL attached to a ATTACHMENT metal backing . On a drum brake, the Friction material attached backing is the brake isshoe. On a to disca metal a drum brake, the brake, backing. a metal On backing plate is used. backing is the brake shoe. On a disc The friction material is either riveted brake, a metal used. or bonded to backing the shoeplate or is backing The is eitheris riveted plate.friction This material attachment very or bonded If to itthecomes shoe or backing important. apart , the plate. This attachment is very brakes can fail suddenly. important. If it comes Riveted-Although rivetingapart, is an the old brakes fail suddenly. way of can attaching friction material, and Riveted-Although riveting is ,anrivet old the method is very reliable way of attaching friction material, and holes can cause cracks in the friction the method reliable, rivet material whenisit very gets hot. The rivets holes can cause cracks the friction friction seldom fail-usually it in is the material gets hot. Thefriction rivets material when itself. i tAlso, if the i t is the friction seldom fail-usually material wears out, the rivets can conmaterial itself.or Also, if thewillfriction tact the drum rotor. This score material wears the ruin rivets the surface and out, usually it. can contact the drummore or rotor. Thisa ttachment will score Bonded-A modern the surface and usually ruin it. is bonding with high-temperature Bonded-A more ismodern attachment adhesive. There less tendency for is with high-temperature the bonding friction material to crack because · adhesive. less iftendency for it has no There holes. is And, the friction the friction material to crack because m aterial wears out, a bonded attachit has does no holes. And, to if the the rotor friction ment less damage or materialsurface. wears out, a bondedbondedattachdrum In addition, ment does less damage to the rotor or drum surface. In addition, bonded37
Brake-specialty shop is best place to get facts for comparing lining materials. Because they often work with repeat customers, shop personnel see long-term of using different materials. Brake-specialty shop is best results place to get facts for comparing Stores selling brake linings typically don'twith seerepeat resultscustomers, of actual lining materials. Because they often work use. personnel see long-term results of using different materials. shop
Passenger car used for towing should have heavy-duty brake linings. Cheap linings may work in light-duty use, but will have high wear and may towing should heavy have loads. heavy-duty Consider vehicle Passenger car fade used when for towing brake use when selecting linings. linings. Cheap linings may work in light-duty use, but will have high
wear and may fade when towing heavy loads. Consider vehicle Stores selling brake linings typically don't see results of actual use when selecting linings. use. with the posItIve mechanical-
attachment feature of riveting. Most with the positive racing disc-brake pads aremechanicalmade this attachment feature riveting. way. Unfortunatelyof , due to Most their racing disc-brake pads are made this curved shape , it is difficult to produce way. Unfortunately, due toassemtheir drum-brake shoe-and-lining curved shape, it is difficult to produce blies with this process.
drum-brake shoe-and-lining assemSELECTING blies with this process. FRICTION MATERIAL
Riveted linings should be replaced when rivets get close to touching the drums. Here's what happens warning when signs Riveted linings shouldwhen be replaced are ignored. Most to of touching lining andthe rivets are rivets get close drums. gone shoe is wornwhen part warning way through! Here'sand what happens signs Drumignored. was alsoMost ruined. are of lining and rivets are
gone and shoe is worn part way through! Drum also ruined. only was linings lasl longer because they
have more usable thickness; there are onlyrivet linings longer because they no headslast to contend with. have more usable thickness; there The disadvantage of bonding isarea no rivetresistance heads to contend with. lower to high temperature. The disadvantage of bonding Sometimes, riveting and bonding isarea lower resistance to high temperature. combined to secure brittle material Sometimes, riveting and bondingRivare for high-temperature operation. combined to secure brittle material ets are much stronger at extreme for high-temperature operation. Rivtemperatures. etsThe arebest much strongeris achieved at extreme attachment by temoeratures. bonding during the lining-molding is achieved process.best-attachment This is called mold bonding by or bonding during During the lining-molding integral molding. this process, process. is calledin mold or holes areThis punched the bonding brake-pad integral molding. During this process, backing plate. A high-temperature holes are ispunched in theto brake-pad adhesive then applied the plate backing plate. is Aputhigh-temperature and the plate into the lining adhesive is thentheapplied to the plate mold. During molding process, and the plate is put into the lining pressure forces the lining material mold. During process, into these holes the and molding high temperature pressure the forces the lining activates adhesive. This material process into these holes and high temperature combines the advantages of bonding
he
activates the adhesive. This process combines the advantages of bonding
38
SELECTING Selection of t he proper friction FRICTION MATERIAL material depends on the following: of the proper friction street driving, • Selection Vehicle use-easy material depends theracing. following: hard street dri vingon , or use-easy • Vehicle Cost versus budget. street driving, hard street driving, racing. • Maintenance youorare willing to put' upCost with.versus budget. Maintenance you are willing put' Easy Street Driving-For streettouse, up with. most people choose the lowest-cost Easy Street Driving-For friction material. However,street you use, get most people the lowest-cost what you paychoose for. Cheap linings or friction However, youfaster get pads maymaterial. squeal and wear out what you pay for. Cheap linings or than the more expensive ones. pads may squeal and wear out faster Consequently, they may end up costthan the Worse moreyet expensive ones. ing more. , they may fade in Consequently, they may up costsome unexpected hard end usage. So , ing more. Worse yet, street they may fade in even though most driving is some unexpected hard usage. So, easy, it is best to get high-quality friceven though most street driving is tion material. easy, is best to get high-quality fric-' t An itauto-parts store usually can tion material. judge friction-material wear or fade An auto-parts store usually a can't resistance. Therefore , consult spejudge friction-material fade cialty shop that deals in wear brakes.orThere resistance. consult a speare usually Therefore, a number of brake-repair cialty shop that deals in brakes. shops in every city or locale. There They are brake-repair deal usually with alla number sorts of of brake failures. shops in every city customers or locale. allow They And their repeat deal all sorts of brake performfailures. them with to judge the long-term And of their repeat customers ance various materials. The allow shop them to judge the long-term foreman or service manager isperformusually ance of various materials. Theadvice shop the person to ask. Take his foreman or service manager is usually rather than that of an overthe person to ask. Take his advice rather than that of an over-
Shoes are fitted with different types of lining. Upper shoe is darker due to extra metallics lining. with This different "harder" types lining of is Shoes arein fitted used severe use.is darker due to extra lining.for Upper shoe
metallics in lining. This "harder" lining is used for severe use.
the-counter general parts salesman. 1 The problem with easy street drivthe-counter generalboth parts salesman. ing is getting good lowThe problem withperformance easy street drivtemperature brake and is gettingEven both goodleisurelowing resistance. fade the most temperature brake performance have and ly street driver will occasionally fade resistance. Even the most leisureto make a hard stop from high speeds. ly street driver The brakes mustwill be occasionally capable of a have hard to make a hardlinings stop from speeds. stop. Organic are high the best for The brakes must be as capable of a hard this type of service, they work best stop. liningsThe areone thehard beststop for at lowOrganic temperature. this type of service, as they work best should be within their capability, but at temperature. The one hardfrom stop notlownecessarily repeated stops should be within their capability, but high speed. notIf you necessarily repeated stops from ' ve selected a lining correctly high speed. matched to easy street driving, dan', you've selected lining LlseIf it for racing or ahard use.correctly If you matched to aeasy street driving, don't have to pull trailer in the mountains, use it for racing or hard use. If either change friction material oryou go have to pull a down trailer hills in theinmountains, very slowly low gear either friction material or go withoutchange riding the brakes. very slowly down hills in lowheavygear Hard Street Driving-Use
without riding the brakes. Hard Street Driving-Use
heavy-
duty friction material for hard street driving or hauling heavy loads. This is duty friction material for hardHeavystreet usually a semimetallic lining. driving or hauling heavy loads. This is duty material has greater wear resisusually a semimetallic lining. Heavytance and better braking performance duty material has greater wearusually resisat high temperature. It will tance and better braking performance cost more initially, but will be more at high temperature. It will usually economical overall . cost more initially, but will bebe more Heavy-duty linings should pureconomical chased onlyoverall. after consulting an expeHeavy-duty shouldSelect be pur-a rienced brake linings specialist. chased only after consulting a n expebrand that he is familiar with and has rienced brake specialist. Select confidence in . Ask him what hea brand that he his is familiar with for andsimihas would use on own vehicle confidence in. Ask him he lar driving conditions. Go towhat several would use on his own vehicle for simishops , if possible, to see if the advice lar driving conditions. G o toBeseveral you are getting is consistent. aware shops, if possible, to see if the advice that many American cars produced you getting is consistent. Be aware afterare 1979 are fitted with semimetallic that many American cars produced disc- brake linings. Most European are fittedcars with semimetallic aftzr and 1979 Japanese use highdisc-brake Most European temperature linings. organic linings. and Japanese cars , use highFor hard street driving you may be temperature organic linings. tempted to use a high-temperature, For hard street driving, you may be organic racing friction material. This tempted to use a high-temperature, may work well under severe organic racing material. This conditions, but friction be prepared for troumay worknormal welldriving. underTheysevere ble during actuconditions, but be troually have some of prepared the samefor characble during normal driving. They actuteristics when cold as organic linings ally have when hot. some of the same characteristics coldmaterial as organic linings Racingwhen friction cannot be when hot. kept hot enough to work on long trips friction This material cannot be onRacing the highway. would require kept hot enough to work on long trips repeated brake applications to keep on thewarm. highway. This would require them A panic stop caused by an repeated brake applications to keep unexpected emergency could have them warm. A panic stop caused by disastrous results with cold brakes. an unexpected emergency couldfriction have Racing-Selecting the correct disastrous results with cold brakes. material for racing is easier than for Racing-Selecting correct friction the street because the driving conditions material racing is easier than for are more for predictable-always severe. the street driving Exact brakebecause use depends on conditions the particare severe. ular more track, predictable-always driver's technique and race Exact brake use depends on the length. Friction material mustparticmeet ular driver's technique and race thesetrack, requirements: length. Friction must meet • No fade during material race. these requirements: • Will not wear out during race. No fade during race. to withstand • Correct composition Will not wear out during.race. temperatures encountered Correct withstand Because composition road racing istousually the temperatures encountered. hardest on brakes, let's look at how to Because road racing is usually the select friction material for this hardest on .brakes, let's look at how to application select friction material for this It turns out that most road-racing application. cars use the same ma terial , Ferodo thatallmost road-racing OSItIIturns . And out , nearly road-racing cars cars use brakes. the same material, Ferodo use disc OS 11 is so common DS11. nearly all brakes road-racing becauseAnd, road-racing are cars deuse disc brakes. D S l l is so common signed to be as light as possible, relabecause road-racing tive to the power a ndbrakes weightare of dethe signed be as light as possible, relacar. Big,to fast cars have bigger brakes tive the slow power weight of that the than to light, carsand . This means
car. Big, fast cars have bigger brakes than light, slow cars. This means that
Racing caliper is fitted with Ferodo DS11 lining material. This lining is popular for all types racing. is Photo courtesy AP Racing. Racingofcaliper fitted with Ferodo DSll
lining material. This lining is popular for all types of racing. Photo courtesy AP Racing.
Super Vee brake is typical of those used on small race cars. Rules require using VWbrake components. cast-iron singleSuper Vee brake is VW typical of those used piston-one piston side-caliper on small race cars. Rulesper require using VWclamps on solid rotor. rotor bolts to brake components. VWVW cast-iron singlespecial aluminum hat that quickpiston-one piston per allows side-caliper change wheel is adeclamps on solidmounting. rotor. V WDesign rotor bolts to quate light hat carsthatwith 160-mph special for aluminum allows quickcapability. change wheel mounting. Design is ade-
quate for capability.
light
cars
with
160-mph
Compare Indy Car brake with Super Vee brake in photo, above right. Indy car uses dual-piston aluminum caliper vented Compare lndy Car brake with and Super Vee rotor. diameter slightly bebrake Rotor in photo, aboveisright, lndylarger car uses cause 15-in. aluminum wheels arecaliper used. Indy has dual-piston and car vented 210-mph capability, is hundreds of rotor. Rotor diameter and is slightly larger bepounds15-in. heavier than are Super Vee. Carcar speed cause wheels used. lndy has and weightcapability, show in the Photo by 210-mph andbrakes. is hundreds of Tom Monroe. pounds heavier than Super Vee. Car speed
and weight show in the brakes. Photo by Tom Monroe.
most road-racing brakes operate at about the same temperature . most road-racing brakesproperly operateatata Ferodo OSII operates about the same temperature. disc temperature of 780-1100F 1 operates at a Ferodo DSl The (416-593C). frictionproperly coefficient disc 780-of 1100F rises totemperature its operatingofvalue about (41 6-593C). The friction coefficient 0.3 and is reasonably constant in this rises to its operating value of about temperature range. Outside this tem0.3 and isrange, reasonably constant in this perature the friction coefficient temperature range. Outside this temis lower. perature range, Most race carsthe canfriction use thecoefficient same fricis lower. tion material because car designers Most cars can use the same size therace brakes in proportion to fricthe tion because speedmaterial and weight of thecarcar.designers Try the size in proportion to theit OS 11themabrakes terial first and see how speed and weight of the car. Try works. Check rotor temperature tothe be D S l l itmaterial firsttheand see how sure is within correct range,it works. rotor temperature paint. to be temperature-indicating using aCheck sure it is within the correct range, Read Chapter 10 for more information using a testing. temperature-indicating paint. on brake Read Chapter 10 wear for more If the linings too information fast or the on brake testing. brakes fade, and cooling cannot be
If the linings wear too fast or the brakes fade, and cooling cannot be
Scoop for Indy Car rear brake projects above body and into airstream. Because drag smallestScoopisforcreated, lndy Cartherear brake possible projects scoop body shouldand be into used . Smaller Because scoops above airstream. mean aisfaster car, but brakes. Maxidrag created, thehotter smallest-possible mum necessary on shortscoops ovals scoopducting shouldis be used. Smaller such asfaster Phoenix International Raceway. mean a car, but hotter brakes. MaxiPhotoducting by Tom Monroe. mum is necessary on short ovals
such as Phoenix International Raceway. Photo by Tom Monroe.
improved, a harder friction material is required. There are materials that can improved, atemperatures harder frictionover material is withstand 1200F required. There are materials that can (649C), but these have disadvantages. withstand over 1200F Raybestostemperatures M 19 and Hardie-Ferodo (649C), are but these have disadvantages. 1103 ultra-high-temperature RaybestosThese M 19 and Hardie-Ferodo materials. friction materials 1103 are ultra-high-temperature tend to wear out rotors and also take a materials. friction little time toThese work after they materials coolon a tend to wear outConsequently, rotors and alsoFerodo take a long straight. little time to work after they cool on a OS 11 is more popular than higherlong straight.mConsequently, Ferodo temperature aterial. It is better to D S l lbigger is more popular than higheruse brakes or improve brake temperature It is extremely better to cooling than material. to live with
use bigger brakes or improve brake cooling than to live with extremely 39
high brake temperatures. If brakes run cool, that's good. You high temperatures. have brake two options: Use softer linings to If brakes run cool, that's good. You give lower pedal effort or reduce airhave two options: Use softer to flow to the brakes. However,linings because give lower pedal effort or reduce airchanges occur during a race that can flow to thethebrakes. overheat brakes,However, reducing because cooling changes occur choice. during Cooling a race that can air is a better airflow overheat the brakes, reducing cooling increases aerodynamic drag , so slightair is a better choice. Cooling airflow ly smaJler ducts or none at all will increases aerodynamic drag, slightreduce drag and make theso car go ly smaller or none at allbrake will faster. Thisducts will also increase reduce drag. and makethethe go temperature Usually, onlycarvalid faster. will alsosoft increase excuse This for running liningsbrake is a temperature. Usually, only very high pedal effort. the If you canvalid run excuse for running soft linings is a soft linings, Hardie-Ferodo Premium very If you can run workshigh well.pedal It iseffort. a low-copper organic soft linings, Hardie-Ferodo material , with a high Premium friction works well. It is a low-copper organic coefficient. material, with a high Always run the same frictionfriction matecoefficient. rial on the front and rear. If you use Always run material the sameatfriction mateOS11 friction one end, use rial front If youwarm use it aton thethe other endand , toorear. . Brakes D l l friction material at one end, use upSduring a race and reach steady-state it at the otherafter end,atoo. warm temperature few Brakes la ps . If the up during a racefriction and reach steady-state brakes change differently from temperature a fewthe laps.warmup If the front to rearafter during brakes change friction defer-encly from period, front-to-rear brake balance front rear during will alsotochange. This canthe causewarmup loss of period, If front-to-rear brakedifference balance control. you find a great will also change. This can cause lossand of in temperature between the front control. If you find a great difference rear brakes, modify the cooling airflow in temperature between the front and or the brake size, not brake friction rear brakes, modify the cooling airflow material.
or the brake size, not brake friction
material. STOCK-CAR BRAKE LININGS Because of their high weight, speed STOCK-CAR BRAKE LININGS and horsepower, a racing stock car is Because of their high weight, the hardest on brakes. The mostspeed diffiand horsepower, a racing car is cult track for brakes is onestock consisting the medium-length hardest on brakes. The most diffiof straightaways and cult track for brakes is one consisting slow corners. And, racing stock-car of medium-length straightaways anda brakes require more attention on slow corners. And, stock-car road course than on aracing superspeedway. brakes require more attention Certain medium-speed ovals are on alsoa road course than on a superspeedway. hard on brakes. Certain medium-speed ovalscars arewere also Disc Brakes - Before stock hard on brakes. used on road courses , most used Disc Brakes-Before stockdrums cars were drum brakes . Their huge with used onlinings road were courses, mostforused metallic adequate sudrum brakes. Their hugesmaller drums with perspeedways and most oval metallic liningshave werechanged adequatein for sutracks. Things stockperspeedways andnow most oval car racing. They use smaller disc brakes. tracks.calipers Things are havehuge, changed in stockThe even when car racing. They now use disc brakes. compared to the high-horsepower The calipers huge, speed even potenwhen Indy cars. The are 200-mph compared to the high-horsepower tial of a stock car combined with a Indy cars. The3000 200-mph weight over Ib , speed makes potenlarge tial of necessary. a stock car combined with a brakes weight over road-racing 3000 lb, makes large As with cars, brake brakes necessary. lining must be chosen according to withof road-racing cars, ofbrake theAstype track and length the liningTracks must can be chosen according to race. vary from short dirt the type track and length of the ovals, to of road courses, to 200-mph race. Tracks can vary from short dirt
ovals, to road courses, to 200-mph 40
Size of caliper used on a stock car indicates how much energy brakes must absorb. Usually, Size of caliper usedthe on abiggest-possible stock car indibrakes how are used. Linings are brakes varied tomust suit cates much energy track and length of race. absorb. Usually, the biggest-possible
brakes are used. Linings are varied to suit track and length of race.
superspeedways. The type of lining that works best for each type of racing superspeedways. The over type of lining has been developed years of that works best for each type of racing experience . If you are new to the has developed over yearssupof sport,been consult your brake-lining experience. you forareadvice. new to the plier or other Ifracers sport, brake-liningracing supManyconsult gradesyour of high-quality plier or other racers for advice. linings are available for stock cars. Many racing-brake grades of high-quality Many suppliers racing offer linings are available stockPremicars. Hardie-Ferodo linings.for Again, Many racing-brake suppliers offer um is the softest lining. HardieHardie-Ferodo linings. Again, PremiFerodo Premium is recommended for um is the ovals softestandlining. high-banked tracks, Hardiesuch as Ferodo Premium where is recommended for superspeedways, little braking high-banked ovals and tracks, such as is required . These soft pads are easiest superspeedways, where little braking on rotors and require no warm-up' is required. These soft pads areIf easiest time for full effectiveness. brake on rotors andarerequire no warm-up temperatures low enough to avoid time or forexcess full effectiveness. If brake fade pad wear, Premium is temperatures the best choice.are low enough to avoid fade Premium is Foror excess runningpad atwear,higher temthe best choice. peratures, try the Hardie-Ferodo For pads. running temOPll These atare higher the mediumperatures, try material. the Hardie-Ferodo hardness racing The DPll D P l l pads. the mediummaterial hasThese more are copper content hardness racing material. The itD Phas ll than Premium . Consequently, material has more copper content increased temperature resistance and thanwear. Premium. Consequently, it has less increased resistance and For roadtemperature racing, a hard lining mateless wear. rial will be required on most stock For Hard road racing, a hard matecars. materials willlining withstand rial will be requiredbeston ofmost high temperatures all. stock They cars. operate Hard materials will withstand will above 1200F (649C) high temperatures best ofOSall. They while the popular Ferodo 11 comwill operate above 1200Fat (649C) pound loses effectiveness about while popular Ferodo D S l l com1100F the (593C). pound loses effectiveness about Two hard materials are theatHardie1IOOF (593C). Ferodo 1103 and Raybestos M19. Twohave hard high materials arecontent, the HardieBoth copper but Ferodo 1103 and Raybestos M19. are still considered organic linings. Both only have do highthey copper content, high but Not withstand are still considered organic linings. temperatures. they wear long enough Notlastonly do they withstand high to in a long hard race. The draw-
temperatures. they wear long enough to last in a long hard race. The draw-
back is that 11 03 or M 19 material tends to wear rotor surfaces more thatcompounds. 1103 or M19 material back than is other Also, pedal tends to wear rotor surfaces effort will be higher and they more take than compounds. Also,usepedal longerother to bed in. Therefore, the effort will be higher theyto, take hard compound if youand have but longer to bed results in. Therefore, use the better overall will be obtained hard compound if you have if you can use the softer to,0 Pbut 11 better overall results will be obtained material. if Other you can use theracing softerpads D Pare ll heavy-duty material. available from various manufacturers. Other racing pads are They alsoheavy-duty tend to be hard on rotors. available from various manufacturers. If you race on supers peed ways, Thev to material. be hard onSuch rotors. don't also use tend a hard mate1 f you race on superspeedways, rial cools off too much and the brakes don't matedon't use worka hard well material. when an Such emergency rial cools off too much and the brakes occurs. don't well when an emergency Drum work Brakes-Although racing occurs. stock cars now use disc brakes, there Drum Although racing are still Brakessome restricted-class mastock cars now use brakes, chines using drums.disc If you racethere in a are restricted-class class still that some is so limited, you mightmabe chines using drums. If you race in a required to use original-equipment class is so limited, drum that brakes at the rear. you might be required to several use original-equipment There are metallic or semidrum brakes at the for rear.use in stock-car metallic materials There aredrum several metallic semiracing with brakes. Oneorpopular metallic materials for use in stock-car brand is made by the Grey Rock diviracing drum brakes. One popular sion ofwith Raybestos Manhattan Corp. brand make is made the Greylinings Rock diviThey twoby metallic with sion of Raybestoscapability: Manhattan high-temperature 5262Corp. and They two metallic linings 519l. make The 5262 compound was with first high-temperature 5262 developed for use capability: on fast ovals andand su5191. The 5262 compound was first perspeedways with the characteristic developed for use on ovals and suof low change in fast friction under perspeedways with the characteristic extreme-temperature conditions. The of change in friction under 5191low material is softer, but is said to extreme-temperature conditions. The wear faster. 5191 is softer, but is said to For material some types of oval-track racing, faster. awear semi metallic or heavy-duty street For some types of oval-track racing, lining may be suitable. This assumes athat semimetallic or heavy-duty speeds are low, cornersstreet are lining suitable. banked,may andbe races are This short.assumes Here, that low, forcorners are brakesspeeds are usedaremostly setting the banked, races and are for short. Here, car up forand cornering unexpectbrakes are used mostly for setting the ed emergencies. The Chevrolet semicar up for cornering and for unexpectmetallic linings or Bendix EOF heavyed emergencies. Themight Chevrolet semiduty service linings be suitable. metallic linings or Bendix E D F heavyCareful testing is required to see if a duty service linings might be suitable. medium-temperature material will Careful testing is required work properly on your car. to see if a
medium-temperature material work properly your car. BEDDING INon LININGS
will
New linings must be bedded in
BEDDING I N LININGS before they are raced to ensure proper New linings be inbedded brake operation. must Bedding brakes in is before they are raced to ensure proper similar to breaking in a new engine. If brake operation. Bedding in brakes is an attempt is made to race on new similar breaking a new engine. If linings, togreen fade in can occur. Green an attempt is made racecaused on new fade is severe brake to fade by linings, green fade can occur. Green gas or liquid coming out of the friction fade is severe fadethecaused by material and lubrake bricating rubbing gas or liquid of the friction surfaces. Thecoming driver out feels green fade material andbrake lubricating the rubbing as a sudden loss. surfaces. The driver feels green fade as a sudden brake loss.
Oval-track cars running on dirt are not extremely hard on brakes. For light cars such as this late-model stockon car, softer racing Oval-track cars running dirt are not exlinings or heavy-duty linings may tremely hard on brakes.street For light cars such work. testing during long practice as thisCareful late-model stock car,a softer racing session is desirable before trying new may linlinings or heavy-duty street linings ings inCareful a race. testing during a long practice work.
session is desirable before trying new linOrganic material in the lining tend~ ings in a race.
to boil off rapidly when first heated. Organic material in the tends This material not only actslining as a lubrito boil off rapidly when first heated. cant between the lining and rotor, but This notthe only acts surface. as a lubriit canmaterial also glaze lining A cant between lining by andthe rotor, but glazed surface the is caused organic it can also glaze the surface. on A material cooling and lining resolidifying glazed surface is caused by the organic the pad surface. A glazed surface is material and resolidifying on hard and cooling slick, and never has the right the pad coefficient. surface. A Once glazedglazed, surfacethe is friction hard andmaterial slick, andmust neverbehas the right friction refaced or friction replaced.coefficient. Once glazed, the friction material mustshould be refaced or Bedding in brakes be done replaced. during a practice session, not during a Bedding brakes isshould done race. If theinpractice long be enough, during a practice session, not during a you can bed in more than one set of race. If the practice is long enough, pads and have them race-ready for you in to more one set of later.can It isbed wise havethan a spare set of pads andbedded-in have them unworn pads race-ready as spares. for later. is wise to procedure have a spare set by of TheI tbedding-in starts unworn bedded-in pads as spares. taking the car out and gradually warmstarts by ingThe up bedding-in the brakes. procedure This is followed by taking out and gradually warmusing the the car brakes very hard several ing up the followedinto by times. Thebrakes. car is This then isbrought using the brakes very hard several the pits for a cooling-off period. times. car is DS then into WhenTheFerodo 11 brought is properly the pits for period. bedded in, aitcooling-off changes from a black or When Ferodo D Sgrey l l or is brownish properly dark grey to a lighter bedded in, it changes from a or tone near the surface. Variousblack brands dark grey to a lighter grey or brownish of lining material have similar colortone nearcharacteristics, the surface. Various change whichbrands you of lining material have similar colorlearn by experience. change which on youa Metalliccharacteristics, particles are visible learn by experience. worn racing-lining surface. Check Metallic are visibleGet onfa-a your brake particles linings frequently. worn surface. of Check miliar racing-lining with the appearance the your linings frequently. G e t are faliningbrake surface when the brakes miliar with the appearance of you the working correctly. This will help lining surface the abrakes are visually detectwhen when problem working correctly. This will help you occurs. Make sure the surface is not visually detect when a problem polished, crumbling or cracking. Also
occurs. Make sure the surface is not polished, crumbling or cracking. Also
Brake-pad appearance changes greatly after bedding in. Pad on left is bedded in, but not raced. Pad at right is new. greatly If new Brake-pad appearance changes pad were used hard,ongreen could after bedding in. Pad left isfade bedded in, result. should bedded in but not Pads raced. Pad atalways right isbenew. If new first. were used hard, green fade could pad
result. be bedded in inspectPads theshould rotoralways surface. Friction first.
material should not transfer from the inspectto the the rotor. rotor surface. Friction lining
material should not transfer from the lining to the rotor. MACHINING FRICTION MATERIAL MACHINING When installing new drum-brake FRICTION MATERIAL linings, you may need to turn or grind drum-brake theWhen drums.installing However,new do not turn the linings, you may need to turn or grind drums unless they are out-of-round the drums. However, do not turn the or deeply grooved. Regardless, brake drums unless be theymachined are out-of-round linings should to fit the or deeply grooved. Regardless, brake drums for best braking performance. linings should be machined to fit the Because brake-lining material drums for best braking performance. usually contains asbestos fiber, Because results brake-lining material machining in dangerous asusuallydust. contains asbestos fiber, bestos Due to recent discoveries machining results dangerous of the hazards of in asbestos dust asto bestos dust. Due to recent discoveries human health, many new safety preof the hazards of asbestos to cautions are required in brakedust shops. human health, many safety have preConsequently, many new of them cautions are required in brake shops. stopped machining brake linings. You Consequently, many of them may have to search for a shop tohave do stopped linings. You this, but machining it is worth brake it in terms of optimay have search for a shop to do mum braketoperformance. this, but it is worth it in terms of optiThe drum-brake-shoe machining m u m brake performance. process is called arcing the shoes. The The must drum-brake-shoe drums be measured,machining so bring shoes. The process them to isthecalled brakearcing shop.the The machine drums must be measured, so bring cuts the correct radius on the shoe so them to thecontact brake shop. The machine the shoes the drum over a cuts correct on the shoebeso large the area. If a radius mismatch exists the shoes contact drum over tween the drum andthe shoes, brake fric-a large area. be If atoomismatch betion may high or exists too low, tween the drum and shoes, brake fricdepending on where the shoe contacts tion may beThetooworst high possibility or too low, the drum. is depending on where thewheels shoe contacts when the right and left have a the drum.fit The worstthepossibility is different between shoes and when the right and left wheels have drums. This will cause dangerous pull-a different fit between the shoes and ing to the side. drums. This will cause Disc-brake pads for dangerous racing usepullare ing to the side. often machined to make them flat. Disc-brake padsonfor racing machine use are This can be done a milling often machined to make them flat. or surface grinder. Be careful. Some This be done on a dull milling machine typescan of brake lining milling cutor grinder. Be careful. Some terssurface in a hurry. types of brake lining dullthey milling As brake pads wear, tendcutto ters in a hurry. As brake pads wear, they tend to
This machine was used to arc, or grind correct radius, on brake linings before asbestos was was discovered to be a health This machine used to arc, or grind corproblem. Consequently, many shops rect radius, on brake linings beforehave asstopped was arcingdiscovered brake shoes. health bestos to Better be a braking is achieved with arced shoes drumshave are problem. Consequently, many ifshops turned. arcing brake shoes. Better braking stopped
is achieved with arced shoes if drums are turned. get tapered. In that condition, the
braking gets worse, with higher pedal
get that condition, the efforttapered. and In longer pedal travel braking with full higherbraking pedal required.gets Toworse, restore effort and longer travel effectiveness, machine pedal the pads so required. To restore full braking the rubbing surface is parallel to the effectiveness, theandpads so back of the pad.machine Deglazing minor the rubbingmay surface is parallel to the flattening be accomplished by back of the Deglazing and minor rubbing thepad. lining on medium-grit flattening laid may onbea accomplished by sandpaper flat surface, such rubbing the lining on medium-grit as a mill table or a piece of glass. sandpaper on a flat after surface, such Rebedding laid is necessary machinas table or a piece of glass. ing aor mill sanding. Rebedding is necessary after machinAlso, it sometimes helps to machine ing or sanding. a groove in the surface of the brake it sometimes helps to machine padAlso, to get rid of the lining dust. Most apads groove surface of theforbrake haveina the groove in them this pad to getIfrid of the seems lining dust. purpose. it always to be Most filled pads have aa second groove groove in themmay forhelp. this with dust, purpose. it always seems be stock filled A grooveIfmachined 90° totothe with a second plan. groove help. one isdust, a reasonable Seemay Chapter A groove machined 90" to the stock 12 for details on modifying brake pads. one a reasonable See Chapter If is you machine theplan. linings, be care12 for on modifying pads. ful notdetails to breathe the dust brake and chips. If you linings, be Wear an machine approvedtherespiralOr andcaredo ful to dust breathe and chips. not not blow withthe andust air hose. Pick and do Wear an approved up asbestos dust respirator with a vacuum not blowThe dustdust with hose. cleaner. in an the air shop mustPick be up asbestos dust the withoperation, a vacuum cleaned up after so cleaner. The dust the shop be other people won'tinbreathe themust potencleaned up stuff. after the operation, so tially deadly other won't breathe the potenSee people your local health authorities for tially stuff. before you take a safetydeadly regulations See your local health authorities for chance. Remember, many organic linsafety regulations before you take ings contain more than 50% asbestos.a chance. organic Most, if Remember, not ali, new many road cars will linuse ings contain more than 50% asbestos. asbestos-free semimetallic or nonMost, if not all, new road will use asbestos organic linings by cars 1990. asbestos-free semimetallic or nonasbestos organic linings by 1990. 41
Hydraulic Systems
5
Modern fast-fill tandem master cylinder, page 50, has plastic reservoir and integral proportioning valves. Cylinder must be mounted so fluid is level in reservoir. Modern fast-fill tandem master cylinder, page 50, has plastic reservoir and integral proportioning valves. Cylinder must be mounted so fluid is level in reservoir.
All modern cars use a hydraulic system to operate the brakes. This hyAll modern use ofa cylinders, hydraulic draulic system cars consists system to operate the brakes. Thisfilled hyvalves, hoses and tubing, all draulic system fluid. consists cylinders, with hydraulic The oftype of hyvalves, hosesused andin tubing, all filled brake systems is draulic fluid with liydra~ilic jlirid. type properof hycalled brake fluid. TheThe special draulic fluid used systems is ties of brake fluid in arebrake discussed later called brake fluid. The special properin this chapter. tiesA of hydraulic brake fluid system are discussed has later two in this chapter. functions : move brake linings into poA hydraulic system has and two sition against drums or rotors; functions: move brake linings into poapply a force to brake linings, creating sition against friction force. drums or rotors; and apply a force brakeabout linings, creating When you tothink a hydraulic friction force. system, remember these important When you think about a hydraulic functions: movemenf and force. A hysystem,system remember important draulic has tothese do both jobs to A hyfunctions:themovement operate brakes. and Theforce. movement draulic system has to do both jobs to must be enough to take up all clearoperateand the deflections brakes. Theinmovement a brake ances must be The enough to take all clearsystem. force mustup be great ances and deflections in a brake enough to stop the car. system. The force must be great enough to stop the car. 42
BASIC HYDRAULICS To understand how a hydraulic BASIC operates, HYDRAULICS we must first considsystem To understand a hydraulic er the basics. For ahow hydraulic system system operates, first considto function it mustwebemust closed and comer the basics. hydraulic pletely filled For witha fluid , andsystem leakto function it must free - no fluid ou t orbeairclosed in. and completely filled properly with fluid, andhydrauleakIn a closed, sealed free-no or air in.laws are true: lic system,fluid the out following In a closed, sealed hydrauto a Fluid cannot properly be compressed lic system, the following lawsare lesser volume, no matter how true: high Fluid cannot. Pressure be compressed the pressure is equal to overa lesser volume, matter how high all surfaces of theno containing system. theTurn pressure. equal to pagePressure 63 for is more on over hyall surfaces containinguse. system. draulic fluidofforthe automotive Turn to Fluid page 63 for more on Pressureis pressurized by hythe draulicoffluid for automotive a piston . The pistonuse. moves in force pressurized by the aPressure-Fluid cylinder and isis sealed to prevent force of a piston. The piston moves in fluid from leaking out or air leaking ain. cylinder and is sealed to prevent The piston must move with little fluid from leaking out or air leaking friction in the cylinder. in.There The piston must move withof little is air on one side the friction in the cylinder. piston and hydraulic fluid on the
There is air on one side of the piston and hydraulic fluid on the
other. The area of each piston is determined by its diameter. other. The area of each piston is deterPiston area = 0.785 Dp2 mined by its diameter. Ap = Area of piston in square inches 0.785 DP2 Piston area = Dp = Piston diameter in inches A, = Area of piston in square inches applied to the piston creates D pForce = Piston diameter in inches pressure in the hydraulic fluid . Th e Force applied to thediv piston is the force ided creates by the pressure pressure in the hydraulic fluid. The area of the piston: pressure is the forceF divided by the Hydraulic area of thepressure piston: =----E.
Ap F Hydraulic = A in pounds pressure per square inch P F p = Force on piston inApounds
in pounds per square inch ' t refer to pressure In = Force on piston in pounds FpDon pounds-it is pounds per square in ch Don't refer to pressure in (psi). pounds-it is pounds per sqimre Let 's illustrate pressure with itich an (psi). example. See accompanying drawing illustrate with one an of Let's a simple hydraulicpressure system with example. See accompanying drawing piston. Fluid pressure is measured of a simple hydraulic system one by a with formula. with a gage or calculated piston. Fluid pressure is measured The amount of pressure depends on with a gage or calculated by a forn~ula. The amount of pressure depends on
Stop Prevents Movement of Piston 2
Piston 1
100POUNDS 100 POUNDS
-".. . . . .,. >'-..1"1 in. 1 in.",
t
'./'<-'---.1 in. .> 1 in.
PRESSURE PRESSURE --Force Force Area
=--
100 Pounds Pounds 100 1.0 Square Inch Inch 1.OSquare
= 100 100 Pounds-Per-Square-Inch = Pounds-Per-Square-I nch
Pressure is is force per unit area. A hydraulic piston piston exerts force on on fluid like like this table leg leg exerts pressure on on the floor. Pressure Pressure is is force divided by area on on which force is exerted. If leg-to-floor contact area is reduced, pressure on on floor is is proportionally proportionally increased. Drawing Drawing by Tom Tom Monroe.
how much force you put on the piston. If the piston has an area of 2 sq in. in. and the force is 400 Ib, the pressure is follows: calculated as follows: 400lb . 4001b = -2--' = 200 pSI. psi. Pressure = = In. 2 SQ sq In.
A smaller piston gives a higher in. pressure. If a piston with only 1-sq I-sq in. in. area is substituted for the 2-sq in. piston, a pressure of 400 psi is obforce. tained with the 400-lb force. Force Multiplication-Pistons Multiplication-Pistons can be used to multiply force in a hydraulic difsystem. By choosing pistons of different sizes, any relationship with forces is possible. A simple hydraulic system with two pistons is shown in the accompanying difdrawing. The pistons can have difareas. The relationship between ferent areas. forces depends on the relathe two forces tionsllip areas. tionship between the piston areas. Assume piston 1 has an area of 2 sq in. and a 400-lb force force applied to it. it. I in. showed in the previous example that this created 200-psi fluid pressure. pressure. Piston 2 now is sUbjected subjected to this fluid pressure. Remember 200-psi fluid that fluid pressure acts equally on all
Hydraulic Fluid
P
A, = = Area of Piston Piston 1 A1 A2 A2 = = Area of piston piston 2 F, = = Force Force on Piston Piston 11 F1 F2 = = Force Force on Piston Piston 2 F2 P P= = Fluid Fluid Pressure
=~(PSi) A1
A F P = F, l ( l b ) A1
Forces Forces can can be be multiplied multiplied with with a simple hydraulic system. In In this drawing, force F1 F, is is applied applied to F, is created. If t o a small piston piston with area A A,.1 . If large piston piston A2 A, is resisted resisted by a stop, stop, force F2 be the bottom bottom of a car. Force Force F,2 is greater than F F1 in a this were a hydraulic jack, stop could be 1 in ratio that's directly related related to t o piston areas. areas. Because Because fluid pressure pressure is is same throughout, ratio bigger piston piston has bigger force.
surfaces of the surrounding container. Fluid pressure acts on the contact surface of the piston, causing movement. face Force 2 will depend on the area of piston 2. Force Force on on piston piston == P A, P = = Hydraulic pressJ're pressure in in pounds per square inch inch Ap A, == Area of piston piston in in square inches
This is the same formula as on page 42, in a different format. format. In the example, example, assume piston 2 has an area of 1 sq in. in. The force force on 011 it at a fluid pressure of 200 psi is 200 lb. Ib. If we change piston 2 to an area of 4 sq in., in., the force force increases to 800 lb. Ib. The pressure does not change-only change-only the force on the piston. The larger the piston, the greater the force force with the same pressure. We can write a simple s i m ~ l eformula formula for for the relationship between the forces forces on the two pistons: _ F1A2 F --2
A1
F1 F, == Force ~ o r c on on e piston piston 11 in in pounds F on piston F,2 == Force Forceon piston 2 in in pounds A, == Area of piston piston 1 in in square A1 inches inches A, == Area ~ r e of a piston is ton 2 in in square sauare A2 inches inches
Piston = Ap Piston Area Area = A, (sq (sq in.) in.)
iI
Hydraulic Fluid Fluid
Sealed Container
W (psi) P= W =(psi) Ap A ,
Simple hydraulic system with one piston piston and and pressure gage. By putting putting force on on piston, fluid is pressurized. Pressure is the force-weight force-weight in in this instance-divided instance-divided by area of piston. Fluid Fluid pressure pressure acts equally on on all surfaces of container.
To increase the force on piston 2, you can reduce piston-l piston-I area or increase piston-2 area. area. Force can only be changed in a brake system by changing piston area (s). area(s). Do not use piston diameter in place area! Piston area varies as the of area! 43
A*x
Output Force
Output Force
Piston Area Ap
Area Piston Direction--.,,-/ of Movement Direction
t
--I
1-
of Movement
I
+
Input Movement
+
Movement Mp
/
=
~~---
lnput Movement
Piston ApMp (cu in.) Movement M,
Fluid Displacement
Output Movement
I
Displacement = ApMp (cuarea in.) of Fluid Fluid displaced by piston equals piston multiplied by distance it moves. LikeI I aFluid car engine, displacement can be given in displaced by piston equals area of cubic (cu in.). pistoninches multiplied by distance it moves. Like a car engine, displacement can be given in cubic inches (cu in.).
t
Hyraulic-brake system operates like this simple lever; increases force and reduces movement. Input side is the brake pedal. Input force and movement are supplied by your leg. Output side is the brake. Output force is exerted perpendicular by brake linings against rubbing surfaces. Output movement takeslnput up all clearance in system brakes by canyour be movement. lnput side is the brake pedal. force and'movement aresosupplied applied. leg. Output side is the brake. Output force is exerted perpendicular by brake linings against
rubbing surfaces. Output movement takes up all clearance in system so brakes can be applied.
To calculate movements in a hydraulic system, you need to consider To calculate movements a hyfluid displacement when ain piston draulic system, you need to consider moves. Displacement is the area of fluid displacement a pistonit the piston times when the distance moves. Displacement is the areadisof moves , or the same as cylinder the piston of times thein distance placement a piston an engine.it moves, stroke or the issame as cylinder dis-; Piston piston movement placement of a piston in an engine. greater piston movement means Piston displacement. stroke is piston movement; greater
greater piston movement means Fluid displacement = Ap M~ greater displacement. Ap = Area of piston in square Floor jack illustrates relationship between force and movement in a hydraulic system. Handle hasillustrates a low forcerelationship and high movement Floor jack between versusand high force and movement at force movement in alow hydraulic system. jack pad. Handle has a low force and high movement
versus high force and low movement at jack pad.
square oj the diameter. Calculate all piston areas first so you won't make squaremistakes. of the diameter. Calculate all costly piston areas first so you won't make Piston Movement-Hydraulic syscostly tems mistakes. must provide both force and Piston Movement-Hydraulic sysmovement. We just looked at how tems must provide both force and forces relate. Piston movement also movement. We just looked at how depends on piston areas, but not on forces relate. Piston movement also, fluid pressure. Pressure affects force depends on piston areas, but not on not movement. fluid affects force, If apressure. system is Pressure filled completely with not movement. fl uid, that fluid cannot change If a system filled completely volume, no ismatter how high with the fluid, fluid is cannot change pressure.that This hydraulic-la'v volume, no This mattermeans how that high any the number 1. pressure. This is hydraulic-la-v motion inward on a piston must result number 1. This means that any in an outward motion elsewhere in motion inward o n a piston mustsystem result the system . A good hydraulic in rigid, an outward motion should elsewhere in is so movement occur the A good hydraulic onlysystem. at another piston. If the system hoses , is rigid, so movement occur lines or cylinders expand should when the hyonly at another piston. If the hoses, draulic fluid is pressurized, the lines or will cylinders expandaswhen the hysystem not function designed .
draulic fluid
is
pressurized,
the
system will not function as designed. 44
Fluid inches displacement = A, M, of piston in square A , = Mp = Area Movement of that piston in inches inches M, = Movement of that piston in Because hydraulic fluid cannot be inches compressed, the following relationBecause fluiddisplacement cannot be ship exists: hydraulic In ward flUid compressed, the following = Outwardfluid displacement. relationship exists: Inward fluid has displacement If the hydraulic system only two = Out wardfluid displacement. pistons, such as shown in in the acIf the hydraulic system only distwo companying drawing, thehas inward pistons, such in the acplacement of as oneshown pistoninmust equal companying drawing, the inward disoutward displacement of the other placement onerelationship piston must equal piston. Thisofbasic remains outward displacement the other constant regardless of of system compiston. This relationship remains plexity. All basic inward-displa cement tolals constant regardless of system commust total all outward-displacem ent plexity. totals. All incva1.d-displacemenr totals must Now,total let's alluseoutwat,d-displacemen( a simple example totals. with a two-piston system . Assume
Now,1 let's usearea a simple piston has an of 2 sq example in. If it with two-piston system. Assume movesa inward 1 inch, its inward dispiston 1 has of 2outward sq in. If placement is 2ancuarea in. The dis-it moves inward 1 inch, its inward dis-2 placement of piston 2 must also be placement is 2 cu in. The outward cu in. If piston 2 has an area of 1dissq placement of piston 2 must will also be be 22 movement in., its outward cu in. change If pistonthe2 move has an area 1 sq in. To men t ofofpiston in., its outward movement will be 2, you must change its area . A larger-2 in. Topiston changewill themove movement piston area less; aofsmaller 2, you mustAssume change now its area. larger-2 one more. that Apiston area piston towill is changed an move area ofless; 4 sqa insmaller . for 2 one more. Assume now that piston 2 is changed to an area of 4 sq in. for 2
cu in. of fluid displacement, piston 2 must move 1/2 in. cuThe in. ofrelationship fluid displacement, betweenpiston piston2 must move 112 movement in in. a simple two-piston The relationship piston system is given by between the following movement in a simple two-piston formul a:
system is given by the following M1A1 formula: M =-2
A2
M, = Movement of piston 1 in inches M 2 = Movement of piston 2 in inches M, == Area Movement of piston 1 in inches A1 of piston 1 in square M, = inches Movement of piston 2 in inches piston 21 in in square A,2 = A = Area of piston inches A, = Area of piston 2 in square
To inches increase the movement of piston 2, increase the area of piston 1 increase movement of or To reduce the area the of piston 2. piston 2, increase the area of piston Remember that fluid mo vement1 or reduce the of piston depends on area piston area 2.and disRemember that fluid place ment. Mistakes in movement calcul ation depends ondiameter piston isarea disoccur when usedand in place placement. Mistakes in calculation of area, and movement in place of occur when diameter is used in place displacement. Use care with your of area, and. Double-check! movement in place of calculations displacement. Use care with your Force/Movement Relationshipscalculations. Double-check! As seen from previous formulas, Force/Movement there is a relationshipRelationshipsbetween force As a seen previous formulas, on pistonfrom and its movement. Both there is a relationship between force are related to piston area . It is possible on a piston its movement. forceand without movementBoth , or to have are related to piston force area. .ItHowever, is possiblea movement without to havesystem force without movement, or has both forces and brake movement without force. However, movements. The relationships be-a brake system has and bothforce forces and tween movement is very movements. The relationships beimportant. tween movement andand force is v&y Formulas for force movement important. both depend on piston area. However, Formulas changes for force cause and movement piston-area opposite both depend on piston However, changes in forces andarea. movements. piston-areain changes opposite Changes area thatcause create more changes in forces and movements. force on a piston result in less move-
Changes in area that create more force on a piston result in less move-
ment of that piston. The system works like a simple lever, as shown in ment of that piston. The system the accompanying drawing. works a simple lever, as hydraulic shown in One like simple two-piston the accompanying drawing. system is used in a hydraulic jack. The One simpleboth two-piston hydraulic jack supplies force and movesystem in a hydraulic jack. as Thea ment atis used the same time , such jack movesystem .both Theforce jack and handle is brakesupplies ment theforce. same time, as a movedatwith This forcesuch is applied brake system. ofThe jack is to the bottom a car and handle it moves moved force.When This force is applied the car with upward. using a jack, to thethat bottom of a car andis less it moves note the handle force than the car upward. When using a jack, the force on the car. You can easily lift that the force is less than anote 2000-lb car handle using less than 50 Ib at the on Force the car.is You can easily lift increased by the the force handle. a 2000-lb car thanNote 50 Ib at difference in using piston less sizes. also the handle. Force is increased by the how great the movement of the difference in piston tosizes. Note also handle is compared the movement howthegreat the ormovement of the of jack pad car. Movement is handle compared the movement reduced,is but force istoincreased by inof the jack padsize or car. is that Movement operates the creased piston reduced, but force is increased by injack pad. creased that Operates the Input & piston Outputsize Pistons-A hydraulic jack pad.uses force and movement apsystem Input & Output an inputPistons-A piston and hydraulic provides plied to system uses force and movement apforce and movement on an ourput plied to an input pistoil and provides piston. With a hydraulic jack, the force movement an o~ltput handleand operates an inputonpiston. The piston. With a hydraulic jack, the piston is connected to the jack pad, handle operates an input piston. The which raises th e car. With a brake piston is aconnected to the the jack input pad, system, pedal operates which the car. Withapply a brake piston raises and output pistons the system, brakes . a pedal operates the input
To Front Brakes~ To Front Brakes*
--w- To Rear Brakes
-
Front-And-Rear Split System
Front -And-Rear Split System
Input Force
Right Front Brake
Master Cylinder
Right Rear Brake
~
Right Front Brake
Right Rear Brake Diagonally Split System Diagonally
Input
Split System
~Force
lnput Force
-
Left Rear Brake
Left Front Brake
I
I
Most modern carsLeft useFront tandem master cylinders-two pistons oneBrake bore. Each piston operLeft in Rear Brake ates brakes at two wheels. If one system fails, 50% braking is left. Most tandem master cylinders operate front and rear systems. Another used on road hasopera diMost modern cars separate use tandem master cylinders-two pistonsone in one bore. Eachcars piston agonally splitatsystem as shown. I deal only fails, with front-and-rear because it's ates brakes two wheels. If one system 50% braking issplit left.systems, Most tandem master the type most high-performance use. systems. Another one used on road cars has a dicylinders operate separate front cars and rear
agonally split system as shown. I deal only with front-and-rear split systems, because it's the type most high-performance cars use. Filler Cap
~:;::::::::::::Lr-
Pushrod
piston and output pistons apply the brakes.
BRAKE-SYSTEM HYDRAULICS These laws of hydraulics explain BRAKE-SY HYDRAULICS how a basic STEM brake system works. AlThese laws of hydraulics though the basics are simple,explain there how acomplications basic brake system Alare with works. the autothough the basics are simple, there motive-brake system. I'll describe are separately. complications with the autoeach motive-brake system. I'll describe The input piston is in the master each separately. cylinder. Modern brake systems use Theinput-piston input piston master is in the master dual cylinders. cylinder. Modern brake systems use Each piston operates two brakes. dual input-piston master front brakes are cylinders. on one Usually, Each piston operates system and rear brakes two are brakes. on the Usually, front brakes are one other. But some dual systems on operate system and rear brakes are on the a diagonal pair of brakes with each other. dual systemsand operate piston,But suchsome as the right-front leftarear, diagonal of brakes with each and vicepair versa. piston, such as the leftOutput pistons right-front are locatedand inside rear, and vice versa. the brakes. Disc-brake calipers use Output pistons arepistons locatedto inside one or more output move the brakes.clamping Disc-brake calipersDrum use the pads, the rotor. one or more output pistons to move brakes use one or more output pistons the moving pads, clamping thetorotor. Drum for the shoes contact the brakes use one or moreoutput output pistons drums. Drum-brake pistons for moving thesame shoesdiameter to contact are about the as the the drums. Drum-brake output pistons master-cylinder input pistons. Disc are about the brakes havethenosame servodiameter action, soas they master-cylinder Disc require higher input force pistons. to operate. brakes have nodisc-brake-caliper servo action, so they Consequently, pis-
require higher force to operate. Consequently, disc-brake-caliper pis-
Dust Boot
Residual-Pressure Check Valve
dual-Pressure CheckFluid Valveenters cylinSingle master cylinder is basic. Fluid reservoir is directly above cylinder. der through ports in reservoir. Pushrod moves piston to right to pressurize brake fluid. Drawing courtesy Bendix Corp. Fluid reservoir is directly above cylinder. Fluid enters cylinSingle master cylinder is basic. der through ports in reservoir. Pushrod moves piston to right to pressurize brake fluid. Drawing tons arecourtesy usually Bendix twice Corp. the diameter of quired to place the lining in contact
master-cylinder pistons. tons usually twice the of A are simple approach to diameter hydraulics master-cylinder seems to "say"pistons. that large-diameter A simple pistons could approach be used at to thehydraulics brakes to seems to "say" that large-diameter produce high forces at the brakes. pistonswould could give be used to This lowat the pedalbrakes effort. produce high forces the brakes. Therefore, power assistatwould not be This would give low pedal effort. required. Unfortunately, this doesn 't Therefore, power assist would not be work. The problem is input-piston required. Unfortunately, this doesn't movement, which translates into work. brake-pedal The problem is input-piston Let's take a excess travel. movement, which translates into closer look at why this is true. excess brake-pedal travel. Let's take Pedal Travel-To take up clearancesa closer looksystem, at why this is true. in a brake pistons must move . Pedal Travel-To takeeach up brake, clearances Clearance is built into and in a brake system, pistons must move. is equal to the piston movement re-
Clearance is built into each brake, and is equal to the piston movement re-
with each rubbing surface. The total quired the fluid liningmust in contact volume toofplace moving equal with each rubbingofsurface. The total the displacement all pistons that volume move. of moving fluid must equal theThis displacement of all pistons that displacement is provided by move. master-cylinder-piston movement. This displacement is provided by Because fluid volume doesn't change, master-cylinder-piston movement. the inward displacement of the input Because fluid volume doesn't change, pistons must equal the outward disthe inward displacement of the input placement of all output pistons in the pistons. This must rule equal the outward dissystem assumes a hydraulic placement all that output pistonsdeflects in the system so of rigid nothing system. This rule assumes a hydraulic from forces in the system. system so rigid that nothing deflects If a small-diameter master-cylinder from in with the system. pistonforces is used large pistons at the If a small-diameter master-cylinder brakes, greater movement is required
piston is used with large pistons at the brakes, greater movement is required 45
Typical master-cylinder piston with seals; larger seal at right seals high-pressure system. master-cylinder Left seal keepspiston fluid with that's beTypical seals; tween from leaking open end of larger seals seal at right sealsouthigh-pressure master Both are cup-type seals.besystem.cylinder. Left seal keeps fluid that's
Girling single master cylinder is type found on many race cars, typically in dual mastercylinder setup. It iscylinder small, issimple and Girling single master type found lightweight. cap/reservoir exon many raceWhite cars, nylon typically in dual mastertension setup. increases capacity. cylinder It is reservoir small, simple and Cylinders areWhite also used operate hydraulightweight. nylontocapheservoir exlic clutches. tension increases reservoir capacity.
tween seals from leaking out open end of master cylinder. Both are cup-type seals.
Cylinders are also used to operate hydraulic clutches.
Fluid-Inlet Port Compensating Port
Force On Piston-_~~ From ForcePushrod
On Piston From Pus
Cup-Type Seal
Cup-Ty pe Seal
L
Cylinder As master-cylinder piston is pushed forward, seal slides past compensating port and traps fluid inside bore. Piston in this position can now pressurize brake fluid to apply brakes. As master-cylinder piston is pushed forward, seal slides past compensating port and traps fluid inside bore. Piston in this position can now pressurize brake fluid to apply brakes.
at the master cylinder to take up clearances. The problem is, only so at the pedal master cylinder to take up much travel is available at the clearances. The This problem only so master cylinder. is whyis,you can't much pedal travel is available at the design a system for forces without master cylinder. This is why you can't considering movement. design a system for without Unfortunately, the forces characteristics considering movement. of a real brake system are worse than a Unfortunately, characteristics theoretically perfectthe hydraulic system. of a real brake system are worse For example, the forces are asthan cal-a theoretically perfect hydraulic system. culated except for a small loss of force For the example, forces are calat outputthepistons fromas seal culated except for a small loss of force friction. However, input-piston moveat theinaoutput pistons from larger seal ments real system are much friction. However, input-piston movethan those of the theoretically perfect larger ments in'a system areormuch system due real to deflections, hydraulic than those of the theoretically perfect hose and line expansion, and bending system due toofdeflections, or hydraulic and twisting brake components. hose and line expansion, bending Specifically, additional and movement and twisting of brake components. comes from places other than clearSpecifically, movement ances in a brakeadditional system . Pedal movecomes from places other than ment comes from the total ofclearthe ances in a brake system. Pedal movefollowing:
ment comes from the total of the following: 46
• Brake clearances. • Designed clearances and wear in Brakeclearances. linkage. Designed of clearances wearand in • Swelling hydraulicandhoses linkage. other parts of the hydraulic system. of of hydraulic • Swelling Compression hydraulichoses fluid. and other parts of theofhydraulic system. • Compression air bubbles in hyCompression of hydraulic fluid. draulic fluid. air bubbles in hyBending of ofpedal, linkage or • Compression draulic fluid. brackets. Deflection ofof pedal, calipers, linkage drums or or • Bending brackets. other parts of brake system. Deflection calipers,atdrums or When total of movement the pedal other parts of brake system. is excessive, the pedal will hit the When total movement the pedal floor before the brakesat are fully is excessive, the pedal will hit the applied. Keeping pedal movement floor the limits brakes is are fully within before reasonable a major applied. pedaldesign. movement problem inKeeping brake-system within reasonable limitsproblems is a major Brake-system-design are problem in brake-system design. discussed in Chapter 9.
Brake-system-design problems are discussed Chapter 9. MASTERinCYLINDERS Brake-fluid movement and pressure
MASTER CYLINDERS Brake-fluid movement and pressure
are created by the master-cylinder piston . This piston is connected to the are by athe master-cylinder brakecreated pedal with simple linkage and piston. This piston is connected to the pushrod. brake withmodern a simpleroad linkage The pedal typical car and has pushrod. one master cylinder containing two T h e typical has pistons, while modern race carsroad are car usually one master containing two equipped withcylinder a separate master cylinpistons, while cars are usually der for each pair race of brakes. equipped with a separate master cylinSingle Master Cylinder-The simder each pair of brakes. plestformaster cylinders, such as those Single Cylinder-The simused on Master production cars with hydraulic plest master such as brakes up to the early '60s, have a used on piston production with hydraulic single to cars operate all four brakes upSeeto the early '60s, have brakes. accompanying photo.a single piston to operate all four Today's safety laws have made them brakes. See accompanying photo. obsolete. Regardless, single masterToday's safety laws made them systems are have still worth lookcylinder obsolete. Regardless, mastering at because they single are easy to cylinder systems stillare worth lookunderstand. And,are they used on ing they are easy to most at racebecause cars. understand. theyhydraulic-fluid are used on Note thatAnd, most most race cars. reservoirs are integral with their Note cylinders that mostand hydraulic-fluid master are directly reservoirs are integral with their above the piston. The piston is moved master in cylinders and by area pushrod directly forward the cylinder above the to piston. piston is moved attached the The brake pedal. The forward in the cylinder by a piston is returned by a springpushrod against attached to when the brake the piston pedalpedal. forceThe is piston is returned by a spring against removed. theThere piston when force is are two holes,pedal or ports, in the removed. reservoir that allow fluid to enter the There are two holes, or ports, the These are called the in fluidcylinder. reservoir that compensating allow fluid toport. enter the inlet port and When arethe called the fluidacylinder. piston isThese at rest, compensating inlet port and compensating port. port is ahead and the fluid inlet When port is a piston is attherest, the compensating just behind lip forming the front port of is ahead and the fluidposition, inlet portthe is face the piston. In this just behind the lip forming front piston rests against a clip or the retaining face theprevents piston. Inthe thisreturn position, the ring of that spring piston rests against a clip or retaining from pushing the piston out the end ring prevents the return spring of thethat cylinder. from pushing outa pushrod the end As the brakesthe arepiston applied, of the cylinder. moves the piston forward in the As the brakes are applied, The piston movesa pushrod forward cylinder. movesthethe piston forward in the lip of the seal covering the with cylinder. The port. pistonBefore moves compensating thisforward port is with the piston lip of the seal forces covering the covered, motion excess compensating port. Before this port is fluid back into the reservoir. Look covered, piston motion reservoir forces excess into a master-cylinder and fluid back into themotion reservoir. Look you see slight fluid just as the into a master-cylinder reservoir and piston begins to move. Once the comyou see slight fluidismotion just asfluid the pensating port covered, piston Once thesystem comtrappedbegins in to themove. hydraulic pensating portprovided is covered, cannot escape, there arefluid no trapped in the hydraulic leaks. Beyond this position, thesystem piston cannot escape, provided there are no moves fluid to apply the brakes. leaks. Beyond position, thereduces piston Initial fluidthismovement moves fluid into apply the brakes. clearances the brakes. When all Initial fluid reduces clearances in movement the system are clearances in the brakes. 'When all eliminated, fluid stops moving and clearances system are pressure rises.inThethe driver's foot coneliminated, fluid moving trols how high fluidstops pressure gets. and As
pressure rises. The driver's foot controls how high fluid pressure gets. As
C up-Type Seal
Cup-Type Seal
During rapid retraction of master-cylinder piston, fluid flows through small holes in front face of piston and past seal. This prevents bubbles from forming in front of seal. Fluid-inlet port Duringairrapid retraction of master-cylinder piston, fluid flows keeps fluid behind seal at all face times. through small holes in front of piston and past seal. This pre-
vents air bubbles from forming in front of seal. Fluid-inlet port keeps fluid behind seal at all times.
Force _ _. -04 on Piston
Piston
Cup-type seal expands outward against cylinder-bore walls when fluid is pressurized, making a tight seal. Flat end of cup-type seal goes toward piston face;outward cup end against toward high-pressure fluid. when Cup-type seal expands cylinder-bore walls
fluid is pressurized, making a tight seal. Flat end of cup-type seal goes toward piston face; cup end toward high-pressure fluid.
Cup-type seal can withstand high pressure while sliding easily within cylinder bore. Seal lips seal press against cylinder Cup-type cantightly withstand high pressure walls sliding when pressurized. higherbore. the while easily withinThe cylinder pressure, tighter the seal. Seal lips the press tightly against cylinder
Residual-pressure valves are used in special applications. For example, Airheart Residual-pressure valves areretracted used in specalipers using mechanically piscia1 For example, valve Airheart tons applications. require a residual-pressure to prevent pistons from retracting too far. piscalipers using mechanically retracted
walls when pressurized. The higher the pressure, the tighter the seal.
tons require a residual-pressure valve t o prevent pistons from retracting too far.
Some Airheart calipers use a padretraction system to prevent pads from dragging on rotors.calipers Two cylindrical Some Airheart use aobjects padprotruding system from body of Airheart X retraction to prevent pads1 75 from 206 caliper are Two partcylindrical of mechanical dragging on rotors. objects retractors. from Residual-pressure valve 175 should X protruding body of Airheart be with these courte206used caliper are calipers. part ofPhoto mechanical sy Hurst Performance. retractors. Residual-pressure valve should
be used with these calipers. Photo courtesy Hurst Performance.
force on the pedal is reduced, hydraulic pressure drops, the drumforce on thereturn pedal springs is reduced, brake-shoe and /hydrauor disclic pressure drops, the drumbrake-piston seals retract, and the brake-shoe returnreturn springs and/ormoves discmaster-cylinder spring brake-piston seals retract, and the the piston back against the retaining master-cylinder return spring moves ring. theThe piston back against the retaining fluid-inlet-port function is ring. more complicated . To understand it The look fluid-inlet-port function is better, at the drawings of the more complicated. To understand it piston and seals. Note that the piston better, look at the drawings of the has sma ll holes drilled through the piston and lip seals. that the front-face . TheNote cup-type sealpiston is in has small holes drilled through stalled ahead of this face , with the the lip front-face The cup-type seal is inextending lip. forward. The fluid-inlet stalled aheadfluid of this face, the withfront the lip port allows behind lip extending forward. of the piston; the holesThe in thefluid-inlet lip allow port allows behind theface front lip this fluid to fluid contact the seal . This of the piston; the holes in the lip allow is to help during brake release when this fluid toreturns. contact the seal face. This the piston
is to help during brake release when the piston returns.
As the brakes are released, the return spring may move the piston As than the brakes the faster the fluidare can released, move . When return springthemay the piston this occurs, seal move lip is drawn away faster thancylinder the fluid can move. When from the wall , allowing fluid this occurs, the seal lip is to flow through the small drawn holes inaway the from theThis cylinder seal lip. keepswall, fluidallowing ahead offluid the to flow at through the small holes in the piston a ll times and prevents the seal lip. This fluid ahead of the formation of keeps a gas bubble in front of piston at all times andthe prevents the the piston . Otherwise, gas bubble formation of aa gas in front of would cause soft bubble pedal with excesthe piston. the gas sive travel. Otherwise, The secondary sealbubble keeps would cause a softout pedal with excesfluid from leaking the open end of sive travel. The secondary seal keeps the cylinder. fluid from leaking outat the end of Let's look closely theopen function of the cylinder.sea l in the accompanying a cup-type Let's The look closely at the faces function of photo. cup always highapressure cup-typefluid. seal inFluid the accompanying pressure acts photo. alwaysasfaces highequally The on allcup surfaces it contacts pressure fluid. pressureagainst acts the cup face and Fluid lip. Pressure
equally on all surfaces as it contacts the cup face and lip. Pressure against
the lip forces it against the cylinder wall, creating a tight seal. The higher the forces the it against the lip pressure, tighter the the cylinder cup lip wall, a tight seal.wall. The This higheris seals creating against the cylinder the pressure, the tighter the cup lip a reliable, long-life seal. seals against the cylinder wall. This is Residual-Pressure Valve-A cupatype reliable, long-life seal. seal has one problem when used Residual-Pressure Valve-A with a drum-brake wheel cylinder.cupAs type seal ishas one problem used the seal retracted, its lipwhen is relaxed with wheel cylinder. As and aairdrum-brake can be introduced in the the seal is retracted, its lip is relaxed system . On drum-type brakes, this and air ofcan introduced the motion the be cup-type seals ininwheel system. brakes, cylinders On will drum-type draw in air each time this the motion of released. the cup-type seals in wheel brakes are cylinders will two drawdevices in air each the There are that time prevent brakes are, released. this . One called a cup expander, is a There arecup twoinstalled devices that prevent thin metal between the this. One, called a cup expander, is a seal and the return spring . This device thin cup on installed between the exertsmetal pressure the lip an d prevents seal and the return the spring. device air from passing sealThis when the
exerts pressure on the lip and prevents air from passing the seal when the 47
Reservoir Diaphrag
Return Spring
Secondary Piston Secondary Cups
Primary Cup
Primary Piston
Secondary Cup
Cross section of typical tandem master cylinder with integral fluid reservoirs. Pushrod is Piston-Stop Bolt retained on pedal, which is out of view to right, not on master-cylinder piston. Drawing courtesy Bendix Cross section ofCorp. typical tandem master cylinder with integral fluid reservoirs. Pushrod is retained on pedal, which is out of view to right, not on master-cylinder piston. Drawing courtesy Bendix Corp.
Reservoir Cover - - - - - , Cover Retainer/Bail
Cover Retainer/Bail
Piston-Stop Bolt Hydraulic lines from tandem master cylinder to front and rear brakes install in outlet ports. Reservoir cover is retained with spring clip, or bail. Drawing courtesy Bendix Corp. Hydraulic lines from tandem master cylinder to front and rear brakes install in outlet ports. Reservoir cover is retained with spring clip, or bail. Drawing courtesy Bendix Corp.
DIAGONALLY SPLIT SYSTEMS DIAGONALLY Most front-wheel-drive cars are SPLIT SYSTEMS designed with tandem master Most front-wheel-drive are cylinders plumbed so theycars operate designed opposite with tandem diagonally wheels.master Each cylinders so they operate half of the plumbed cylinder operates a diagdiagonally opposite wheels. onally opposite pair of brakes.Each The half offront the cylinder operates diagbrake and left rearabrake right onally oppos~te of brakes. The comprise one pair system. Opposite right front brake and rear brake pair of brakes are left operated by comprise other half one of thesystem. master Opposite cylinder. pair of brakes by Because a front are andoperated rear brake other half of together, the master always work thiscylinder. system Because an3 inrear is claimedatofront be safer the brake event always work together, this system is claimed to be safer in the event
48
one system fails. Brake balance cannot be adjustone system fails. way withadiagoed inthe normal Brake balance be I'm adjustnally split brake cannot system. not ed in the waycars with or a diagoaware of normal any race highnally split brake system. I'm not performance sports cars using diaware any brakes, race cars or highagonallyof split so hopefully performance sports cars using diyou won't have to concern yourself agonally brakes, hopefully with them.split If you have asocar with di~ you won't split havebrakes, to concern agonally the yourself system with them. car with diwould haveIftoyou be have totallya redesigned agonally split brakes, front-to-rear the system to use conventional would have techniques to be totally redesigned balancing discussed to usebook. conventional front-to-rear in this balancing techniques discussed in this book.
brakes are released. The second is a simple spring brakes are released. loaded valve in the master cylinder. The second is a simple spring This valve, the reSidual-pressure valve, loaded valve in the pressure master cylinder. keeps slight fluid on the residual-pressure This valve, thetimes-even system at all whenvalve, the keeps slight fluid pressure on the brakes are released. When fluid resystem all master times-even when the turns toat the cylinder as the brakes fluid rebrakes are are released. released, When a spring closes turnsvalve to the master cylinder the when pressure dropsas tothea brakes value-usually are released, a6-25 spring preset psi.closes This the valve when pressure drops to a pressure is enough to keep the cuppreset value-usually 6-25 psi. This type seals in wheel cylinders against pressure is enough to keep the cuptheir cylinder walls, but not enough to type seals in wheel cylinders overcome return-spring force. against Excess their cylinder walls, but not enough to pressure would cause brakeresidual overcome shoe drag. return-spring force. ~ x c e s s residual cause brakeIf youpressure change would master cylinders, shoe drag. make sure you get one designed for you change theIf specific system. master It must cylinders, have the make sure you get one designed for correct residual-pressure valve. Most the specificsystems system. and It must have the some drumdisc-brake residual-pressure Most brake systems do not use residualdisc-brake systems and some drumpressure valves, so master cylinders do not even use residualbrake not systems may interchange, if they pressureto valves, so master appear be identical. Checkcylinders mastermay notspecifications interchange,to even if they cylinder be sure. appear to be identical. Check masterResidual-pressure valves are used cylinder specifications to be sure. that on Airheart disc-brake calipers Residual-pressure valves aresystem used have a mechanical-retraction on Airheart disc-brake calipers that to pull the pads away from the rotors. have a residual-pressure mechanical-retraction valve system is also A 2-psi to pull the padsbyaway from the rotors. recommended Airheart for use on A 2-psi residual-pressure valve are brake systems where calipersis also recommended by Airheart use on mounted higher than thefor masterbrake systems are This iscalipers to prevent cylinder reservoir.where mounted higher than masterfluid flowing back to the the reservoir by cylinder Other reservoir. This ismanufacturto prevent gravity. disc-brake fluid do flowing to the reservoir by ers not back recommend residualgravity. pressureOther valves.disc-brake manufacturersThisdobrings not up recommend residualan important point: pressure valves. If you have a special car or a race car This brings up an important point: with modified brakes, always consult If have a special car or a race car theyou brake manufacturer before with brakes, making any changes. the brake manufacturer before Tandem Master Cylinders - Master making any changes. cylinders with two pistons in a single Tandem Master bore are used on Cylinders-Master modern road cars. cylindersarewithcalled two pistons in amaster single They tandem bore are used on modern road cars. cylinders. Tandem master cylinders They are introduced called tandem master were first on American cylinders. Tandem master cylinders passenger cars in 1962; they've been were first introduced on American universal since 1967. A typical passenger cars incylinder 1962; they've been tandem master is illustrated universal since 1967. A typical nearby. tandem master cylinder is illustrated Each section of a tandem master nearby. cylinder works as a single cylinder. Each of and a tandem master compensating Each hassection fluid-inlet cylinder a single cylinder. ports. Theworks pistonasclosest to the brake Each andpiston compensating pedal has is fluid-inlet the primary and the ports. isThe closest to the brake other thepiston secondary piston. Usually, primary piston and the is the pedal the primary operates the front brakes piston. Usually, othertheis secondary the secondary and the rear brakes.
the primary operates the front brakes and the secondary the rear brakes.
Primary Piston
Force
,-L-----,_. Force Force
Force
To Rear Brakes To Rear Brake If leak develops in front-brake system, primary piston moves forBrakes System ward until it bottoms against secondary piston. Force from pushrod is develops transmitted to secondary piston by piston piston-to-piston If leak in front-brake system, primary moves forcontact. allows against secondary piston to pressurize rear-brake ward untilThis it bottoms secondary piston. Force from pushsystem. rod is transmitted to secondary piston by piston-to-piston contact. This allows secondary piston to pressurize rear-brake system.
As the driver operates the brake pedal, the primary piston moves As the closing driver operates the brake forward, the primGlY compedal, theport.primary moves Fluid ispiston trapped bepensating forward, the and primary comprimary secondary tween theclosing pensating port. trapped Fluid is fluid trapped bepiston. This cannot tween the primary and secondary compress, so it moves the secondary piston. forward This trapped fluidsecondary cannot piston to seal the compress, so itport. moves the both secondary compensating With compiston forward seal the secondary pensating ports toclosed, trapped fluid compensating With both comin front of the secondbuilds pressure port. pensating closed, trapped primary fluid and ary piston,ports and between builds pressure in front of the for secondExcept the secondary pistons. ary piston, and return between primary primary-piston spring, thereand is secondary pistons. Except for the the no direct mechanical link moving primary-piston return spring, there is secondary piston-only pressure from no directfluid mechanical link moving the trapped . secondary piston-onlyin the pressure When clearances brakesfrom are trapped fluid. taken up, the pistons stop moving , When clearances in theand brakes pressure increases forceare is fluid taken up,to the moving, applied thepistons brakes.stop When the fluid pressure and the forcetwo is driver reduces increases pedal force, applied to the brakes. When the piston-return springs plus brakedriver reduces move pedal the force, the to twoa return springs pistons piston-return springs plus brakeretracted position. As mentioned return , springs the pistons to a before holes inmove the front lip of each retracted Asto flow mentioned piston allowposition. brake fluid to the before,ofholes in the front of each front the cup-type seal lip when the piston allow brake fluid to flow to the brakes are released. Compensating front of theexcess cup-type ports allow fluidseal to when return the to brakes are released. Compensating when the brakes are the reservoir ports allow excess fluid to return to released . theThe reservoir brakes are purposewhen of a the tandem master released. cylinder is to protect against total loss purpose of a tandem mastera of The brakes when failure occurs. With cylinder is to protect loss leak in the front brakeagainst systemtotal , almost of brakes when failure occurs. With no pressure exists in the front brakea leak in the front system, almost system. Note thebrake metal pushrod beno pressure brake tween the exists primaryin the and front secondary system. Note theleaks metal bepistons. As fluid out pushrod of the fronttween the primary and secondary brake system, the primary piston conpistons. As fluid out of until the fronttinues to moveleaks forward this brake primary conmetal system, pushrod the contacts thepiston secondary tinues move forward untilmovethis piston. to Then, primary-piston
metal pushrod contacts the secondary piston. Then, primary-piston move-
To Front Brakes To Front Brake Brakes If rear-brake system should leak, secondary piston moves forward System until it contacts end of master cylinder. This allows trapped fluid between pistons to be pressurized by primary piston, actuating If rear-brake system should leak, secondary piston moves forward front brakes. until it contacts end of master cylinder. This allows trapped fluid between pistons to be pressurized by primary piston, actuating front brakes.
Cross section of fast-fill master cylinder used on front-wheel-drive cars shows fluidcontrol valve below primary reservoir (arrow). In-line proportioning valves are in rear-brake ports bottom of of cylinder. portsused are not Crossatsection fast-fill Front-brake master cylinder on shown. front-wheel-drive cars shows fluidcontrol valve below primary reservoir (arrow). In-line proportioning valves are in rear-brake ports of cylinder. ports arethe not shown. mentatisbottom transmitted to Front-brake the secondary pedal moves closer to the
piston , moving it forward and applying
ment is brakes. transmitted thecondition, secondarya the rear With tothis piston, moving it forward and applying driver will have to exert more pedal the rear brakes. With this condition, a force than normal to stop the car. driver exert in more Whenwilla have leak to occurs the pedal rear force thanfluid normal to stop the car. the system, is trapped between When a leak occurs in the with rear primary and secondary pistons, system, fluid is trapped between the fluid leakage behind the secondary primary and secondary pistons, allows both pistonswith to piston . This fluid leakage in behind the secondary move forward the cylinder until the piston. both piston pistonsconto pushrod This of theallows secondary move forward in the cylinder until the tacts the end of the master cylinder. pushrod contact of the secondary conWhen occurs, piston secondarytacts end stops, of the allowing master cylinder. motion pressure pistonthe When occurs, secondaryto build contact up between the two pistons. piston motion stops, allowing This pressure operates thepressure front to build Again, up between the two brakes. the driver will pistons. have to This pressure the Also, front exert more force operates on the pedal. brakes. Again, the driver will have to exert more force on the pedal. Also,
floor- travel is higher. During an the pedal moves to the emergency, with closer one system floor-travel is higher. During m alfunctioning, stopping distance an is emergency, withbecause one only system greatly increased two malfunctioning, stopping distance is wheels are braking. greatly two When increased designingbecause a brakeonly system wheels are braking. using a tandem master cylinder, When designing a brake remember that all force appliedsystem to the using tandem master to cylinder, master acylinder is applied primary remember that pistons all forceequally. applied to the and secondary Force master cylinder is applied to primary it is not split like a dual masterand secondary equally. bar. Force cylinder system pistons using a balance it Some is notmaster split cylinders like a dual masterare designed cylinder usingata balance bar. to to be system mounted an angle Some master cylinders are designed horizontal. If so , the cylinder may to mounted angle to havebe a bleeder screw.at Thisanscrew allows horizontal. If the so, master the cylinder air trapped in cylindermay to have a bleeder screw. Thisfluid. screwBleeder allows be bled from the brake
air trapped in the master cylinder to be bled from the brake fluid. Bleeder 49
Dual master-cylinder setup manufactured by Neal Products, fitted with Howe cylinders, is popular for use in racing stock cars and other special vehicles.setup Hurst! Airheart, Girling or Lockheed Dual master-cylinder manufactured by Neal Products,master fitted cylinders can be used with this setup. with Howe cylinders, is popular for use in racing stock cars and
Single master cylinders found on most race cars; from left to right they are Airheart, Lockheed, Girling and Howe.
Single master cylinders found on most race cars; from left to right they are Airheart, Lockheed, Girling and Howe.
other special vehicles. HursVAirheart, Girling or Lockheed master cylinders can be used with this setup.
Rubber bellows in nylon- reservoir cap seals air from brake fluid. When reservoir is full, bellows is compressed. Bellows cap exRubber bellows in nylon-reservoir tends as from fluidbrake level fluid. drops. Vented cap seals air When reservoir allows air to enter and exit above bellows is full, bellows is compressed. Bellows exto compensate fluid-volume changes.cap tends as fluidforlevel drops. Vented
allows air t o enter and exit above bellows t o compensate for fluid-volume changes.
Some reservoir caps have a float. When fluid level falls too low, float activates an electrical switch caps that have turns aonfloat. a warning Some reservoir When light on instrument This light, instead fluid level falls toopanel. low, float activates an of brake loss, warns of low fluid. electrical switch that turns on a warning
light on instrument panel. This light, instead of brake loss, warns of low fluid.
Large translucent nylon reservoirs used on this Indy Car make it easy to check fluid It levels. Caps don't nylon have reservoirs to be removed. Large translucent used on helpslndy to have good i tlight checking this Car make easywhen t o check fluid fluid this way. don't have to be removed. I t levels. Caps
helps t o have good light when checking fluid this way.
screws look similar to grease fittings. 1 have seen unknowing persons try to screws look similar grease shoot chassis greaseto into thefittings. bleeder1 have seen persons try to The internal screws with unknowing a grease gun!
shoot chassis grease into the bleeder screws with a grease gun! The internal 50
end of the bleeder has a taper that seals when it is tightened down on its end ofWhen the bleeder has ais taper that loosened seat. the bleeder seals when it is tightened down on its slightly, this seat seal is opened, then seat. When the bleeder is loosened brake fluid and trapped air can come slightly, thisthe seathole sealinisthe opened, out through bleeder.then brake fluidusing and this trapped come cylinder, When typeairofcan out through the hole in the bleeder. make sure you mount it where it can using this type of cylinder, beWhen bled. For a master cylinder that is make suretoyou it where can designed be mount mounted level, itmake be bled. For a master cylinder that is sure it's level. designed be mounted level, make Fast-Fill toMaster Cylinders-Note sure it's level. the master-cylinder drawing, page 49. Fast-Fill Master Cylinders-Note It differs from a straight-bore master the master-cylinder 49. in two ways:drawing, It has a page stepped cylinder It differs from a straight-bore master primary, or fast-fill bore, and second, cylinder in twovalve. ways: It has a stepped a fluid-control primary, fast-fill bore, and second, Duringorinitial brake application, the alarger fluid-control fast-fill valve. bore provides fluid for Duringtakeup initial by brake application, the forcing fluid past system larger fast-fill bore provides fluid for the primary-piston seal into the main system takeup by forcing fluid uppast in bore. After clearances are taken the primary-piston seal into main the rotors and/or drums, any the pressure
bore. After clearances are taken up in the rotors and/or drums, any pressure
buildup in the fast-fill bore would result in high pedal effort. The fluidbuildup valve in the fast-fillthisbore would by divertcontrol prevents result in high pedal effort. The fluiding fluid from the fast-fill bore to the control prevents this bycylinder divertprimary valve reservoir. The master ing from the the brakes fast-fillinbore to the a conventhenfluid operates primary reservoir. The master cylinder tional manner using the smaller main then a convenbore. operates During the the brakes return instroke, the tional mannervalve usingallows the smaller main fluid-control fluid unresbore. thereturn fast-fill stroke, bore. the tricted During return tothe fluid-control valve allows fluid unresThe major advantage of fast-fill tricted return to the fast-fill bore. master cylinders is to increase fluid The major advantage of fast-fill displacement during initial pedal master cylinders is to increase fluid travel. This allows smaller masterdisplacement during initial pedal cylinder main-bore diameter, and retravel. pedal This effort allowsand smaller duced travel masterand/or cylinder main-bore and redisc-brake calipers diameter, with increased duced pedal effort and travel and/or piston retraction distance, or rollback, disc-brake calipers with increased for brake-drag reduction. piston retractionCylinders-Most distance, or ~~ollback, Dual Master race for brake-drag reduction. cars use two single master cylinders Dual Master Cylinders-Most side with a link race bemounted side by cars use two single tween them called a master balance cylinders bar. Balmounted by side fully with ina Chapter link beance bars side are covered tween called a balance bar:a Bal6. Dualthem master cylinders with balance bars are covered fullyofinforce Chapter ance bar allow the ratio be6 . Dualfront master with ato balbe tween andcylinders rear brakes ance bar This allowadjustment the ratio of force beadjusted. is necessary tweento front and track rear conditions brakes to be changing or due adjusted. This adjustment is necessary arrangevariations in car setup. This due track system conditions or menttois changing also a fail-safe similar variations in car setup. This arrangeto the tandem master cylinder. Racing ment is cylinders also a fail-safe system similar master are usually paired to the tandem master cylinder. Racing single master cylinders, often the masterascylinders are usually same those found on olderpaired road single cars. master cylinders, often the
same as those found on older road cars. RESERVOIRS
The fluid reservoir is often integral RESERVOIRS with the master cylinder. However, fluid accommodation reservoir is oftenonintegral forThe service some with the master However, is separate, or cars the reservoircylinder. for service accommodation some reservoir remote. This type of fluid on cars reservoir is separate, or usuallytheis made of translucent plastic
remote. This type of fluid reservoir usually is made of translucent plastic
Dust
Dust Bc
Piston
s t Boot
'
Piston
Cup'
cup
I
Expander
kpring
Wheel cylinders with two pistons are used and-trailing-shoe drum brakes. Spring keeps brakes cylinders are released. are used this Wheel withPushrods two pistons are inused courtesy Bendix Corp. and-trailing-shoe drum brakes. Spring keeps
CUP' Expander
'cup
'
piston
At left is remote reservoir for dual master cylinders; reservoir at right mounts directly on left Girling master-cylinder port. At is remote reservoir for outlet dual master Reservoirsreservoir are large enough for directly racing cylinders; at right mounts disc-brake on Girling systems. master-cylinder outlet port.
Reservoirs are large enough for racing disc-brake systems.
on most modern duo-servo or leadingpistons or pushrod against shoes when cylinder operateduo-servo brake shoes. on most tomodern or Drawing leading-
pistons or pushrod against shoes when brakes are released. Pushrods are used in this cylinder to operate brake shoes. Drawing courtesy Bendix Corp.
so the fluid level can be checked without opening the reservoir. Many of so thehave fluid graduations level can beon checked withthem the side inout opening the low reservoir. of dicating full and levels. Many Separate them have graduations on the side influid reservoirs are mounted above dicating full to andthelow levels. Separate and connect master cylinder by fluid reservoirs are mounted above flexible hose. andThe connect to the master by fluid reservoir mustcylinder not allow flexible hose. any contamination of the brake fluid. The fluid reservoir must not on allow The reservoir cap, which screws or any contamination of the brake fluid. is fastened by nuts, clamps or bolts, is The reservoir which screws on or vented to thecap, atmosphere, allowing is fastened by nuts, clamps is the fluid level to rise and or fallbolts, freely. vented to the atmosphere, allowing Water vapor in the air will contamithe to so risemany and fall freely. nate fluid brakelevel fluid, reservoirs Water vapor diaphragm in the air under will contamiuse a rubber the cap nate brake fluid, so the many reservoirs that isolates it from atmosphere. use a rubber diaphragm under the cap This diaphragm flexes easily, allowing that isolates it from the atmosphere. the rise and fall of fluid , while sealing This diaphragm flexes The easily, allowing out air and moisture. diaphragm the rise and fall of fluid, while must be removed on some sealing master out air and diaphragm cylinders to moisture. check or The replenish fluid. mustbest be overall removed on issome master The design a translucent cylinders to check or replenish reservoir with a rubber diaphragm.fluid. The best overall design is a translucent Reservoir capacity must be large reservoirtowith a rubber diaphragm. enough allow fluid to fill a system, Reservoir capacitylinings must are be worn large even when brake enough to allow fluid to fill a system, totally. A brake system must never even whenofbrake are worn run short fluid. linings Otherwise, total totally. system must never braking A lossbrake can occur. Disc-brake pisrun of more fluid.fluid, Otherwise, tons short displace so they total usubraking loss can occur. Disc-brake pisally require more reservoir capacity tons displace more fluid, so they usuthan drum brakes. Reservoir volume ally reservoir capacity mustrequire exceed more the displacement of all than drum brakes. Reservoir output pistons, plus allow forvolume lining must exceed the displacement of all wear.
output pistons, plus allow for lining wear.
With either a tandem or dual master-cylinder system, two separate With either a tandem or with dual reservoirs or a single reservoir master-cylinder system, two compartments shouldtwo be separate used. If reservoirs or a single with this isn't done, a leak reservoir in one system two compartments should be used. If will drain the fluid available to both this isn't eliminating done, a leakthein fail-safe one system systems, feawill fluid available both ture drain of thethe tandem and dual tomaster systems, eliminating the fail-safe feacylinders. ture of the tandem and dual master Race-Car Reservoirs - Most race cars cylinders. use remote reservoirs from road cars. Race-Car Most race cars If your raceReservoirs car uses aroad-car master use remote and reservoirs from calipers, road cars.a cylinder(s) large racing If yourreservoir race car uses master larger may aberoad-car installed. The cylinder(s) and large racing calipers, reservoir normally used with road-cara larger be small installed. The masterreservoir cylindersmay is too for large reservoir normally used with road-car racing calipers. Larger reservoirs are master cylinders is too small for large available from Tilton Engineering, racing calipers. Larger reservoirs are Neal Products and other suppliers. available fromreservoirs Tilton Engineering, Custom-built can also be Neal Products used on race cars.and other suppliers. Custom-built reservoirs alsoused be Remote reservoirs are can often used strength on race cars. for and reliability. Most Remote reservoirson are often used remote reservoirs modern road for strength and reliability. cars are plastic. However, withMost the remote reservoirs modern road risk of heat, fire oron physical damage cars are plastic. However, the associated with race cars, with all-metal risk of heat, fire or physical damage reservoirs offer extra protection. associated with raceis cars, all-metal Another advantage that mounting reservoirs offer can extra protection. lugs or brackets be added to a Another advantage that mounting. mounting metal reservoir for iseasy lugs or brackets canreservoir be addedcanto bea Obviously, a metal metal reservoir for easy made in any size and shape mounting. you need. Obviously, can the be Remember, aairmetal mustreservoir never enter made in r-any size and shape youpassage need. reservoi to- master-cylinder Remember, air must never enter the during hard cornering, acceleration or
reservoir-to-master-cylinder passage during hard cornering, acceleration or
Custom-built remote metal reservoir mounted atop fro':,t bulkhead on this Indy Car is stronger remote than plastiC reservoir. Cap Custom-built metal reservoir must be removed to check fluid on level. mounted atop front bulkhead this lndy
Car is stronger than plastic reservoir. Cap braking, so a tall reservoir is better must b e removed to check fluid level.
than a short one. braking, so a tall reservoir is better Often, special remote reservoirs are than a short one. used on off-road race cars. These cars Often, special remote reservoirs are experience incredible up-and-down used on off-road race cars.This These cars bouncing and pounding. results experience incredible up-and-down in severe slosh and aeration of brake bouncing and pounding. results fluid. To prevent this, tallThis reservoirs in severe and .aeration of brake with bafflesslosh are used
fluid. To prevent this, tall reservoirs with baffles are used. DRUM-BRAKE WHEEL CYLINDERS
DRUM-BRAKE There are a number of drum-brake WHEEL CYLINDERS wheel-cylinder designs . However, all There are a number drum-brake share common features of . For instance, wheel-cylinder designs. However, all all use cup-type seals. Some have share common features. For instance, seals with internal springs, or all use cup-type seals. have expanders, that keep the Some seal lips in seals with internal or contact with the cylindersprings, walls. With expanders, that keep the seal lips in contact with the cylinder walls. With 51
-\
Wheel-Cyl~nderBody
Clever design combats brake fluid sloshing in main reservoirs. Caps to reservoirs were modified to accept plastic tube. Fluid is fed Clever design combats brake fluid sloshing from third reservoir mounted high inwere car. in main reservoirs. Caps t o reservoirs There's air plastic bubbles will Fluid develop in modifiedno to way accept tube. is fed the fullyreservoir filled reservoirs. fromtwo third mounted Any highsloshing in car. and resulting air air bubbles willwill be develop contained There's no way bubbles in in third reservoir. Modification inthe two fully filled reservoirs. Any also sloshing creases fluid capacity. and resulting air bubbles will be contained in third reservoir. Modification also increases fluid capacity.
expanders in the cup-type seals, a residual-pressure valve in the master expanders in required. the cup-type seals, a cylinder is not residual-pressure valve in thepage master Duo-servo drum brakes, 17, cylinder is not required. use a single wheel cylinder with two Duo-servo drum cylinder brakes, page 17, pistons. The wheel has both use a open singleand wheel two ends fluid cylinder betweenwith the two pistons. wheelbetween cylinderthehas both pistons. The A spring pistons ends open and fluid between the maintains slight pressure against two the A spring the pistons pistons.This shoes. springbetween also prevents the maintains slight pressure the pistons from blocking theagainst fluid-inlet shoes. This spring also prevents the port in the wheel cylinder. pistons blocking the fluid-inlet There from is usually a rubber dust boot port wheel end cylinder. on in thetheopen (s) of a wheel There isThis usually a rubberlining dust boot cylinder. prevents dust on the open end(s) of a wheel and moisture from contaminating the cylinder.cylinder, This prevents dusta wheel possibly lining causing and moisture the sticking piston.from Dirtcontaminating is a major enemy wheel possiblyThe causing of any cylinder, brake system. rubbera sticking Dirt major pistonenemy boots piston. also hold is a the of any brake system. The rubber to-brake-shoe push rods in position, boots also holdpush the on systems that use rods. pistonto-brake-shoe pushrods have in position, Some wheel cylinders a single on systems that use pushrods. piston and a closed end, as shown Some They wheel are cylinders have a single above. usually found on piston andleading-shoe a closed end, as shown double brakes-each above. Theyis are usually on brake shoe operated by afound separate double leading-shoe bra kes-each single-piston wheel cylinder. Similar brake is operated a separate to the shoe dual-piston type, by single-piston single-piston wheelhave cylinder. Similar wheel cylinders an internal to the to dual-piston type, single-piston spring keep the piston and push rod wheel cylinders have shoe. an internal in contact with the brake spring to keep the piston and pushrod A wheel cylinder usually is in contact with shoe. equipped with the a brake bleeder screw. It A be wheel cylinderat the usually is must positioned highest equipped with a bleeder screw. It point in a wheel cylinder so all trapped must be positioned at the highest air can be bled off. Usually the posipointofina ableeder wheel cylinder so all trapped is the only difference tion
air can be bled off. Usually the position of a bleeder is the only difference 52
Single-piston wheel cylinder is used on two-leading-shoe drum brakes. Each shoe has its own wheel spring Single-piston wheelcylinder. cylinderReturn is used on holds piston against shoe when brakes are two-leading-shoe drum brakes. Each shoe released. Drawing has its own wheelcourtesy cylinder.Bendix ReturnCorp. spring holds piston against shoe when brakes are released. Drawing courtesy Bendix Corp.
Bleeder screws allows trapped air to be removed from high spots in hydraulic system. One is used at each spot air so to airbe bubBleeder screws allowshigh trapped rebles can be high bledspots off toinprevent spongy moved from hydraulica system. pedal. you at mount cylinders, so air drum bubOne isIfused eachmaster high spot brakes calipers a prevent differenta position bles canorbe bled offin t o spongy from intended by thecylinders, manufacturer, pedal.that If you mount master drum bleeder screws may in be a out of position. brakes or calipers different position from that intended by the manufacturer, bleeder screws may be out of position.
I
c Cotter Pin
1
Caliper-Support Key
Caliper Housing Bendix CA floating disc-brake caliper has single piston on inboard side of rotor only. Caliper housing contains both pads. Not shown is sturdy mounting bracket that bolts to suspension and supports and guides caliper.caliper Drawing Bendix Bendix CA floating disc-brake hascourtesy single piston on Corp. inboard side of rotor only. Caliper housing contains both pads. Not shown is sturdy mounting bracket that bolts to suspension and supports and guides caliper. Drawing courtesy Bendix Corp.
between a right-hand and left-hand wheel cylinder, so use care not to mix between a right-hand and left-hand wheel cylinders when installing them. wheel cylinder, so use care mix Some cars have rubber not capsto over wheel cylinders whentoinstalling them. the bleeder screws keep out dirt Some cars have rubber caps and moisture. This is a good ideaover for the bleeder screwsmost to keep out dirt road cars because bleeder-screw and moisture. This is a goodcaused idea for breakage is from corrosion by road cars because most bleeder-screw moisture. Moisture reaches the breakage is fromseat corrosion by bleeder-screw and caused threads moisture. Moisture reaches the through the hole in its center. Brake bleeder-screw seat in Chapter and threads bleeding is discussed 11. throughWheel the hole in its center. Brake Note: cylinders are usually 11. bleeding is discussed in Chapter made of cast iron or aluminum. Most Note: cylindersThese are usually pistons Wheel are aluminum. metals made of and castcorrode iron or from aluminum. Most can rust moisture in
pistons are aluminum. These metals can rust and corrode from moisture in
the system. Wheel cylinders probably fail more often due to these than any the system. Wheel cylinders probably other reason. Frequent bleeding of fail more often due to these than any brakes protects against rust and other reason. Frequent bleeding of corrosion.
brakes protects against rust corrosion. DISC-BRAKE CALIPER
and
Disc-brake calipers have one or DISC-BRAKE CALIPER more pistons. They perform the same Disc-brake calipers have one or function as the wheel-cylinder pistons more pistons. They perform the same in a drum brake. The caliper piston (s) function as the pistons is moved by wheel-cylinder hydraulic fluid and in a drum caliper pushes thebrake. pads The against the piston(s) rotor. As is movedpressure by hydraulic and hydraulic increases,fluid the pads pushes the pads against the rotor. As are pushed harder against the rotor. hydraulic pressure increases, theequal pads The caliper is designed to apply
are pushed harder against the rotor. The caliper is designed to apply equal
AP Racing/Lockheed caliper has one large piston on each side of rotor. Caliper body is Racing/Lockheed bolted rigidly to caliper suspension. AP has one Fixed large calipers, this, are used on most piston on such each as side of rotor. Caliper body race cars; road cars use floating is bolted rigidly totypically suspension. Fixed calipers. AP Racing. calipers, Photo such courtesy as this, are used on most race cars; road cars typically use floating calipers. courtesy AP Racing. pressurePhoto to the pads. This is done ·with
one or more pistons on each side of pressure thewith pads.piston(s) This is done'with the rotor,to or on one one and or more pistons on each side of side a moving caliper. theDisc-brake-caliper rotor, or with piston(s) one cylindersondiffer side a moving caliper. fromand drum-brake wheel cylinders in Disc-brake-caliper cylinders differ several ways. First, caliper pistons are from drum-brake in larger in diameterwheel than cylinders drum-brake several ways. First, caliperThe pistons are wheel-cylinder pistons. reason larger thanrequire drum-brake for thisin isdiameter disc brakes more wheel-cylinder pistons. The force because they have no reason servo for this is disc brakes require more action. force because they have no servo Another difference between discaction. and drum-brake cylinders is the type discof Another seals useddifference with the between pistons. Cupand cylinders is the type type drum-brake seals are used in drum-brake of sealscylinders; used with the pistons. wheel usually, O-ring Cuptype type seals are used in drum-brake seals are used in disc brakes. The wheel O-ring cylinders; m ay haveusually, a roundO-ring or squtype are seals are used in disc brakes. The cross-section. O-ring may have a round or square The O-ring seal on most calipers recross-section. tracts the piston and brake pad from O-ring on most calipers theThe rotor, just seal as return springs do inre-a tracts brake. the piston and brake pad from drum The amount of retraction the rotor, just by as return springs do in a is controlled seal and seal-groove drum brake. The amount of retraction design. Movement is slight in a disc is controlled sealrubber and seal-groove brake becausebythe parts only design. Movement is slight in a disc flex a small amount, compared to brake because the springs. rubber parts only brake-shoe return However, flex small amount, a littlea motion is all that compared is required to to brake-shoe return springs. release a disc brake. And, it However, is desired atolittle required to keepmotion the padisveall ry that closeis to the rotor release disc brake.isAnd, is desired so fluid amovement slightit when the to keep are the applied. pad very Otherwise, close to the pedal rotor brakes so fluid movement is slight when the travel would be e xcessive due to the brakesdisc-brake are applied. Otherwise, pedal larger piston. travel be excessive duemountto the Somewould calipers have springs larger disc-brake piston. ed behind the pistons that hold the Some mountpads verycalipers close have to thesprings rotor surface. ed behind the add pistons thatforce hold supthe These springs to the pads the rotor surface. plied very by close the tohydraulic system. These springs add to seal the provides force sup-a However, the piston plied by the hydraulic system. greater force; thus , the piston is
However, the piston seal provides a greater force; thus, the piston is
If brake balance is wrong for wet weather driving, you could be in trouble. Photo taken at Goodyear proving ground near San Angelo, Texas shows how car behaves when wheels lock up during braking . Here testingdriving, difference tires in wet condiIf brake balance is wrong forthey wetare weather you between could be various in trouble. Photo taken at tions near limit of adhesion. Photo courtesy Goodyear. Goodyear proving ground near San Angelo, Texas shows how car behaves when wheels
lock up during braking. Here they are testing difference between various tires in wet conditions near limit of adhesion. Photo courtesy Goodyear.
pulled back from the rotor. Like drum-brake wheel cylinders , pulleddisc-brake back from calipers the rotor.have bleeder most Like drum-brake cylinders, screws. The bleeder wheel screw must also most disc-brake calipers have bleeder be located on top of the caliper so screws. trapped The air bleeder can be screw bled must from also the be located on top the caliper so system. Rightand of left-hand calipers trapped air can be bled from the often differ only by location of the system. Right- because and left-hand bleeder screw of this,calipers so be often differ the careful not toonly get by the location calipers of mixed bleeder screw because of this, so up. Otherwise, you won ' t be able be to careful to get the calipers mixed bleed thenot brakes properly.
up. Otherwise, you won't be able to
bleed the brakes properly. METERING VALVES In a brake system with discs on the METERING VALVES front and drums on the rear, there i~ In a the brake system discs on the often need for with a metering valve. front and drums on thea rear, there of is This device prevents pplication often the need for a metering valve. the front brakes below a preset presThis device of sure in the prevents hydraulic application system. The the front brakes a preset presfront brakes arebelow applied at about sure in psi, the depending hydraulic onsystem. The 75-135 the system. front brakes are applied at about The reason for a metering valve is 75-135 depending on the system. the forcepsi,and fluid movement reThe reason for a metering valve is quired to overcome drum-brake the force and Also fluid, disc-brake movement pads rereturn springs. quired to overcome drum-brake lightly touch the rotor when not return springs. Also,less disc-brake applied, so it takes pressure pads and lightly touch the rotor contact when with not fluid movement to make applied, it takesbrakes less pressure and the rotor.so Drum take much fluid make contact with more movement force and to movement to bring the rotor. Drum brakes take much their friction material into contact more the force and movement to valve bring with drums. The metering their friction material into contact balances these requirements and with thethedrums. valve allows front The and metering rear brakes to balances work more these evenly. requirements and allows the afront and valve rear ,brakes to Without metering the front work more evenly. brakes do all the braking in an easy Without valve, thesefront stop with aa metering disc/drum-brake tup . brakesaccelerates do all thefront-pad braking wear. in an Also easy, This stop with I-drive a disc/drum-brake setup. rear-whee cars without meterThis accelerates front-pad wear. ing valves tend to lock the Also, front rear-wheel-drive cars on without meterwheels when stopping snow or ice . ing valves tend to lock the front wheels when stopping on snow or ice.
Metering valves allow pressure to be apI plied to rear brakes before front brakes. I Because may be combined Metering they valves allow pressure with to beother apbrake-system components, not plied to rear brakes before you frontmay brakes. recognize them. If your car has awith metering Because they may be combined other valve, you maycomponents, have to push or may pull the brake-system you not stem during See shop recognize them.bleeding. If your car has your a metering manual for may specifics. valves valve, you have Metering to push or pull are the used on roadbleeding. cars with stem during See combination your shop drum/disc brakes. Metering Drawing valves courtesy manual for specifics. are Bendix on Corp. used road cars with combination
drum/disc brakes. Bendix Corp.
Drawing
Not with Not setups.
metering valves disc/drum-brake ametering metering valves valve
all cars use production all carshave use Some
courtesy
with production discldrum-brake setups. Some have a metering valve 53
Front vs. Rear Fluid Pressure Relationships For Maximum Decleration at Various Traction Front vs. Conditions Rear Fluid Pressure Relationships
For Maximum Decleration atBrake Various System Traction Conditions Without Proportioning
-.-
1.2g
Ideal Relationship
al x
&.
E
c2 (/J
OJ
>-
~(/)
(/J OJ (/J.:.t:.
OJ
ro
Changeover
Pressure In FrontBrake System (psi)
Pressure in Front-Brake System (psi) Upper curve represents ratio of front-to-rear brake Pressure in Front-Brake System (psi)pressures in system not using a proportioning valve. Pressure ratio is built into master cylinder or balance Ideal pressure relationship Upper curve represents ratiobar. of front-to-rear brake pressuresfor in maximum regardless of surface, is ratio shown in lower system notdeceleration, using a proportioning valve. Pressure is built into curve. would bar. look ldeal like this if brake system could masterPressure cylinder curve or balance pressure relationship for automatically proportionregardless pressures ofto surface, make front and rear tires maximum deceleration, is shown in lower reach a system proportioning curve. traction-limits Pressure curvesimultaneously. would look likeThe this closer if brake could valve comes toproportion this ideal curve, the faster a carfront will stop any automatically pressures t o make and under rear tires condition. reach traction-limits simultaneously. The closer a proportioning
Pressure In Front-
Ideal pressure curve plotted with curve from proportioning valve : Brake System (psi) At pressures above changeover pressure A , proportioning valve ldeal pressure curve with curve Notice from proportioning valve: reduces pressure riseplotted to rear brakes. that proportioning valve does notabove reproduce ideal curve, but itA,comes close . Without At pressures changeover pressure proportioning valve a proportioning valve pressure at pOint pressure to reduces pressure risemodifying to rear brakes. Notice thatA,proportioning rear brakes would continue to curve, rise in but direct proportion frontvalve does not reproduce ideal i t comes close.toWithout brake pressure. valve modifying pressure at point A, pressure to a proportioning
rear brakes would continue t o rise in direct proportion to frontbrakepressure.
valve comes t o this ideal curve, the faster a car will stop under inside theany combination condition.
This proportioning valve looks like a brake fitting. It contains a spring-loaded valve that changes pressure-rise rear This proportioning valve looksrate like atobrake brakes. IValves sucha as this are found in fitting. t contains spring-loaded valve many changes production cars with disc brakes on that pressure-rise rate to rear front andValves drums such on rear. brakes. as Drawing this are courtesy in Bendixproduction Corp. many cars with disc brakes on
front and drums on rear. Drawing courtesy Bendix Corp.
Kelsey- Hayes adjustable proportioning valve was used on 1965-'68 Corvettes and some Ford products. It has been used Kelsey-Hayes adjustable proportioning for adjusting brake on many race valve was used on balance 1965-'68 Corvettes cars. ValveFord is adjusted loosening jam and some products,by has been used nut and turningbrake threaded shaft. for adjusting balance on many race
cars. Valve is adjusted by loosening jam nut and turning threaded shaft.
54
Relationship With Proportioning Valve
ldeal Relationship For Maximum Deceleration
0.2g
O~----~--~----~----~----~-
/
:?:u~~
0: cO
O.4g
Without Proportioning
Valve Relationship With (~rOportioning Valve
ro~
'-
/ / /
(/J
~o.
Ideal Relationship 1.0g
/
,
Valve
Relationship Without Proportioning Valve Relationship
valve. Therefore, don't be concerned if you inside find the combination can't a metering valve on valve. your Therefore, don't be concerned if you car as a sepa rate unit. Metering valves can't find a used metering valve on even your are seldom on race cars, car a separate unit. Metering valves withasdisc/drum-brake setups because are seldom on very race hard, cars, and evena race braking used is done with disc/drum-brake setups because metering valve isn't needed in hard race braking is done very hard, and a braking. metering valve isn't hard The metering valve needed operatesin much braking. like a residual-pressure valve. A The meteringpoppet valve valve operates much spring-loaded is seated like a residual-pressure valve. A with a precise amount of spring forc~. spring-loaded poppet valve is seated When hydraulic pressure exerts suffiwith aforce precise of spring force. cient on amount the poppet, the spring When hydraulic pressure exerts suffiforce is overcome and the poppet cient force on the poppet, the spring opens to aJlow fluid flow. Another force is allows overcome the through poppet passage fluid and return opens to allow fluid flow. Another the valve when the brake(s) is passage allows fluid return through re leased. the valve when the brake(s) is
BRAKE BALANCE As discussed in Chapter 1, a car unBRAKE BALANCE dergoes weight transfer during a carfront unAs discussed braking. WeightinisChapter added to1, the dergoes transfer during wheels as itweight is removed from the rear braking.inWeight is amount. added toThe the probfront wheels the same it is removed from the wheels as lem is that braking force should berear apwheels the same The probwheelamount. in proportion to plied toineach lem weight is that braking force weight, should be apthe on it-more more plied to and eachvice wheel in proportion to braking, versa. theWeight weighttransfer on it-more weight, more depends on vehicle braking, and vice versa. deceleratio n deceleration. Maximum Weight mostly transferondepends vehicle depends frictiononbetween deceleration. Maximum deceleration the tires and road surface. If the fricdepends mostly of on the friction tion coefficient tires between is high , the tires and road surface. fricdeceleration is high, as Ifis the weight tion coefficient of surface the tireswith is ahigh, transfer. On a slick low deceleration is high, is weight friction coefficient, bothasdeceleration transfer. Ontransfer a slick are surface and weight low . with a low
friction coefficient, both deceleration and weight transfer are low.
Correct brake balance means that front-to-rear braking forces are proCorrect so brake balance means that portioned neither front nor rear front-to-rear braking forces are prowheels lock first. Pu t another way, the portioned so neither front norsimulrear front and rear brakes wiJl lock wheels lock iffirst. Put another way, the taneously correctly balanced. If front andwas rearadjusted brakes will lock simulbraking to be equal on taneously if correctly balanced. If both the front and rear wheels , a hard braking adjusted be equal on stop withwas high weight to transfe r would both the and rear wheels, a hard cause the front rear wheel to lock up first. If stop with high weight transfer the brakes were proportioned onwould thi s cause rearbraking wheel tooccurred lock up on first.the If car so the more yropot.tiot?ed on this the brakes were front, the car could stop quicker. car so more braking occurred the Greatest deceleration occurs onwhen front, the car could stop quicker. both front and rear tires reach their Greatest deceleration occurs traction limit at the same time . when Tires both frontmaximum and rear grip tires ju reach their develop st before traction at the same time. Tires they slid.limit Remember, slatic friction is develop maximum grip just before higher than sliding/riction. they slid. Remember, static.fr.iction is Correct slidingfriction. brake balance is different higherthan for high deceleration than for low . Correct brake for balance is different Brakes balanced dry pavement will for deceleration thanpavement. for low. not high be balanced for wet Brakes balanced for dry will For examp le , a hard stoppavement on wet pavenot be balanced for wet pavement. ment will give less deceleration than For example, a hard stop on wet pavefo r dry pavement; less weight transfer ment will less wheels deceleration than occurs and give the front lock up. forAdry pavement; less weight transfer system that corrects the various occurs and the front iswheels lockProporup. traction conditions needed. A system that corrects the various tioning valves are designed to do this. traction conditions issystem needed, hasPt.opor.a cerA hydraulic-brake tionirig valves are designed to do this. tain ratio between front and rear A hydraulic-brake a cerbrake pressures. A system tandemhas mastertain ratio between front and rear cylinder brake system with equal brake pressures. A tandem masterpiston diameters has the same prescylinder brake system with equal sures front and rear. This means that piston diameters thewith same presif you push on thehas pedal enough sures front and rear. This means that force to produce 100 psi in the front if YOU lines push , on pedal withlines enough brake thethe rear brake will forcehave to produce 100them. psi inIf the also 100 psi in you front step
brake lines, the rear brake lines will also have 100 psi in them. If you step
down harder and raise the pressure to 400 psi, both front and rear brakes down harder and raise the pressure to will have 400-psi pressure. This is not 400ideal psi, situation both front rear brakes an for and maximum stopwill pressure. This is not pinghave on all400-psi surfaces. anLet's ideal assume situation that for maximum we have astopcar ping all surfaces.disc brakes . Disc with on four-wheel Let's have assume that we havesoa that car no servo action, brakes with four-wheel disc brakes. Disc simplifies this example. Let 's also brakes have action, are so that assume that no all servo four brakes the simplifies thisdiameter example.andLet's also same-rotor caliperassume thatare all the four brakes the piston sizes same. Thisare means same-rotor diameter and caliperthat the torque output of the brakes is piston sizesfront are the means the same and same. rear ifThis front and that the torquepressures output ofare thethebrakes rear hydraulic same.is theWesame frontassume and rear front will also thatif the car and has rear hydraulic pressures are the same.of a 50/50 weight distribution-50% will also assume that wheels the car and has theWe weight is on the front a50% 50/50 distribution-50% of is onweight the rear. If we make a panic the weight is on the front wheels and stop on a slick surface , weight transfer 50% is onzero. the rear. we maketorque a panic is nearly EqualIf braking is stop on a from slick surface, weightand transfer desired both front rear is nearlyIfzero. Equal braking torque we are trying to stop in is a brakes. desired from both front and rear hurry on ice, the condition of hard brakes. we are to stop in a brak ing Ifwith lowtrying weight transfer hurry on ice, exist. the condition of hard might actually braking Now lewith t's trylowto weight design atransfer brake might actually exist. system that gives maximum Now let's regardless try to design brake deceleration, of thea coeffisystemof friction that between gives themaximum tires and cient deceleration, regardless of the coeffithe road. This brake system would cient of friction between tires and have to adjust the ratio the of pressures the road.thThis brake would between e front and system rear brakes to have to adjust ratio of in pressures account for thethe difference weight between the and brake rear brakes to transfer. Thefront ideal system
account for the difference in weight transfer. The ideal brake system
flects high deceleration rates obtained with high tire grip and the resulting flects deceleration rates obtained weighthigh transfer.
would be designed to lock all four wheels at once, regardless of weight would transfer.be designed to lock all four wheels once, onregardless weight In theatgraph page 54, ofI plotted transfer. the relationship between front- and In the graph on page plotted rear-brake pressures for 54, our Iexample the relationship between frontcar. If master-cylinder-piston sizes and are rear-brake our example equal , therepressures is alwaysforequal pressure car. If master-cylinder-piston sizes are in the front- and rear-brake systems. equal, there is always equal This is the straight line in thepressure graph . in the the frontand rear-brake systems. When pressure in the front-brake This is the in the system is straight doubled,linethe reargraph. also When the pressure in the front-brake doubles. This is not ideal for maxisystem is doubled, thevarious rear tracalso mum deceleration under doubles. This is not ideal for maxition conditions. mum under various tracWithdeceleration a high-traction surface, tion conditions. weight transfer increases. This reWithlessa pressure high-traction quires at the rearsurface, brakes weight transfer increases. This the reand more at the front because quires pressure at the reartires brakes verticalless force on the front is and more thethe front because the greater thanat on rears. A brake vertical with forceequal on brake the front tiresand is system pressure greater than on the rears. A brake equal brake torque will lock the rear system equal wheels with before the brake fronts.pressure This is and not equal brake will lock the rear desirable fortorque maximum deceleration wheels beforeA the This is rear not or stability. car fronts. with locked desirable for maximum deceleration wheels and rolling front wheels will or spinstability. easily. A car with locked rear wheels and rolling front the wheels The lower curve shows ratio will bespin easily. tween front-and rear- brake pressures The lower curve shows ratio beautomatically changed to the account for tween frontandItrear-brake weight transfer. shows thepressures need to automatically changed account for the to percentage of gradually reduce weight transfer. It shows the needrear to brake pressure going to the gradually reduce increased. the percentage of brakes as traction This re-
with high tire grip and the resulting weight transfer. PROPORTIONING VALVE
Now that we have an ideal frontPROPORTIONING to-rear brake-pressureVALVE curve for this an the idealstraightfrontcar,Now howthat can we we have modify to-rear brake-pressure curve forclose this line pressure relationship to get car, how can we modify the straightto the ideal curve? Answer: It is done line relationship with pressure a proportioning valve. to get close to Atheproportioning ideal curve? Answer: It is done valve reduces the with a proportioning pressure increase tovalve. the rear brakes. A does proportioning reduces the This not meanvalve that pressure to pressnre increase to the rear the rear brakes is preven tedbrakes. from This does merely not mean to rising-it risesthat at apressure lower rate the rear brakes ispressure prevented froma than front-brake when rising-it merely riseschangeover at a lower presrate specified pressurethan front-brake pressure when sure-is reached. Th e curve of front-a specified pressurecharigeover presto-rear- brake pressure with a proporstlre-is valve reached. Therear curve of line fronttioning in the brake is to-rear-brake pressure with plotted in the graph, page 54 . a proportioning valve in the rear brake curves line is The accompanying pressure plotted the graph, pageaxes 54. because do not in have numbered Thevary accompanying pressure they with each car. Exactcurves presdo not have numbered axes because sures in a brake system vary with they vary with each car. Exact brake preshydraulic-cylinder dimensions, sures a brake systemweight vary with location, and design,in CG hydraulic-cylinder brake wheelbase of the dimensions, car. The curve design, has CGthelocation, weightin and always shapes shown the wheelbase of the car. The curve two figures, but the numbers vary always the shapes shown in the from carhas to car. twoMost figures, but the numbers proportioning valves vary are from car to car. preset at the factory . They cannot be Most orproportioning are adjusted serviced later. valves Each valve
brake pressure going to the rear brakes as traction increased. This re1100
5
AP Racing Adjustable Proportioning Valve CP 2611-3 Adjustable AP Racing
900
900
preset at the factory. They cannot be adjusted or serviced later. Each valve
ProportioningValve
4
Nominal Performance
4 3
CP 261 1-3 Nominal Performance Graph
-
700 .-
E- 700 -
3 2
-::;aIn
2
C/J
.::;
Q.
500
0
1
3
0 300
100 Tilton Engineering offers this AP Racing adjustable proportioning valve. Lever has five positions, each with a different changeover pressure. Valve is ideal road occasionally raced on racing Tilton Engineering offersfor this APcar Racing adjustable proportioning tires. weight each transfer racing tires means valve. Improved Lever hasgrip fiveand positions, withwith a different changeover less pressure should go to Photo courtesy AP Racing. pressure. Valve is ideal forbrakes. road car occasionally raced on racing
tires. Improved grip and weight transfer with racing tires means less pressure should go to brakes. Photo courtesy AP Racing.
1
100
300
1
I
-
900
500 700 900 1100 Graph shows AP RaCing adjustable proportioning-valve pressure Input (psi) 100
300
500 700 1 I nput (psi) I
changes to rear brakes. With valve at setting 2, pressure rises as if thereshows were no until 200-psi proportioning-valve changeover point is pressure reached. Graph APvalve, Racing adjustable Pressure tothen at With a lesser This effectively changes rearrises brakes. valverate. at setting 2, pressure reduces rises as pressure-rise rate to rear delays orpoint prevents rearif there were no valve, until brakes 200-psiand changeover is reached. wheel lockup. Tiltonrate. Engineering, Inc. Pressure thenGraph risescourtesy at a lesser This effectively reduces
pressure-rise rate to rear brakes and delays or prevents rearwheel lockup. Graph courtesy Tilton Engineering, Inc.
55
is suitable for use only on the car for which it was adjusted. This is unfortuis suitable for you use may only like o n the car for nate because an adjustwhich it was adjusted. This unfortuable proportioning valve as ais means of nate because youhigh-performance may like an adjustbalancing your or able proportioning valve as a means of race-car brakes. Fortunately, some balancing yourvalves high-performance or proportioning allow an external race-car brakes. some adjustment. Some Fortunately, of these are shown proportioning valves photos. allow an external in the accompanying adjustment. S o m e of these are shown Porsche, Chrysler, Chevrolet and in the accompanying photos. Ford have adjustable proportioning Porsche, Chrysler, Chevrolet and valves for high-performance use. The Ford have proportioning Porsche 914 adjustable uses an adjustable val ve valvescanForbehigh-performance use. T h ea that changed by loosening Porsche 914 uses an adjustable valve lock nut and turning a screw. Turning that screw can beinward changed by loosening the on this valve putsa lock and turning a screw. morenut pressure on the rear Turning brakes the screw inward o n this valve puts during a hard stop. Adjusting the more ispressure o n the rear brakes valve a trial-and-error process, as during a inhard stop.10.Adjusting the described Chapter valve a trial-and-error as The isChevrolet Corvetteprocess, adjustable described in Chapter 10. proportioning valve, 3878944, is T h e Chevrolet Corvette adjustable available both from Chevrolet and proportioning valve, specializing 3878944, in is from racing shops available both fromChrysler's Chevroletvalve, and brake components. from racingis available shops specializing in P4120999, through their brake components. Chrysler's valve, performance-parts division, Direct P4120999, is available their Connection. Ford's through proportioning performance-parts division, through Direct valve, M-2328-A is available Connection. Ford's dealers. proportioning Ford Motorsport These valve, M-2328-A valves work muchis available the samethrough as the Ford dealers. begins These PorscheMotorsport valve. Proportioning valves work much t h e same as the between 100 and 1000 psi, depending Porsche valve. Proportioning begins where adjustment is set. between 100 and 1000 psi, depending Another proportioning val ve, where adjustment is set. which operates like the Porsche and Anothervalves, proportioning Corvette is available valve, from which operates like and Alston Industries the of Porsche Sacramento, Corvette valves, available from California. This oneis was designed by Alston Airheart Industries Sacramento, Frank to goof with his highCalifornia. o n e was designed by performanceThis dual, tandem master Frank Airheart to go with his highcylinder. performance dual,valve tandem master A proportioning is installed in cylinder. line between the master cylinder and valve in theA proportioning rear brakes. It willis installed work with line between cylindercylinand either a singlet hore amaster dual master the inrear will work with der the brakes. system, Itbecause all it does either a single or a dual master cylinis affect the maximum pressure at the der in t h e system, because all it does rear brakes. is An affect t h e maximum pressure valve, at the adjustable proportioning rear brakes.is sold by Tilton EngineerCP2611-3, proportioning ingA n ofadjustable Buellton, California. valve, This CP2611-3, is sold by Tilton Engineerdevice can be mounted in the cockpit inga race of car Buellton, Thisit of so the driCalifornia. ver can adjust device can be mounted in the acockpit during a race. He can move lever of a anyone race car so the driver canpositions adjust it into of five different during a race. H e can move as brake or track conditions, aorlever the into anydistribution o n e of five of different weight the carpositions changes as brake o r track conditions, or the during a race. weight distribution the car changes Curves of inlet ofpressure versus during a race. outlet pressure for this valve are Curves of inlet pressure versus shown on page 55. Note that pressure outlet for this are rises in pressure a one-to-one ratio valve until the
shown o n page 55. Note that pressure rises in a one-to-one ratio until the 56
Inlet and Outlet ,-------- Ports are 7/1624 Thread for 3/16Inlet and Outlet or 1 /4-in.-OD Ports are 7/16-Tubing 24 Thread for 3/16or 1/4-in.-OD Tubing
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0.351 -0.342 dia.
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1000
1200
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Front-Brake Pressure (psi) lMO
Kelsey-Hayes adjustable proportioning valve is available from Kelsey Products Division Front-Brake Pressure (PSI) and many U.S. automobile dealers through their high-performance catalogs. Valve functions the same as APadjustable RaCing valve except it'svalve infinitely adjustable between and 1000 psi. Kelsey-Hayes proportioning is available from Kelsey100 Products Division Adjustments are made withdealers thumbscrew. courtesy Kelsey-Hayes Corp. automobile throughDrawing their high-performance catalogs. Valve functions and many U.S. the same as AP Racing valve except it's infinitely adjustable between 100 and 1000 psi. Adjustments are made with thumbscrew. Drawing courtesy Kelsey-Hayes Corp.
600 .(/J Q.
-600 500
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-E -500 OJ
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-
Ideal Front vs. Rear Fluid Pressure Relationships For Different Weight Distributions ldeal Front vs. Rear Fluid Pressure Relationships For Different Weight Distributions Car A Car weight, wheelbase, and CG height are Tail-Heavy Car the same for all three cars. Only With front-to-rear weight distribution varies.are Car A40/60 Weight Car weight, wheelbase, and CG height DistributionCar Tail-Heavy the same for all three cars. Only With 40/60 Weight front-to-rear weight distribution varies. Distribution Car B
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Pressure I n Front-Brake System (psi)
Pressure In Front-Brake System (psi) cars with different weight Ideal front-to-rear brake-system pressures for three different distributions: Nose-heavy car has less pressure to rear wheels; tail-heavy car has more. Ideal front-to-rear brake-system pressures for three different cars with different weight distributions: Nose-heavy car has less pressure to rear wheels; tail-heavy car has more.
changeover pressure is reached. For position 5, pressure rises as if the prochangeover pressure For portioning valve is notis inreached. the system position 5, pressure rises as if the prountil about 950 psi is reached. At that portioning valve is not inpoppet the system point, the spring-loaded valve until about 950 psi is reached. that inside the proportioning valve At opens, point, the spring-loaded poppet valve and output-pressure increase is reinside with the proportioning valve opens, duced increasing input pressure. and output-pressure increase is reMeanwhile, front-brake pressure is duced with increasing not affected. It increasesinput as it pressure. did withMeanwhile, front-brake out a proportioning valve. pressure is notMost affected. increases as it did withroad Itcars have proportioning out a proportioning valve. valves that give approximate correct Mostbalance road cars brake withhave an proportioning average load
valves that give approximate correct brake balance with an average load
using street tires. If the car is set up for racing, its total weight, weight using street and tires.tire If grip the car set up distribution are islikely to for racing, its total weight, weight change from the average values the distribution and tire arebrake likelybalto car was designed for. grip Thus, change the average valueseven the ance mayfrom be incorrect for racing, car was designed for. Thus, brake balthough it has a proportioning valve. ance may be incorrect for racing, even Remember, a proportioning valve thoughtheit approximate has a proportioning gives correct valve. brake Remember, proportioning balance over aa limited range of valve tracgives the approximate correct brake tion conditions. balance range of tracIf you over drivea a limited car on the street and tion conditions. race it on occasion, you may want to youadjustable drive a car o n the streetvalve and useIf an proportioning
race it o n occasion, you may want to use a n adjustable proportioning valve
1
to change brake balance. For street driving, the car should be correct as to For change brake balance. street is. racing, brake balanceFor probably driving, should be tocorrect as havethe to car be readjusted provide will is. For racing, brake balance probably more braking force on the front-less will haverear. to be readjusted to provide on the Racing tires have more more than braking forcetires; on the front-less grip street thus, weight on the rear. Racing under tires have more transfer is greater maximum grip than street tires; thus, weight braking . transfer is greater maximum Let's say you haveunder a sports car that braking. you drive to work and slalom on the Let's say With you have a sports car that weekends. the quick-adjustable you drive to work and on the Tilton valve, you don't slalom even have to weekends. With the quick-adjustable get your hands dirty. In the example Tilton valve, yourun don't to given, you might the even valve have at posiget In drop the example tion your 5 for hands street dirty. use and to posigiven, the valve at posi4 reduces tion 4 you for might racing run . Position tion 5 for street use and drop to posirear-wheel braking, starting at a lower tion 4 forthan racing. Position 4 reduces pressure position 5. This comrear-wheel starting at a translower pensates forbraking, the greater weight pressure than position 5. This fer when braking on racing comtires. pensates for setting the greater weightbalance transMore about up brake fer when 10. braking on racing tires. in Chapter More about setting up balance One disadvantage of brake proportioning in Chapter 10. valves is that they increase pedal One without disadvantage of proportioning effort reducing displacement valves high-deceleration is that they increase during stops. pedal effort without reducing displacement If you wish to add a proportioning during stops. valve tohigh-deceleration a car that doesn't have one, If you to does add anot proportioning make surewish the car have a diagvalve to a car thatsystem doesn't have rearone, brake . Some onally split not have a diagmake sure the car does wheel-drive cars and most frontonally split brake system. Somesorearwheel-drive cars are designed the wheel-drive and most left-front andcars right-rear brakesfrontare wheel-drive carssame are designed so the operated by the half of a tandem left-front and right-rear brakes are master cylinder; right-front and leftoperated by the same half of a tandem rear brakes are operated by the other master cylinder; and alefthalf of the masterright-front cylinder. With direar brakes arebrake operated by the other agonally split system, a single half of the master cylinder. valve With awill diadjustable proportioning
agonally split brake system, a single adjustable proportioning valve will
Proportioning-
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Actual-Pressure Relationship
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Pressure In Front-Brake System (psi)
In different Front-Brake System (psi) Two ideal pressure curves Pressure for cars of weight distributions show how one proportioning valve can be adjusted to work with either. Two ideal pressure curves for cars of different weight distributions show how one proportioning valve can be adjusted t o work with either.
not work. It only works where both rear brakes are fed by a single hydraunotline. work. I t only works where both lic I cover adding a proportioning rear brakes are fed by a single hydrauvalve to an existing car in Chapter 12.
lic line. I cover adding a proportioning valve to an existing car in Chapter 12. PRESSURE-LIMITING VALVES
A pressure-limiting valve is used on PRESSURE-LIMITING VALVES some cars with disc brakes on the A pressure-limiting valve is used on front and drums on the rear. It persome with function disc brakes on the forms cars a similar as a proporfront drums on pressure-limiting the rear. It pertioningandvalve. The forms a similar function as ata the proporvalve prevents the pressure rear tioning valve. The pressure-limiting brakes from exceeding a preset value. valvedifference prevents the pressure at the rear The between a proportionbrakes from exceeding a preset value. ing valve and a pressure-limiting
The difference between a proportioning valve and a pressure-limiting
-.L g
valve can be seen by comparing the accompanying graphs. valve be seen by between comparingpressure the acThecan relationship companying graphs. in the front-brake system and rearThe system relationship between brake is shown in thepressure graph , in the Note front-brake and rearhow thesystem pressure-limiting below. brake system shown in the graph, valve differs isfrom a proportioning below. Note how the pressure-limiting valve . Remember, a proportioning valve differs the from a proportioning valve allows pressure in the rear valve. proportioning system Remember, to rise if thea driver pushes valve pressure rear harderallows on thethe pedalbut atina the reduced system to rise if the driver pushes rate. However, a pressure-limiting harder the pedal-but reduced valve on limits pressure toat athe rear rate. However, a pressure-limiting brakes. valve pressure rear Whenlimits this preset valueto is the reached,
brakes. When this preset value is reached,
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_ _ _ _ _ _ _ _ _ Maximum Pressure
Maximum Pressure
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Pressure In Front-Brake System (psi)
Pressure In Front-Brake System (psi)
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Honda Civic has diagonally split braking system with two proportioning valves. Valves are shown at bottom. One adjustable proportioning cannot besplit used with system diagonally braking Honda Civicvalve has diagonally braking withsplit two proporsystem.valves. Two proportioning valves at willbottom. work, but tioning Valves are shown Oneadjustment adjustable must probe synchronized. Portioning valve cannot be used with diagonally split braking
Relationship between front- and rear-brake system pressure of pressure-limiting valve : Compare curve to that of ideal pressure curve on pagebetween 54. Withfronta proportioning valve, system pressure continues Relationship and rear-brake pressure of to rise in rear-brake system beyond changeover With pressure-limiting valve: Compare curve to that of pressure. ideal pressure pressure-limiting changeover pressure is continues reached, curve on page 54.valve, With aonce proportioning valve, pressure that's as it gets. For a high-performance car,pressure. use a proporto riseasinhigh rear-brake system beyond changeover With tioning valve, not avalve, pressure-limiting valve-unless car is extremepressure-limiting once changeover pressure reached, ly nose-heavy. that's as high as i t gets. For a high-performance car, use a propor-
system. Two proportioning valves will work, but adjustment must be synchronized.
tioning valve, not a pressure-limiting valve-unless car is extremely nose-heavy.
57
Both proportioning valves are adjusted by spring between rear axle and proportioning-valve lever. Valve adjustment changes with rearsuspension travel from weight on rear wheels. Rear-axle movement moves lever and changes valve setting. As weight on rear wheels increases, so doesvalves rear-wheel-brake pressure. Cars that suchproportioning-valve large weight-distribution changes, such changes as this with Plymouth Both proportioning are adjusted by spring between rearhave axle and lever. Valve adjustment rearVoyager/Dodge Caravan (left) or stationRear-axle wagon (right), will benefit from a height-sensing proportioning suspension travel from weight onPeugeot rear wheels. movement moves lever and changes valve setting. valve. As weight on rear wheels increases, so does rear-wheel-brake pressure. Cars that have such large weight-distribution changes, such as this Plymouth Voyager/Dodge Caravan (left) or Peugeot station wagon (right), will benefit from a height-sensing proportioning valve.
pressure to the rear brakes cannot increase, regardless of how hard the pressure to the on rear the brakes cannot driver pushes pedal. A increase, regardlessvalve of how hard well the pressure-limiting works driver on the pedal. A only on pushes an extremely nose-h eavy car, pressure-limiting valve workssedan. well such as a front-wheel-drive only an extremely nose-heavy car, pressure-limiting valves usually Also,on such as a front-wheel-drive sedan. are not useful for race cars because Also, pressure-limiting most are not nose heavy.valves usually
are not useful for race cars because most are not nose heavy. ANTI-SKID SYSTEM A nti-skid systems are designed to
ANTI-SKID prevent wheelSYSTEM lockup, no matter how Anti-skid sysrenls are designed to the brakes are applied. hard prevent wheel lockup, how Many manufacturersno clmatter aim their hard the brakes applied. properties. systems have are anti-skid Manytheymanufacturers claim their What real ly do is prevent one systems havefrom anti-skid pair of wheels locking properties. before the What they reallya good do is propo prevent one other. In a sense, rtioning pair ofiswheels from locking the valve an anti-skid device;before it keeps other. In awheels sense, from a goodlocking proportioning the rear before valve is an In anti-skid device; I itdiscuss keeps the fronts. this section, the rear wheels from locking before systems other than.!7xedproportioning thepressure-limiting fronts. In this section, valves. I discuss or systems than.fixedproportioning Some other anti-skid devices amount to or pressure-limiting valves. propornothing more than adjustable Some anti-skid devices to some extioning valves controlled byamount nothingmeans. more The thanvalve adjustable proporternal is adjusted by tioning valves controlled by some rear-suspension movement or exby ternal means. The valve is adjusted by sensing the actual decelera tion of the rear-suspension movement or by car. The type that operates from rearsensing the actual deceleration of the suspension movement compensates car. The that operates rearfor bothtype deceleration andfrom vehicle suspension movement compensates weight. This is particularly important fora both deceleration and vehicle in truck or a station wagon, where weight. is particularly the CG This can move a great important deal with in a truck or a instation wagon, changes in load the cargo area. where the CG can move a great with The anti-skid valve thatdeal senses changes in load in the cargo area. deceleration uses the bal/-and-ramp The anti-skid valve that senses prinCiple. The valve is positioned so deceleration theup,ball-and-ramp that the rampuses angles toward the principle. Thevehicle. valve isThe positioned so front of the valve conthat the ramp angles up, toward the front of the vehicle. The valve con58
tains a conventional proportioning valve and a bypass. At low tains a conventional proportioning deceleration, brake fluid passes the valve a bypass. At low ball andand bypasses the proportioning deceleration, brake fluid passes the valve, regardless of pressure. At a preball and bypasses the proportioning determined transition decelerationvalve, of pressure. about regardless 0 .3 g-the ball rollsAtupa prethe determined transition ramp, closes the bypass,decelerationand proporabout g-the ball rolls up the starts. tioning 0.3 ramp, and proporThis closes valve the canbypass, compensate for a tioning starts. changing CG location . As weight at compensate theThis rear valve of thecan vehicle increases,forthea changing C G location. As weight at rear suspension compresses and the the rear of the vehicle This increases, the ramp angle increases. increases rear the the suspension transition compresses decelerationand and, ramp angle increases. This increases therefore, rear-brake pressure at the transition deceleration and,transition. Thus, the rear brakes share rear-brake pressure at atherefore, larger portion of the braking. transition. the rear brakessenses share A true Thus, anti-skid system awhen largera wheel portionstarts of thetobraking. lock . It closes a A true senses line to system that wheel to valve in theanti-skid when a wheel starts to It lock. It closes reduce the pressure. then sensesa valvewheel in the line toup that to the speeding and wheel reapplies reduce the pressure. It then senses pressure. A typical system uses the wheel sensors speeding to up sense and reapplies magnetic wheel pressure. A typical system uses speed. magnetic sensors to are sense Wheel-speed signals sent wheel to an speed. electronic module, or computer, Wheel-speed sent to an which computessignals wheelare deceleration electronic module, computer, and slip values for eachor wheel. Decelwhich computes wheel deceleration eration and slip values for that wheel and slip values for each wheel.for Decelare compared with values the erationwheels and slip for that wheel other andvalues with fixed thresholds are compared for are the (preset values) . with Whenvalues thresholds other wheels and with fixed thresholds exceeded, the module sends a signal (preset values). When thresholds the proper controller. The valveare is to exceeded, module a signal and the pressure to sends that wheel is closed to the proper controller. valve is reduced. When wheel The deceleration closed pressure to thatlevels, wheeltheis and slipand go below threshold reduced. When wheel deceleration module signals the controller to inand slippressure go below threshold levels,hapthe . All this shuttling crease module signals the hard controller to inpens rapidly during applications,
crease pressure. All this shuttling happens rapidly during hard applications,
ATE skid-control front-wheel sensor, introduced on '85 Lincoln Mark VII, is ilATE skid-control front-wheel sensor, lustrated on display model with sectioned introduced '85 Lincoln VII,speed is ilfront-wheel onrotor/hub. As Mark wheel lustratedrapidly on display sectioned changes whenmodel brake with lockup begins, front-wheel rotor/hub. wheel speed brakes are rapidly cycled As on and off to prechanges rapidly when brake lockup begins, vent lockup. Photo by Tom Monroe. brakes are rapidly cycled on and off to prevent lockup. Photo Monroe. so the wheel (s)by Tom never completely
lock. so theControllers wheel($ require never an completely Note: external lock. power source, which can be hydraulic, Note: Controllers electric or vacuum. require an external power source, which can behave hydraulic, Skid-control systems been electric or vacuum. used on large aircraft since the '50s. Skid-control systems have been The first vacuum-powered road-car used on developed large aircraftby since the '50s. systems Kelsey-Hayes The Delco first were vacuum-powered and introduced in road-car the late systems developed by Chrysler. Kelsey-Hayes '60s by Ford, GM and The and Delco were systems introduced in the late Ford and GM operated on '60s rear by Ford, andChrysler Chrysler.had Thea the wheelsG M only; Ford and Gsystem. M systems operated on four-wheel Porsche experithe rear wheels only; Chrysler had mented with mo re sophisticated sys-a four-wheel system. experitems in the early '7 0s Porsche on 911 and 917 mented race cars.with more sophisticated systems in the early '70s car on manufactur911 and 917 most major Today, race cars. ers are developing four-wheel Today, 1984 most Porsche major carand manufactursystems. Mercedes ers are developing models use Bosch anti-skidfour-wheel systems, systems.and 1984 Porsche and Honda Mitsubishi haveMercedes systems models use Bosch anti-skid systems. in production, Ford introduced a
Honda and Mitsubishi have systems in production. Ford introduced a
Safety Braker is fancy cylinder mounted in brake line from nearest master cylinder. It damps Braker pressure pulses in brake fluid, Safety is fancy cylinder mounted in giving more consistent brakingcylinder. and less brake line from nearest master It pedal pulsation. is slightly difficult damps pressureIt pulses in more brake fluid, to lock more one wheel with a braking Safety Braker in giving consistent and less the device is an pedal system. pulsation. Because It is slightly more difficult accumulator, it displaces fluid Braker and into lock one wheel with a Safety in creases pedal travel slightly. Safety isBrakthe system. Because device an ers are no longer made. fluid and inaccumulator, it being displaces
Three different types of mechanical stoplight switches each have plunger to operate electrical switch. Usually, switch is operated by movement of brake pedal. Drawing courtesy Bendix Corp. types of mechanical stoplight switches each have plunger to operate Three different
electrical switch. Usually, switch is operated by movement of brake pedal. Drawing courtesy Bendix Corp.
creases pedal travel slightly. Safety Brakers are no longer being made.
system developed by ATE for the 1985 Mark VII. GM released systems system developed by and ATE ATE for the developed by Bosch for 1985 Mark VII. G M released systems 1986 models. These systems are developed but by they Bosch and much ATE imfor expensive, provide 1986 models. systems are proved directionalThese stability, steerabiliexpensive, but they provide much imty and deceleration in critical braking proved directional stability, steerabilimaneuvers on all road surfaces. ty Anti-skid and deceleration in critical braking systems can provide maneuvers all road surfaces. these same on advantages in racing, plus Anti-skid systems provide they can eliminate tire can flat spotting. these same advantages in racing, plus To date, an ti-skid systems have been they can eliminate tire flat spotting. used little because of their weight and To date, anti-skid systems have been questionable reliability. However, used little because of their weight and recent advancements in technology questionable reliability. However, should change that. Many highrecent advancements in technology powered, exotic road-racing cars will should Many highprobably change be using that. anti-skid devices by powered, road-racing will 1990. But exotic for now, a skilledcars racingprobably feel be using anti-skid devices by driver's is considered to be the 1990. But for now, a skilled racingmost effective anti-skid device. driver's feel is considered to be the most effective anti-skid device. STOP-LIGHT SWITCHES Stop-light switches are either meSTOP-LIGHT SWITCHES chanical or hydraulic. Both are conStop-light are either menected to theswitches electric circuit and turn chanical or hydraulic. Both are conon the brakelights when activated. nected to the electric circuit and turn The hydraulic switch is designed as a on the brakelights when activated. hydraulic fitting and is operated by The hydraulic pressure. switch is The designed as a brake-system mechanihydraulic fitting and is operated by cal type is operated directly by brakebrake-system pressure. The mechanipedal-linkage motion. Most newer cal type is operated directly by brakecars use the mechanical switch. pedal-linkage motion. newer With both switch types,Most the electricars use the mechanical switch. cal circuit is open until the brakes are With both switch types, the electriapplied. When the switch closes, the cal circuit open until the brakes the are stop lightsis illuminate. Usually, applied. When theisswitch closes, the mechanical switch designed to close stop lights illuminate. Usually, the mechanical switch is designed to close
Hydraulic stoplight switches screw into a fitting in hydraulic system. Fluid pressure operates switch. Although easier to install, mechanical switches are better for racing. HydrauliC switch takes a smallswitches amount of fluid into movement to in operate it, and a mechanical switch operdoes Hydraulic stoplight screw a fitting hydraulic system. Fluid pressure not. Also, hydraulic switches leak. Drawing courtesy Bendix ates switch. Although easier can to install, mechanical switches are Corp. better for racing. Hydraulic
switch takes a small amount of fluid movement to operate it, and a mechanical switch does not. Also, hydraulic switches can leak. Drawing courtesy Bendix Corp.
when the brake pedal has been moved about 112 in. The hydraulic switch is when the tobrake beenpressure moved designed closepedal with has a small 112 in. The hydraulic switch is about buildup in the system . The exact designed to close with a small pressure point at which the switch closes is not buildupbecause in the any system. exact critical modestThe brake appoint at which theclose switchthe closes is not plication should electrical critical because any modest brake apcontacts. plication close the electrical If you should are selecting a stop-light contacts. swi tch for a race car, use a mechanical If . you are selecting stop-light type Although more adifficult to switch for a race car, use a mechanical install, a mechanical switch will not type. the Although moreif itdifficult to affect brake system fails. A hyinstall, switch a mechanical switch will not draulic is just another possible affect the brake system it fails. A hyleak. Also, slight fluid ifmovement is draulic switch is just another necessary for operation. Everypossible possileak. Also, must slightbefluid movement ble failure eliminated from isa necessary race car. for operation. Every possible failure must be eliminated from a race car. WARNING-LIGHT BRAKE SWITCHES BRAKE Brake WARNING-LIGHT warning-light switches have SWITCHES been in use since tandem master cylinBrake ders werewarning-light introduced in switches the '60s. have This been in use since tandem master cylinpressure switch illuminates a warning ders introduced in the '60s.which This light were on the instrument panel, pressure switch illuminates a warning light on the instrument panel, which
indicates a problem with the brake system. The switch senses any indicates a problem with the brake hydraulic-pressure imbalance between system. The switch senses any the front and rear brake systems. hydraulic-pressure imbalance between And, the light · illuminates when a the and-rear brake systems. presetfront pressure imbalance occurs. And, will thewarn lighttheilluminates when a driver of problems This preset as pressure occurs. such fluid imbalance leaks, masterThis will warn tlie driver in the cylinder-fluid bypass or ofairproblems such leaks, mastersystem. as fluid cylinder-fluid air in the A typical bypass brake orwarning-light system. switch is shown on the following page. warning-light AtAthe typical center of brake the switch, a piston is switch following page. located isbeshown tween on twothe spri ngs. Pressure At the center of the switch, a piston is from the front brakes is on one side of located between two springs. Pressure the piston and rear-brake pressure is from frontDifferences brakes is oninone of on thethe other. theside force thethe piston and rear-brake pressure is of two springs compensa te for the on the other. pressure Differences in the force designed-in differential of of two springs compensate the thethefront and rear systems. for When designed-in pressure differential severe pressure differential occ ursof, the front and rear toward systems.theWhen the piston is moved lowsevere pressure differential pressure side . This closes the occurs, switch the turns pistononisthe moved toward and warning light.the lowpressure side. This closes the of switch There are many variations this and turns on the warning light. simple switch . Some have centering There are many variations of this simple switch. Some have centering 59
Brake WarningLight Switch
Brake WarningPiston Off-Center
Stem
houlder of Piston Touching Terminal
Brake warning-light switch is indicating hydraulic-system malfunction. Piston between two centering springs is pushed to left by higher pressure in right chamber. Piston contact with electrical terminal turns on instrument-panel warning light. malfunction. Drawing courtesy Corp. Brake warning-light switch is indicating hydraulic-system PistonBendix between two
centering springs is pushed t o left by higher pressure in right chamber. Piston contact with electrical terminal turns on instrument-panel warning light. Drawing courtesy Bendix Corp.
springs; some even have two pistons. The switch type used varies with the springs; even have two pistons. design ofsome car and brake system.
near the master cylinder so lines to the front and rear brakes can be easily near the master cylinder so lines to connected to the valve.
In recent years, car manufacturers COMBINATION VALVE have combined the function of the In recentvalve, years,proportioning car manufacturers metering valve havebrake combined the function and warning-light switch of intothea metering valve, proportioning valve single combination valve. Some manuand brakecombine warning-light switch into a facturers the brake warningsingle combination valve. Some manulight switch with either the proporfacturers combine the brake warningtioning valve or the metering valve. light switch with either the Some front-wheel-drive carsproporwith tioning valve orsystems the metering valve. combine two diagonally-split Some front-wheel-drive with proportioning valves with cars the brake diagonally-split systems combine two warning-light switch. Because external proportioning valves with the brake appearances of these valves are warning-light similar, be switch. careful Because when external moving appearances of these are brake-system componentsvalves from one similar, be careful when moving car to another. Check part numbers brake-system components from one and car shop manuals to be sure. carCombination to another. valves Check are partfound numbers only and car shop manuals to be sure. in brake systems using a tandem Combination are found master cylinder.valves Usually, they only are in brake systems usingdisca and tandem found on cars with front rear master brakes. cylinder. Most Usually, they are drum combination found on cars with front disc and rear valves cannot be disassembled for drum brakes. Most combination service or adjustment. If defective, a valves cannot be disassembled for be replaced. valve must service or adjustment. If defective, Combination valves work similar toa valve must be replaced. the individual valves they replace. By Combination work similar to combining in avalves common housing, the individual valves replace. By fewer fittings are used.they Consequently, combining a common the valve isinsimpler, costs housing, less and fewer fittings are used. Consequently, leak possibilities are reduced. thePictured valve isis simpler, less and a typical costs three-function leak possibilities are reduced. combination valve. The metering Pictured is a the typical three-function valve operates front system and combination valve. The the proportioning valve themetering rear. A valve operates the must front be system and combination valve mounted
A fluid-level indicator consists of a FLUID-LEVEL INDICATOR device in the fluid reservoir and a A fluid-level indicator brake warning light. It consists switchesofona device in the fluid reservoir and aa when reservoir fluid drops below brake warning level. light. This It switches on predetermined indicating when reservoir fluid drops device consists of a float andbelow a me-a predetermined level. This indicating chanically or magnetically actuated device consists of a float and a meswitch. chanically or magnetically actuated Like the brake warning-light switch. switch, low fluid-level indicator warns brakeleakswarning-light theLike driverthe of fluid or masterswitch, low fluid-level indicator cylinder bypass. It can also warns signal the of fluid leaksbutornot masterworndriver disc-brake linings, air in cylinder bypass. It can the system. Usually, twoalso are signal used worn linings,cylinders. but not airBein with disc-brake tandem master the system. Usually, two are used cause fluid-level indicators perform with master cylinders. Bemany tandem of the same functions as brake cause fluid-level indicators perform warning-light switches, they are rarely many of the same functions as brake used together.
The switch type used varies with the design of car and brake system. COMBINATION VALVE
the proportioning valve the rear. A combination valve must be mounted 60
Three-function combination valve combines metering valve, proportioning valve and brake warning-light switch Three-function combination valve into com-a single metering unit. Metering is at leftvalve end bines valve, valve proportioning and proportioning valve is under brake warning-light switchlarge intonut a on bottom. courtesy Bendix Corp. single unit.Drawing Metering valve is at left end
and proportioning valve is under large nut on bottom. Drawing courtesy Bendix Corp.
the front and rear brakes can be easily connected to the valve. FLUID-LEVEL INDICATOR
warning-light switches, they are rarely used together. HOSES Hydraulic fluid is carried to the cali-
HOSES pers or wheel cylinders by flexible Hydraulic is carried to the calihoses. Thesefluid hoses allow suspension perssteering or wheel cylinders by flexible and motion. hoses. suspension In theThese early hoses days ofallow the automobile, and steering motion. high-pressure flexible hoses did not In the early days ofitthe exist. Consequently, wasautomobile, difficult to high-pressure get hydraulic flexible fluid to hoses brakesdid at not the exist. it was difficult to wheels.Consequently, It was amazing that early get hydraulic fluid to brakes at the hydraulic-brake systems worked at wheels. amazing that Fluid Itwaswas routed through axleearly and all. hydraulic-brake workedThis at suspension links systems to the brakes. all. Fluid was routed through axlefront and was particularly difficult on the suspension links seals to thewere brakes. wheels. Sliding usedThis to was particularly difficult on the front allow steering and suspension wheels. Sliding seals were used to allow steering and suspension
Although old, cracked brake hose stills holds pressure; it should be replaced. Condition of outSide rubber is the only to Although old, cracked brake hoseway stills judge condition of a brake It's better holds pressure; it should behose. replaced. Conto replace a cracked hose than to way risk to a dition of outs~de rubber is the only suddencondition brake failure. judge of a brake hose. It's better
to replace a cracked hose than to risk a sudden brake failure.
motion . To contrast this, the modern brake hose is simple and reliable. motion. To contrast this,from the multiple modern Brake hoses are made brake hose is simple and reliable. layers of fabric impregnated with Brake hoses areThey made are from multiple synthetic rubber. tough and layers of years, fabricbutimpregnated with last many are still the weaksynthetic They are tough Itand est link inrubber. the hydraulic system. is last many years, but are still thecontact weakeasy to damage a hose through est the hydraulic It is withlinka in wheel, tire , system. suspension easy to damage a hose through contact member, exhaust or road debris. Or with a wheel, tire, can suspension an overzealous mechanic damage exhaust or road debris. Or amember, brake hose during installation. A an overzealous mechanic can brake hose can fail if twisted damage or imaproperly brake installed hose during installation. A . brake hose can fail if imBrake hoses expand twisted slightly or under properly installed. high internal pressure. This swelling Brake additional hoses expand under requires fluid slightly movement to high internalfor pressure. This swelling compensate the increased hose requires The additional movement to volume. driver fluid senses hose swellcompensate for the increased hose ing or expansion as a soft or spongy volume. The driver sensesand hose swellbrake pedal. Racing high-
ing or expansion as a soft or spongy brake pedal. Racing and high-
Imperial tube bender is available from good tool stores. Neats bends can be made without risk of crimping Beforefrom youI good bend Imperial tube bendertube. is available brake lines, Neats invest bends in a good bender. withtool stores. cantube be made "Ultimate" brake hoses are steel-braided teflon. Because exterior is braided stainless steel, hoses more resistant to me"Ultimate" brake are hoses are steel-braided chanicalBecause damage than is ordinary teflon. exterior braided rubber stainhoses. Steel-braided hoses areto mealso less steel, hoses are more resistant stiffer, giving a firmer pedal. chanical damage than ordinary rubber
hoses. Steel-braided hoses stiffer, giving a firmer pedal.
are
also
Don't use high-pressure plastic tubing for a brake hose! After repeated flexing, tubing cracks at fittings. I've seentubing this failDon't use high-pressure plastic for urebrake on several cars.repeated Plastic tubing is a hose!race After flexing, also easily damaged by heat mechanical tubing cracks at fittings. I've or seen this failcontact. Although tubingtubing can be ure on several raceplastic cars. Plastic is usedeasily if rigidly mounted to frame, weight also damaged by heat or mechanical saved isn't worth risking brake failure. contact. Although plastic tubing can be
out risk of crimping tube. Before you bend brake lines, invest in a good tube bendler.
used if rigidly mounted to frame, weight saved isn't worth risking brake failure.
performance brake systems require that rubber brake hoses be replaced performance with somethingbrake better.systems require that rubber brake hoses be replaced High-pressure stainless-steelbraidwith something ed brake hoses, better. developed for aircraft High-pressure and military use,stainless-steel-braidare available from ed brake hoses,. Suppliers developedare forlisted aircraft specialty shops at and military use, are available from the back of the book. Steel-braided specialty Suppliers are listed at hoses areshops. available in custom lengths the of the book.to Steel-braided with back adapter fittings suit special hoses are available custom applications. These inhoses are lengths Teflon with adapter fittings to suit lined and externally reinforcedspecial with applications. These are almost Teflon stainless-steel braid. hoses They are lined and externally reinforced with "bulletproof' and resist expansion stainless-steel braid. They are almost under pressure. "bulletproof' and resistTeflon-lined expansion Aeroquip 6600-series under pressure. hose with Super Gem fittings is a type Aeroquipused 6600-series Teflon-lined commonly on race cars. I highly hose with Super G e m fittings is a hose type recommend this flexible brake I highly commonly used on race cars. to make the brake pedal firmer, and recommend this flexible brake hose for overall safety. Remember, use to make hose the brake flexible only pedal wherefirmer, thereand is for overall safety.components Remember,being use motion between flexible hoseEven onlythewhere is connected. best there flexible motion between components being hose expands more under pressure connected. Even the best flexible than steel hydraulic tubing. hose expands more under Some race cars use plastic pressure hose for than hydraulic tubing. both steel the brake tubing and the flexible Somehoses. race cars plastic hose for brake Thisuse tubing may work bothsome the brake tubing andapplications, the flexible for low-pressure brakeit ishoses. This tubing mayflexible work but dangerous to use as for some low-pressure applications, brake hose. Plastic tends to crack but it isthe dangerous to usethe as flexible where tube enters fitting. brake repeated hose. Plastic After flexing,tends even to thecrack spewhere the developed tube enters cial fittings for the this fitting. tubing Afternotrepeated spe-a will preventflexing, failure. even If youthe have cial fittings for this tubing race car withdeveloped plastic brake hoses, rewill not prevent If you Teflon have a place them with failure. steel-braided
race car with plastic brake hoses, replace them with steel-braided Teflon
hoses. Failure of the plastic hose will occur without warning and cause hoses. Failure the plastic hose will sudden brakingof loss.
occur without warning and cause sudden braking loss. HYDRAULIC TUBING
Most cars use tubing manufactured HYDRAULIC TUBING from steel for the brake system. ComMost cars use tubing manufactured monly called brake lubing, it is availafrom steel for the brake system. Comble in diameters from 1/8 in . through monly is availa3/8 in.called Mostbrake of tubing, today ' sit cars use ble in diameters 118 in, through 3/16-in. tubing ;from 1I4-in. tubing is 318 in.onMost today's use found most ofolder cars. cars Smaller 3116-in. tubing;and114-in. tubing is tubing is stiffer lighter and easier found most tubing older has cars.less Smaller to bend.onLarger resistubing stiffermovement and lighterand and iseasier tance tois fluid less to bend. Larger tubing has resis-. prone to damage during less handling tance3/16-in to fluid movement less The .-diameter tubeand is aiscomprone damage atduring promiseto arrived after handling. years of The 3116-in.-diameter tube is a using comexperience. I recommend promise arrived at after years of 3/16-in . hydraulic tubing for all brake experience. I recommend using systems. 3116-in. for all brake Copperhydraulic tubing ortubing any tubing of an systems. unknown material should never be Copper tubingtubing or any tubing isofsoft an used for brake . Copper unknown material should never be and prone to cracking. Ordinary steel used formay brake Copper isbut soft tubing be tubing. strong enough, it and pronemeet to cracking. doesn't the rigidOrdinary quality steel and tubing may be strong but it design standards of enough, brake tubing. doesn't meet the rigid quality and Tubing manufactured for brake sysdesignby standards of brake tubing. tems Bendix is made of soft-steel Tubingsheathed manufactured for brakeThese sysstrips with copper. tems by Bendix is made of soft-steel strips are then rolled into a doublestripstube sheathed with at copper. These wall and bonded high temperastrips in area then rolled a doubletures furnace . Theinto tu be is then wall tube and at highresistance. temperatin-coated forbonded corrosion tures in a furnace. The tube is then Ordinary steel tube is only single wall tin-coated for corrosion resistance. and not copperor tin-plated. It could Ordinary steela few tubeyears is only wall rust out after andsingle suddenly
and not copper- or tin-plated. It could rust out after a few years and suddenly
Automotive brake-tubing flares : Doubleflare used on most American cars is at left; at right is iso-flare used on some Doubleforeign Automotive brake-tubing flares: cars. used Flares match fittings toat which flare on must most American cars is left; they attach, otherwise a leak or failure will at right is iso-flare used on some foreign result.Flares must match fittings t o which cars.
they attach, otherwise a leak or failure will result.
Making double flare: Flaring tool comes with dies needed to do both forming operations. Tool flare: and tubing aretool set comes up to Making double Flaring do second with dies forming neededoperation. to do both forming
operations. Tool and tubing are set up to do second forming operation.
61
Flaring tool folds tube end back on itself to finish double-flaring operation. Drawing courtesy Chrysler Corporation. Flaring tool folds tube end back on itself to
finish double-flaring operation. Drawing courtesy Chrysler Corporation.
Fittings used with steel-braided hose are different than standard automotive brake fittings. High-pressure steel-braided-hose fittings meet aircraft standards, not automotive standards. Special adapter fittings aircraft-type fittings to automotive brakes. Fittings used with steel-braided hose attach are different than standard automotive brake fittings. Photo courtesy C & D Engineering Supply Ltd. meet aircraft standards, not automotive High-pressure steel-braided-hose fittings
standards. Special adapter fittings attach aircraft-type fittings to automotive brakes. threads. Accompanying Photo courtesy C & D ~ n ~ i nphotos eerin supply g show Ltd. seat for the flare they mate to.
Race cars often require fittings not normally found in auto-parts stores. Bulkhead fitting handy mounting lines Race is cars often for require fittings brake not normalwhere they pass through a panel such fitas ly found in auto-parts stores. Bulkhead this fire wall. Two nuts support ting is handy for jam mounting brake fitting lines at hole they in panel. where pass through a panel such as
this fire wall. Two jam nuts support fitting at hole in panel.
burst. Always use proper-quality brake-tubing material, available from burst. Always auto-parts stores. use proper-quality brake-tubing material,tubing available from Double Flare-Brake is availaauto-parts stores. ble in several standard lengths with Doublefittings Flare-Brake is availamale at each tubing end. Common ble in several standard lengths are 8, 12, 20, 30lengths , 40, 50 with and male at each end. diameters Common 60 in . fittings Commonly available lengths 40, 50 cars and are 3/16are or 8, 11412, in. 20, for 30, American 60 in. Commonly available diameters and 3/16 in. or 4.762mm for imported 114 isin.doubleIlared-tube for American cars are 3/16 cars. Eachorend and 3/16 in. or 4.762mm for imported is doubled over on itself-in a convex cars. Each end is double7/lared-tube or concave shape. American and imis doubled itself-in flares a convex ported carsover useondifferent and
or concave shape. American and imported cars use different flares and 62
some of these differences. threads. photosforshow DoubleAccompanying flares are important the some of these differences. strength and safety of a brake system. Doublewith flares are important for can the Anyone a cheap flaring tool strength and safety of a brake system. make single flares. NEVER singleAnyone with a cheap brake lines. If youflaring don't tool wantcan to flare make single flares.double-flaring NEVER singleinvest in a special tool, flare lines.brake If you tudon't to buy brake preflared bes want or pay invest in a special double-flaring tool, someone to custom-make double buy preflared brake are tubes or will pay flares. Single flares weak, someone custom-make doublea eventually to fatigue, crack and cause flares. Single flaressystem. are weak, will leak in the hydraulic eventually fatigue, crack cause toa Armor-Brake tubing is and exposed leak in the hydraulic system. harsh conditions under a car. It gets Armor-Brake tubing is isexposed to blasted by dirt and debris, immersed harsh conditions under a car.continue It gets in water and salt, but should blasted by dirt debris, is immersed to function forand years without failure. in water and salt, but should Anytime you are under your continue car, look to function for years without for brake-line damage . A failure. rusty, Anytime you are look kinked, nicked or under leakingyour line car, must be for brake-line damage. A rusty, replaced. If you want extra protection kinked, leaking must be with newnicked brakeortubing , itline is available replaced. with If you want extra This protection wrapped a coil spring. armor with new the brake tubing, is available protects tube fromit damage by wrapped with asharp coil spring. armor rocks o r other objects.This Armored protects the can tubebe from by brake lines founddamage in major rocks or other sharp objects. Armored au to- parts stores.
brake lines can be found in major auto-parts FITTINGSstores.
Brake lines are connected with steel FITTINGS or brass fittings of various types, such are connected steel as Brake tees, lines junction blocks andwith unions. or brass fittings of various types, such Be careful when selecting brake-line as tees, They junction blocks fittings. must have and the unions. correct
Be careful when selecting brake-line fittings. They must have the correct
Otherwise, they will leak. Many fit-
seat for look the OK flare matepropto. tings that willthey not mate Otherwise, theytubing. will leak. Many erly with the Never use fittatings OK will mate proppered that pipelook threads in a not brake system. erly with use taThey will the leak tubing. under Never high pressure, pered pipe threads in a brake system. particularly if installed without They willThey leak will underalso highsplit pressure, sealant. when particularly if installed without overtorqued. sealant. They will switches also split when Some stop-light have taovertorqued. pered pipe threads. They will seal if Some tape stop-light switches have you taTeflon is used . However, pered pipe threads. sealanyif must be very careful They not towill allow Teflon tape tape to is extend used. However, you Teflon past the first must be very careful not to allow any thread. A shred of Teflon tape floating Teflon tape to extend past the first around in the brake fluid can plug a A shred ofsystem. Teflon tape thread. port critical in the The floating best soaround in the brake fluid plug a lution is avoiding the use can of tapered critical port in the system. The best sopipe threads. Take a tip from the airlutionindustry: is avoiding theTeflon-tape use of tapered craft Leave seapipe threads. Takeand a tippipe fromfitters. the airlant to plumbers It craft industry: Leave Teflon-tape seacan cause many problems in a brake lant to plumbers and pipe fitters. It system. canOncause in a brake race many cars, problems steel-braided hoses system. are used to improve reliability and On race cars,brakes. steel-braided provide firmer Fittings hoses used are used to improve reliability and with steel-braided hoses are different provide firmer used than those usedbrakes. with Fittings conventional with are different different hoses.steel-braided They have hoses entirely than those used with conventional specifications for threads, flares and hoses. dimensions. They have entirely other Adapter different fittings specifications threads, flaressteeland must be used for when installing other dimensions. Adapter fittings braided hoses on vehicles with must be used when automotive-type brakeinstalling fittings. steelbraided hoses on with Adapter fittings are vehicles available from automotive-type brake fittings. Adapter fittings are available from
Of
·c
*F
'C
600
'E
500
~
300
Selected High BoilingPoint Glycol Brake Fluids elected High Boiling-
300 250
20e 250
oint Glycol Brake '0
20c
al 300
150
2o0o!----'---!;2-~3-~--!--....::::6100
Weight % Water 1
Brake tube in fitting fractured during a race, causing complete brake failure. Driver but luckily Brake was tube without in fittingbrakes, fractured during ita happened where complete he could recover race, causing brake without failure. crashing. Failure occurred because fittingDriver was without brakes, but luckily it mounting was installed. happened bolt where henot could recoverVibrating without fitting andFailure hose occurred was supported byfittingtube, crashing. because which eventually failed fatigue. Brake mounting bolt was not from installed. Vibrating tubes and must supported be securelybymountfitting andfittings hose was tube, ed to prevent suchfailed failure. which eventually from fatigue. Brake
tubes and fittings must be securely mounted prevent such theto sources thatfailure. supply the hoses,
such as e & D Engineering Supply the that supply the hoses, Ltd., sources or WREP Industries. Some such asoffer C &brake-hose D Engineering Supply shops kits that inWREP Industries. Some Ltd., or clude ada pter fittings and correctshops that inlength offer hoses.brake-hose Don't mixkits automotive cludeaircraft adapter fittings correctand fittings. This and will result in length hoses. Don'tleaks mix automotive damaged threads, or cracked and aircraft Thisrecognize will resultthe in fittings. If fittings. you can't damaged threads, leaks or cracked difference, ask the adv ice of a shop fittings. If you recognize the that supplies thesecan't fittings. difference, ask the advice shop Adapter-fitting usage will ofbea minithat supplies these fittings. mized if a race car is constructed using usage will besystem. miniall Adapter-fitting aircraft fittings in the brake mizedcan if aberace carbyis getting constructed using This done the proper all aircraft fittings in the brake system. fittings from an aircraft hardware This can be done getting supplier. You maybystill havethe toproper adapt fittings fromlineCs) an aircraft the brake to yourhardware master supplier. You still using have automoto adapt cylinder(s) andmay brakes the brake line(s) to your master tive flares or fittings. cylinder(s1 and brakes using automoAircraft flar es are not the same as tive flares or fittings. automotive flares. They use Aircraft flares are notthe the tubes same as ferrules-sleeves-over to automotive They and use reinforce them. flares. Aircraft hoses fitferrules-sleeves-over tubes AN to tings are identifiedthe as reinforce them. Aircraft and fit(Army-Navy) or MShoses(Mi litary tings are AN identified AN Standards). and MSas specI(Army-Navy) or M S (Military fications, written by the U.S. Standards). ANstandards and MS specigovern ment , are recognized fications, by Automotive the U.S. throughout written the world. government, specifications are are standards written byrecognized the Societhroughout the world. Automotive ty of Automotive Engineers (SAE) . specifications arealso written by the SAE standards have the Sociesame ty of Automotive Engineers (SAE). worldwide recognition .
SAE standards also have the same worldwideFLUID recognition. BRAKE Once a brake system is installed, it
BRAKE must be FLUID filled with fluid so it can Once a brake system is installed, it must be filled with fluid so it can
Brake fluid is lifeblood of any brake system. For race cars, you must keep fresh new fluid in brake system atof all times. Fluid Brake fluid is lifeblood any brake with highest possible boiling is a system. For race cars, you must point keep fresh must for raCing. new fluid in brake system at all times. Fluid
with highest possible boiling point is a must for racing.
function. Hydraulic fluid for an automotive brake system is simply function. Hydraulic for an aucalled brake fluid. Thisfluid distinguishes it tomotive system simply from fluidsbrake used for other ishydraulic This distinguishes it called brakefluid. applications and systems. Automotive from fluids used for other hydraulic brake fluid is designed to work the applications Automotive brake systemand of asystems. car. Other hydraulic brake have fluid totally is designed to work the fluids diffe rent chemical brakephysical systemproperties. of a car. Other hydraulic and Always use aufluids have totally tomotive brake fluiddifferent in a car.chemical Aircraft and physical properties. Alwaysand use aubrake fluid is totally different will tomotive brake not work in a car.fluid in a car. Aircraft brake fluid is totally differentmixture, and will Brake fluid is a chemical not work in a car. which varies with manufacturer. Each Brake fluid has is aa chemical mixture, manufacturer secret formula dewhich varies with manufacturer. signed to perform a "better job ."Each All manufacturer has a secret formulatheir demanufacturers must formulate signed to perform a "better brake fluid so it m ee ts rigid job." SAE, All inmanufacturers must formulate their dustry and government standards. In brake fluid it meets rigid SAE, inthe U.S. , thesoDepartment ofTranspordustry and government standards. In tation (DOT) sets the standards. theHydraulic U.S., the brake Department of Transporfluid used in racing tation (DOT) sets the standards. and road cars is mostly a Polyalkylene Hydraulic brakemixture-commonly fluid used in racing Glycol Ether and road cars is mostly a Polyalkylene called glycol. This type of fluid can be Glycol Ether mixture-commonly found in any auto-parts store and is called glycol.with Thisthetype fluid can inbe compatible fluidoforiginally found in store type and of is stalled in any yourauto-parts car. A newer compatible fluid originally brake fluid with has the a si licone base . inIts stalled in A newer type of properti es your differcar.from glycol-based brake fluid has a silicone base. fluids . Silicone-based brake fluid Its is propertieslater differ from glycol-based discussed in this chapter. fluids. Silicone-based brakemust fluid is Glycol-based brak e fluid have discussed later in this chapter. the following properties to work corGlycol-based brake fluid must have rectly in an automobile: the following properties to work • Must not boil at tempera tures corenrectly in an automobile: countered during severe braking Must not conditions . boil at temperatures en-
countered during conditions.
severe
braking
2
3
4
5
I00 6
Weight % Water Graph shows how boiling point of glycolbased brake fluid drops with exposure to moisture. Notice how brakepoint fluid with highGraph shows how boiling of glycolest boiling when with new exposure is affected based brakepoint fluid drops to most by Notice water how content. courtesy moisture. brakeGraph fluid with highYankee Silicones, est boiling point Inc. when new is affected most by water content. Graph courtesy Yankee Silicones, Inc.
• Must not freeze or thicken in cold temperatures. Must not not compress. freeze or thicken in cold • Must temperatures. • Must flow through system passages Must not compress. minimal no res istance. with Must passages not through corrode system or react with • Must flow with minimal no resistance. brake-system materials. not corrode or sliding react parts with Must lubricate internal • Must brake-system materials. of brake system. Must lubricate sliding parts • Must not alter internal its properties after of brake system.for extended periods. being in system its properties after Must not be alter compatible with other • Must being in system for extended periods. glycol-based brake fluids . Must not be decompose, compatible orwith form other gum • Must glycol-based brake fluids. or sludge at any temperature. Must Boiling-The not decompose,most or formcritical gum Fluid or sludge at any temperature. property of brake fluid is its resistance Fluid Boiling-The most critical to boiling at high temperature. When property of brake fluid is its resistance brake fluid boils , small bubbles form. to boiling at high temperature. When These bubbles collect and are trapped brake boils,Because small bubbles form. in the fluid system. gas bubbles These bubbles collect and are trapped are compressible, this results in a in the brake system. Because gas bubbles spongy pedal. areBoiling compressible, this results in a generally is caused by water spongy brake pedal. vapor being absorbed by the brake Boiling is caused by water fluid . Thegenerally mo re water brake fluid vapor being absorbed by the brake contains, the lower its boiling point. fluid. more water high-quality brake fluid New,The uncontaminated, contains, lower its boiling point. brake fluidthe boils at 550F (288e) ~ pure New, uncontaminated, high-quality water boils at 212F (lOOe). A mixture brake fluidfluid boilsand at 550F pure of brake water(288C); boils somewater at 212Fthese (100C). A mixture where boils between temperatures. of brake fluidpoints and water boils someTwo boiling are referred to in where between these temperatures. brake-fluid specifications: dry boiling Two boiling points paint. are referred in wet bailing Withouttogetpoil1l and brake-fluid specifications: dry boiling of the specifications, ting into details and wet should boilingpoint. Without getpoint the meaning be clear. Dry boilting into details of the specifications, ing point refers to fresh fluid out of a
the meaning should be clear. Dry boiling point refers to fresh fluid out of63a
,B RAKE-FLUID SPECIFICATIONS The print on brake-fluid cans is 8RAKE-FLUID SPECIFICATIONS confusing. Even worse, specifica- , The on constantly, brake-fluidsocans is tions print change an old confusing. worse, specif icacan of fluid Even may say something diftions constantly, an old ferent change than a new can . Theso following can may say something difis of an fluid explanation ' of current ferent than a new can. The following specifications. is Allan explanation of current brake fluids must meet federal
standard 116. Under this standard are three Department of Transportastandard Under thisfor standard tion (DOT)116. specifications brakeare Department of Transportafluidthree performance : DOT 3, DOT 4 tion (DOT) and DOT 5. specifications All brake fluidsfor arebrakesuitafluid DOT 3, or DOT 4 ble forperformance: use in either drum disc and DOTBoiling 5. All brake are suitabrakes. pointfluids for the three ble forof use either drum or disc types flu,i dsinare as follows:
specifications. All brake fluids must meet federal
brakes. Boiling point for the three types of fluids are as follows:
Dry Boiling Point
Degrees F , Degrees C
Dry Boiling Point
Degrees F
Wet Boiling Point
Degrees F Degrees C Degrees C
Wet Boiling Point
Degrees F Degrees C
DOT3
DOT 4
DOTS
401 DOT 3 205
446 DOT 4 230
500 DOT 5 260
40 1 284 205 140 284 140
446 311 230 155 31 1 155
500 356 260 180 356 180
it.
I
~
I
e
a ap:!
:-
[ s~ RACinG 550 Racing 5 5PlUld 0 BtaWl
"k
I"IGt contents 1 hre
us Brake 338 us II", id """"""""~,
Iqtl81101 rkatr*nlmlm
U Sr "
e-':I l •• 1" 5
1 1 H U S Ilrv 1 , 18 ~ t t , ~ , . I
..
700
~
'we ~ 600 ~,
!j'"9 m u
500
'" o
5~
503400
~ ::l
300
y
,~
Typical Glyco l-Based {Brake Fluid Typical Glycol-Based
g 200 L----'-----'1'-2---':18---'---'
Months in Service , I I I I 200 6 24 Curve shows what 'I2 happens18 to boiling Months inbrake Service point of glycol-based fluid in typical road-car use. , toWeather Curve shows what happens boiling changes point of curve'-boiling glycol-based point brakegradually fluid in drops in extremely climates. Sili,typical road-cardamp, use. Weather cone brake fluid is not point susceptible to changes curve-boiling gradually moisture as it· damp doesn't pick Siliup drops in extremely climates. moisture. Consequently, silicone cone brake fluid is not susceptible to Ibrake-fluid ~ boiling remains moisture as it' point doesn't pick high up moisture. silicone after long Consequently, use. Graphcoi!rtesy brake-fhid boilingInc. point remains high Yankee Silicones, after long use. Graph courtesy Yankee Silicones, of a fluid is by lnc. its DOT number. A
UC-,~
AP 550 Racing Brake Fluid is used ~. in ,most-severe racing applications. Its dry 550 boiling pointBrake of 550F AP Racing Fluid(288C) is used is h ' highest for a glycol-based fluid, Photo most-severe racing applications. Its courtesy APpoint Racing. dry boiling of 550F (288C) is highest for a glycol-based Old brake fluid meetsfluid. DOTPhoto 2 or courtesy AP Racing. , SAE J1703 or 70R3 specifications.
Old brake fluidrequirements meets DOT refer 2 or These obsolete SAE 31 703 specifications. to , fluid withora 70R3 dry boiling paint of These obsolete requirements 374F (190C). If you have any ofrefer th is to a dryit. boiling point of old fluid fluid,with discard Don't use any374F (190C). If you have this thing less than DOT 3 any fluidof in a old fluid, discard it. Don't anybrake system . Prior to theuse DOT 2 thing less thanthere DOT was 3 fluid in a specifications, a 70Rlbrake system.brake 2 Prior fluid to the DOTfor specification meant specifications, there was this a 70R1drum brakes only. Throw away specification for too if you find brake any. Itfluid has ameant dry boildrum brakes only. Throw this away ing paint of only 302F (150C). tooSpecified if you find boiling any. It has a dry boilpoints are ing point of only 302F (150C). minimums. Many brake fluids have Specified points are higher boiling boiling points, as indicated minimums. Many brake fluids have on their containers. As for what to highera dry boiling points, asover indicated use, bailing point 500F on theiris containers. for what to (260C) best for hardAs driving. use, a 3dryand boiling over 500F DOT DOT point 4 specifications (260C) is best for hard driving. are for glycol-based brake fluid and DOT and DOT 4You specifications DOT 5 is3 for silicone. can tell imare for glycol-based brakechemistry fluid and mediately what the basic DOT 5 is for silicone. You can tell immediately what the basic chemistry 64
glycol-based
brake
fluid
with , a
of a fluid is bydry its boiling DOT number. A 500F(260C) point is glycol-based tested to DOT 3brake or DOT fluid 4, not with DOT 5.a 500F (260C) dry boilingpoint point is Sometimes boiling tested to to DOT 3 o r DOTon 4, not OT5 referred asERBP the DbrakeSometimes point is fluid can. This boiling means' equilibrium referred to aspoint, ERBPwhich on the brakeisanothreflux boiling fluid can. This means equilibrium er way of saying wet boiling point. reflux boiling whichin is anothERBP refers topoint, a method the speer way offor saying wet is boiling point. cification how fluid exposed to ERBP refers a method in. the spemoisture and to tested . cification forfluid howboiling fluid isp~oint exposed to ' Note that drops moisture tested.to water. Glycolafter it isand exposed Notebrake that fluid boiling point drops based fluids absorb moisture. after resulting it is exposed to water. GlycolThe mixture of brake fluid based brake fluids in absorb moisture. and water results a boiling~point The of brakewater fluid drop.resulting Fluids mixture that · absorb and water in' a hydrostopic. boiling-point ' easily areresults called drop. Fluids that absorb water Water in brake-fluid also causes easily hydroscopic. corrosionare and called impurities to accumuWater in hydraulic brake-fluid also causes late in the system. corrosion and impurities to accumulate in the hydraulic system.
sealed can ; wet boiling point refers to fluid that has been exposed to moissealed can; wet boiling point refers to ture under specific conditions . Both fluid that has been exposed to moisboiling points should be of concern to ture, under conditions. you but thespecific most important oneBoth will boiling points should be of concern Lo de pend on how you use your car. you, but the most important one will Dry boiling point is important for depend you usethat youracar. racing . on It ishow assumed properly Dry boiling i s important for m aintained racepoint car will always have racing. I t is assumed that a properly fresh brake fluid, For best permaintained race car must will always have form ance, the fluid be changed fresh brakeduring fluid.a racing For best many times seasonperto formance, the boiling fluid must changed avoid a lower point.beCh anging many timesis during a racing season the fluid an inexpensive way to to avoid a lower boiling point. Changing ensure the brakes work bes t at temthe fluid encountered is an inexpensive to peratures in racingway . ensure the brakes best at temWet boiling pointwork is most important peratures n racing. for street encountered use , Brake ifluid in streetWet boiling point is most driven cars is not changed important often-if for Brake fluid i n streetever.street If youuse. could bleed your brakes driven week cars isornot often-if every so ,changed the brake fluid ever. I fhave you could bleedsimilar your brakes would properties to a every week or who so, can thetake brake race car's. But, the fluid time would have their properties similar to a to bleed brakes weekly? race car's. But, canmust take function the time Normally, the who brakes to bleed their brakes weekly? with moisture in the brake fluid over Normally, the brakes must function long periods of driving during all with the brake fluid over types moisture of weathe irnconditions. long periods o f driving during all Brake fluids with a high wet boiling types o f weather conditions. point do not necessarily ha ve the highfluids with boiling estBrake dry boiling point.a high Mostwet racers use do not necessarily have the ahighapoint glycol-based brake fluid with dry est dry boiling Most(288C) racers use bo iling point point. of 550F for a glycol-based brakehigh-performance fluid with a dry racing. A common boiling point (288C)is AP for brake fluid usedo fin 550F road racing A common high-performance racing. Racing 550 . This fluid exceeds DOT 4 brake fluid used roadboiling racing point, is AP specifications fori ndry Racing 550. This fluid exceeds DOT and meets DOT 3 specifications for4 specifications for dry boiling point, wet boiling point. To maintain your and meets Dsystem O T 3 specifications racing-brake properly, it isfora wet boiling good choice . point. To maintain your racing-brake properly, s a For street system use, you shouldi t iuse good choice. brake fluid that meets DOT 4 specifiFor street you point. shouldIf use cations for wetuse, boiling the brake meets fluid that meets DOT 4 specififluid DOT 4 specifications, it I f the cations for all wet boiling point. also meets parts of DOT 4, includfluid meets D Opoint. T 4 specifications, boiling Your choice of ita ing wet partsshould o f DOT includalso meets all brake-fluid brand be 4,based on ing boiling point. Your choice of a the wet following requirements: brake-fluid brand should on • Use a fluid that your be carbased m anuthe following requirements: facturer recommends. fluid that of your car manuDon ' a t mix brands fluids. • Use facturer recommends. Violate either of these rules, and Don't mix brands o f fluids. long-term harm may occur to your Violate either For of these rules,some and brake system. instance, long-term your brake fluidsharm maymay reactoccur with torubber brake insystem. instance, seals a brake For system. Over asome long brake fluids may react with rubber period of time , this may cause swelling sealsleakage. i n a brake a long or Thissystem. occurs Over commonly period o f.S.-manufactured time, this may cause swelling when U brake fluid or leakage. is used in anThis olderoccurs foreigncommonly car with when U.S.-manufactured fluid natural-rubber seals . The brake seals swell is used i n an older foreign car and have to be replaced eventuwith ally. natural-rubber seals. The seals swell and have to be replaced eventually.
You wouldn't dare do this with ordinary glycol-based brake fluid; it would remove the There's to paint with You paint. wouldn't darenododanger this with ordinary silicone fluid. Silicone fluiditiswould ideal for cars glycol-based brake fluid; remove that have There's problems with brake-system no danger to paint with the paint. contamination and corrosion. courtesilicone fluid. Silicone fluid isPhoto ideal for cars sy Yankee that have Silicones, problemsInc. with brake-system contamination and corrosion. Photo courtesy Yankee Silicones, Inc.
Consult the factory shop manual or your dealer for brake-fluid recomConsult t h e factory shop manual or mendations. your dealer brake-fluid Brake-fluid for brands contain recomblends mendations. of chemicals, so their properties Brake-fluid change when brands mixed. contain If you blends must of chemicals, s o their properties change brands, flush out the brake change and when mixed. If you system replace all brake fluid.must See change brands, flush out the brake brake Chapter 11 for tips on changing system fluid. and replace a l l brake fluid. See for the tips highest on changing brake Chapter If you 11 want wet boiling fluid. point and a different combination of If you want highest wet changboili~~g properties, youthe might consider point and a different combination of ing to silicone-based brake fluid. Siliproperties, you might consider changcone fluid is required to meet DOT 5 ing to silicone-based specifications. This brake fluid fluid. does Silinot cone fluid is required DOT 5 absorb moisture like toa meet glycol-based. specifications. Thisits fluid does not fluid. Therefore, wet boiling is absorb moisture like a glycol-based much higher. Also, silicone fluid will fluid. Therefore, its wet boiling not damage the paint on your car is if much higher. Also, silicone fluidfluid will brake spilled. But glycol-based not damage h e paint o n your car if makes good tpaint remover on some spilled. But glycol-based brake fluid finishes.
makes good paint remover on s o m e finishes.
A good application for silicone brake fluid is in antique and collector A Brakes good in application silicone cars. these typesforof cars are brake fluid is in to antique and collector never subjected high temperatures cars. Brakes in types oftemperacars are encountered in these racing-high never subjected to high temperatures tures that can cause si licone fl uid to encountered in protection racing-highof the temperacompress' And intertures that can silicone isfluid to nal parts fromcause corrosion most compress! And protection of the interimportant. Silicone brake nuid serves nal parts from corrosion is most this purpose beautifully, because the important.ofSilicone brake serves absence moisture in fluid the system this purposeeliminates beautifully, practically thebecause chance the of absence of moisture in the system dreaded internal corrosion. However, practically chance of for racing, eliminates use only atheglycol-based dreaded internal racing brake fluid. corrosion. However, forSilicone racing, fluid use only glycol-based has abeen tried in racing brake fluid. raci ng, bu tit has a tendency to gi ve a Silicone fluid been tried in spongy pedal afterhasexposure to high racing, but it has tendency to give temperatures. Thisa is due to the slighta spongy pedal after exposure to fluid high compressibility of silicone brake temperatures. This is d u e to t h e slight at high temperature. For ordinary compressibility of silicone brake but fluida street driving, this is not critical, at high temperature, For ordinary racer needs all the brake-system stiffstreethedriving, ness can get.this is not critical, but a racer needs the brake-system stiffSwitching toallSilicone-If you change ness h e can brake get. fluid, you must first to silicone Switching to the Silicone-If change clean all of old fluidyou from the to silicone brake fluid, you must first brake system to get the maximum clean of the fluid from the benefitall of the oldsilicone fluid's brake system maximum properties. The to bestget waythe to accomplish benefit of brake-system the siliconeoverhaul. fluid's this is during properties. T h e best way to accomplish Totally drain and clean out the old this isIfduring brake-system overhaul. you merely bleed out and influid. Totally cleanhave outa mixture the old stall newdrain fluid, and you will fluid. you merely out and of the Iftwo fluids. Thisbleed will work, butinit stall new fluid, you will have a mixture won't be as good as it could be.
of the two This will work, but Keep Outfluids. Contaminants-If youit won't as good as it could don't be use silicone brake be. fluid, do Keep O u t possible Contaminants-If everything to keep water you out don't use silicone brake fluid, do of the brake fluid. Although it's more everything possible to keep water out expensive, always buy brake fluid in of t h e brake more small cans. fluid. KeepAlthough the cansit'sclosed expensive, always buy opened, brake fluid in before using. Once don't small cans. Keep t h e cans closed keep an old can of brake fluid around before using. Once opened, don'tit long. Use it immediately or throw keep an old can of bleed brake some fluid around of the away. Periodically long.fluid. Use This i t immediately or throw it old removes contaminated away. Periodically bleed s o m e ofreuse the fluid from the system. Never old fluid. This removes contaminated dra ined/hi id. fluid from the system. Never reiise hained,fluid.
Howe master cylinder has rubber diaphragm built into lid. This keeps air from contacting and cylinder contaminating brake fluid. Howe master has rubber diaUnfortunately, caplid.must removed to phragm built into This be keeps air from check fluid level, partially defeating advancontacting and contaminating brake fluid. tage of rubber diaphragm. unfortunately, cap must b e removed to check fluid level, partially defeating advantage Of rubber diaphragm.
If you have a choice, always use a master cylinder with a rubber diaIf you inhave choice, always phragm the acap to seal the use fluid.a master cylinder withfrom a rubber This keeps the fluid exposurediato phragm the cap to fluid. air. Mostin moisture in seal brakethefluid is This keeps the fluid from exposure to picked up from air on damp days. All air. Most moisture brake fluid is master cylinders andinreservoirs must picked up from air o n damp days. All be vented to atmosphere, so don't master cylinders plug vent holes. and reservoirs must be Invented to toatmosphere, so don't addition moisture, brake fluid plug can vent be holes. contaminated by other In addition moisture, brake fluid materials. Dirtto can enter the system can be contaminated by other when nuid is added to the reservoir. It materials. can enter system is critical Dirt to keep dirt the from the when fluid added to the reservoir. It system, so isuse extreme care when is critical to keep dirt from the working on your brakes. Usual consystem, s o isuse when tamination by extreme petroleumcare products working o n your brakes. Usual consuch as oil, grease or solvents. Petrotamination is bymix petroleum products leum solvents with brake fluid such can as oil, gre'aserubber or solvents. Petroand damage seals in the leum solvents mix with brake fluid system. Never clean brake-system and can damage rubber Use sealsalcohol, in the components with solvent. system. cleat7 brake-systet77 brake fluidNever or brake-system cleaners. cot7~ponenfs alcohol, Solvents are with too solvenf. difficult Use to wash off, brake fluid or brake-system cleaners. and will contaminate brake fluid.
Solvents are too difficult to wash off, and will contaminate brake fluid.
65
Brake Pedals & Linkages Brake Pedals 8 Linkages
Bird's-eye view of foot-box area of formula car shows pedals, linkages and brake and clutch master cylinders. Dual brake master cylinders with remotely adjustable balance bar is used. Note bumper protecting master cylinders head-on impact. Bird's-eye view of foot-box area of formula carfrom shows pedals, linkages and brake and
clutch master cylinders. Dual brake master cylinders with remotely adjustable balance bar is used. Note bumper protecting master cylinders from head-on impact.
Most road-car pedals are hanging-pivots are above pedal pad-and pedal bracket doubles as a pedals steering-column bracket. Most road-car are hanging-pivots Device nearpedal top of brake pedal a meare above pad-and pedalisbracket chanical switch. doubles brakelight as a steering-column bracket.
Device near top of brake pedal is a mechanical brakelight switch.
66
The brake pedal and linkage transmil force and movement from the The brake driver's footpedal to and the linkage mastertranscymit force and movement from the linder(s). Design and construction of driver's to affect the how master cythese partsfoot greatly a brake l i n d e r ( ~operates ) Design . and how construction system and it feels of to these parts greatly affect how a brake the driver. The brake pedal must be system operates andpart howofit afeels to the most reliable brake the driver. The brake system because failurepedal can must mean bea the most loss reliable part .ofThe a result brake complete of braking system because failure can mean a can be catastrophic. complete loss of braking. The result When building a car, you may want can be catastrophic. to design and fabricate the brake pedal When building a car, want and linkage. These partsyou aremay some of to design and fabricate the brake pedal the components that can be fabricated and linkage. parts This are some of by the home These craftsman. chapter the components that can fabricated describes how pedals and be linkages are by the home chapter designed and craftsman. fabricated This for safe and describes how pedals and linkages are reliable brake operation. The pedal designed and fabricated for safe and and linkage are normally designed as a reliable operation. The pedal part of a brake comp lete brake system. This and linkage are normally designed as a is discussed in Chapter 9.
part of a complete brake system. This is discussed in Chapter 9. BRAKE PEDAL A
brake
pedal
BRAKE PEDAL A brake pedal
is
familiar
to
is familiar
to
&
everyone who has driven a motor vehicle. Take a good look at the pedal everyone has important driven a design motor in a car. who It has vehicle. Take a good look at the pedal features . Good brake pedals have the in a car. It has important design following characteristics: features. Goodbreak brake or pedals have the • Must not permanently following characteristics: bend under the greatest load a driver Must can apply.not break or permanently bend under the greatest driver • Must be stiff and notload flexa during can apply. hard braking. befree stiffofand not flex during • Must Must be excessive friction . hard braking. • Must provide proper leverage at Mustcylinder. be free of excessive friction. master Must provide proper leverage at • Must match requirements of driver master cylinder.cylinder, linkage and and master Must match requirements of driver system. andA brake masterpedal cylinder, and consistslinkage of the arm, system. pad and pivot attachments. The pedal brake pedal consists This of the arm, is A connected to a linkage. linkage pad and pivot attachments. The pedal transmits force and movement to the is connected to aThe linkage. Thiscan linkage master cylinder. linkage be as transmits force and movement the simple as a straight pushrod, ortomore master cylinder. The linkage can be as complex. simple as a straight pushrod, to or bendmore The pedal arm is subjected complex. ing loads from the driver 's foot. It is The pedal arm is subjected to bendusually constructed of steel plate. The ing loads driver's is arm may from havethe holes in itfoot. for Itthe usually constructed of steel plate. The pivots. Often pivot bushings are conit for the arm have steel holes intubes-pivot tainedmay in pivots. Often pivot bushings housings-that are inserted in are the conarm tained in in place steel . A tubes-pivot and welded good pedal housings-that inserted in the arm design will not are have welds completely and welded in place. A good across the arm, particularly atpedal the design have iswelds pivots. will A not weld a completely source of across the arm, riser-at particularlya critical at the weakness-stress pivots. A weld is a source of area of the arm. weakness-stress riser-at a critical A pedal arm is usually straight - the driver's seat. If area the arm. whenofviewed from is usually straight it A has pedal bends arm or curves in it , the arm when viewed from the driver's seat. If tends to twist when the pedal is it has bends or curves it, arm the arm pushed . Twisting in the in pedal can tends movement to twist when is create at thethepadpedal , giving pushed. Twisting the pedal armAlso, can the driver feel ofin sponginess. create movement giving stresses in a pedal at willthe be pad, higher due the driver feel of sponginess. to twisting forces. To overcome Also, these stresses in pedals a pedalwith will be higher due problems, bends, offsets to twisting forces. overcome these or curves must be To fabricated of heavproblems, ier material.pedals with bends, offsets or Acurves fabricated good must pedalbearm should ofbeheavdeier material. signed to take side loads and forward A good be deloads. Side pedal loads arm on a should pedal arm are signed to take side loads and forward most likely to cause failure , because loads.arms Side are loads on alaterally. pedal arm are most weaker Pedals most likely to cause failure, because shou ld be installed so they won't be most weaker loadedarms fromarethe side. laterally. A brake Pedals pedal should be installed so won'tleg.be should be in line with thethey driver's loaded the side. brake pedal Pedalsfrom in most road A cars are made should be in line with the driver's leg. of steel. This gives a pedal the highest
Pedals in most road cars are made of steel. This gives a pedal the highest
Pedal Bracket
Pedal Bracket
Pivot Housing
Master-Cylinder Pushrod
Master-Cylinder Pushrod Pad
Hanging pecial has pivot housing at top of arm. On many pedals, pivot housing is a steel tube welded into a hole in pedal arm. Pivot bushing is inside pivot housing. For rear-mounted master master-cylinder-pushrod pivotOn installs pivot, 70. is a steel tube Hangingcylinder, pecial has pivot housing at top of arm. manyabove pedals, pivotpage housing
welded into a hole in pedal arm. Pivot bushing is inside pivot housing. For rear-mounted master cylinder, master-cylinder-pushrod pivot installs above pivot, page 70.
stiffness and strength of any low-cost material. Older cars often used steel stiffness strengthbut of modern any low-cost forgings and for pedals, cars material. Older cars often used steel steel use parts cut or stamped from forgings for cars pedals, but modern cars plate. Race sometimes use lightuse parts cut or stamped from steel weight materials such as aluminum or plate. Race cars sometimes use lighttitanium. Consequently, race-car weight materials such as aluminum or pedals are expensive when compared titanium. Consequently, race-car to those for road cars. However, steel pedals arethe expensive whenItscompared will offer best results. stiffness to for road cars. However, is as high assteel any for those a given weight will the bestand results. stiffness it isItseasier to otheroffer material, for a givenDesigning weight is as as any fabricate. an high aluminum other material, and itbecause is easier to be difficult of its pedal can fabricate. Designing an aluminum low stiffness. pedal difficult because its be of rigid. A can pedalbe arm must low stiffness. Therefore, it usually has a deep cross A pedal must has be arigid. section. A roadarm car usually flatTherefore, has a deep cross cross plate or itanusually open-channel section. Abutroad car usually has ause flat-a section, a race cars often plate or an open-channel cross tube. Tubular pedals are lighter for a section, but a race cars often useex-a given stiffness. However, they are tube. Tubular pedals toaremass lighter for a pensive and difficult produce. given stiffness. However, they are exWith a tubular pedal, a thin-wall tube pensive and difficult to mass produce. can be used and still have enough With a tubular pedal, a thin-wall tube stiffness. canA be used stillbehave enough pad and should shaped to fit pedal stiffness. the foot. A tiny pad is hard to push A pedal padand should to off fit with comfort your be footshaped can slip A tiny padpad is hard to push the foot. is about shoe easily. A good pedal with comfort and yourallows. foot can off width; wider if space A slip rubber easily. A good pedal pad is about shoe pad is used on road cars for aesthetics, A rubber width; wider if space comfort and grip. Forallows. race cars, a texpad used on cars for is used for aesthetics, maximum turedis metal padroad comfort andisgrip. For race cars, a texespecially important in grip. This tured metal pad is used for maximum grip. This is especially important in
Small pedal pads are in a Formula Ford road-racing car. These little single-seat racers have pads barelyare enough room for Ford the Small pedal in a Formula driver's feet,car. making small pedal pads a road-racing These little single-seat must. surfaces are made racersNonskid have barely enough roomfrom for exthe panded pads.pedal pads a driver's metal feet, welded makingtosmall
must. Nonskid surfaces are made from expanded metal welded t o pads.
open race cars that run in the rain. Some race-car pedals have an adopen racepad, cars that run in the justable adjustable to rain. suit the Some race-car pedals have an adare driver. Seats in many race cars justable pad, adjustable adjustable pedal to suit pads the fixed, so driver. Seats teo in many race cars are com pensa fixed, so adjustable pedal With adjustable pads, you can pads vary compensate. the distance between the steering Withand adjustable pads,This youwill canaffect vary wheel brake pedal. the distance between the steering arm position when the driver is seated wheel This adjustable will affect in the and car. brake A racepedal. car with arm position when the driver is seated pedal pads and seat can be made to in the A race carperfectly. with adjustable sui t thecar. driver nearly pedal pads and seat can be made to suit the driver nearly perfectly.
Room and weight are not a problem in this racing stock car, allowing big and sturdy pedal Such pedals not fit in a Room pads. and weight are not would a problem in this cramped Grand Prix-car cockpit. racing stock car, allowing big and sturdy
pedal pads. Such pedals would not fit in a cramped Grand ~ r i x - c acockpit. r
Pedal pad is adjusted by releasing jam nut and screwing pad in and out. Pad is welded to a bolt, threads a tapped Pedal padwhich is adjusted byinto releasing jamtube nut at top of pedalpad arm. Moreout. than l-in. of adand screwing in and Pad is welded justment movinginto driver's seat. tube to a bolt, requires which threads a tapped at top of pedal arm. More than 1 -in. of ad-
justment requires moving driver's If heel-and-roe brakeandseat. accel-
erator-pedal operation is desired, the heel-and-toe and acceltwoIf pedals should brakebe positioned no erator-pedal is desired, the I-I/2-in. apa rt laterally. more than operation two pedals should be positioned be adjus ted no so Also, the pedals should more than 1-112-in. apart laterally. that during hard braking , the brake Also, pedals adjusted so to should about be 1/4-in. above pedal the travels that during hard braking, the brake the accelerator pedal. pedal travels to about 1/4-in. above the accelerator pedal. PEDAL FORCES The two forces a pedal designer PEDAL FORCES must consider are: twoforce forces n everdesigner be ap• The Highest thata capedal must consider are: Highest force that can ever be ap67
ti-*hh, b*
4
Once wheels are locked, driver's strength is the only thing limiting brake-pedal force. As fear increases, the harder he pushes. This condition represents the maximum force that . Once can bewheels appliedare to a brake driver's system. strength Brake-pedal force maximum-deceleration, conlocked, is the onlyduring thing alimiting brake-pedal force. As trolled stop is much fear increases, the lower. harder he pushes. This condition represents the maximum force that
can be applied to a brake system. Brake-pedal force during a maximum-deceleration, controlled stop is much lower.
plied to a pedal. • Force normally applied in a hard pliedattomaximum a pedal. deceleration. stop Force hard These normally two forcesapplied are not inthea same. stop at maximum Maximum forcedeceleration. is considerably Thesethan twothe forces not theapplied same. higher force are normally Maximum force is considerably during a hard stop. To keep the terms higher thanthetheforce forcenormally normally applied applied separate, during aahard To iskeep the terms during hardstop. stop called pedal separate, normally applied effort. Thistheis force the force applied to a during hard stopwhen is called pedal pedal bya the driver he tries to is the force applied In to aa efforl. atThis stop maximum deceleration. pedal by pedal the driver he tries to race car, effort when is applied by the stop at almost maximum In a driver everydeceleration. time he brakes race car,This pedalis effort applied by thea the car. rarelyisthe case with driver almost every time he brakes road car. theDuring car. This rarely the case an isemergency, the with drivera road car.stop the car at maximum decelshould During an the emergency, theverge driver eration with tires on the of should stop the car at maximum decellockup. Often, though, a driver in eration theabout tires on the vergethe of trouble with forgets controlling lockup. Often,he though, a driver in car. Instead, panics and jams on trouble forgets about controlling the the brakes as hard as he can and locks car. Instead,Often he panics and jams and on the wheels. he loses control the brakes hard as heiscan and maxilocks skids. This as type of stop where the losesoccurs. control The and mumwheels. force Often on a he pedal skids. This type of stop is where maxipedal and linkage must be designed on ora pedal occurs. bend The mum not toforce break permanently pedal and condition. linkage must be designed under this not break or permanently bend Pedalto Effort-A high-performance under this condition. brake system usually is designed for Pedal 75-lb Effortpedal -A effort high-performance about at maximum brake system This usually is designed for deceleration. feels OK to most about pedal effort maximum people.75-lb Anyone personat can easily deceleration. This his feels apply 75 lb with leg.OK If to youmost are people. Any one person can designing a truck or race car, youeasily may Ib with his leg. you are apply wish to75use a higher pedalIf effort. A designing a truck you may 100-lb pedal effortoris race still car, manageable, wish use like a higher A but it tofeels a hardpedal push.effort. I don't 100-lb pedal effort is still manageable, recommend usin!1 more than 100 lb. I don't but it there feels would like a hard Then not bepush. any reserve
recommend using more than 100 lb. Then there would not be any reserve
68
force left for brake fade or other system failures . force for brake other Mostleftpassenger carsfade haveor powersystem failures. assisted brakes. With power assist, Most passenger powerpedal effort is usuallycars less have than 50 lb. assisted brakes. With power Maximum Pedal Force-A assist, heavy pedal usuallypush less with than 50 Ib. personeffort can iseasily a force Maximum Pedal Force-A heavy greater than his weight-about 300 Ib person canman. easilyIf push with aquickly force for a large he stomps greater than his weight-about 300 Ib on the pedal, the effect of the sudden for a large man. If he stomps force further increases stress quickly on the on the Engineers pedal, the know effectthat of the pedal. if asudden load is force further increases stress applied quickly, stress on a on partthe is pedal. Engineers know pedals that if aare loaddeis doubled. Most brake applied toquickly, stressthe on maximum a part is signed take twice doubled. brake pedals areI use de; force that Most a strong leg can apply. twice the maximum signed to take 600 Ib for designing pedals. force a strong legpedal can apply. I use Safetythat Factor-The should be 600 Ib for designing pedals. designed to withstand a force much Safety than Factor-The pedal force should be higher the maximum . The designed to withstand a force much ratio of the force required to break a higher the maximum force. The part to than the maximum applied load is ratio ofthe thesafety forcefactor. required to abreak called I use safetya part toofthe maximum applied load factor 3 on critical parts such as isa safe@ factor. I use a safety called the brake pedal. This means the part is defactor of on critical parts suchthree as a signed to 3break at a load at least brake pedal. This means the applied part is detimes the maximum force to signed to break at a loadthe at least three the part. Therefore, breaking times theformaximum forceshould applied strength a brake pedal be to at the part. Therefore, the breaking least 1800 lb, or 3 X 600 lb . strength a braketo pedal be at If you for wanted test should your brakeleast 1800 Ib, or 3 X 600 Ib. pedal design, apply an 1800-lb force youpadwanted to test your onIfthe in a direction in linebrakewith pedalforce design, the that apply wouldanbe 1800-lb applied force by a on the padfoot. in a Ifdirection in line with person's the pedal doesn't the force would be applied by a break, thethat safety factor is adequate. person's foot. If the pedal doesn't You may bend the pedal doing such a break,never the safety factor inis aadequate. testuse a pedal car after You may the strength pedal doing such a testing its bend breaking . test-never use a pedal in a car after The master-cylinder pushrod must testing its breaking strength. withstand the maximum pedal force
The master-cylinder pushrod must withstand the maximum pedal force
Bird's-eye view of formula-car pedal box: Note that pedal pad is not centered on pedal arm. view This oftwists pedal pedal arm when Bird's-eye formula-car box: driver pushes on pad. tubular arm Note that pedal pad Although is not centered on can withstand thistwists twisting load,arm pedal aspedal arm. This pedal when semblypushes would on be pad. stronger if padtubular and pedal driver Although arm arm were centered. can withstand this twisting load, pedal as-
sembly would be stronger if pad and pedal times thecentered. pedal ratio. Pedal ratio can be arm were
obtained by dividing pedal travel at times the pad pedalbyratio. Pedaltravel. ratio can be the foot pushrod Pedal obtained by dividing pedal travel at ratio is discussed in more detail on the the foot padpage by .pushrod Pedal following Also, travel. a push rod ratio is discussed more detail should always be in straight. One on thatthe is following page. Also, a pushrod straight is many times stronger than a should be straight. One that is bent or always offset rod. straight is many totimes stronger In addition normal load,than thea bent offset pedalormust berod. able to resist some side In addition normal load, the load. A driver'sto foot is not always pedal must be able to resist some side aligned with the pedal pad. The worst load. occurs A driver's not always case wherefoot the isdriver's foot aligned with the pad.This The puts worsta hangs halfway offpedal the pad. case force occurs the arm. driver's foot side intowhere the pedal I recomhangs halfway off the pad. This puts mend using a side load of 200 lb ona side force pad intointhe pedal arm. I recomthe pedal addition to the 600-lb mend using side of 200 Ib on forward load.a If youload apply the safety the pedal pad in addition to the 600-lb factor of of 3, the pedal should not forward load. Ifwith youa apply break if tested 600-lbthe sidesafety load factortheof pad. of 3, Note: the pedal not on The should side load break ifbetested withat athe 600-lb load should applied sameside time as othe n forward the pad. Note: The side load load. should be applied the same timeyou as All this suggestsat that perhaps the forward should leaveload. brake-pedal design to an All this Ifsuggests engineer. you arethat notperhaps trainedyou in should leave brake-pedal design to an stress analysis, a mistake here could engineer. If option you areis not trained in be fatal. An to use a pedal stress analysis, a mistake could that fits from another car. here All pedals be fatal. An using optionsimilar is to use a pedal are designed techniques. that fits from another car. All Safety factors may vary, but the pedals maxiare designed techniques. mum force ausing pedalsimilar can withstand is Safety the factors may but the maxiabout same forvary, all cars. Be aware mum force from a pedal cancarwithstand is that a pedal a road will probaabout the same for all cars. Be aware bly be stronger than a race-car pedal. that a pedal fromdesigners a road cartry willtoprobaMany race-car save
bly be stronger than a race-car pedal. Many race-car designers try to save
Bad pedal design on homemade race car has pedal arm off-center to pad and pivot housing. pushed on, twistrace of arm Bad pedalWhen design on homemade car causes excessive flexibility and has pedal arm off-center to pad andhigher pivot stresses. If arm were moved right,ofpedal housing. When pushed on, to twist arm would beexcessive stiffer and stronger. causes flexibility and higher stresses. If arm were moved to right, pedal would be stiffer and stronger.
weight at the expense of strength. If you insist on designing your own weight at the follow expense of strength. brake pedal, these rules: on designing Doyou not insist weld across a pedal your arm. own • If brake pedal, rules: when • Make the follow pedal these arm straight D o not weldtheacross a pedal viewed from driver's seat.arm. Make the pedal arm straight when • Use steel, not aluminum or other viewedalloys. from the driver's light Steel givesseat. maximum Use steel, not of aluminum or Weldother stiffness and ease fabrication. light alloys. Steel gives maximum ing drastically weakens aluminum. stiffness andtheease of fabrication. Weld• Position pedal arm in the center ingthe drastically aluminum. of pad - notweakens off to one side.
Position the pedal arm in the center of the pad-not off to one side. PEDAL PIVOTS Pivots in brake pedals should have
PEDAL plastic orPIVOTS bronze bushings to reduce Pivots in brake bushings pedals should have friction. Plastic are often plastic or road bronzecars bushings to reduce used on to reduce cost; friction. Plastic bushings often bronze bushings are found are on some used on road cars to reduce race cars. The best pedal pivots cost; have bronze bushings are found o n plastic some provision for lubrication. Most race cars.are T hdesigned e best pedal pivots withhave bushings to operate provision for lubrication. Most plastic out lubrication, but this does not bushings aremaximum designed durability. to operate withalways give outAvoid lubrication. but that this use doesunlunot pedal pivots always maximum durability. bricatedgive clevis pins or bolts. Some Avoid pedalhave pivots unlubrake pedals beenthat so use designed. bricated clevis pins or bolts. S o mofe They work for a while, but the lack brake pedals havearea been designed. adequate bearing andsolubrication They for athe while, buttothe lackout of usuallywork causes pivot wear adequate bearing area and lubrication rapidly. Then the pedal gets loose and usually causes theextra pivot pedal to wear out sloppy, requiring moverapidly. h e n up thethe pedal loose and ment to Ttake slop.gets Pedal movesloppy, ment is requiring a valuable extra item. pedal Don't movewaste ment to take up the slop. Pedal moveit with potentially sloppy pivots. ment is a valuable item. Don't waste it with potentially sloppy pivots.
Spherical bearings on master-cylinder pushrods minimize friction and wear. Neal Products pedal uses a balance bar with special spherical bearing at each end. Balls in spherical bearings are pinned to on allow motion in onlypushrods one direction. Ordinary would Spherical bearings master-cylinder minimize frictionspherical and wear.bearings Neal Products allow ends to cock, with potentially disastrous results. pedal rod uses a balance bar with special spherical bearing at each end. Balls in spherical bearings are pinned to allow motion in only one direction. Ordinary spherical bearings would allow rod ends to cock, with potentially disastrous results.
If you have a car with sloppy or unbushed pedal pivots, consider modifyyou have a car have with sloppy or un-a If you to enlarge ingIf them. bushed pedal pivots, consider modifyhole to install a bushing, make sure ing them. you have to enlarge a you don't If weaken a critical area. If hole are to install a bushing, you uncertain, leave it make alone.sure Or, you weakendoa acritical area. If have don't an engineer stress analysis you are uncertain, leave it alone. Or, of the modification. If you don't bush havepivots, an engineer a stress them analysis the at leastdolubricate at of the modification. If youwear. don't bush regular intervals to reduce
the pivots, at least lubricate them at regular PEDALintervals RATIO to reduce wear.
The force required on the masterPEDAL piston RATIOis usually much higher cylinder T h e force required o n the masterthan the pedal effort supplied by the cylinder piston is usually muchact higher driver. Thus, the pedal must as a than pedal effort supplied by the the force supplied by lever the to increase driver. Thus, The the pedal must act the driver. leverage of as thea lever to increase the force pedal-pedal rario-is alsosupplied known by as the driver. T h e leverage of the mechanical advantage. Pedal ratio for pedal-pedal as manual brakesratio-is is aboutalso 5 toknown 1; power mechanical advantage. Pedal pedal ratios are about 3 to 1. ratio for 1; powera manual is about If youbrakes plan to design 5 orto modify 3 to 1. pedal ratios are about brake system, you need to determine you plan design modify theIf pedal ratio.toThere areorthree waysa brake you need determine to do system, this. Choose the to method that the pedal There works best ratio. for you. Theyare are:three ways to do this. forces. Choose the method that • Measure works best for you. They are: • Measure movements. Measure forces. • Measure brake pedal and linkage Measure movements. geometry. MeasureForces-If brake pedal and measure linkage Measure you can geometry. the force on the pedal pad and the M e a s u r e Forces-If simultaneous force you on can the measure masterthe force o n the pedal pad cylinder piston, the pedal ratioand can the be
simultaneous force o n the mastercylinder piston, the pedal ratio can be
Typical road-car pedal design; pivot bolt and bushing are removed. Plastic bushings last longer if greased occasionally. Typical road-car pedal design; pivot bolt and bushing are removed. Plastic bushings last longer if greased occasionally.
calculated from this simple formula:
calculated from F this simple formula:
~ Fpp F M FMC Force on~ master cylinder in Pedal=ratio =pounds FPP FMc= =Force Force on master Fpp on pedal pad in cylinder pounds in
Pedal ratio
=
pounds
Forces are measured in inpounds; Fpp= Force on pedal pad pounds the pedal ratio is just a number. If you Forcespush are on measured pounds; could the pedalinwith a scalethe or pedal ratio isto just a number. you instrument measure force,If you could pushsimultaneously o n the pedal with ameasure scale or could instrument to measure force, you hydraulic-system pressure. If you could measure know the simultaneously master-cylinder-piston area, hydraulic-system pressure.into If force you pressure can be converted know the master-cylinder-piston area, on the piston.
pressure can be converted into force o n the piston. 69
FMc*q ~ ~ ~~ Master-Cylinder
i
-
<+-:/,
..;---'
~ I
-"1- ____ .1 I
Position
Master-Cy linder Position
Pedal Bracket
FMC = Force on Master Cylinder F pp = Force on Peda I Pad FMc = Force on Master Cylinder FMC Fpp =Ratio Force= on-Pedal Pad Pedal -
Pedal Ratio =-
Fpp
Fpp F~~
FPP
I V
Pedal ratio can be found by simultaneously measuring forces at pedal pad and master cylinder. Small spring scales may be used for this. Disconnect master-cylinder pushrod so it doesn't readings. sure one scale lines up with pushrod and other scale with Pedal ratioaffect can be found Make by simultaneously measuring forces at pedal pad and master line-of-action driver's leg. may See be drawing at right. Pushrod force divided by pedal force so is -cylinder. Smallofspring scales used for this. Disconnect master-cylinder pushrod pedal ratio.affect readings. Make sure one scale lines up with pushrod and other scale with i t doesn't
Steel tape is used to measure pedal-pad movement. Measure movement of mastercylinder piston at same time. Pedal travel Steel tape is used to measure pedal-pad divided by pushrod travel is pedalofratio. movement. Measure movement master-
cylinder piston at same time. Pedal travel divided by pushrod travel is pedal ratio.
line-of-action of driver's leg. See drawing at right. Pushrod force divided by pedal force is pedal ratio.
)~- - ---J
L MasterCylinder Position
Pedal ratio is equal to AlB. Pedal pivot is at point P. Force F, applied by driver, is multiplied by pedal ratio to produce a larger force at master cylinder. If driver applies 50 Ib and pedal ratio 4, force at to master cylinder is is200 lb. Trick in measuring A multiplied and B is Pedalis ratio is equal A/B. Pedal pivot at point P. Force F, applieddistances by driver, is measuring them to line-of-action of forces . If driver applies 50 Ib and pedal by pedal ratio t operpendicular produce a larger force at master cylinder. ratio is 4, force at master cylinder is 200 Ib. Trick in measuring distances A and B is
measuring them perpendicular to line-of-action of forces.
The force method requires special measuring equipment. So skip this The force method requires method, unless you have the special equipmeasuring equipment. So skip and this ment that will measure force method, unless you have the equippressure. ment that Movements-Pedal will measure force ratio and Measure pressure. can be found by measuring movement Measure Pedal ratio at the pedalMovementspad and master-cylinder can be found by measuring piston. Don't include movement movement at the pedal pad up andclearance master-cylinder needed to take or free piston. play. The Don't formula include for pedal movement ratio using needed to take movements is: up clearance or free
play. The formula for pedal ratio using Pedal ratio = is: ~pp movements MC
M Pedal ratio = 2 Mpp = Movement of pedal pad in MMC
inches Mpp == Movement pad of in MMC MovementOf in inches inches master-cylinder piston for a single or a MMc = Movement of tandem master cylinder, inor inches movement master-cvlinder tonbalance for a sinale or aa center pivot ofist the bar for of tandem master cylinder, or mo;ement car with dual master cylinders.
of center pivot of the balance bar for a car with dual master cylinders. 70
To use this formula , you must be careful to get the direction of moveTo use this formula, must be ment right. Pedal-pad you movement careful to get the direction of moveshould be measured through the full ment right. Pedal-pad movement stroke of the pedal. You will have to should be measured through thefrom full open a bleeder or drain the fluid stroke of the system pedal. You have to the hydraulic to dowill this . Start open a bleeder or drain the fluid from the measurement from the point the hydraulic system are to do this.out Start where all clearances taken of the linkage measurement from the the and the pushrod just point starts where all the clearances are taken piston out of. to move master-cylinder the linkage and the pushrod just To hold the pedal in this position,starts put move between the master-cylinder piston. ato spacer the pedal stop and To hold the pedal in this position, put pedal. a spacer thepoint, pedal move stop and Startingbetween from this the pedal. pedal all the way to the floor. Measure Starting from this point, full move the piston movement through travel pedal the way to thethe floor. Measure of the all pedal. Indicate starting and piston movement fullpad travel stopping points ofthrough the pedal by of the pedal. Indicate the starting and placing a piece of plywood or cardstopping points of pad by board alongside thethe padpedal and making
placing a piece of plywood or cardboard alongside the pad and making
' M Pedal Ratio =--EE.. MMC
Mpp = Pedal-Pad Movement MMC = Master-CylinderPiston Movement Mpp = Pedal-Pad Movement
MMC= Master-C.ylinderPedal ratio can Movement be determined from simulPiston taneous pedal-pad and mastercylinder-piston Measure Pedal ratio can bemovements: determined from simullarge movements to keep measuring errors taneous pedal-pad and mastersmall. Measure movements as shown. cylinder-piston movements: Measure
large movements t o keep measuring errors small. Measure movements as shown.
marks on it. Total movement of the pedal pad between the starting and marks onpoints it. Total of the stopping is Mmovement pp , or the number pedal the starting and to usepad inbetween the formula. MasterM,,,or the stopping points is cylinder-piston movement is number how far to the formula. the use pistonin moved down theMasterbore. cylinder-piston movement is howis far How to measure this movement ilthe piston moved down the bore. lustrated above. How to measure this ratio movement is ilFinding the pedal by measurlustrated above. ing movements gives an average pedal Finding ratio measurratio for thethe fullpedal stroke. It isbynot a very ing movements givesThe an average pedal accurate number. problem is ratio for the full stroke. It is not a very pedal ratio changes as the pedal accurate Theaccurate problem is moves. Tonumber. get a more pedal pedal ratio changes as the pedal ratio, use the method described
moves. To get a more accurate pedal ratio, use the method described
below. This uses the geometry of the pedal and linkage. It can give instantabelow. pedal This uses the neous ratio the at geometry any point of along pedal and linkage. It can give instantathe pedal movement. neous pedal ratio at any point along Pedal Geometry-Dimensions of a the pedal movement. pedal determine its ratio. Formulas to Pedal use for Geometry-Dimensions various pedal mountingsofarea pedal determine its ratio. Formulas to given in the drawing at left. Use the use for various pedal mountings are formula that matches your pedal given. in Use the setup In the eachdrawing formulaatis left. a distance A formula that matches your pedal and B. Measuring these distances acsetup. Iniseach is a distance curately the formula only problem. To do A it and Measuring these distances acright,B. you need to know the linecurately only problem. To do it of-action is of the the forces on the pedal. right, you need to know the lineThe line-of-action is drawn from of-action of the forces on the pedal. the driver's hip to the ball of his foot. The line line-of-action drawn from This changes, is depending on the driver's hip to his foot. where the pedal padthe is ball in itsoftravel. To This linematters, changes, on simplify pick depending a spot in the where the pedal pad is in its travel. To movement of the brake pedal to measimplify matters, pick a stick spot toinit.the sure lines-of-action-and movement of the brake to meaThe line-of-action for pedal a pushrod is sure lines-of-action-and stick to it. always a straight line joining the ends for pushrods a pushrodare is of The the line-of-action pushrod. Bra ke always a straight line joining the ends usually straight, so it is easy to of the pushrod. pushrods determine. If yourBrake pushrod makes are an usually straight, so it is angle with the pedal arm, be easy sure to to determine. If yourBpushrod measure distance at a 90°makes angle an to angle with the pedal arm, be nearby. sure to the pushrod. This is illustrated measure distance B at a 90" angle to If the brake-pedal linkage has an inthe pushrod. This is illustrated nearby. termediate mechanism, such as a If the brake-pedal linkage an beinbellcrank, determining pedalhas ratio termediate mechanism, such as comes more complicated. The pedala bellcrank, determining ratio beratio for the pedal itselfpedal can be meascomes more complicated. pedal ured using the methodsThealready ratio for the pedalyou itselfmust can be discussed . Then findmeasthe ured using the methods already leverage of the rest of the linkage. discussed. Then youthemust Call that leverage ratiofind of the the leverage Pretend of the rest the into linkage. linkage. the of force the Call thatis leverage ratio of the linkage the force the from a driver's linkage. Pretend the force leg , and treat the linkage the into samethe as linkage is the force from a driver's you would a pedal. When you find the leg, and" treat linkage the, multiply same as "pedal ratio the of the linkage you a pedal. When youto find it bywould the ratio for the pedal get the the "pedal" ratio of the linkage, multiply total brake-pedal ratio. The accomipanying t by thedrawing ratio forshows the pedal get the how atocomplex total brake-pedal The accomsystem is analyzedratio. for overall pedal panying drawing shows how a complex ratio. system analyzed for overall pedal and linkage geomet ry, Using ispedal ratio. pedal ratio can be found for a particupedal linkageYou geometry, larUsing position of and the pedal. should pedal ratiopedal can be found for a particumeasure ratio at several posilar position the pedal. You how should tions of theof pedal to see it measure Itpedal ratiotoatdraw several posichanges. is useful a graph of tions of the pedal to see pos how pedal ratio versus pedal-pad ition.it changes. is useful to draw graph of This givesIt you a picture of ahow your pedal ratio versus pedal-pad position. brake system works. You want a pedal This you aa picture how your that gives avoids radical ofpedal-ratio brake system works. as Youthewant a pedal change , particularly pedal gets that toavoids a radical pedal-ratio close the floor. change, particularly as the pedal Choosing the correct pedal ratiogets on close to the floor. a special car is a compromise because
Choosing the correct pedal ratio on a special car is a compromise because
PUSHROD LlNE-OF -ACTION
PUSHROD LINE-0F.ACTION
PUSHROD LEG LlNE-OF-ACTION FOOT -TO-PEDAL CONTACT POINT
E G LINE-OF-ACTIO FOOT.TO-PEDAL CONTACT P O I N T Line-ot-action ot leg is between pedal pad and driver's hip. Measure distance A perpendicular to this line. Distance B is measured perpendicular to line-ot-action of mastercylinder pushrod, Pushrods shouldpedal not be shown, but if one is, its line-of-action Line-of-action of leg is between padbent and as driver's hip. Measure distance A perpenwould pushrod ends.BDrawing by Tomperpendicular Monroe. dicularbetothrough this line. Distance is measured t o line-of-action of mastercylinder pushrod. Pushrods should not be bent as shown, but if one is, its line-of-action would be through pushrod ends. Drawing by Tom Monroe. Master Cylinder
Q
8
C;
a:
8 7 -g
poor-",,/
um
nrOJ
67 -0..3
---u a,
6-a 5r4 5
Pedal Ratio Linkage Ratio = = Overall Ratio =
J
Force From Driver's Leg
~L
~
L
X
~~
-
A AL Overall Ratio = - X If pedal operates a bellcrank, B through BL rocker or other linkage, pedal ratio alone is not the final answer. through Overall ratio between If pedal operates a bellcrank, driver's foot andlinkage, master cylinder is required rocker or other pedal ratio alone is for calculations. Once pedal not brake-system the final answer. Overall ratio between ratio is foot determined, ratio of intermediate driver's and master cylinder is required linkage is determined, When determining for brake-system calculations. Once pedal linkage force from is the same ratio is ratio, determined, ratiopedal of intermediate as force isfrom driver's foot. Note that linklinkage determined. When determining age pictured has afrom ratio lessis than 1.0. linkage ratio, force pedal the same Force from pedal is reduced by linkage beas force from driver's foot. Note that linkcausepictured AL is smaller B L , less than 1.0. age has than a ratio Force from pedal is reduced by linkage because A, is smaller than B,.
of conflicts between high and low pedal ratios. A low pedal ratio inof conflicts between high and and low creases pedal-linkage stiffness pedal inreducesratios. forcesAonlow the pedal pivots.ratio A high creases pedal-linkage stiffness pedal ratio reduces pedal effort and and reducesa forces on the pivots. high allows large-diameter masterAcylinpedal ratio reduces pedal effort and der to be used . I detail these trade-offs allows a large-diameter in Chapter 9. Total travelmaster at the cylinpedal der used. by I detail these 'strade-offs pad to is be limited the driver leg. His in Chapter 9. Total travel the pedal anatomy determines the at distance he pad move is limited by the driver's leg.floor His can his foot back from the anatomy determines he or accelerator pedal the to distance the brake can move his foot back from the floor pedal. If he has to stop quickly, he or accelerator pedal histofoot theverybrake doesn't want to move far.
pedal. If he has to stop quickly, he doesn't want to move his foot very far.
-
/ --;r-/
./
-----
-- --
Good ---"" A
Good
3 2 -
4 3
2
-
-
1 Retracted
o
1I
On Floor 2I
3I
4I
5I
Pedal-Pad Movement (in.)On Floor Retracted 0 shows 1 2 curves 3 of 4 5 Graph two pedal-pad Pedal-Pad Movement (in.) movement versus pedal ratio. Solid line is for a good changes Graph showsdesign-pedal two curves ratio of pedal-pad little with pedal movement; dotted movement versus pedal ratio. Solidcurve line is is poor-pedal ratio - changes ratio considerably, for a good design-pedal changes Angle changes pedal ordotted linkagecurve movelittle with pedalwith movement; is ment determines curve shape. considerably. poor-pedal ratio. changes Angle changes with pedal or linkage movement determines curve shape.
Pedal Movement-Another consideration is how far the brake pedal moves Pedal Movement-Another considerduring brake application. Most brake ation how far the the brake pedal moves pedalsjs move from retracted posiduring application. tion to brake the floor in less Most than brake 6 in. pedals move from retracted posimeasured at the pad.the Pedal movement tion to the floor in less than 6 in. must be less than this for safety and measured When at the pad. Pedal movement comfort. designing a special must less than for movement safety and brake be system, keepthis pedal comfort. When designing special during normal braking as ashort as brake system, keep pedal movement possible. during as shortThe as Let's normal review braking some basics: possible. brake pedal must supply movement some movement basics: The as Let's well asreview force. Pedal inbrake pedal must supply cludes all slop and clearancemovement takeup in as as system force. Pedal movement inthewell brake , movement of friccludes all slop and in tion material, and clearance combinedtakeup deflecthe brake system, movement of friction of all parts in the system . In
tion material, and combined deflection of all parts in the system. In 71
Tilton Engineering pedal-and-bracket assembly mounts dual master cylinders to rear. Assembly is used with hanging-pedal Tilton Engineering pedal-and-bracket asmount. Stock cars withmaster clearance problems sembly mounts dual cylinders to in engine compartment benefit from this rear. Assembly is used with hanging-pedal setup. Stock Mastercars cylinders install inproblems driver's mount. with clearance compartment, away from benefit engine heat. in engine compartment from this
setup. Master cylinders install in driver's compartment, away from engine heat.
Neal Products offers a complete line of pedals, brackets and other brake-system hardware for special cars. Neal pedals and brackets accept various master cylinders. Dual units shown include offers balance bar and are up for brackets floor mounting . Pedal and cylinders can be Neal Products a complete line set of pedals, and other brake-system hardware changed for cars. hanging-pedal installation. for special Neal pedals and brackets accept various master cylinders. Dual units
shown include balance bar and are set up for floor mounting. Pedal and cylinders can be
addition, extra movement must be available at the pedal pad in case there addition, extra lining movement must be is fade , non-flat wear, hot-lining available at the pedal pad in case there compression, or air in the brake fluid. is fade, non-flat lining wear, hot-lining Normal brake-pedal movement must compression, air in the be as short asorpossible to brake allow fluid. extra Normal brake-pedal movement must movement for these emergencies or be as short as possible to allow extra failures in a brake system . There 's movement emergencies or more if youfor ' re these working with a dualfailures in a orbrake brake system d rum system. brakes. There's more you're orworking with a dualIn a iftandem dual master-cylinder brake system or drum brakes. system , extra pedal movement must a tandem dual master-cylinder be Inprovided in or case one brake system system, extrahave pedal movement must fails. It must enough pedal travel be provided in case available to lock up one two brake wheelssystem when fails. It must travel the brakes arehave hot enough and one pedal system has available to lock up two wheels when failed . theInbrakes are hot overheating and one system has addition, drum failed. brakes can cause extra pedal In addition, movement. When overheating the drums getdrum hot, brakes can cause pedal they expand away fromextra the shoes. movement. When drums getmust hot, Consequently, the the brake shoes they expand away from the shoes. move farther. If the pedal hits the Consequently, the be brake floor, you may not able shoes to stopmust the move farther. If the pedal hits disc the car. This is not a problem with floor, brakes.you may not be able to stop the car.If you Thiscannot is not achieve a problem withtravel disc a pedal brakes. less than the 6-in. maximum , possible If you pedal assists travel cures are cannot bigger achieve brakes, apower lessother than the 6-in.changes. maximum, possible9 or design Chapter cures are bigger brakes, . power discusses this problem Beforeassists you or other design changes. Chapter panic , though , minimize each contri-9 discusses this pedal problem. Before Start you bution to total movement. panic,some though, minimize eachand contriwith careful measuring testbution to total movement. ing to find whatpedal is causing most ofStart the with some careful measuring and testpedal movement.
ing to find what is causing most of the
pedal movement. 72
changed for hanging-pedal SPECIAL PEDALS installation.
PEDAL BRACKETS
If you'd rather not design the brake SPECIAL PEDALS pedal, excellent aftermarket pedal asIf you'd are rather not design brake semblies available fromtheseveral pedal, excellent aftermarket pedal assources. Neal Products of San Diego, semblies are available from several California offers a complete line of sources. Products San Diego, pedals, Neal linkages and of other brakeCalifornia offers A a Neal complete of system hardware. ped al line assempedals, linkages and other brakebly can be purch ased with its own inteNeal pedal assemsystem hardware. gral bracket , Aincluding master bly can be. purchased with its own inte- . cylinders This assembly is easily gral bracket, including mounted on a special car. Neal master pedals· cylinders. This sizes assembly is easily come in various and mounting mounted on a special car. Neal configurations to suit most pedals applicome various sizes and mounting cations.in Winters Performance Prodconfigurations to suit most appliucts of York, Pennsylvania also offers cations. Winters Performance Prodsimilar pedal-and-master-cylinder asucts of York, also offers semblies with Pennsylvania integral brackets. similar pedal-and-master-cylinder A special brake-pedal assembly asis semblies with integral brackets. They offered by Tilton Engineering. A special is offer a racing brake-pedal brake-pedal-assembly and- bracket offered by Tilton Engineering. They assembly that positions the master offer a racing brake-pedal-and-bracket cylinders toward the rear of the car assembly positions master rather thanthat the front. This the installation cylinders toward the rear of the car is designed for stock-car and GT rather than the front. This installation racing, where having the master cylinis designed for stock-car and can GT ders in the engine compartment racing, where havingWith the master cylincause problems. rear-facing ders in cylinders, the enginethecompartment can master master cylinders cause problems. With rear-facing are not subject to heat from the master cylinders, thenot master cylinders engine, and they do interfere with are subject to heat fromvalve the parts notsuch as carburetors, engine, and they do not interfere with covers or headers, or with sparkplug parts such as , the carburetors, valve removal. Instead master cylinders covers headers, or with sparkplug end up or under the instrument panel or removal. thedisadvantage master cylinders front cowl.Instead, The one with end up under the instrument or this setup may be servicing thepanel master front cowl. The one disadvantage with cylinders.
The strength of a brake-pedal brackPEDAL et shouldBRACKETS match that of a properly deThe strength of a brake-pedal bracksigned brake pedal. It is essential to et should match that of a properly demount a brake pedal on a strong and signed brake pedal. It is essential to rigid bracket. In addition, the master mount a brake pedal on a strong and cylinder should be part of the brakerigid addition, the master pedal bracket. mount toInreduce the relative decylinder should be part of the. Forces brakeflection of the two assemblies pedal to reduce the relative deon themount brake-pedal bracket can ex ceed flection of the two assemblies. Forces 2000 lb, so it must be rigid . on the brake-pedal bracket exceed Otherwise , the bracket may can be danger2000 Ib, so it must be rigid. ous and can cause a spongy feel to the Otherwise, the bracket may be dangerbrake pedal. ous and can causeand a spongy feel to the Neal, Tilton Winters brake brake pedals pedal. come witb their own bracket, Neal,links Tilton and Winters which the pedal directly tobrake the pedals come with their bracket, master cylinder. This isown important. whichbracket links isthemounted pedal directly to but the The to the car, master oncylinder. This mounting is important. forces the bracket are The is mounted the car, butl lowerbracket than forces on theto brake-peda forces on the bracket mounting are pivot and master cylinder or the lower than forces on the brake-pedal pushrod . Still , the mounting of the pivot and master cylinder or This the pedal bracket to the car is cri tical. pushrod. Still, the mounting of mounting should also be rigid sothe it pedal bracket the to the car of is critical. This will support force the driver 's mounting shoulddon't also mount be rigid so it Therefore, a brake foot. will force of the pedalsupport on a flatthe sheet-metal firedriver's wall or foot. Therefore, don't mount a brake unreinforced floorboard . Mount the pedal on a flat sheet-metal fire or pedal in a corner or on a boxedwall beam unreinforced floorboard. Mount the so there won't be excessive deflection . pedal in aroad corner on a boxed beam Many carsor have brake-pedal so there won't be excessive deflection. brackets that can be adapted to other Many road have brake-pedal cars. Some havecars small compact brackbrackets that can be adapted to other ets that can be purchased with the cars.alsSome small compact ped for have a reasonable price. brackIt is ets thatbetter can beto purchased the much adapt an with existing pedals for a reasonable price. It is bracket-and- pedal assem bly to a car
this setup may be servicing the master cylinders.
much better to adapt an existing bracket-and-pedal assembly to a car
Pedal bracket on homemade sports car is built into frame structure. It pays to work in pedal-bracket design with frame ro"Pedal bracket on homemade sportsorcar is cage design. Save time, weight and built into frame structure. I t pays t o cost workby in planning ahead. design with frame or rollpedal-bracket
cage design. Save time, weight and cost by planning ahead.
than to design and build one yourself. It's a lot less expensive , too , to buy an than to design existing unit. and build one yourself. It'sMany a lot less expensive, too, tobrackets buy an race-car brake-pedal existing unit. are integrated into the frame Many race-car brake-pedal brackets structure. This approach is excellent if are integrated intoentire thecar. frame designing the Most you are structure. This approach is excellent if race-car frames have tubes or rigid you are designing the entire car. Most bulkheads that make excellent strucrace-car have pedals. tubes or rigida tures forframes mounting With bulkheads that makestructure excellent like struc-a sheet-metal large tures for mounting With a passenger-car fire wall,pedals. the mounting large sheet-metal likethea requires a special structure bracket for passenger-car fire wall, the mounting pedals. requires a special bracket fortypes the Pedal Location - There are two pedals. of brake-pedal mounts: floor-mounted Pedalhanging. Location-There are two and Both are used and types both of brake-pedal mounts: have advantages. Most floor-mounted modern road and use hanging. Bothpedals. are used andis both There a lot cars hanging have advantages. Most modern road of room under the dash for brackets, cars often use hanging pedals.column There is lot and the steering is asupof roombyunder the structure. dash for brackets, ported the same andHanging often the steering suppedals alsocolumn can beislong, ported same are ou tby ofthe sight andstructure. the pivots are less Hanging pedals also can be floorlong, than susceptible to corrosion are out of sight and the pivots are mounted pedals. Additionally, less the susceptible to corrosion than infloormaster cylinder ends up high the mounted pedals. Additionally, the engine compartment, where it is easy master cylinder endsadvantage up high of in this the Another to service. engine compartment, where it is easy is air bubbles rise to the master to service.then Another advantage of this cylinder, into the fluid reservoir. is air the bubbles rise istoself-bleeding, the master Thus, system cylinder, theat fluid reservoir. except forthen a fewinto spots the wheels. Thus, the system is self-bleeding, On low-profile race cars, floorexcept for apedals few spots the wheels. mounted areat more popular. On low-profile race Race-car design demandscars, a lowfloorCG, mounted pedals popular. so it's best to are keepmore components Race-car as design demands low CG, mounted low as possible.a Also, the so it's ofbest to keep components height the body nose of a rear- or mounted as low as Also, the midship-engine carpossible. is often deter-
height of the body nose of a rear- or midship-engine car is often deter-
Eagle Indy Car has large hole in pedal box for easy pedal access. Balance bar has remote brake-balance adjuster, so frequent access to the brake pedal is not required. Cable balance-bar adjuster (arrow) to knob panel. Eagle lndy Car has large holegoes in pedal boxon forinstrument easy pedal access. Balance bar has remote
brake-balance adjuster, so frequent access t o the brake pedal is not required. Cable balance-bar adjuster (arrow) goes to knob on instrument panel.
Sturdy universal bracket mounts dual master-cylinder-and-bracket assembly to frame roll cage. bracket Photo courtesy Sturdy oruniversal mounts Tilton dual Engineering. master-cylinder-and-bracket assembly t o Hanging pedal-and-bracket assembly is ready to mount in car. Unit includes pivot bushings, return spring and assembly pedal stop Hanging pedal-and-bracket is (arrow)t o . . Such assemready mountbracket-and-pedal in car. Unit includes pivot blies can return be found in junkyards a bushings, spring and pedal for stop modest (arrow). price. .Such bracket-and-pedal assem-
frame or roll cage. Photo courtesy Tilton Engineering.
blies can be found in junkyards for a modest price.
mined by the height of the driver's feet inside the cockpit. If hanging mined by used, the height of theheight driver's pedals are the added refeet inside the cockpit. If hanging quired above the driver's feet raises pedals are used, added height re-a the height of thethe nose. Therefore, quired abovecar theor driver's feetusually raises formula car racing sports the floor-mounted height of the nose. has pedals.Therefore, a racing sportscylinders car or formula car usually Master with floorhas floor-mounted pedals. mounted pedals are difficult to Masterunless cylinders floorservice, they are inwith front of the mounted pedals are difficult front suspension. The balance bar to is service. unless areWorst in front of , the also difficult to they adjust. of all air L s ~ e n stends i o n to end up at barthe is in the ssystem also difficult to adjust. all, air wheels rather than Worst the of master in the systemandtends to end (s). up atConthe cylinder(s) reservoirs
wheels rather than the master cylinder(s) and reservoirs(s) . Con-
Hanging pedals are neat and package we" in most large cars. Such a setup with dual Inangins pedals are and package wel: master cylinders canneat be difficult to adjust, particularly when a hurry-just inmost large cars. you're such ainsetup with dual the place for a remote adjuster. master cylinders can be difficult to adjust,
particularly when you're in a hurry-just the place a adjuster.
73
BALANCE BARS VS. ADJUSTABLE BALANCE BARS VS. PROPORTIONING VALVES
ADJUSTABLE Both a balance bar and an adjustPROPORTIONING able proportioning VALVES valve can be
Stock car uses tandem master cylinder and adjustable proportioning valve mounted in cockpit. drivermaster simplycylinder moves Stock car usesThe tandem leveradjustable on valve to adjust brake balance. It and proportioning valve mountwould've been difficult to use dual master ed in cockpit. The driver simply moves cylinders with to a balance bar because lever on valve adjust brake balance. of It frame-tube interference. would've been difficult to use dual master
cylinders with a balance bar because of frame-tube sequently, interference. floor-mounted pedals usu-
ally are more sensitive to air buildup
sequently, floor-mounted pedals usuin the system. As a result they require ally are more sensitive to air buildup more frequent bleeding. in Brake-fluid the system. As a result they reservoirs for arequire floormore frequent mounted pedalbleeding. often must be remote Brake-fluid reservoirs a floorfrom the master cylinders.forThis adds mounted pedal often must be remote complexity to the brake system . In from the dirt master cylinders. Thisshoes adds addition, from the driver's complexity the pedal brake linkage system.and In can get intoto the addition, dirt from the driver's shoes cause problems; hanging pedal lincan the pedal kagesget stayinto relatively clean. linkage and cause problems; use hanging pedalpedal linTo summarize, a hanging kages mountstay if relatively possible. clean. If not, a floorTo summarize, a hanging pedal mounted setup wi lluse work even though mount if possible. If not, a floorit has disadvantages. mounted setup will work even though BALANCE BARS it has disadvantages.
Bath bar relationship and an adjustused ato balance change the beable valve can;;l$F tween proportioning front- and rear-brake hydrauused to change and, the.rqlatians.hip.boL' lic pressure consequently, tween andHowever, tBar-brake hydraubrake fronfbalance. they work lic pressure and, consequenlly, in different ways. brake balance. However, work A balance bar divides they the pedal In dllferenl ways. force between two separate master A balance divides ratio. the pedal cylinders in bar a preset This force between two be aparate master ratio can adjusted by cylinders a p rpivot e e f .ratio. moving theIncenter of the This balcan ha adjusted by force tatio closer ance bar to one mastermoving centerorpivot of thethus, balcylinderthe pushrod the other, ance bar closer increasing pressureto inone one rnastersystem cylinder pushrod the other, ano reducing it in w another. On thus, most jncreaslng in mecylinder $yslem road cars, aprMaure tandem master and reducilig another. most is used, whichit in cannot be On changed road cars,brake a tandem master cylirlder to adjust balance. is used, which cannot be changed to adjust brake balance.
-
An adjustable proportioning valve varies the ratio of front-to-rear An adjustable v.qlve brake pressure proportioning in the direction of varies thebrakes ratio above of front-lo-liar' the front a preset brake pressure in the The direction changeover pressure. valve of is the frontplaced brakesin above a preset usually the rear brake mangeover pressu:t?~~~Tfi~~FBlve @'i system to compensate for weight udually .in ' rear-wheel w r brafit transfer placed to prevent sysfehn t~ mrnperigete tor weight lockup under hard braking. transfer to prevent A proportioning valveroar-wheel gives a lockup under hard braking.hydraulicfront-to-rear brake A propbrtloning valve a pressure relationship that gives approxifront-to-rear brake hydraulicmates the ideal relationship for varipressure thet approxlous valuesrelationship of tire grip. A balance bar mates theautomatically Ideal relationship br varldoes not compensate ous values ofintire for variation tiregrip. grip.A balance bar dm6 not aaubrnatlcallyproportioning -comprnsate Nonadjustable tr3r variation tire grip. valves are in used on most modern Wonad]ustabie praportionlng road cars . An adjustable proportionvalves are on most ing valve canused be easily addedmodwn to any road An adjustable proportionbrakecars. system to make the balance Ing valve can be easily added to any adjustable within a limited range. brdce system to maka t k belance
.N€i
adjustable within a llmited range.
Rear-Brake Master Cylinder
A balance bar is used to adjust the
BALANCE BARS brake balance for only one value of A balance bar isnot used to adjust the tire grip. It does compensate for brake balance for only one value changing traction conditions the wayofa tire grip. It does not compensate for proportioning valve does. For this changing traction bars conditions reason , balance usuallythe areway nota proportioning valve does. For this used on a road car. reason, balance bars usually are race not Balance bars are used on most used with on a road cars dual car. master cylinders. The Balancebar barsproportions are used on the mostforce race balance cars with dual master cylinders. from the brake pedal to the The two balance bar proportions the force master cylinders. Most balance bars fromadjustable the braketo pedal two are vary to the the braking mastergoing cylinders. Most balance force to the front and bars rear are adjustable theand braking cylinders, thus tothevary front rear force going to the front and rear brakes. The most-exotic balance bars cylinders, thus bythe can be adjusted the front driver and from rear the brakes. The most-exotic balance bars cockpit. canThe be adjusted the driver the simplest by balance bar isfrom a cross cockpit. link, or beam. The brake pedal pushes simplest balance cross onThe a pivot near the centerbar of isthea cross beam.then The pushes brake pedal pushes link, or link, which on the two on a pivot near the center of that the cross master-cylinder pushrods are link, which pushes two. mounted to then the ends of on thethe beam master-cylinder pushrods that are Where the brake-pedal pivot is in relamounted themaster-cylinder ends of the beam. tion to thetotwo pushWhere the brake-pedal pivot is in relation to the two master-cylinder push74
Pedal Pushrod
Pedal Pushrod Force From Pedal Simplest balance bar is a link with three holes. Ratio between front and rear brake pressure is determined by proximity of center hole to outer holes. To adjust this type of balance bar, it must bebalance replacedbar with newwith bar with in between a different place. Simplest is aa link threecenter holes.hole Ratio front and rear brake pressure
is determined by proximity of center hole to outer holes. To adjust this type of balance bar, it must be replaced with a new bar with center hole in a different place.
rods determines front-to-rear brake balance. Some balance bars can be rods determines front-to-rear adjusted; some cannot. A simplebrake balbalance. Some balance ance bar is shown above .bars This can type be is adjusted; someascannot. A simple balnot adjustable is. ance bar are is shown above. balance This type is There other simple bars not adjustable as is. that are adjustable, but not easily. Thereorare other simple balance Shims washers must be movedbars to that arebrake adjustable, not can easily. change balance. but Balance be Shims or washers be , moved to determined throughmust testing and once change brake balance. Balance can be set, it never gets changed again. determined testing, For racing,through a balance bar and mustonce be set, it neveraccording gets changed adjusted to again. track conFor racing, a balanceif bar ditions. For instance, the must track be is adjusted the according to should track beconslippery, balance bar additions.toFor thethe track is justed giveinstance, less forceif on front
slippery, the balance bar should be adjusted to give less force on the front
brakes . Less forward weight transfer with a slick track means the front brakes. must Less forward wheels do less weight braking.transfer If the with slickgood tracktraction, means the the front track ahas front wheels less more braking.braking. If the brakes must shoulddo do track has good traction,would the front Balance-bar adjustment then brakes should do more braking. be made to give more front-braking Balance-bar adjustment would then force. Normally, the balance bar be made give more front-braking would be toadjusted during a prerace force. Normally, thethebalance bar practice session. Once race starts, would be adjusted during a prerace the bar is left alone . practice session.inOnce the race equipstarts, The ultimate sophisticated the bar is left alone. ment is a balance bar that can be adThe ultimate in sophisticated equipjusted by the driver during a race . If ment is a balance thator can adthe driver desires bar more lessbefront justed the driver duringchange, a race. he If brakes by as track conditions
the driver desires more or less front brakes as track conditions change, he
eR Simple Link
FL
Simple Link
Pedal Arm MasterCylinder Pushrod
Homemade balance bar is not good because it is weak and hard to adjust. Threaded rods are not strongbar in bending-a failure Homemade balance is not good becould Correctly engineered cause be it isdisastrous. weak and hard t o adjust. Threadbalance barsnot are large in atbending-a the center failure where ed rods are strong stresses are highest.Correctly Also, balance bar could be disastrous. engineered probably would if one master-cylinder balance bars arebind large at the center where pushrod moved much Also, more balance than other stresses are highest. bar pushrod. would bind if one master-cylinder probably
pushrod moved much more than other pushrod.
Neal Products' adjustable balance bar : Center ball slides in tubular housing welded into pedal arm. Turning threaded Neal Products' adjustable balance bar: bar moves right housing or left Center ball center slides bearing in tubular inside pedal housing. welded into pedal arm. Special Turning spherical threaded bearings have threads inside bore bar moves center bearing right and or pins left (arrows)pedal to restrict ball Special movement to only inside housing. spherical pivoting one threads direction. bearingsinhave inside bore and pins
(arrows) to restrict ball movement to only pivoting in one direction.
Fs Adjustable Balance Bars
FBBalance-Bar Center Pivot Fs = Force on Adjustable Balance Bars
FL = Force on Left Master Force on (Ib) Balance-Bar Center Pivot FB = Cylinder
FL = FR = Force Force on on Left RightMaster Master Cylinder Cylinder (Ib) (lb) Force on From Right Center Master Pivot to FR== Distance d l Cylinder (Ib) (in.) Pushrod Left dL = Distance Distance From From Center Center Pivot Pivot to to d R = Left Pushrod(in.) (in.) RightPushrod dR = Distance From Center Pivot to Right Pushrod (in.) FL =
qdSR) +
FB = FL FR Compute forces on master cylinders with formulas given above. If center bearing (F L) is moved toward front-brake pushrod, Compute forces on master cylinders with front brakes getabove. more hydraulic formulas given If centerpressure bearing and versa.toward Note that sphericalpushrod, bearing (F,) vice is moved front-brake in bottom drawing is off-center pedalfront brakes get more hydraulic in pressure arm vice housing. It Note slidesthat sideways when adand versa. spherical bearing justing screw is turned. Distances from in bottom drawing is off-center in pedalspherical-bearing center to pushrod arm housing. It slides sideways whenbearadings determines balance-not distances justing screw is turned. Distances from from center of pedal arm. to pushrod bearspherical-bearing center ings determines balance-not from center of pedal arm.
distances
can make the change. For example, if it rains, and traction suddenly drops, a can make brake-balance the change. For example, isif adjustment rearward it rains, and required. It traction takes asuddenly skilled drops, race-cara rearward adjustment is driver to brake-balance know when a brake-balance required. It takes a skilled race-car change is needed. driver to know when a brake-balance In-cockpit adjustable balance bars change are usedisinneeded. Grand Prix cars and similar In-cockpitmachines, adjustablewhere balance bars high-priced the drivare used in Grand Prix cars and similar ers are sufficiently skilled to make use high-priced where the drivof the featuremachines, . ersThe are sufficiently skilled to make use most popular balance-bar
of the feature. The most
.popular
balance-bar
Neal pedal assembly is fitted with remote adjuster that can be operated by driver. Handle is mounted so adjustments can be made while racing. Driver must be able to sense need for brake-balance changes beforewith he can use adjuster that effectively. Neal pedal assembly is fitted remote can be operated by driver. Handle is
mounted so adjustments can be made while racing. Driver must be able t o sense need for brake-balance before use adjusterSetting effectively. up a balance bar can be design is one changes where the barhe is can mount-I difficult. First , choose master-cylinder ed in the pedal arm . A spherical bearSetting up a balance bar becan design is one where the bar is mountsize(s) so the balance bar can set be in ing rides inside a tube welded into a difficult. First, choose master-cylinder ed pedal arm. A spherical the center for average track holein inthethe brake-pedal arm . Thebearbalsize(s) so the be setnot in ing rides a tube welded into a conditions. A balance balance bar barcan should ance bar isinside a high-strength rod mountthe center for average track hole in the brake-pedal arm. The balbe used to compensate for the wrong ed firmly inside the bore of the sphericonditions. A balance bar (s). should not ance bar is a high-strength master-cylinder diameter If you cal bearing. A clevis to rod eachmountbrake be used compensate forbar the awrong ed firmlyisinside the bore of the need to to vary the balance great pushrod mounted at each endspheriof the . If youto master-cylinder clevisistothreaded each brake cal deal from the diameter center (s) position rod. bearing. Each endA fitting so a need to vary the balance bar a great pushrod is mounted at each end of the obtain proper brake balance, a change turn of the rod will move the spherical deal from the center position to rod. Each endorfitting is threaded so a in a master-cylinder diameter would bearing right left inside the pedal obtain proper balance, a change turn of theforce rod will move the spherical be better. The brake balance-bar adjustment arm. The on the bearing is then in a master-cylinder diameter would bearingtoright or left pedal range should be sufficient to compencloser one end of inside the rod,themaking be better. T h e balance-bar adjustment arm. The force on the bearing is then sate for conditions encountered at the that master cylinder share more of the range closer one and endthe of other the rod, track. should be sufficient to compenbrakingtoforce less.making sate formotion conditions the that master cylindercars share of the Most road-racing usemore adjustable The of aencountered balance bar atmust track. braking force and the other less. balance bars. You can adapt one of allow one master cylinder to operate Mostto road-racing carscan usepurchase adjustablea The the motion of aone balance bar must when other bottoms. The these your car. You allow one masterbecylinder to operate balance adapt one of balance bars. bar You from can Neal Products, system should designed so the when the not other The these toEngineering, your car. You can purchase Tilton Winters Perform-a pedal does run one au t ofbottoms. travel before system should be designed so the balance bar from Neal Products, both master cylinders bottom. Someance Products or other racingpedal notoverlook run out this of travel before Tilton Engineering, times does people , so difficulcomponent outlets. Winters Perform-
ance Products or component outlets.
other
racing-
both master cylinders bottom. Sometimes people overlook this, so difficul75
Handle in upper left corner of Indy Car instrument panel adjusts balance bar. Slots in handle mount provide positive setting and lock handle in position. Handle in upper left corner of lndy Car instrument panel adjusts balance bar. Slots in handle mount provide positive setting and lock handle in position.
Hanging pedals operate reverse-mounted master cylinders installed above pedal box. Setup gets master cylinders out of engine As shown, balance bar must be cylinders able to operHangingcompartment. pedals operate reverse-mounted master inate at extreme one Setup hydraulic system fails.cylinders out of stalled above angles pedal if box. gets master engine compartment. As shown, balance bar must be able to operat extreme angles if positive-return one hydraulic system fails.built into the stops deal.ateThis potential
stroke a great movement should be checked using stroke a great deal. during This potential accurate drawings design. movement should be checked using should be Actual balance-bar action accurate ondrawings during adesign. checked the car by opening bleedActual balance-bar actionandshould be er on one brake system stroking checked on the car by opening a bleedthe pedal. This forces the balance bar er on one brake system and stroking to move into extreme angles.
Upper end of production road-car hanging pedal is equipped with return spring, pedal stop pushrod. Pedal stop is rubber pad Upperand end of production road-car hanging at endisofequipped arm to right-it's not adjustable. pedal with return spring, pedal Hairpin-type return spring around stop and pushrod. Pedal stopwraps is rubber pad pivot housing. at end of arm to right-it's not adjustable. Hairpin-type return spring wraps around pivot housing.
Stop for Piston Adjustable Pushrod (Too Long) Adjustable Pushrod
If piston can't return to its retracted position, seal covers compensating port and brakescan't won't fully torelease. Adjust If piston return its retracted pedal stopseal or pushrod move piston back position, covers tocompensating port in its brakes bore. If pedal or pushrod be and won'tstop fully release. can't Adjust adjusted, master cylinder pedal stopshim or pushrod to moveforward. piston back in its bore. If pedal stop or pushrod can't be ties ariseshim in emergency situations. adjusted, master cylinder forward.
A balance bar must not bind when ties arise inatemergency situations. operating extreme angles possible A balance bar must not bindstrokes when when one master cylinder operating at extreme angles possible much more than the other. For when oneboiling master strokes example, fluidcylinder or a slow leak muchrequire more one thanmaster the cylinder other. For may to
example, boiling fluid or a slow leak may require one master cylinder to
76
the pedal. This forces the balance bar to move into extreme angles. RETURN SPRINGS & PEDAL STOPS RETURN SPRINGS & There must be a return spring to PEDAL STOPS push a brake pedal back to its retracted There when must the be brakes a return to position are spring released. push areturn brake pedal retracted The springback thatto its pushes the position when thepiston brakesback are released. master-cylinder can also The spring thatpedal pushes the returnreturn the pedal, if the is light, master-cylinder piston back can also the pedal is mounted vertically, and return the have pedal,low if friction. the pedalOn is some light, the pivots the pedal mountedreturn vertically, road cars, is a separate springand is the pivotson have friction. Onsure some mounted the low pedal to make it road cars,Ona separate return is returns. race cars, the spring mastermountedreturn on thespring pedal (s) to make it cylinder usuallysure does returns. thejob. On race cars, the mastercylinder return usually does A brake pedalspring(s) must have a positive the job. stop in the retracted position. This poA brake have a positive sition must pedal alwaysmust be the same so the stop incan the find retracted position. This podriver the pedal immediately. sitionpositive must always thepushrod same sousuthe The stop orbethe driver can find the pedal immediately. ally is adjustable to make sure the The positive stoppiston or the returns pushrod fully. usumaster-cylinder allytheispiston adjustable to make sure the If is prevented from reachmaster-cylinder piston returns fully. ing its retracted position, the ports in If pistoncylinder is prevented fromopen reachthethe master may not as ing itsshould retracted the pressure ports in andposition, hydraulic they the build, mastercausing cylinder may brake not open will severe drag. as they should and hydraulic pressure With the pedal in the retracted posiwill severe drag. tion build, againstcausing its stop, therebrake should be a Withamount the pedalofin the small free retracted play in posithe tion against its stop, thereThis should be a master-cylinder pushrod. ensures small of free piston play in the that theamount master-cylinder is fully master-cylinder pushrod. This ensures retracted. Most road cars have that the master-cylinder piston is fully retracted. Most road cars have
master cylinder or brake booster. If positive-return stops built the your car has an external stop,into see the master cylinder brake adjustment booster. If shop manual or for your car has an external stop, see the instructions. shop for adjustment If youmanual are designing your own instructions. system, be careful not to use a sepaIf return you are designing your ifown rate spring on the pedal the system, not from to useits asocket sepapushrod be cancareful be pulled rate return spring on thepiston. pedal ifMost the in the master-cylinder pushrod can be pulled from its socket pushrods are retained in the piston, in the master-cylinder Most but some are loose. If a piston. return spring pushrods retained in thethan piston, the are pedal back faster the forces but some are loose. If a return spring master-cylinder piston, the pushrod forces than can fall the out pedal unlessback it is faster retained in the the master-cylinder piston. Therefore,piston, use onlythe the pushrod mastercan fall out unless it isspring retained in the cylinder-piston return to retract piston. Therefore, use only the masterthe pedal if the master-cylinder pushcylinder-piston return spring to retract rod is not retained to the piston. theAllpedal if theand master-cylinder pushtandem most single master rod is not retained to the piston.so that cylinders are strong enough tandem mostmaster-cylinder single master theAll closed endand of the cylinders are strong enough that bore can be used as the forwardsopedal the closed master-cylinder stop. If youend are of notthe sure about this or bore can be used as the forward pedal don't want to bottom the masterstop. If you are not sure about this or cylinder piston for fear of damage, indon't want to bottom the masterstall a forward pedal stop. Many cars cylinder piston for fear of damage, inuse the floorboard as the stop. If you stall forward pedal stop. Manyin cars use aa stop, allow some stroke the use the cylinder floorboard as the you master with the stop. pedalIf hard use a stop, allow some stroke in the against the floorboard. master cylinder withpedal the pedal hard Test the forward stop when against thethe floorboard. you bleed brakes. With the bleeder Test the pedal when screws open,forward push the pedalstop gently all you bleed the brakes. With the bleeder the way down. Make sure it is hard screws push the floor pedalbefore gently the all against open, the stop or the the way down. Make it is hard master-cylinder piston sure bottoms. The against the stophave or the floor1/16 before piston should about in. the of master-cylinder piston bottoms. travel left before it bottoms. If The the piston hits should about 1/16sure in. of pedal thehave floor, make it travel left If the cannot get before jammedit inbottoms. the carpet or pedalother hitsobject. the floor, make sure i t any
cannot get jammed in the carpet or any other object.
Power Assist
7
Girlock LSC 50 vacuum booster and tandem master cylinder has threaded rods passing through booster from master-cylinder mounting flange. Rods transmit forces on master-cylinder mounting flange directly to booster mounting bracket . Because booster chamber is not loaded forces from master cylinder, booster master is lightercylinder than it would otherwise be.passing Boosterthrough weighs only 4 lb.from Photo courtesy Girlock Ltd. Girlockby LSC 50 vacuum booster and tandem has threaded rods booster master-cylinder mounting
flange. Rods transmit forces on master-cylinder mounting flange directly to booster mounting bracket. Because booster chamber is not loaded by road forcescars fromand master cylinder, lighter than it wouldthe otherwise Booster weighs Photo courtesy Most a few large booster race ismounted withGirlock less Ltd. servo canonlybe4 Ib.designed behind master be. cylinder.
cars use power assist-boosters-to Most braking road carseffort. and a A fewcar large racea reduce with cars use power assist-boosters-to power assist is said to have power reduce braking effort. the A brakes car with brakes. To the driver, feela power assist said stopping to have power; power like they haveismore brakes. Toit's thejust driver, thepedal brakes feel however, lower effort. like they have more stopping power; Most power-brake systems are dehowever, it'sa just effort. signed with lowerlower pedal pedal ratio so the Most power-brake systems are dedriver also senses less pedal travel. signed with a lower pedal ratio so Power brakes can fade the same the as driver also brakes. senses less pedal travel. standard Luckily, power Power can fade sameperas brakes brakes are reliable and the usually standard brakes. Luckily, form well for the life of the car. power brakes are reliable andbrakes usuallycomes perThe power in power form well for the life of the car. from a uni t called a brake booster. It is The power in power comes usually mounted on thebrakes fire wall befrom a unit called a brake booster. is tween the brake- pedal linkage and Itthe usually mounted on the fire wall bemaster cylinder. The brake booster tween like the abrake-pedal andtype the looks large tank, linkage if it is the master The vacuum. brake booster operatedcylinder. by engine Some looksuse likea ahydraulic-powered large tank, if it is the type cars booster operated by engine vacuum. Some that looks like a complex valve
cars use a hydraulic-powered booster that looks like a complex valve
Whatever the design of the booster,
mounted the master cylinder. they all dobehind the same thing-add extra Whatever the design of the booster, force to the master cylinder when the they allpushes do theon same driver the thing-add brake pedal.extra The force the driver master pushes, cylinder the whenmore the harderto the driver the pushes on the brake force booster adds. Thepedal. effectThe to harder theis driver the more the driver reducedpushes, pedal effort. force the brakes booster are adds. Theoneffect to Power used heavy the driver pedaldisc effort. cars and is onreduced cars with brakes. Powerassist brakeswasareused used before on heavy Power the cars and on cars with disc switch was made from drums tobrakes. discs. Power most assist large was used beforepower the Now, cars use switch madesmall fromcars drums to discs. brakes. was M any using disc Now, largepower cars assist. use Power power brakes most also have brakes. Many small cars using disc assist makes the job of designing brakes have assist.thePower brakes also easier. Forpower example, disc assist jobaction of designing brake'smakes lack ofthe servo requires brakes For example, theforce disc more easier. master-cylinder-piston brake's lack of servo action requires than a drum brake . If a drum brake is more master-cylinder-piston force designed with a large servo action, it than a drum brake. If a drum brake is can stop a heavy car without power designed with a large servo action, it assist. With power assist, drum brakes can stop a heavy car without power assist. With power assist, drum brakes
action. That makes them less affected can be designed with less shoes servo by changes in friction between action. That makes them less affected and drum. Thus, a car can have drum by changes in friction between shoes brakes that are more fade resistant by and usingdrum. powerThus, assist.a car can have drum brakes are more fade resistant by Manythat early power-brake systems using too power assist. The power assist were sensitive. Many early systems was so great thatpower-brake the slightest push on were too sensitive. The power assist the brake pedal locked the wheels. was so great the from slightest on, Nothing was that gained this push design the the brakebrakes pedalwere locked the wheels. and dangerous . In a Nothing was gainedwith from overassisted this design, panic situation and the brakes were dangerous. In a brakes, it is nearly impossible to avoid panic situation with overassisted locking the wheels and losing control. brakes, it is nearly avoid Fortunately, mostimpossible modern topowerlocking the wheels losing control. brake systems are and designed to feel Fortunately, most modern system. powermore like an unboosted brake systems are designed to feel Therefore, a driver should have few more likewith an aunboosted system. problems later power-brake Therefore, a driver have with few system. Power assistshould combined problems with a later power-brake the consistency of disc brakes gives system. Power assist combined the modern car excellent brakes. with
the consistency of disc brakes gives the modern car excellent brakes. 77
1_--- Fire Wall
SaO-psi Hydraulic Pressure
500-psi Hydraulic Pressure Master Cylinder - - - _ ' l l ~SOO-Ib
Master Cylinder
Force
b1 - 005 -&r >
Vacuum Hose Intake Manifol
-Brake
Pedal
Valve Rod
Force
Piston Area = 1 sq in . Hydraulic-Cylinder Force & Pressure Piston Area = 1 sq in. \:' 10-psi Vacuum Hydraulic-Cylinder Force & Pressure BoosterSaO-lb. \ Diaphragm Force Area = BoosterAddedb.to 500-1 Diaphragm 50 sq in. Master I Force Area = Cylinder ' I Added to 50 sq in.
JjjT _--__..... ~II
Typical vacuum-booster setup : Intake manifold supplies vacuum to booster. Brake pedal pushes directly on booster-valve rod, which controls force booster applies to master cylinder. If vacuum supply dropsIntake to zero or booster fails,vacuum a mechanical linkage operates Typical vacuum-booster setup: manifold supplies to booster. Brake pedal master-cylinder by pushing harder on pedal. Effort increases pushes directly piston on booster-valve rod, which controls force boostersignificantly applies t o without master boost. Drawing courtesy Bendix Corporation. cylinder. If vacuum supply drops to zero or booster fails, a mechanical linkage operates
master-cylinder piston by pushing harder on pedal. Effort increases significantly without boost. Drawing courtesy Bendix Corporation. Diaphragm
Booster Housing ~_ _
Vacuum Line
OpenTo Atmosphere
1O-psi Vacuum Zero-psi Atmospheric Pressure
Zero-psi Atmospheric Piston F
=
Force on Master Cylinder Piston
Pressure on diaphragm is difference between vacuum and atmospheric pressures. Because F = Force on Master Cylinder Piston vacuum is below atmospheric pressure, it is given a minus value. In this example -10 psi is in vacuumonside of chamber and 0 pSi-atmospheric in other side. Vacuum of Pressure diaphragm is difference between vacuumpressure-is and atmospheric pressures. Because -10 psi is vacuum below atmospheric i t is given a minus value. Inbut thisresulting exampleforce -10 psi is gives same force as 1pressure, O-psi pressure above atmospheric, is in oPPosite in vacuumdirection. side of chamber and 0 psi-atmospheric pressure-is in other side. Vacuum of
-10 psi gives same force as 10-psi pressure above atmospheric, but resulting force is in opposite direction.
VACUUM-BOOSTER TYPES Most power-brake systems use a VACUUM-BOOSTER TYPES booster operated by vacuum from the Most power-brake systems use a intake manifold of a naturally aspiratbooster operated by vacuum from the ed engine. Because manifold vacuum intake manifold of a naturally aspiratis highest-pressure is lowest-when ed Because manifold vacuum the engine. driver lifts his foot off the throttle, is highestpressure is lowest-when vacuum in the booster is maximum as the driver liftsare his foot off theThis, throttle, the brakes applied. of vacuum isindifferent the booster maximum as course, for ais supercharged the brakes applied. This,usuof engine, whereare manifold pressure course, is different for a supercharged ally is greater than ambient air engine, pressure.where manifold pressure usually greater air Theis extra forcethan on ambient the masterpressure. cylinder piston is provided by a large The inside extra the force on booster. the masterpiston power In a cylinder piston isthis provided a largea vacuum booster, piston by is called piston inside theseepower booster.ofInthea diaphragm. You the outside vacuum booster, this piston is called cylinder-chamber- when you looka
diaphragm. You see the outside of the cylinder-chamberwhen you look 78
at a vacuum booster. It's the large, round object that looks like a tank. at Vacuum a vacuumboosters booster. have It's thea large, large round object that looks like a tank. diameter because vacuum exerts a Vacuum boosters have a large Actually, the very low "pressure." diameter because vacuum exerts outside air exerts pressure; vacuuma very low it."pressure." the removes Ambient Actually, air pressure outside air exerts pressure; vacuum (14.7 psi) is one one side of the diaremoves it. engine Ambient air pressure phragm and manifold vacuum (14.7 psi) is one one side of the diathe other. Air pressure is reduced on phragm and side engine manifold vacuum the vacuum by engine vacuum. A the other. Air pressure is reduced on perfect vacuum on one side of the dithe vacuum side abymaximum engine vacuum. A aphragm allows pressure perfect vacuum on one side of the diof only 14.7 psi. This is a pelfec! aphragm allows maximum pressure vacuum. In real alife, it is never that of only 14.7 psi. This is a pellfect high. Compared to about lOOO-psi vacuum. real life, is never that maximumInpressure in ait brake hydrauhigh. Compared to about pressure 1000-psi lic system, the vacuum-boost maximum a brake hydrauis about 10 pressure psi. The in result is the large-
lic system, the vacuum-boost pressure is about 10 psi. The result is the large-
Master Cylinder
I,ll
II
II
---
Vacuum- Booster Force & Pressure
VacuumBooster operates Force & Pressure Master cylinder at about 1 OOO-psi maximum hydraulic pressure. Because at Master vacuum cylinderdiaphragm operates operates at about about 10-psi maximum pressure, booster 1000-psi maximum hydraulic pressure. Bediaphragm is 5 to 10 times operates diameter of cause vacuum diaphragm at master-cylinder piston pressure, to give required about 10-psi maximum booster area. diaphragm is 5 to 1 0 times diameter of master-cylinder piston t o give required diameter cylinder. Remember, total area. force equals pressure multiplied by diameter Remember, total the area ofcylinder. the piston - diaphragm in force equals pressure multiplied by the pressure is hythis case-whether the areaorof the piston-diaphragm in draulic a vacuum . this casewhether the pressure is hyThe pedal linkage is connected to a draulic or a vacuum. mechanical linkage that pushes on the The pedal linkage connected to a master cylinder. The isdriver can push mechanical-linkage that pushes on the master cylinder the same as inthea master The driver can push normal cylinder. brake system. However, the the the same asfrom in a pedalmaster effort cylinder is high without assist normal brakeThe system. the the booster. boosterHowever, merely adds pedal effort is high without assist from force to the master-cylinder pushrod the booster. The pushes boosteron merely adds when the driver the pedal. forcetotal to the master-cylinder pushrod The force on the master-cylinder when driver on pedal the pedal. piston the is the forcepushes from the plus The total force on the master-cylinder the booster force. piston the force fromlook the pedal plusa Let'sis take a closer at how the booster force.works . To restate, a vacuum boost Let's take a closer look atforce how bya booster diaphragm supplies vacuum boost works. To restate, having a vacuum on one side of the di-a booster supplies force on by aphragm diaphragm and atmospheric pressure having a vacuum on one sidewhenever of the dithe other. A vacuum exists aphragm on pressure and in atmospheric a gas falls pressure below atthe other. A vacuum exists whenever mospheric pressure. Most pressure pressure a ingasthefalls below , atgages read inzero atmosphere so mospheric pressure. vacuum gagesMost are pressure used to special gages read zero in the atmosphere, so measure pressure below one special vacuum gages are used atmosphere. If most of the air to is measure one pumped out pressure of a cylinder,below atmospheric atmosphere. the on air the is pressure triesIfto most push of inward pumped out of a cylinder, atmospheric outside of the cylinder. There is a pressure tries to push inward on the lower pressure-vacuum-inside the outside of themain cylinder. There is a cylinder. The parts of a simple lower the vacuumpressure-vacuum-inside booster are the power chamber
cylinder. The main parts of a simple vacuum booster are the power chamber
ber is the diaphragm and its housing. They supply the force. The control valve lets air or vacuum into the power chamber. and the control valve. The power chamAir-Suspended Boosters early ber is the diaphragm and itsAll housing. boosters operated under no load with They supply the force. The control air on lets both air sidesor ofvacuum the diaphragm at valve into the one atmosphere pressure. When the power chamber. brakes were applied, a valve between Air-Suspended Boosters - All early the booster and intake manifold was boosters operated under no load with opened. Air was pumped from one air on both sides of the diaphragm at side of the diaphragm. This type of one atmosphere pressure. When the booster is called an air-suspended brakes were applied, a valve between booster. That means there is air on the booster and intake manifold was both sides of the diaphragm when it opened . Air was pumped from one has no force on it. side of the diaphragm . This type of Vacuum-Suspended Booster-The booster is cailed an air-suspended more modern type of vacuum booster booster. That means there is air on is called vacuum suspended. It has a both sides of the diaphragm when it vacuum on both sides of the diahas no force on it. phragm when there is no force on it. Vacuum-Suspended Booster-The Atmospheric air is let into the power more modern type of vacuum booster chamber on one side of the diaphragm is called vacuum suspended. It has a when the brakes are applied. It is vacuum on both sides of the diaeasier to let air into a vacuum than it phragm when there is no force on it. is to pump air out-particularly when Atmospheric air is let into the power it must be done quickly. Because chamber on one side of the diaphragm vacuum is an absence of ail; air naturalwhen the brakes are applied. It is ly flows into the vacuum when the easier to let air into a vacuum than it valve is opened. Also, the vacuumis to pump air out-particularly when suspended booster is more fail-safe it must be done quickly. Because than an air-suspended booster. That's vacuum is an absence of ail; air naturalanother reason it is popular today. ly flows into the vacuum when the Tandem Booster-Most vacuum valve is opened. Also, the vacuumboosters have one diaphragm in the suspended booster is more fail-safe power chamber. If a large force is rethan an air-suspended booster. That's quired from the booster, cylinder another reason it is popular today. diameter must be large. To make a Tandem Booster-Most more compact booster, some vacuum use two boosters have one diaphragm in the diaphragms. This type of booster is power chamber. If a large force is recalled a tandem booster: The diaquired from the booster, cylinder phragms are mounted in front of each diameter must be large. To make a other in the power chamber, as are more compact booster, some use two the pistons in a tandem master diaphragms. This type of booster is cylinder. They each provide part of called a tandem booster. The diathe booster force. phragms are mounted in front of each Brake-Booster Operation-There are other in the power chamber, as are three basic vacuum-booster operating the pistons in a tandem master conditions: cylinder. They each provide part of Brakes released. the booster force. Brake being applied. Brake- Booster Operation - There are Brakes holding at constant force. three basic vacuum-booster operating The control valve is operating difconditions: ferently each of these conditions. • Brakes for released. operation is shown in •Control-valve Brake being applied. drawing, pageat80. •the Brakes holding constant force. The power chamber of a vacuumThe control valve is operating difsuspended booster is divided into a ferently for each of these conditions. front chamber and a rear chamber by Control-valve operation is shown in the diaphragm. There is always the drawing, page 80. vacuum applied to the front chamber. The power chamber of a vacuumThe vacuum line contains a check
suspended booster is divided into a front chamber and a rear chamber by the diaphragm. There is always vacuum applied to the front chamber. The vacuum line contains a check
Vacuum In Front of Diaphragm
Air to Rear
Hydraulic
Hydraulic Pistons Move Forwar I I Pushrod Typical vacuum-suspended booster: Diaphragm acts like a piston. When brakes are r: ":; -:·.1 Vacuum applied, air is admitted t o chamber behind diaphragm, applying force to master-cylinder ".'·:·'1 Air Corporation. pushrod. Drawing courtesy Bendix
I Typical vacuum-suspended booster: Diaphragm acts like a piston. When brakes are applied, air is admitted to chamber behind diaphragm, applying force to master-cylinder .agrns and pushrod. Drawing courtesy Bendix Corporation. Move Forw
Diaphragms and Plates Move Forward
~ l i Pistons c Move Forward Vacuum Air
I
I
Vacuum in Front of Each Diaphragm-Air to Rear of Each Diaphragm
1::::;...::1Vacuum
Bendix tandem-diaphragm Master-Vac booster in applied position: Vacuum acts on each of [':::-;:::-:1Airbooster force. Unit is used where high force is required and t w o diaphragms, doubling space is limited. Drawing courtesy Bendix Corporation. Vacuum in Front of Each Diaphragm-Air to Rear of Each Diaphragm
-
Bendix tandem-diaphragm Master-Vac booster Vacuum acts on each of Front Shell 3vRear in applied position: Shell two diaphragms, doubling booster force. Unit is used where high force is required and Vacuum Check Valve Bendix Corporation. space is limited . Drawing courtesy
Reaction Disc
Vacuum Check Valve - - - 1
/
W
V
V
-
\ Control Vallie Rod Val
Hydraulic Pushrod
.agm Return Spring Diaphr Master Cylinder Power Section
~rJtJJ Plate \ Valve Rod
I
I
Cross-section of Master-Vac booster with working parts indicated. Control valve admits Diaphragm Plate air into chamber behind diaphragm. Valve rod is moved when driver pushes on brake pedal. Drawing courtesy Bendix Corporation.
Cross-section of Master- Vac booster with working parts indicated. Control valve admits air into chamber behind diaphragm. Valve rod is moved when driver pushes on brake pedal. Drawing courtesy Bendix Corporation.
79
I
I
Atmospheric Port closed
'i-
Atmospheric Air
Valve Rod (Retracted) (Retracted)
Diaphragm 3 (Retracted)
L ~ e aShell l Vacuum Released Position Atmospheric Port Open
Atomspheric Air
Valve Rod Rod (Forward) (Forward)
-
\
Diaphragm--' (Forward) ~.
~
lI'lf-'fl,,·'1l
Rear Shell
-vacuum
port closed
Atmospheric Air Applied Position
Atmospheric Port Closed
Atmospheric
Valve Rod (Forward)
Diaphragm (Forward) (Forward)
\
'vacuum Port Closed Atmospheric Air (Trapped) Holding Position
Vacuum-booster control-valve operation shown in simplified form: Rear shellencloses rear chamber of booster and mounts booster-and-master-cylinder assembly to fire wall. wall, Parts move relative to each other. Valve rod rod moves when driver steps on pedal. pedal. Diaphragm Diaphragm moves moves when acted on by atmospheric air pressure and vacuum.
80
valve to prevent vacuum loss in booster when rnnti~folbklpress~rre rises above boosler pressure-or manifold vacuum booster presslrre-or drops below booster vacuum. A check valve opens to allow air to flow flow from bu t closes when ai airr tries to booster, but flow into the booster. booster, With bbrakes r a k e s released, control valve opens a vacuum port that connects front and rear cham bel's. Preschambers. sure on o n both sides of the diaphragm is ized with the brakes released. equalized Both chambers contain a vacuum as running. long as the engine is running. With brakes applied, control valve moves forward. This shuts the vacuum port between front frolit and rear chambers and opens the atmospheric port. Air flows into rear chamber through the t h e atmospheric port, raising The pressure against the diaphragm. T he diaphragm is pushed forward by the air pressure on o n its rear side. The T h e diaphragm then pushes on o n tthe h e mastercylinder pushrod and adds to the force ver. being supplied by the t h e dri driver. If the brake pedal is applied without moving, forces forces on o n the control valve shut both the atmospheric port and vacuum port. This maintains a constant force on o n the master-cylinder pushrod. IIff tthe h e brake pedal is pushed harder, atmospheric port is opened again and additional force is applied by the booster. Wirh With brakes /.elensed, vacuum port is opened: Booster force and assist disappear, disappear. Booster Spring-Boosters Spring-Boosters often are fitted with springs to give the driver the t h e correct amount of feel. feel. It is important that pedal effort not be too low. low. This makes the brakes too sensitive_ sensitive. For the correct amount of feel, pedal effort should increase with pedal travel. As the spring is compressed, pedal effort increases. HYDRAULIC B O O S T E R Some S o m e brake boosters use hydraulics rather than vacuum. Fluid is pressurized by the t h e ppump u m p that also supplies the power-steering system. A hydraulic brake booster is used on o n cars that have a poor source of vacuum from the manifold, t h e intake manifold. Not only does a su supercharged engine eliminate the t h e manifold as a source of vacuum, many newer cars are are equipped with emission controls and vacuum-operated accessories that reduce manifold vacuum, vacuum. On such
cars, hydraulic boosters are more practical, particularly if the car is also
-
Accumulator Port
(j)
-
E- 1500
Pedal Rod
Accumulator Port
.~ (I]
Pressure Port
:::J
(j) _a 1500(j)
With power Ass'lst
?
OJ
tl: 1000 ,g0F :::J C1l 1000.-0 V)
;
Booster-Runout with power A s Point s i s t
f32
500
Booster-Runout Point
2
500-
u
/Output Pushrod /
0~~--2~0--~~40~--~6~0----~8~0-----1~0~0----1~20
0
20
40
Pedal60 Effort (lb) 80
100
Output Pushrod
120
Pedalon Effort (Ib)effort. Runout pOint Curves show effect of power assist pedal is where power booster supplies maximum possible force. If pedal effort isshow higher thanof50 Ib, brake-fluid pressure the Curves effect power assist on pedal effort.increases Runout point same as itpower wouldbooster withoutsupplies power assist-curve with power is is where maximum possible force.assist If pedal parallel non-power-assist past runout point.increases Runout point effort istohigher than 50 Ib, curve brake-fluid pressure the variesas according to eachpower car. Boost force is with limited by available same it would without assist-curve power assist is vacuum tor power-steering-pump pressure. parallel o non-power-assist curve past runout point. Runout point varies according t o each car. Boost force is limited by available vacuum or power-steering-pump pressure. equipped with power steering. And, Power-Steering Gear
there's the advantage of fitting the
equipped hydraulic with powerbooster steering.into And,a smaller there's the advantage of fitting the crowded engine compartment. smaller hydraulic booster into a Like the vacuum booster, hydraulic crowded compartment. booster isengine located between the brakeLike linkage the vacuum pedal and booster, master hydraulic cylinder. booster is located between the brakeThe boost piston has hydraulic prespedal behind linkageit and master sure to add forcecylinder. to the The boost pistonpushrod. has hydraulic presmaster-cylinder In the event sure behind it to the adddriver forcecantopush the of booster failure, master-cylinder pushrod. In the event on t he master-cylinder piston just like driverHowever, can push aof booster normal failure, brake the system. on theeffort master-cylinder piston justto like pedal is much higher due the alownormal brake system. However, pedal ratio. pedal effort is much higherparts dueare: to the Basic hydraulicbooster low pedal ratio. • Boost piston. Basic hydraulic-booster parts are: • Sliding spool valve, which regulates Boost pressure. piston. braking valve, regulates • Sliding Lever spool system to which operate spool braking valve. pressure. system tosystem. operate spool • Lever Reserve-pressure valve. The boost piston operates much Reserve-pressure like any hydraulic system. piston. Because The boost piston operates much power-steering hydraulic pressure is like any hydraulic Because much higher than piston. the "pressure" power-steering hydraulicthe pressure available from vacuum, piston is is much higher than the "pressure" much smaller than a vacuum-booster available from the ispiston is diaphragm. The vacuum, boost piston located much smaller than a vacuum-booster between the rod from the brake pedal diaphragm. The boost piston ispushrod. located and the master-cylinder between the rod from the brake When the brakes are applied,pedal the and thethemaster-cylinder pushrod. lever on input rod slides the valve When the brakes are high-pressure applied, the to a position that allows lever on the input rod slides valve hydraulic fluid to enter the the chamber to a position that allows high-pressure behind the piston. This applies force hydraulic fluid to enter the chamber to the master-cylinderpushrod. behind the pressure piston. This Reserve is applies stored force in a to the master-cylinder ,pushrod. cylinder called an accumulator. There pressure stored in a is Reserve a very heavy spring is inside the accuThere cylinder called an accurn~~lato~: is a very heavy spring inside the accu-
Return Port Return Port
Power Section Power Section
Linkage Bracket
Bendix Hydro- Boost hydraulic brake booster mounts between master cylinder and brake pedal. High-pressure hydraulic fluid allows to be much smaller brake than vacuum Bendix unit Hydro-Boost hydraulic boosterbooster. mounts Hydraulic between pressure is supplied power-steering pump. Drawing courtesy master cylinder and by brake pedal. High-pressure hydraulic fluid Bendix unit Corporation. allows to be much smaller than vacuum booster. Hydraulic pressure is supplied by power-steering pump. Drawing courtesy Bendix Corporation.
f Accumulator ,-----\ I Power-Steering Gear f Accumulator
Spool Spool
t
t
Master Hydro-Boost Cylinder
Power-Steering D Pump C
Return Lines High-Pressure Lines
-
With Bendix Hydro-Boost power section in Pump ~7 High-Pressure Lines released position, most fluid from pump is. routed through power section powerWith Bendix Hydro-Boost powerto section in steering gear. Some fluid returns pump released position, most fluid from to pump is. reservoir throughpower return section port. Spring accurouted through to powermulator sufficient under pressteering stores gear. Some fluid fluid returns to pump sure to through provide return two port. or three reservoir Springpoweraccuassisted stores brake sufficient applications case presfluid mulator fluidinunder flow from power-steering sure t o provide two or pump three ceases. powerAccumulator is applications charged within fluid assisted brake case when fluid steering is turned or brakes are flow fromwheel power-steering pump ceases. applied. Drawing courtesy Accumulator is charged with fluidBendix when Corporation. steering wheel is turned or brakes are applied. Drawing mulator that appliescourtesy a force Bendix to a Corporation.
piston. Hydraulic fluid contained be-
mulator applies a force tween thethat piston and the end oftothea piston. Hydraulic fluid by contained becylinder is pressurized the spring. tween pistonis and of the If the the engine shutthe off,end pressure cylinder pressurized bypump the ceases. spring. from the is power-steering If the engine is shut off, pressure The pressurized fluid stored in the acfrom the power-steering pump ceases. cumulator is enough to apply the The pressurized fluid stored in the acbrakes several times with the engine cumulator is enough to apply the shut off. This safety feature allows the brakes times the stalls engine car to beseveral stopped if thewith engine or shut off. safety allows the car is This rolling with feature the engine off.the car to be stopped if the engine stalls or the car is rolling with the engine off. ADJUSTABLE PUSHRODS Most boosters are designed with adADJUSTABLE PUSHRODS justable master-cylinder push rods. Most are touch designed adThis rodboosters should just the with masterjustable master-cylinder pushrods. cylinder piston with the brakes
This rod should just touch the mastercylinder piston with the brakes
Hydro- Boost in released position (above) and applied position (below): With brake pedal depressed, input position rod and (above) piston Hydro-Boost in released moveapplied forward slightly. LeverWith assembly and position (below): brake moves sleeve forward, four pedal depressed, input clOSing rod andoffpiston holes center of spool. Formove leading forwardto open slightly. Lever assembly ward of spool closing allows additional movesmovement sleeve forward, off four hydraulic fluidt to entercenter cavity of behind holes leading o open spool.boosForter piston to pressurize This moves ward movement of spool area. allows additional piston and rod forward hydraulic fluidoutput t o enter cavity behindagainst boosmaster-cylinder pistons area. to apply ter piston to pressurize This brakes. moves Drawingand courtesy Bendix piston output rod Corporation. forward against master-cylinder pistons to apply brakes. Drawing Spool courtesy Moved Bendix Corporation. Forward Spool Moved
Piston , Pushrod and End Moved Forward Piston, Pushrod and End long rod will leave Moved Forward
released. A the master-cylinder compensating port released.and A cause long rod leave the covered brakewill drag. A short master-cylinder compensating port rod will add slop or excess pedal travel covered and cause brake A short to the system. See yourdrag. car's shop rod will add or excesson pedal travel manual for slop instructions adjusting to system. Seepushrod. your car's shop the the master-cylinder
manual for instructions on adjusting the master-cylinder pushrod. 81
Other Types of Brakes
8
Outlawed by most racing organizations, movable air brakes, such as one at rear of this 1955 300SLR Mercedes, are extremely effective at over 100 mph. Frontal area and drag coefficient are increased dramatically when air brake is activated. Photo courtesy Mercedes-Benz .
Outlawed by most racing organizations, movable air brakes, such as one at rear of this 1955 300SLR Mercedes, are extremely effective at over 1 0 0 mph. Frontal area and drag coefficient are increased dramatically when air brake is activated. Photo courtesy Mercedes-Benz.
In this chapter, I briefly describe brakes other than the traditional In this chapter, I briefly describe drum or disc brakes. Also, there are brakes other than the traditional several differeht ways to operate drum disc there brakes.areAlso, brakes.orAnd, otherthere waysare of several ways than to operate stopping different a vehicle other friction brakes. thereAlthough are other ways of at the And, tires. briefly stopping a vehicle other than friction discussed, I don't go into details on at the Although briefly other braketires. systems. The subject is discussed, I don't go into details on too extensive for this book.
FF = Force on Front Tires FA = Force on Rear Tires FF = Force on Front Tires We = Car Weight FR= Force on Rear Tires FD = Aerodynam ic Drag Wc = Car Weight RD = Rolling Drag FD= Aerodynamic Drag FT = Forward Thrust RD= Rolling Drag FA = Aerodynamic Downforce FT = Forward Thrust
FA = Aerodynamic Downforce
other brake systems. The subject is too extensive for thisDRAG book. AERODYNAMIC
& FA
v-
Drag acts to slow a moving car.
AERODYNAMIC DRAG Drag forces act toward the rear of the Drag acts to slow moving car. car when it is moving aforward . Drag
0 FR
FT
Forces on moving car: Vertical forces on the tires, FF and F R, are determined by car's weight and aerodynamic forces. Aerodynamic-drag force, F o' acts on car near center of body cross section,car: viewed from forces the front. Downforce, any,F actdetermined anywhere on Forces on moving Vertical on the tires, FFifand ,, canare by body. car's With thisand car,aerodynamic downforce isforces. mostly Aerodynamic-drag on rear wing. weight force, F, acts on car near center of
body cross section, viewed from the front. Downforce, if any, can act anywhere on body, With this car, downforce is mostly on rear wing.
82
Drag forces act toward theaerodynamrear of the consists of rolling drag and car when it is moving forward. Drag ic drag. Rolling drag is caused by resisrolling drag and aerodynarnconsists of tance of the tires to rolling, friction in ic drag. Rolling drag is caused the wheel bearings, and allby resisother tance of the tires to rolling, drive-train friction forces. friction in theRolling wheel drag bearings, and allexists other or resistance, at drive-train friction forces. all speeds, but increases with speed. Rolling drag or resistance, at You can experience rolling exists drag by all speeds, but on increases pushing a car a level with road.speed. You You drag will by must can keepexperience pushing or rolling rolling drag pushing a car on a level road. You stop the car. The force you use to drag must pushing O r stop the car. The force you use to
maintain speed equals rolling drag. Aerodynamic drag is caused by air maintain around speed equals rolling drag.The flowing the car body. Aerodynamic drag is caused by air force on the car is zero when air speed flowing around the car body. is zero. It increases with the squareThe of forceaironspeed. the carThis is zero whenthat air speed the means aerois zero. It increases with the square of dynamic drag quadruples if you the air speed. This means that aerodouble car speed. If a car has 100 lb of dynamic drag will aerodynamic dragquadruples at 30 mph ,if it you double carlbspeed. a carIfhas 100islbinof have 400 at 60 If mph. speed aerodynamic drag at 30 mph, it will creased to 90 mph, aerodynamic drag have 400 Ib atto 60900 mph. If speed inis increased Ib-9 timesis the creased to 90 mph, aerodynamic drag aerodynamic at 30 mph. drag At is increased 900 lb-9 force times onthea racing speeds,toaerodynamic aerodynamic dragtheatcar's 30 weight. mph. On At car can approach racing speeds, aerodynamic force on the very powerful land-speed-recorda car can the car's weight. On cars runapproach at the Bonneville Salt Flats, the very powerful land-speed-record aerodynamic drag gets so high the cars run theatBonneville Flats, to tires can at spin high speedSalt trying aerodynamic drag gets so high the overcome it! tires can spin atdrag highisspeed trying by to Aerodynamic determined overcome it! maximum cross-section size and the Aerodynamic dragThe is determined by of the car. cross-section shape maximum cross-section size and the size is called /rontal area. Frontal area shape of the car, cross-section is approximately theThe height of the car size is called frontal area. Frontal area is nearly times its width . Frontal area is a ~ ~ r o x i m a t e l the v height of the the same for most road cars, as it is car for most race cars in a given class. Shape the same for most cars,one as itcar is foi var ies a great dealroad from to most race cars in a given class. Shape another. Reducing drag by improving varies great streamlining. deal from one car to A streamshape isa called another. Reducing by improving aerodynamic drag lined shape has lowdrag shape is called streamlining. A streamfor its size. lined aerodynsmic Theshape shapehas of low the car compared drag to a for its size. standard flat shape is described by a The shape the drag car compared a coefficient.to A number calledof the standard shape is means described by a high dragflat coefficient a highnumber calledA the A lowdrag dragcoefficient. coefficient drag shape. high drag coefficient means a highmeans a streamlined shape. The worst drag shape.have A low drag coefficient of car shapes a drag coefficient means a streamlined shape. The worst nearly 1.0. The most streamlined cars car a drag coefficient of haveshapes a draghave coefficient of about 0.2. nearly 1 .O. The most streamlined cars Aerodynamic drag on a car varies have a drag of about 0.2. directly with coefficient its drag coefficient. For Aerodynamic drag on a car varies example, a car with a drag coefficient directly with its the dragaerodynamic coefficient. drag For of 0.6 has twice example, car with a drag coefficient as the same-size car at a givena speed of 0.6a drag has twice the aerodynamic drag of 0.3. with coefficient at When a giventhespeed the his same-size driveraslifts foot off car the with a drag coefficient of 0.3. throttle at high speed, drag on the car When the driver foot off the will rapidly slow lifts it. hisDeceleration throttle at high speed, drag on the car by equals the total drag force divided will rapidly slow it. Deceleration car weight. Above 60 mph, most drag equals the total drag force divided is aerodynamic. If a 2000-lb car hasbya car Above drag 500 lb60, itmph, will most decelerate dragweight. force of is aerodynamic. If a 2000-lb car has a at 0.25 g when not under power. Bedrag force of 500 Ib, it will decelerate cause aerodynamic drag drops as at 0.25drops, g when not under drops power.asBespeed deceleration car
cause aerodynamic drag drops as speed drops, deceleration drops as car
Except for lights atop body, custom Camaro pace car has improved streamlining on an already excellent body shape. Note smooth-flowing lines with a minimum of projections or corners. Except for lights atop body, Custom Camar0 pace car has improved streamlining on an al-
ready excellent body shape. Note smooth-flowing lines with a minimum of projections or corners.
Old sports cars are unstreamlined. Body shapes are rough, angular and have lots of parts sticking into airflow. Streamlining of cars refers to shape, not size of body. An unstreamlinedsports car has a higher drag force on itBody than shapes a streamlined car ofangular the same . lots of parts Old cars are unstreamlined. are rough, andsize have
sticking into airflow. Streamlining of cars refers to shape, not size of body. An unstreamlined has a higher drag force on drag it than is a streamlined car of of theobject same size. W = Weight in pounds speedcar drops. Aerodynamic
very low at low speeds.
speed drops.is Aerodynamic is the formula fordrag the acFollowing very low at low speeds. celeration of an object in g's. RememFollowing is the formulais fornegative the acber that deceleration celeration of an object in g's. Rememacceleration. ber that deceleration is negative Acceleration = ~ acceleration. F force on object in F = Unbalanced Acceleration = pounds F = Unbalanced force on object in pounds
w
that ifin the unbalanced W Remember = Weight of object pounds force acts in a direction to slow the Remember thathasif athe unbalanced object, that force negative value. force acts inforce a direction to slow the A negative makes the acceleraobject, thatobject force negative. has a negative value. tion of the A If negative force makes to the be a acceleraspeeding an object happens tion of the object negative. car and the driver lifts off the throttle, object hamens a speedinn force. theIf an unbalanced forcetoisbedrag
car and t h k drive; lifts off the throttle, the unbalanced force is drag force.
83
HOW TO CALCULATE AERODYNAMIC-DRAG FORCE HOWformula TO CALCULATE The for aerodynamic-drag AERODYNAMIC-DRAG FORCE force is simple: The formula for aerodynamic-drag Aerodynamic drag force is simple: = 0.00256AFCoS2 in pounds Aerodynamic AF = Frontal drag area of car in square = 0.00256A,CDS2 in pounds feet Frontal area Of ofcar in 'quare CD == Drag coefficient body shape feet S == car speed in miles per hour D ' TheDrag 'OeffiCient Of body frontal area is the shape crossS = car speed in miles per hour sect·ional area of a car as viewed frontfrom front. area If you isdraw Thethefrontal the a crosssectional area of a viewed outline of the carcar on as a sheet of view from the front. You draw a frontandIf count the squares graph paper view of that the Car a sheet of will on approximate insideoutline outline, graph Raper andarea. COunt the squares the car's frontal H each square inside outline, that will approximate the car's frontal area. If each square
-
on the paper is scaled at 1 inch on a side,the frontal area will come out on the paper is scaled at 1divide inch on a inches. If you the in square side, theoffrontal area will come out number square inches by 144, in square inches. you get square feet.If you divide the square number has inches nothingbyto144, do Frontalofarea you get with thesquare shapefeet. of the front ofa car. Frontal area has cross-sectional nothing to do Only the maximum front of Shape a car. with thethe shape size of car of is the important. Only the cross-sectional affects themaximum drag coefficient, not the size of the is important. Shape frontal area.carTypical drag coeffiaffects theproduction drag coefficient, notfrom the cients for cars vary frontal Typical coeffia low of area. 0.30 to a high drag of 0.60. The ' cientscoefficients for production cars vary for many carsfrom are drag a low in of magazine 0.30 to a articles high of 0.60. The and road given drag for article many cars are tests.coefficients Find such an for your given in magazine and road car to determine its articles drag coefficient. tests. Find such an article for your car to determine its drag coefficient.
1500 Cd = Drag Coefficient
1500
Frontal Area = 25.4 sq It Cd = Drag Coefficient Frontal Area = 25.4 sq f t
Cd = 0.6
1000 Air Drag
1000 -
,/ /'
(Ib) Air
Drag (I b)
/ 500
500
/" - C d =0.3
./
-
/
- --
/
/
oL---~~~~--+-----~------+-----~----80 160 200 40 120
0
40
80
Car SpeedI (mph)
120
I
I
160
200
I
Graph shows how aerodynamic drag varies with car speed and drag coefficient. Solid line is Car Speed (rnph) for unstreamlined car with a 0 .6 drag coefficient. Dotted curve is for streamlined car with the same frontal but half the drag, or 0.3 coefficient. Drag figures areSolid typical Graph shows howarea, aerodynamic drag varies withdrag car speed and drag coefficient. linefor is a large sedan. for unstreamlined car with a 0.6 drag coefficient. Dotted curve is for streamlined car with
the same frontal area, but half the drag, or 0.3 drag coefficient. Drag figures are typical for a large sedan.
The formu la for dece leration can be written another way:
The formula for deceleration can be . written another way: FD Deceleration of a car = WFDc Fa = Drag force of aoncarcar=in -- pounds Deceleration W,LJpounds Wc = Weight of the car in F, = Drag force on car in pounds W, = Weight of the car in pounds In this formul a, deceleration is In g's. If you know the drag forc e on a thiscan formula, deceleration is In. calculate its deceleration car,Inyou g's. If you know dragway, forceif on Approaching it anthe o ther youa car, you can calculate its deceleration. could measure deceleration , you Approaching another you could calculateitdrag force .way, This if is how could measure you vehicle drag can bedeceleration, determined withcould calculate drag force. This is how out using a wind tunnel.
vehicle drag can be determined without using a wind tunnel. AERODYNAMIC BRAKING If a car is streamlined and suddenly
AERODYNAMIC BRAKING If a car is streamlined and suddenly 84
increases its drag coefficient for braking while at high speed, it can slow increases This its dragis coefficient for brakquicker. how aerodynamic ing whileworks. at high speed, slow braking Added dragit iscan created quicker. This is how aerodynamic by changing the shape or size of the braking Added dragchange is created car. Theworks. drag-coefficient has by changing or size of the to be large tothe getshape a significant effect car. drag-coefficient fromThe aerodynamic braking.change Also, has the to be must large be to high. get a Itsignificant speed also helps effect if the from aerodynamic braking. Also, the car is light because deceleration speed mustonbe weight. high. It also helps aeroif the depends Finally, car is light because deceleration dynamic braking is worthwhile only depends weight. Finally, on a race on car that brakes at very aerohigh dynamic braking is worthwhile only speed . onAerodynamic a race car thatbraking brakes atis very high efficient speed. because there is no heat to dissipate in braking is efficient theAerodynamic brake system. Instead, aerono heat dissipate in because there dynamic drag isheats thetosurrounding the asbrake Instead, it. aeroair the carsystem. passes through The
dynamic drag heats the surrounding air as the car passes through it. The
wheel brakes can be applied along with aerodynamic braking for even wheel can be applied along higher brakes deceleration. Deceleration with aerodynamic brakingoperating for even with both brake systems is higher than deceleration. greater either systemDeceleration can achieve with both brake systems operating is Singularly! greater than either system can achieve If aerodynamic braking is so singularly!why is it used infrequently efficient, braking is so or If onlyaerodynamic on a few specialized race cars? efficient, why is it used infrequently • The braking force is useful only at or only onspeeds-near a few specialized very high 200 race mph.cars? braking force is useful at • The Aerodynamic braking will notonly bring very high speeds-near 200 mph. a car to a dead stop. The braking force Aerodynamic not nears bring approaches zerobraking as ca r will speed a car. to a dead stop. The braking force zero approaches zero brakes as car add speedweight, nears • Aerodynamic zero. complexity and cost. Aerodynamic brakesareaadd weight, • Because car frontal should incomplexity and cost. crease for aerodynamic braking to be Because the car frontal should ineffective, car willarea occupy more crease for aerodynamic braking to be space on the road with the brakes effective,This themay car mwill more applied. a ke occupy it difficult to space near on other the road drive cars. with the brakes applied. Thisracing may make it difficult to • In most classes, movable drive near other cars. aerodynamic devices are illegal. In most racingbrakes classes,have movable Aerodynamic been aerodynamic illegal. tried in roaddevices racing,are such as on the Aerodynamic brakes have Mercedes sports cars of the mid-been ' 50s tried in road racing, such as on the and early winged Can-Am Chaparral Mercedes sports cars of the mid-'50s racers. and early winged Chaparral Mercedes used aCan-Am flap-mounted flat racers. on the tail of their 300SLR. This fl ap Mercedes used a flap-mounted flata was raised hydraulically by operating on the tail of their 300SLR. flap control valve in the cockpitThis , nearly was raisedthe hydraulically doubling frontal areabyofoperating the car. Ita control valve in the cockpit, nearly also made the airflow more turbulent. doubling the frontal area of the car.tal It The combination of the larger fron also made the airflow more and air turbulence more thanturbulent. doubled The combination the larger frontal aerodynamic drag .of Because this car exand air turbulence more than doubled ceeded 180 mph on the 3-mile aerodynamic drag. Becauseand this car straightaway at LeMans, had exto ceeded mph hairpin on theturn, 3-mile slow for 180 a 30-mph the straightaway LeMans, hadload to aerodynamic at brake took a and lot of slow for a 30-mph hairpin turn, the off the wheel brakes. Competing drivaerodynamic brake a lot ofprobload ers complained abouttook a visibility off wheel Competing drivlemthe when thebrakes. Mercedes aerodynamic ers complained about a visibility brake was raised. This, however,probwas lem when the Mercedes aerodynamic probably due to the superiority of the brake was raised. was Mercedes rather This, than ahowever, "visibility" probably hazard. due to the superiority of the Mercedes rather ran than a "visibility" The Chaparral a large wing over hazard. the rear wheels, which could be The Chaparral large wing over varied in its angleran of aattack. The wing the rear wheels, which could be ran at low angles when the car was varied in its angle of attack. The wing accelerating, to give some downforce ran at anglesdrag when the car and to low minimize created by was the accelerating, to give some downforce wing. When braking, the driver could and to minimize drag created by the tip the wing to maximize downforce wing. When braking, the driver could and drag . The downforce increase on tip to maximize downforce the the rear wing tires allowed more rear-wheel and drag.Because The downforce on braking. this car increase was highly the rear tires allowed more rear-wheel successful, the racing rules were braking. Because car was highly changed, banningthismovable aerosuccessful, the racing rules were dynamic devices.
changed, banning dynamic devices.
movable
aero-
High-Drag Position
High-Drag Position
Aerodynamic brake on the Chaparral Can-Am car was similar to this. Wing in low-drag position supplied downforce to rear tires for improved high-speed cornering. When flipped to high-drag Aerodynamic brake on the Chaparral Can-Am car was similar to position, aerodynamic increased deceleration . Movathis. Wingadded in low-drag positiondrag supplied downforce to rear tires for ble wings are illegal in road racing today. improved high-speed cornering. When flipped to high-drag
Aerodynamic braking has been used for years in drag racing. Racing chutes stop funny cars much quicker than ordinary brakes. Cars are traveling near has 250 been mph atused finishfor line. After in each run,racing. paraAerodynamic braking years drag chute ischutes repacked. would work for cars brakes are Racing stopThis funny cars not much quicker thanwhere ordinary brakes. applied than once during a race. mph at finish line. After each run, paraCars aremore traveling near 250
position, added aerodynamic drag increased deceleration. MovableAerodynamic wings are illegalbraking in road racing has today. found a
chute is repacked. This would not work for cars where brakes are applied more than once during a race.
home in drag racing. All the really fast Aerodynamic braking has found drag cars, such as top fuelers , funnya homeand in drag racing. All really fast cars pro stockers, usethe a parachu te drag cars, such asBecause top fuelers, funny to assist stopping. a parachute cars pro stockers, use a parachute reliesandon aerodynamic drag for to assist stopping. Because a parachute effectiveness, it is true aerodynamic relies aerodynamic dragwon't for braking. on Obviously, a parachute effectiveness, it is ortrue aerodynamic work in road racing on the street bebraking. Obviously, a parachute cause it has to be repacked afterwon't each work in road racing or on the streetis beapplication. In a drag race, this no cause it has to be repacked after each problem because the car makes one application. a drag this is no stop per run.InThe chuterace, is repacked by problem because the car makes the pit crew prior to the next run . one stop per drag run. The is repacked by Some cars chute reach or exceed 250 the pitand crew the next run. , the mph areprior veryto light. If large Someapplies drag cars reachmore or exceed 250 chute much stopping mph and are very light. If large, force than the wheel brakes, thusthe is chute applies muchin more stopping extremely effective reducing speed force than100themph wheel thus is to under in a brakes, short distance. extremely In fact, theeffective only limitintoreducing how fastspeed a car to under mphwith in a ashort distance. could be 100 slowed chute is the In fact,force the only to how fastwitha car inertia that limit the driver must could when be slowed withopens. a chute is the stand the chute inertia force that The critical partthe of driver settingmust up a withdragstand opens. racingwhen chutetheischute where and how the Themounts critical part of setting a dragchute to the frame. up If mountracing chute is where and the howchute the ed off-center, when opened chute mounts to the frame. If mountwill cause the car to swerve. Ideally, ed when opened the off-center, mount should be near the thechute CG will cause car to swerve. Ideally, height, andthe centered. The maximum the mount should bemount near is themany CG force on a parachute height, and centered. The maximum tons, so mount strength is critical. force on a mounts parachutehave mount is many Parachute ripped off tons, leav so ing mount strength cars, the driver only isthecritical. wheel Parachute haveThe ripped off brakes to mounts stop with. mount cars, leaving the driver theseveral wheel should be strong enoughonly to lift brakes stop with. who Thesellmount race cars to from it. Those dragshould be strong enough to several race parachutes, such as liftSimpson race cars from it. Those who sell dragSafety Equipment Co., can provide inrace parachutes, such and as setting Simpson structions on mounting up Safety Equipment Co., can provide inthe system.
structions on mounting and setting up the system.
Compressed air moves brake shoes by means of an actuating chamber mounted on axle housing. chamber rotates Compressed airActuating moves brake shoes by tube (arrow) pushrod and mounted lever to means of an through actuating chamber move brake shoes against chamber drum. Note lack on axle housing. Actuating rotates of backing plate on these truck and brakes. tube (arrow) through pushrod lever to
move brake shoes against drum. Note lack of backing plate on these truck brakes.
PNEUMATIC BRAKES Pneumatic brakes, commonly called PNEUMATIC BRAKES air brakes, refer to the actuating Pneumatic brakes, commonly system. Pneumatic brakes use called comair brakes, to the the brakes actuating pressed air torefer operate insystem. Pneumatic This brakes comstead of hydraulics. typeuse of brake pressed isair to primarily operate the brakes insystem used for large comstead of hydraulics. This type of brake mercial vehicles. A truck usually uses system is used primarily for large pneumatic brakes because therecomare mercial vehicles. usuallybrake uses advantages over Aa truck hydraulic pneumatic brakes because there are system. advantages a hydraulic brake Pneumaticover brakes are actuated by system. compressed air supplied by an enginePneumatic brakes areThe actuated by driven air compressor. comprescompressed air supplied by an enginesor supplies high-pressure air to a stordriven compressor. The compresage tankair , which is big enough to mainsor supplies high-pressure to a stortain pressure when the air brakes are age tank, which is big enough to mainapplied. tain pressure air when theto brakes are Compressed is fed the brakeapplied. system by valves controlled actuating is fedIfto the the brakeby Compressed the brake air pedal. driver actuating system by valves controlled by the brake pedal. If the driver
Pneumatic truck brakes are actuated by compressed air supplied by engine-driven air compressor. reservoir emergenPneumatic truckAirbrakes arehas actuated by cy supply of air brakes by won't fail if comcompressed air so supplied engine-driven pressor belts break. air compressor. Air reservoir has emergen-
cy supply of air so brakes won't fail if compressor belts break.
pushes harder on the brake pedal, more air pressure is applied to the pushes on the brake pedal, brakes. harder The driver is not supplying more air pressure is applied to the force or air movement, so the his brakes. The driver is not supplying strength doesn't matter. theBecause force ortrucks air movement, his are very so heavy strength doesn't matter. under full load, power-assisted hyBecause trucks very heavy draulic brakes wouldare be necessary. A under full load, ofpower-assisted hymajor advantage pneumatic brakes draulic necessary. A is they brakes have would built-inbe power assist. major advantage of pneumatic brakes Another advantage is pneumatic is theyarehave built-in by power brakes not affected smallassist. leaks Another advantage is pneumatic in the system. Air is supplied continubrakes by arethe not compressor, affected by small leaks ously so unless in the system. Air is supplied continuthere is a huge hole in the system, ously by the compressor, unless there is never a loss of so pressure. there is athe hugeairhole in the system, Instead, compressor must there harder is never a loss ofpressure pressure. work to maintain in Instead, the storagethe tank.air compressor must work to maintain pressure in The harder pneumatic system does not use the storage tank. hydraulic fluid, so it is not affected by
The pneumatic system does not use hydraulic fluid, so it is not affected by 85
Aircraft multi-disc brake: Brake, which is buried in wheel, is good for one stop after landing. Brake must cool Brake, before which another Aircraft multi-disc brake: is landing in can be made. buried wheel, is good for one stop after landing. Brake must cool before another landing can be made.
the reduced boiling point of old, contaminated fluid. Thus, the system can the much reducedlonger boilingbetween point of servicing. old, congo taminated fluid. Thus, the system can This is important on long-haul trucks. goThe much longer between servicing. disadvantages of a pneumatic This important n long-haul trucks. brakeissystem are osize, complexity and T h eAlso, disadvantages of a pneumatic cost. it takes engine power to brakethe system are size, complexity and run air compressor. System prescost. Also, it takes engine power to sure is much lower than that of a hyrun the system. air compressor. System presdraulic Thus, the diameters sureallis much than that of a and hyof the lower cylinders-master draulic system. T h u s , the diameters wheel- are much larger. Trucks have of the cylinders-master and lots all of room, so there's no problem wheel-are larger. Trucks havea fitting large much cylinders. But size has lots of room, so there's no problem definite disadvantage: It takes time to fitting large cylinders. But size has a build up pressure at the brakes. definite It takes timethe to There disadvantage: is a small delay between build the up pressure at the time driver hits thebrakes. pedal and the Thereactually is a small delayEngineers between can the brakes apply. time the driver hits the pedal and the design a system to reduce, but not brakes actually apply. Engineers can eliminate, this time lag. design a system reduce, but not Compressor costtomakes a pneumateliminate, this time lag.expensive than ic brake system more Compressor cost makes a pneumata hydraulic system. However, because ic brakecommercial system morevehicles expensive than many require a hydraulic system. However, because compressed air to run other systems many vehicles on the commercial vehicle, the cost of therequire comcompressed air to run other systems pressor is justified, considering its o n the vehicle, the cost of the comdouble-duty function. pressor consideringin itsa There isarejustified, other complexities double-duty function. pneumatic brake system. The comThere must are other in a pressor have complexities a pressure-relief pneumatic brake over system. T h e comvalve to prevent pressurizing the pressor must a pressure-relief system. Also, have there's a pressurevalve to prevent overpressurizing controlled unloader that takes the the system. Also, there's a pressureload off the compressor once storagecontrol led unloader the reaches that abouttakes 100 psi. tank pressure load off the compressor once storageThere are also one-way valves to tank pressure reaches pressure about 100if psi. maintain storage-tank the There are also one-way valves to compressor fails. maintain storage-tank introduce pressure ifboth the Air compressors compressor fails. water and oil into a brake system.
Air compressors introduce both water and oil into a brake system.
86
HPBooks' very "slippery" Monza at Bonneville Salt Flats. To illustrate effect aerodynamic drag has on speed, Tom Monroe set C/Production record in car at 217.849 mph. Power was by fuel-injected 370-cubic inch small-block Chevy. Salt AlProduction record iseffect 219.334 mph, set in drag a '67 HPBooks' very "slippery" Monza at Bonneville Flats. To illustrate aerodynamic Camaro powered by Monroe a 510-cubic inch big-block-Chevy-37% displacement andwas 0.68% has on speed, Tom set ClProduction record in car atmore 217.849 mph. Power by faster! This is a good-news/bad-news when it comes to is braking. two set cars fuel-injected 370-cubic inch small-block situation Chevy. NProduction record 219.334 Ifmph, in awith '67 different drag coefficients are traveling at the same speed and more stop at the same deceleration Camaro powered by a 510-cubic inch big-block-Chevy-37% displacement and 0.68% rate, carThis withisthe lower Cd will require the higherwhen braking force. Photo by BillIf Fisher. faster! a good-newslbad-news situation it comes to braking. two cars with different drag coefficients are traveling at the same speed and stop at the same deceleration rate, car with the lower C, will require the higher braking force. Photo by Bill Fisher.
These liquids are removed to prevent the pneumatic system from being These liquids removed prevent damaged. Not are only can the toparts corthe systembutfrom rode pneumatic due to moisture, they being could damaged. only brake can the parts corfreeze andNot cause failure. The rode d u e to moisture, they could fluid-removal system but is similar to freezetraps and in cause brake failure. T h e compressed-air fluid a shop fluid-removal system is similar to system. fluid traps in brakes a shoparecompressed-air Pneumatic actuated by a system. diaphragm inside a housing, rather Pneumatic actuatedThese by a than a pistonbrakes in a are cylinder. diaphragm inside a housing, rather units are the brake chambers. You can thanthem a piston in aoncylinder. see mounted the rearThese axles units are trucks the brake You can of large and chambers. trailers. They are see n the rear too them big to mounted fit insideo wheels, so axles they of large the trucks andthrough trailers.a They are operate brakes shaft and too big to fit inside wheels, so they mechanical linkage. A return spring operatethe t h e chamber brakes through a shaft and inside returns the diamechanical A position return spring phragm to itslinkage. retracted when inside the are chamber returns the diathe brakes released. phragm to its retracted position when On some large off-road commercial the brakes are as released. vehicles such earth movers, graders O n road s o m e large off-road commercial and rollers, a combination vehicles such as earth movers, hydraulic/pneumatic system isgraders used. and road to rollers, a combination Referred as an air-aver-hydraulic hydraulic/pneumatic is used. system, the brakes aresystem operated by a Referred to as an air-over-hydraulic hydraulic system, but the hydraulic system, the brakes are by a system is applied by operated a pneumatic hydraulicbetween system,thebutbrake the pedal hydraulic system and system is applied a ispneumatic the hydraulic system.byThis a type of system assist between brake and power thattheuses air pedal pressure the hydraulic system. This is a type of rather than vacuum.
power assist that uses air pressure rather than vacuum. MULTIDISC BRAKES A multi disc brake works like a mul-
MULTIDISC BRAKES A multidisc brake works like a mul-
tidisc clutch. There are a number of driven and statianalY discs in a stack. tidisc clutch. There are a number of Friction material is between the discs. drivendriven and stationary discs inwith a stack. The discs rotate the FrictionWhen material between discs. wheel. theisbrakes arethe applied, T h e driven discs rotate with the the stack is clamped together. The stawheel. h e n thebecause brakes are tionary Wdiscs, theyapplied, can't the stack is clamped together.discs T h e starota te, slow the rotating by tionary discs, because they can't friction. rotate, slowbrakes the rotating by Multidisc are small discs and light friction. compared to other types of brakes Multidisc small and light that absorbbrakes the are same energy. compared to other types of brakes However, because the rubbing surthat are absorb the same energy. faces all "buried" inside the unit, However, becausecool theslowly. rubbing sur-a multidisc brakes Thus, faces are all "buried" inside the unit, multidisc brake is good for only one multidisc cool slowly. Thus, hard stop. brakes Considerable cooling timea multidisc is good for only is needed brake before the next stopone is hard made.stop. Considerable cooling time is The needed before theof next stop is compactness a multidisc made. brake makes it desirable for aircraft T h An e compactness of a wheels multidisc use. airplane has small to brakespace, makesmaking it desirable aircraft save a tight for fit for any use. hasstops small wheels to brake.A nA airplane plane only hard once as save space, making a tight fit for any it lands, and has a great deal of cooling brake.before A plane only stops hardand once as time another landing stop. it lands, has a great of cooling And, theand extremely highdeal temperatures time beforein another landingdictate and stop. generated aircraft brakes the And, the extremely high temperatures use of sintered-metallic or graphitegenerated in aircraft brakes dictate the composite friction materials. useAircraft-type of sintered-metallic or graphitemultidisc brakes composite friction materials. might work well on dragsters or landAircraft-typecars, multidisc brakes speed-record but to my knowlmightthey workhave wellyet o ntodragsters edge be used or on landsuch speed-record cars, but to my knowlvehicles.
edge they have yet to be used o n such vehicles.
Dragster brake is operated by hand lever. Note pushrod between lever and master cylinder (arrow). Hand-lever movement can be more than a brake pedal, so higher pedal ratio is possible lever-operated Dragsterwith brake is operated bybrakes. hand lever. Note pushrod between lever and master cylinder
(arrow). Hand-lever movement can be more than a brake pedal, so higher pedal ratio is possible with lever-operated brakes.
HAND-OPERATED BRAKES Some specialized cars use a brake HAND-OPERATED system operated by BRAKES a hand lever Somethan specialized cars use a brake rather a brake pedal. A dragster system by dragster a hand handLever is one ofoperated these. The rather than a brake pedal. A dragster lever brake operates identically to a is one of these. dragster foot-pedal brake,Thebut with handtwo lever brake operates identically to a differences: foot-pedal but awith two • Maximum brake, force with person's differences: hand is less than can be applied with a Maximum force with a person's foot. hand is -lever less than can becan applied with a • Hand stroke be longer foot. than a foot pedal, allowing a higher Hand-lever stroke can be longer ratio . than pedal, allowing a higher Likea foot a foot-brake pedal, the hand ratio. operates a master cylinder lever Like aa foot-brake pedal, the hand through pushrod . Because dragsters lever operates a master cylinder have rear-wheel brakes only, a single through a pushrod. Because dragsters master cylinder is used. Most of the have rear-wheel only, a single stopping is donebrakes by the parachute. masterwheel cylinder is used. Most atof low the The brakes are used stopping is done by the parachute. speeds, particularly for holding the The brakesline. are used at low car onwheel the starting speeds, particularly holding the Another type offorhand-operated car on the starting line. brake is found on dune buggies. Another hand-operated Known as a type CUllingofbrake or steering brake found dunelevers buggies. brake, itis has one on or two with Known as a cutting brake or two separate master cylinders tosteering operit hasorone or two levers with brake, ate the right left rear wheel. two separate master cylinders to operCutting brakes are used for steering ate rightinorsoft left sand rear wheel. the the buggy or tight turns. Cutting brakes are do used steering The front tires often notfor have suffithe buggy in soft sand or tight cient bite for steering control in turns. these The front tires often do not tires have suffisituations. Because rear have cient steering these more bite bite,forthey can control turn thein buggy situations. Because rear is tires have quickly when one wheel braked. A
more bite, they can turn the buggy quickly when one wheel is braked. A
Ja-Mar cutting-brake assembly is used on sand buggies for steering control in soft sand. One operates one master cylinder Ja-Mar cutting-brake assembly is used on when buggies pulled; other lever operates sand for steering controlopposite in soft cylinder. Each master one cylinder is designed sand. One operates master cylinder to operate a single when pulled; other rear leverbrake. operates opposite
cylinder. Each master cylinder is designed t o operate a single rear brake.
Disc-brake caliper can be operated by either hydraulic pressure or separate mechanical linkage. Used on competition rally cars at the rear wheels and operated by a mechanical linkage by a caliper parking-brake driver pull hydraulic lever to slide out rear formechanical entering a Disc-brake can be lever, operated bycan either pressure or wheels separate turn. This allows ultra-tight turns to beatnegotiated quicklyand in operated dirt or onbyslick surfaces. linkage. Used on competition rally cars the rear wheels a mechanical Courtesy Racing. linkage byAP a parking-brake lever, driver can pull lever to slide out rear wheels for entering a
turn. This allows ultra-tight turns t o be negotiated quickly in dirt or on slick surfaces. conventional brake pedal is used for wheel drive. It is handy for the driver Courtesy AP Racing.
braking the
buggy during
normal
conventional brake pedal is used for operation . braking the buggy during normal Hand-operated rear-wheel brakes operation. also are found on competition rally Hand-operated rear-wheel cars. Unlike a cutting brake,brakes rearalso are found on competition rally wheel rally-car brakes are operated cars. Unlike a cutting rearsimultaneously with brake, one hand wheel rally-car brakesRally are operated lever/master cylinder. cars run simultaneously with hand on slick roads and often one have frontleverlmaster cylinder. Rally cars run on slick roads and often have front-
to brake only the rear wheels to throw
wheel handy for skid. the driver the cardrive. into Ita isdeliberate This to brake the rear wheels to throw helps to only negotiate tight slippery turns the car steering into a deliberate where control skid. might This be helps to negotiate tight slippery turns marginal. Separate from the hydraulic where steering control might be system, special mechanical linkages marginal. are often Separate used forfrom the the rearhydraulic brakes. system,is special linkages This similarmechanical to parking-brake are often used for the rear brakes. linkage, but is designed for severe use . This is similar to parking-brake linkage, but is designed for severe use. 87
High-Performance Brakes
High-Performance Brakes
9
Design of modern race-ear-brake system is not arrived at through magic. Instead, carefully planned steps are required. Success starts with a written statement of what brake system must do. This is your design criteria. Don't lose sight of it when you're deep into the design. Design of modern race-car-brake system is not arrived at through magic. Instead, carefully planned steps are required. Success starts with a written statement of what brake system must do. This is your design criteria. Don't lose sight of it when you're deep into the design.
If you are designing a special car for either street or racing use, you'll also If you are designing a special car for have to design the brake system . It's either racing use, you'llbrake also difficultstreet to or take a complete have to from designone thecarbrake It'sa system and system. use it on difficult to take a complete brake different one and have it work system car andconfiguration use it on a Carone weight, properly.from work different one andall have and performance affeciit brakeproperly. Car weight, configuration system design . and performance design all affecr brakeBy brake-system I mean putsystem design.a group of components ting together Bywork brake-system mean putthat properly. design I'll notI attempt to ting together a group of components discuss how to design a brake rotor or that work properly. not attempt to proportioning valve.I'll Instead, I will discusshow how to brakenecessary rotor or show to design make a the proportioning plan valve. I will the Instead, entire system, calculations, show how to make the necessary and select the components to do the calculations, plancomponents the entire system, job . The correct already and select the components to doprobthe exist, regardless of the car. The job. The correct components already lem is selecting the right ones for your exist, regardless of the car. The probcar. lem is selecting the right ones forbrakeyour This chapter covers complete car. system design . If you have an existing covers to complete brakeare trying improve the carThis andchapter system design. If you have an existing brakes, read Chapter 12. However, if car and are tryingthetocarimprove the you are designing rather than brakes, read Chapter 12. However, if modifying it, you have more choices.
you are designing the car rather than modifying it, you have more choices.
88
There are fewer ways you can easily change an existing car. This is why the There fewerbeways you canplanned easily design are should carefully change an existing car. This is why the before buying or building parts. design should be carefully Brake-system design requiresplanned severbefore buying or building al steps. There are many parts. ways to apBrake-system design requires proach the design process, butseverhere al steps. There are many ways to apare my suggestions: proach the design • List design criteria.process, but here are my suggestions: • Calculate forces on tires. List design brake criteria.torques at maxi• Calculate Calculate forces on tires. mum deceleration. braketype torques at maxi• Calculate Choose brake and mounting mum deceleration. location . Choose brake type and mounting • Determine hydraulic pressure relocation. quired. Determine hydraulic pressure pedal-and-linkage design.re• Choose quired. • Calculate master-cylinder diameter Choose pedal-and-linkage design. required. Design restmaster-cylinder of brake system.diameter • Calculate required. There may be some reason to rearDesign reststeps. of brake range these Forsystem. instance, you There mayhave be some reasonand to rearthe pedals wish may already range these steps. For instance, you to retain them. That'll work fine may already have the pedals and wish unless you have to compromise braketo retainperformance them. That'll system to do work it. But,fine if unless you have to compromise existing components won't givebrakegood
system performance to do it. But, if existing components won't give good
brake performance, don't use them. The brakes are too critical to comprobrake performance, use them. mise because of a few don't extra dollars.
The brakes are too critical to compromise because of a few extra dollars. DESIGN CRITERIA The first step in any design process
DESIGN is listing CRITERIA the reasons for the design
The step in any and thefirst objectives. Thisdesign writtenprocess docuis listing the reasons the design ment is your design for criteria. For a and objectives. Thissheets written brakethe system, several of docupaper ment is your design criteria. For a should be enough. You are writing brake system, several the criteria so you can sheets refer toofit paper later. should be enough. You are Keep your design-criteria list writing handy t later. the criteria you can referthe to idesign during and read itsooften Keep your design-criteria list process. Don't lose track of handy your and read it often during the design objectives. process. Don't lose criteria track ofshould your A brake-design objectives. answer the following questions: brake-design criteria will should Under what conditions the • A answer the following brake system have to questions: operate? Underlong what conditions the • How do you expect thewill system brake system have to operate? to last? How youfor expect thestreet system • Is car long to bedo used rac ing, or to last? both? car toperformance be used for racing, street or • Is What specifications both? the brakes meet? should What specifications • If you performance have to compromise on should the brakes meet? If you have to compromise on
Road will withstand withstand exRoad cars must have have brake brake components components that will treme cold. cold. Corvette master cylinder cylinder and and booster booster are being being tested at S8F 58F below below zero (-SOC). (-50C). Road-car brake brake manufacturers manufacturers must must test components components under extremely severe conditions. conditions. If designing designing a special special car, you can can save money by limiting limiting conditions conditions car has has to operate under. under. Photo Photo courtesy Girlock Girlock Ltd. Ltd.
)
, I)
specifications, what is most important? What is least important? • What are maximum loads imposed on system? system? What are normal operatloads? ing loads? Conditions-Think twice Operating Conditions-Think about this one: It is much harder to design a brake system to perform under every possible operating condicondiuse. For tion than it is to limit its use. instance, do you want the brake system to function in the rain? Will it get used in sand dunes like an off-road vehicle? Is it used strictly for drag racing, where there's a long cool-down racing, period after each stop? stop? Will the car be roads? used on icy, icy, salted roads? specific and practical about the Be specific conditions your vehicle will likely encounter. The more operating condiencounter. tions you can eliminate or minimize, the easier and cheaper the job will be. The most difficult job an engineer has to do is design a car that will be driven on the street, in races, off-road and in weather conditions ranging from the burning deserts to sub-zero cold. cold. With luck, your special car will have specialized operating conditions for specialized the brakes. brakes. This will eliminate some extremes. Life-Every car component Design Life-Every or system has a certain life assumed when the engineer designs it. it. Most road-car parts are expected to last at
Easiest Easiest car to design design is is one with a special special purpose-win purpose-win sportscar races, races, in in this case. If car also also had had to transport wife and and kids kids to church would church on on Sunday, Sunday, and and still still win races, races, race-car designer would really really have a tough tough job. Be Be realistic, realistic, but limit limit functions car must must perform-design will be easier. perform-design job will easier.
least 50,000 miles, but often last twice that. If every car were designed to last 40 years, the cars would be too expensive and much heavier. If something is designed for a long life, more. So life, it costs more. restrict long-life items to those that are safety-related. safety-related. Because brakes are safety-related, the structure of the brake system should be extremely durable. You choose the miles, time or number or races. If you are using passenger-car brake parts and will be operating them at less than their original design loads, you can expect them to last a long time. Some brake-system parts wear out quicker than the basic system. This includes the linings, seals and, rotors. sometimes, the drums and rotors. Parts that wear should be designed to don't manner-so they don't do so in a safe manner-so cause a loss of braking. Conventional brake systems are so designed. Therefore, if you use conventional design practice, the brakes will be safe when parts wear out. out. What life do you expect wear-prone brake parts to have? If the linings you 10,000 miles on a are using last 10,000 2500-lb sedan, you can expect them 1500-lb to last at least that long on a 1500-lb way. Use sports car driven the same way. life. comparisons to predict useful life. However, if you drive your special car
Always consider the application: application: If stockcar designer failed to consider consider that car might might compete compete in in road road races with right right turns, driver would be be in in trouble. It is is easier design a car for left turns only. only. Likewise, Likewise, to design it's easier to design design brakes brakes for a short track with high-banked high-banked turns than than one with long long straights and and flat turns.
harder than the sedan that weighs the same, don't expect the linings to last the same. More brake-lining area or a harder lining would be needed to compensate. You cannot make an exact predicprediction of brake life. life. However, write down what you are expecting and keep the desired life in mind while designing the brake system. system. You must have a design goal. goal. This decision Racing vs. Street UseUse-This must be made early in the design process. Make usage part of your criteria. The brake system that works 89
Production-sedan designers have the most difficult design job. I wonder if the VW brakedesign engineers visualized Rabbits racing at Riverside on a hot summer day? Brakes get a severe workout compared to their Production-sedan designers haveeveryday the most highway difficult service. design job. I wonder if the VW brake-
design engineers visualized Rabbits racing at Riverside on a hot summer day? Brakes get a severe workout compared to their everyday highway service.
SAMPLE PERFORMANCE SPECIFICATIONS Car SPECIFICATIONS A Car B SAMPLE PERFORMANCE Type of car Usage Type of car Percent racing use Usage Horsepower Percent racing use Car weight Ob) -average racing Horsepower distribution (front/rear) Weight Car weightcar (Ib)weight -average (Ib) racing Maximum Weight distribution Minimum car weight(fronthear) (Ib) Maximum speed car weight (Ib) Maximum (mph) Minimumrace car weight (Ib) Average speed (mph) Maximum race speedduration (mph) (minutes) Maximum Average race 0-60 speedmph (mph) Acceleration (seconds) Maximum tire racegrip-street duration (minutes) Maximum Acceleration mph (seconds) Maximum tire0-60 grip-racing Maximum tire grip-street Maximum deceleration-street (g's) Maximum tire grip-racing Maximum deceleration-racing (g's) Maximum deceleration-street (g's) Downforce at top speed (Ib)
Maximum deceleration-racing (g's) Downforce at top speed (Ib)
Sports Car Car A Street & slalom Sports Car 5% or less Street 200 8 slalom 5% or less 2000 200 50/50 2000 2400 (street) 50/50 2000 (racing) 2400 125 (street)
2000 (racing) 60
5125 860 5 0.9 8 1.2
0.9 0.9 1.2 1.2
Race car Car B Road racing Race 100% car Road 150 racing 100% 1100 150 40/60 1100 (max fuel) 1150 40/60 1050 (min fuel) 1 150 (max fuel) 150 1050 (min fuel) 100
150 60 6100 60 6 1.4
-
0.9 o
1.4 (with wings) 2.0 500
0
500
1.2
2.0 (with wings)
Performance specifications for two imaginary cars: Car A is a sports car designed for both street use and slaloms; car B is an all-out race car for a small formula-car class. Note how road-car's weight can vary. for Brake must be able to is accommodate all variations, but Performance specifications twosystem imaginary cars: Car A a sports car designed for both remain balanced. street use and slaloms; car B is an all-out race car for a small formula-car class. Note how
road-car's weight can vary. Brake system must be able to accommodate all variations, but remain balanced.
best for racing is not the best for the street and vice versa. Either system best bestwhile for the will for workracing OK isfornota the little in street and vice versa. either application, but Either you willsystem have will worksooner OK for a little while in problems or later. either application, but youracing, will have Remember that while the problems sooner or later. brakes are usually warmed up before a Remember the hard stop; theythat are while not onracing, the street. brakes are usually warmedrequire up before Street-driving conditions pro-a hard stop; on the street. tection fromthey dirtare andnot corrosion; racing Street-driving conditions require conditions may not. Some formsproof tection from dirt and corrosion; racing are much worse than racing street conditions Some formsand of driving for may bothnot. contamination racing are much worse than street high temperatures. driving for both contamination The hardest thing to design is a and car high istemperatures. that used for both street driving and
The hardest thing to design is a car that is used for both street driving and
90
racing . If you attempt this, you must make design compromises that will racing.theIf you this, you hurt car'sattempt performance in must both make design compromises situations. Therefore, try to that limit will the hurt' s operating the car's conditions, performance both car for in highest situations. Therefore, to limit the performance and lowesttry cost. car's operating conditions, highest Performance Specs - List for specificaperformance andtolowest tions you want meet. cost. Because each Performance -List specificatype of vehicleSpecs has different specs, I tions you want to meet. Because can't give you a list for your each car. type of vehicle has different specs, aI However, the above table gives can't youfora two list types for your car. samplegive listing of cars. However, the weight above and tablespeed givesarea Note that car sample for two ittypes cars. included.listing Obviously, takesof more Note that car weight and speed bra ke to stop a fast, heavy car thanare it included. takes more does to stopObviously, a light, slowitone.
brake to stop a fast, heavy car than it does to stop a light, slow one.
Maximum loads on car may occur during an off-road excursion or some other emergency situation. Normal loads don't Maximum loads on caroperating may occur during an include unexpected in other the rough stuff, off-road excursion ortrips some emergenbut such conditions be allowed in cy situation. Normalmust operating loads for don't a design,unexpected including driver include trips error. in the rough stuff,
but such conditions must be allowed for in
a design, including driverand error. Include car weight CO location
in the performance specifications. Include weight CG you location You must car know theseand before can in the performance specifications. design the brake system. When startYou know ,these youknow can ing amust car design you before may not design the weight brake system. When startthe exact or CO location. To ing a the car design, you may not , know start brake-system design estithe exact weightand or CO CG location location.forToa mate the weight start the brake-system design, esticar such as yours. Then you can begin mate brake-system the weight and C G location for a your design . carAfter such as can begin caryours. and Then brakeyou system are your brake-system design. designed, go back and do all the calcuAfter again car and brake lations using the system exact are car designed, go CO back location and do all calcuweight and . Ifthe you eslations using car timated again correctly the the first exact time , few weight and C Gchanges location. should If you esbrake-design be timated .correctly theit first time,takes few required However, usually brake-design changes shouldeffort be two or three rounds of design required. However, it usually takes before an entire car design is two or three completed . rounds of design effort
before an entire car design completed. BRAKE-SYSTEM LOADS
is
As already discussed , the two loads
BRAKE-SYSTEM LOADS to be concerned with are maximum As and already discussed, two Maxiloads loads normal operatingthe loads. to be concerned with are maximum mum loads on most brake compoloads and normal operating loads. Maxinents occur during an emergency. It mum loads on most brake where compo-a could be a panic situation nents occur during It crash may be aboutan toemergency. occur. The could be a panic situation where driver panics and slams his foot on thea crash may as be hard about to can, occur. The brake pedal as he usually driver panics and slams footresult on the locking the wheels. Thishis may in brakeofpedal as hard he can, loss control or as worse . It usually is the locking the wheels. This may result in maximum-loading condition for the loss of control or worse. It is the brake pedal and linkage. maximum-loading condition for the There may be different maximumbrake pedal and linkage. load conditions for parts of the brake There other may bethan different system the maximumpedal and load conditions for parts the brake linkage. A brake-reservoirofbracket exsystem than the periencesother maximum load pedal when and the linkage. A brake-reservoir bracket experiences maximum load when the
MAXIMUM LOADING FOR BRAKE-SYSTEM COMPONENTS Component
Maximum-Load Maximum Load on Component MAXIMUM LOADING FOR Condition BRAKE-SYSTEM COMPONENTS Panic stop-wheels locked 600 Ib forward 200 Ib side Maximum-Load Condition Maximum Load&on Component load on pedal pad. Brake pedal 8 Panic stop-wheels locked Ib forward & 200 Ib side Hydraulic system Panic stop-wheels locked 600 Calculated hydraulic linkage load on pedal pad. pressure with 300 Ib on pedal. Hydraulic system Panic stop-wheels locked Calculated hydraulic pressure Brake caliper Panic stop-wheels locked Calculated hydraulic pressure with 300 Ib on pedal. with 300 Ib on pedal. Brake caliper Panic stop-wheels locked Maximum Calculatedcalculated hydraulic brake pressure Caliper bracket Maximum deceleration with 300 torque . Ib on pedal. Caliper bracket Maximum deceleration Maximum calculated brake Brake rotor Maximum deceleration Maximum calculated brake torque. torque. Brake rotor Maximum deceleration Maximum calculated brake Fluid-reservoir Maximum bump & 5-g downward load & 2.5-g torque. bracket cornering side load on reservoir. Fluid-reservoir 5-g downward load & 2.5-9 Maximum bump 8 bracket cornering side load on reservoir.
Brake pedal & Component linkage
Formula car ran head-on into barrier with brakes locked. Forward-projecting master cylinders pushed bulkhead rearward and Formula car ran head-on into barrier with broke brake Forward-projecting pedal due to resistance of brakesoff locked. master driver's foot. Because of rearward severe and leg cylinders pushed bulkhead injuries, Indy Car prohibited broke off '85 brake pedal duerules to resistance of forward-mounted master cylinders. driver's foot. Because of severeLater leg rules prohibit mounted of injuries, ' 8 5 pedals lndy Car rules forward prohibited front-wheel centermaster line. forward-mounted cylinders. Later rules prohibit pedals mounted forward of
car hits acenter bump. front-wheel line.Assume that the
driver runs off the road and hi ts a car a The bump. Assume that the hard hits bump. bracket should be dedriver for runs off the road and hits signed similar maximum-load co n-a hard bump. The bracket should be desuspension and frame. dition as the signed for similar maximum-load This maximum-load condition is condifdition than as the and frame. ferent thesuspension maximum-load condiThis tion maximum-load for the brake condition pedal. Seeis difthe ferent than the maximum-load sample list of maximum loads condiin the tion for table. the brake See the above Writepedal. down the sample list of maximum loadsforin the maximum-load conditions all above parts table. Write the down system and calculate loads.the maximum-load conditions for all For all parts of the system receiving system partsthe andbrake calculate loads from fluid,the theloads. normal For all parts systemmaximumreceiving operating load ofisthe during loads from theSlamming brake fluid, the foot normal deceleration. your on operating load is during maximumthe pedal and locking the wheels does deceleration. Slamming your footInona 1101 give maximum-deceleration. the pedal and locking the wheels maximum-deceleration stop, does the not give maximum-deceleration. In a wheels are not locked, but the brakes maximum-deceleration the develop maximum torque. stop, The driver wheels but than the brakes pushes are lessnot on locked, the pedal he is develop of. maximum driver capable This is atorque. normalThe stop in a pushes less on the pedal than is race or a controlled fast stop onhethe capable of. This is a normal stop in a road. race a controlled fast stopmust on the All orbrake-system parts be road. made to operate properly at normal All brake-system be operating loads. And, parts they must must not made to operate properly atload normal breakwhile under maximum . operating loads. And, they must not Maximum Loads-Each car and car breakwhile under maximum load. designer will have different requireMaximum Loads-Each car ments for what loads to usecar for and designdesigner will have different requireing the brake system. I use the followments fordesigning what loadsa race to use for designcar: ing when
ing the brake system. I use the follow-
75-lb pedal force at maximum ing when designing a race car: deceleration- normal operating 75-lb pedal force at maximum condition; decelerationoperating 600-lb forward normal and 200-lb sideways condition; maximum force on pedal-panic-stop 600-lb forward and 200-lb sideways conditions.
maximum force on pedal-panic-stop conditions.
Exact values and loading conditions will vary from one car to another. Make sure you select the worst loading condition for each component-that is, the Exact values and loading conditions willNotice vary from car to condition another. Make condition most likely to cause a failure. that one the worst is notsure the you select the worst loading each component-that the same for each component in condition the brake for system. Hydraulic-system is, components condition mosttolikely to cause thethan worst is not are designed withstand 300aIbfailure. on the Notice pedal, that rather thecondition 600-lb load thethe same each component in the load brakeincludes system.aHydraulic-system for. The pedal factor for sudden components load pedal for is designed are designedwhich to withstand Ib on rather than the 600-lb load the application, does not300 apply to the the pedal, hydraulic system.
pedal is designed for. The pedal load includes a factor for sudden load application, which does not apply to the hydraulic system.
Factor of Safety-The maximum loads discussed in the previous section Factor of effects Safety-The maximum incl ude the of suddenly applied loads discussed the previous sectiona However,inthey do nol include forces. include the applied of effects safety.of suddenly As previously factor do not include forces. However, they factor discussed, the safety accountsa factor of safety.between As previously for the difference the maxidiscussed, factor mum load the on asafety part and its accounts breaking between for the difference strength. Never design a partthe to maxibreak mum load on a part and its breaking just as it reaches its maximum load. strength. design adesign part toisbreak Not evenNever an airplane that just as it reaches its maximum load. marginal. Not an factor airplane design for is that Theeven safety accounts unmarginal. knowns that cannot be calculated. Theis safety factor accounts unOne needed because parts for someknowns that cannot calculated. times have hidden flaws,bethey corrode One long is needed because parts someafter use, and loads are often diftimes tohave hiddenaccurately. flaws, they corrode ficult calculate after long use, and using loads are often difI recommend a factor of ficult to calculate accurately. safety of 3 on critical components. I recommend using a factor of This means that the breaking strength safety on critical of the of part3 should be atcomponents. least three This that the breaking strength timesmeans the maximum load on the part. of the part should be at least three You can test a part to see if it is strong times theifmaximum load ontothe part. enough, you can afford destroy You to see if test, it is strong one can part.test Ina apart breaking apply enough, if you afford toload destroy three times thecan maximum the one part. In a breaking test, apply part was designed for. If it doesn't three the amaximum load But, the break, times you have good design. part wasthedesigned it and doesn't destroy part afterfor. theIftest use design. abreak, brandyou newhave one aingood the car. The But, test destroy the part after the test and Reuse may have caused damage. amember, brand new in the Thetimes test you one tested it tocar. three may have load caused Rethe highest that itdamage. should ever member, you tested it to three times experience.
the highest load that it should ever experience.
Loads - Brake-system componen ts also are lo aded inertiaJly when the car Loads -Brake-system components is accelerating , decelerating, cornering alsohitting are loaded inertially the excar or bumps. Inertia when loads are is accelerating, decelerating, cornering pressed in g's. One g is an inertia load or hitting bumps. loads are exequal to the weightInertia of a part, assembly pressed One equal g is antoinertia load or car; 2ing g's. is a load two times equal to the weight of aI use part,the assembly the weight , and so on. follow2 gtoisdesign a load bracke equal to two structimes or ingcar; loads ts and the weight, and so on. I use the followtures that hold parts together: ing loads to design struc• Maximum bump brackets load = 5and g except turesoff-road that holdcars parts for or together: dirt-track racers. = 5 cars g except Maximum Use 10 g or bump more load for race that for off-road cars or dirt-track racers. normally hit large bumps. Use 10 g or cornering more for race thatg • Maximum load cars = 2.5 normally large bumps. on a car hit without wings or at speeds 2.5 g Maximum cornering below 100 mph. Cars load with= wings on a car without wings or at speeds above this speed will have higher below 100 mph. Cars with wings loads. above this speed will have • Maximum deceleration = higher 2.5 g loads. on a car without wings or at speeds Maximum deceleration = wings 2.5 g below 100 mph. Cars with on a carthiswithout or at speeds above speed wings will have higher below loads. 100 mph. Cars with wings above this speed will have higher acceleration = 2.0 g on • Maximum loads. all cars except dragsters. Use 5.0 g or Maximum acceleration = 2.0 g on higher for dragsters. allOn carssmall exceptparts dragsters. 5.0 g or such Use as brackets higher forother dragsters. holding parts to the frame, viOn small such as Abrackets bration must parts be considered. small, holding other parts to the frame, vilightweight part is subjected to higher A small, bration must considered. vibration loadbe s than a large, heavy lightweight is subjected higher part. The part amount of to vibration vibration onloads than a large, heavy depends engine design , suspension part. The amount of vibration stiffness, engine mounts , road
depends on engine design, suspension stiffness, engine mounts, road 91
Maximum loads can occur in two directions at once. Here, stockcar driver cuts a close apex. Resulting bump load from going over curb on right front wheel occurs same timeatasonce. maximum Maximum loads can occur in twoatdirections Here,cornerstocking load. car driver cuts a close apex. Resulting bump load from going over
curb on right front wheel occurs at same time as maximum cornering load.
surface, and many other factors. If in doubt , design small parts to withstand surface, many other If in twice theand maximum loadsfactors. just given. doubt, design small to withstand If anything falls offparts the car, increase twice the maximum its design load when loads doing just the given. repair. If anything falls off the car, increase The only way to measure vibration its design loadexpensive when doing the repair. loads is with sophisticated The only way to measure vibration equipment, which most people can't loads is with expensive sophisticated afford .
equipment, which most people can't afford. CALCULATING TIRE FORCES
To start a brake-system design , first CALCULATING determine forces TIRE acting FORCES on the tires To start aa brake-system first during stop at design, maximum determine forces onthe theeffects tires deceleration. This acting includes during a stoptransfer at and maximum of both weight aerodeceleration. This includes the effects dynamic forces on the car. To do the of both transfer and some aerojob right, weight you need to know dynamicfacts forces ont the thecar: car. To do the specific abou job right, you need to driversome and • Weight of car includingknow specific facts about the car: other loads. of car including driver and • Weight Wheelbase length. other loads. • CG height and fore-and-aft Wheelbase length. location . G height fore-and-aft • C Maximum tire gr and ip. location. • Aerodynamic forces on body. Maximum grip. almost completely A car has tire to be Aerodynamic on body. designed before forces this information can car has to accurately. be almost completely be Adetermined Therefore, designed before this information all the above information may notcan be be determined accurately. Therefore, available at the time the brake system all first the above information may notyou be is designed . Consequently, available at theassumptions-educated time the brake system must make is first designed. you guesses. Start by Consequently, making the brake must make assumptions-educated system adjustable if you don't start guesses. Start byinformation. making the Later, brake with accurate system car adjustable during testing, if youyou candon't makestart adwith accurate information. justments to the brake system . Later, during carThe testing, youof can make adWeightweight a car greatly justments the brake system. affects thetobrake-system design. The
Weight-The weight of a car greatly affects the brake-system design. The
92
Toughest type of vehicle to maintain brake balance under all loading conditions is nose-heavy, front-wheel-drive pickup. Loadsensing proportioning valve between brake body balance and rear under axle ofallDodge Toughest type of vehicle to maintain loadRampage adjusts so brake balance is maintained under all ing conditions is brakes nose-heavy, front-wheel-drive pickup. Loadload conditions. sensing proportioning valve between body and rear axle of Dodge
Rampage adjusts brakes so brake balance is maintained under all load conditions.
car will have to stop in its heaviest form, traveling at m aximum speed. If car will ishave to stoptheincalculation its heaviest the car for racing, is form, traveling at maximum speed. If easy. Most race cars have nearly a conthe carweight is for racing, is stant except the for calculation fuel weight. easy. Most race cars have nearly a conSo , design race-car brakes assuming stant weight full fuel load. except for fuel weight. So,Ondesign race-car brakes assuming a road car, weight can vary full fuel load. The hardest vehicle to considerably. On abrakes road for car, isweight canTrucks vary design a truck. considerably. The hardest vehicle to weigh much more fully loaded than design brakes for is a truck. Trucks when empty. In addition , their centers weigh much more fully when loaded than. of gravity move greatly loaded when empty. In addition, their centers The design of a brake system for such gravityshouId move be greatly aofvehicle basedwhen on itsloaded. maxiThe design of a brake system such mum weight. However, brake for balance amust vehicle be basedaton the its maxibeshould considered nomum weight. However, balance load/full-load extremes .brake Unless the must has be anconsidered at the notruck adjustable brake balance load/full-load extremes. Unless the or a special anti-skid device , balance truck probably has an adjustable brake balance will be incorrect when or a special balance empty. Mostanti-skid trucks device, lock the rear will probably be incorrect when wheels under hard braking if reasonaempty. Most trucks lock the rear bly well balanced when loaded . wheels under -CG hard braking reasonaCG Location location ifcan be esbly well balanced whenwith loaded. timated or calculated reasonable CG Location-CG location be esaccuracy. Most sedans arecanslightly timated or calculated with reasonable nose-heavy when empty and closer to accuracy. Most sedans are slightly 50/50 weight distribution when fully nose-heavy when empty and closer to loaded. This puts the CG at the mid50/50 weight distribution when fully point of the wheelbase at full load. loaded. This puts the sports C G at cars the midThe majority of road also point 50/50 of theweight wheelbase at full Most load. have distribution. The majority road sportswith cars drag also race cars are oftail-heavy, have 50/50 weight distribution. Most racers being the most tail heavy and race cars draga stock cars are the tail-heavy, least. You with can get racersfeel being the most and good for weights andtail CGheavy locations stock cars the least. You can get from automotive-magazine road tests.a good for weights and CG locations CGfeel height is harder to guess at. from automotive-magazine tests. Most sports-car CGs areroadslightly
CG height is harder to guess at. Most sports-car CGs are slightly
above wheel center. A race-car CG is lower than on a road car. If you know above wheel A race-car CGare is where all the center. heavy parts of the car lower than a road car. IfCG you height know located, youoncan calculate where all the heavy parts ofBut the, car are with reasonable accuracy. if you located, you can calculate CG height don't know where they are, it is probawith reasonable you bly too soon toaccuracy. design But, the ifbrake don't where the theycar are,design it is probasystemknow . Establish first, bly design brake then too comesoon back to to the brake the system . system. Establish simple the car chart designcan first, As illustrated, be then back to the system. used come to calculate CGbrake location. Find illustrated, simple can be theAsweight of each majorchart component used to calculate CG location. Find of the car and its planned CG location the weight from of each component measured the major ground and disof the from car and planned CG location tance theitsfront-axle center line. measured from the ground and Multiply the weight times dis-a tance from thelong front-axle distance-as as it'scenter from line. the Multiply the write weight times ina same point-and the number distance-as longcarasweight it's seems from too the the chart. If total same point-and write the number in low , you left out something. Miscellathe chart.small If totalitems car weight neous are seems hard too to low, you left out something. estimate. However, try to Miscellaestimate neous small when items designing are hard the to their weight estimate. However, try toliquids estimate brakes. Also, don't forget and their weight whenof designing the people. The sum the individual brakes. Also, don't forget liquids and weights is obviously tota l car weight. people. sum of the The sumThe of the weight timesindividual distance weights is obviously totalweight car weight. column divided by total gives The sum of the weight times distance CG location. column divided by weight gives Tire Grip-Tire griptotal is important. It C G location.maximum deceleration of determines Tire Grip-Tire grip is important. It the car. On a car without aerodynamic determines maximum deceleration of downforce , maximum deceleration of the car. a carmaximum without aerodynamic the car On equals tire friction downforce, On maximum deceleration of coefficient. a car with aerodynamic the car equals maximum tire friction downforce, deceleration is higher. coefficient. a car with aerodynamic Tire grip On varies considerably. Road downforce, deceleration higher. condition is as importantis as the tires Tire grip varies Road themselves. Racingconsiderably. tires on dry pavecondition as important the tires ment can ishave a grip ofasover 1.0 .
themselves. Racing tires on dry pavement can have a grip of over 1.0.
Component Engine Component Transmission Engine Driver Transmission Front wheels/tires Driver Rear wheels/tires Front wheels/tires Front suspension Rear wheels/tires Rear suspension Front suspension Front brakes Rear suspension Rear brakes Front Framebrakes Rear Body brakes Frame Fuel tank Body Radiator & water Fuel tank Battery Radiator Pedals 8, water Battery Seats
W
x
(WX)
y
(WY)
W
X
(WX)
Y
(WY)
Pedals Seats
Totals
W(total) -
Totals
W(total)
XCG=:t~t~~tal
-
WX(total) -
WX(total) WY (total) ~ ~ Y
(WX) total CG X~~ == (WY) total Y W total CG (WY) total W= each compoment in Y~~ = X = distance CG W totalof component CG from front-wheel inches = weight center of eachincompoment in pounds W 'CG Y= = distance height of of component CGCG from the ground in inches X component from front-wheel center in inches XCG = CG location behind front-wheel center in inches = height of component frominthe ground in inches Y Y CG = CG location above CG ground inches XCG= CG location behind front-wheel center in inches = CG location above ground in inches ,Y ,
we%~~t~~
WY(totail -
pound~
- -
:
CG
Ground
t
Ground
CG location can be determined by filling out chart and performing calculations. Each component in a car has its own weight and CG location. List weight and CG location for each component If component is out forward front-wheel center, use a negative CG location can as beshown. determined by filling chartof and performing calculations. Each number for X-in thishas case times X will negative. forlocation WX, make component in a car its W own weight andbeCG location.When List adding weight totals and CG for sure you add negative numbers correctly orisWX total will be too large. center, use a negative each component as shown. If component forward of front-wheel number for X-in this case W times X will be negative. When adding totals for WX, make sure you add negative numbers correctly or WX total will be too large.
Road tires seldom exceed 0.8. You'll have to choose the tires before you Roadestimate tires seldom exceedgrip. 0.8. If You'll can maximum you have to the tires before guess toochoose high, weight transfer willyou be can estimate maximum grip. If you too high. guess too high,Forces-Most weight transfer willcars be Aerodynamic race too high. quickly at high speed bedecelerate Aerodynamic Forces-Most racefrom cars cause of aerodynamic downforce decelerate quickly at high speed bewings and the shape of the body. cause of aerodynamic downforce from Downforce varies with car design and wings the that shape of huge the wings body. speed. and On cars have Downforce withdownforce car design may and or ground varies effects, speed. On cars that have huge wings exceed the weight of the car! or ground effects, may Consequently, you downforce should know exceed weight of thebefore car! somethingtheabout downforce Consequently, brakeshould system. know First, you can design ayou something before the supplier about of your downforce wing(s) should be you a brake system. inforFirst, able can to design give you downforce the supplier of youronwing(s) should be mation. However, a ground-effects able to give you downforce inforcar, testing in a wind tunnel is usually mation. However, on a ground-effects the only way to get this information. car, testing in a wind anything tunnel is by usually You can't estimate just the onlyatway to get this information. looking the car. You estimate anything by just At can't highway speed, aerodynamic looking are at thesmall. car. So ignore aeroforces At highway speed, aerodynamic dynamic forces on a road car unless forces are small. So ignore aeroyou have accurate information.
dynamic forces on a road car unless you have accurate information.
Again, be ready to change the brake system during testing if things don't Again,as be to change the brake work youready estimated . system during totesting if things In addition the amount of don't aerowork as you estimated. dynamic force, you must know where In force addition of aerothis acts to on the the amount body. The point dynamic force, you must know where where the center of all aerodynamic this force the body. point forces actsactsis oncalled the The center of where the allcenter aerodynamic pressure. Oncenter a wing of , the of presof forcesis acts is called theof center sure roughly a fourth the way pressure. a wing, center of wing pres-. front the edge of the back fromOnthe sure fourthbeofanywhere the way. On a is carroughly body, ita could back from the front edge of the wing. If you don't have any information, On a car body, it could be anywhere. assume the center of pressure is at the If you don't center of have the any bodyinformation, - not the assume the center of is at the wheelbase. Designingpressure a ground-effects center of testing the tobody-not the car without find the center wheelbase. a ground-effects of pressureDesigning may cause big trouble . car without testing to findonthegroundcenter Many handling problems of pressure may cause big trouble. effects cars have been caused by a Many handling problems center of pressure being inonangroundunexeffects cars have been caused by a pected place. center pressure being in anwith unexAdd Upofthe Numbers-Now, all pected place. the estimated weights or loads, calcuAdd tire Up the Numbers-Now, all simple, late forces. To make life with the estimated weights or loads, calcuassume that friction force on a tire late tirevertical forces.force To make lifegrip. simple, equals times its For
assume that friction force on a tire equals vertical force times its grip. For
a tire with 1000 Ib of vertical force on it and a grip of 0.8, friction force is a tirelb.with 1000 Ib were of vertical on 800 If the grip raisedforce to 1.1, i t and grip ofdeliver 0.8, friction is that tirea could 1100 lb force of fric800 lb. If the were force raised istowhat 1.1, Thegrip friction tion force. that tire deliver lb high of fricstops thecould car-it should1100 be as as tion force. The friction force is what possible. stops car-it page should as high as See the drawing, 94,bethat shows possible. the forces acting on a car during See drawing, 94, that shows braking. For this page calculation, I assume the forces acting on a car during the right and left tires at both ends of braking. For loaded this calculation, assume the car are equally. IThis asthe right and left tires at both ends of sumption is more accurate than other the car are loaded equally. This asdata usually used for this calculation. sumption is more accurate than other The formulas with the drawing are data usedtire for forces this calculation. used usually to calculate . If you are The formulas the drawing are assuming somewith aerodynamic lift, put used to calculate tire forces. If you are a negative number into the formula assuming some aerodynamic lift, put for downforce . a When negative numbera car intoto the designing run formula on varifor downforce. ous surfaces or different types of tires, When the designing car to accordingly. run on varichange grip avalue ous surfaces or different types of tires, Then perform a calculation for each change the grip value accordingly. grip. Grip might be as low as 0.3 for a Then performto aperhaps calculation for aeach 1.4 for hot slick surface grip. low .asResulting 0.3 for a racingGrip tire might on a be dryastrack slick surface to the perhaps for forces a hot answers will be range 1.4 of tire racing tire on a dry track. Resulting you must deal with.
answers will be the range of tire forces you must deal with.BRAKE TORQUE CALCULATING
Brake torque is the friction force on CALCULATING BRAKE TORQUE the tire, multiplied by the rolling Brakeoflorque is the friction on radius the tire. For designforce of the the tire, multiplied by the rolling brake system, always use maximum radius the tire.Maximum For design torque of the brake oftorque. brake when: system, always use maximum occurs brake torque. torque • Vertical force onMaximum tire is maximum . occurs when: • Tire grip is maximum. Vertical force on tireare is maximum. tires used. • Largest-radius Tire grip is maximum. • Car is stopped at maximum possible Largest-radius tires are used. deceleration. Car possible If a is carstopped has a at nutmaximum on the center of deceleration. each wheel, you could measure brake If a car hasa a large nut on the center of torque with torque wrench. each you on could Whilewheel, pushing themeasure brake brake pedal torquean with large torque with efforta needed to givewrench. maxiWhile pushing on the pedal mum deceleration, turn brake the wheel with an effort give maxiwith the torqueneeded wrenchtoand measure mum deceleration, turnEven the though wheel torque as the wheel turns. with the torque wrench and measure this test is done rarely, this example iltorque aswhat the wheel Even though lustrates braketurns. torque means. A ilthis test is donemust rarely, brake system be this ableexample to deliver lustrates what braketorque. torqueOtherwise, means. A the needed brake brake system must be able to deliver the driver won't be able to stop the the needed brake torque. Otherwise, car at maximum deceleration with an the driver won't be ableHe to may stop not the acceptable pedal effort. car maximum an haveat the strengthdeceleration to achievewith maxiacceptable pedal effort. He may not mum deceleration' have the strength to achieve maxiCalculate maximum brake torque mum using deceleration! the formulas given . Use the Calculate maximum brake values of grip, car weight andtorque aerousing the formulas given. Use the dynamic force that give maximum values offorce grip,oncarthe weight aerofriction tire. and Calculate
dynamic force that give maximum friction force on the tire. Calculate 93
Modern cars with wings and ground effects generate much more downforce than ordinary cars. Indy Car cornering and braking loads arecars much higher than forground a modified roadgenerate car. You much must know Modern with wings and effects more speed and downforce to correctly calculate loads generated by downforce than ordinary cars, lndy Car cornering and braking tires. loads are much higher than for a modified road car. You must know
speed and downforce t o correctly calculate loads generated by tires.
~---------b--------~·~I Center of
Design of ground-effects car should be left to experts. Windtunnel testing is the only sure way to determine aerodynamic loads Note ground-effects at rear of car. Designonof car. ground-effects car shouldexit be tunnels left to experts. WindPhoto by Tom Monroe. tunnel testing is the only sure way t o determine aerodynamic
loads on car. Note ground-effects exit tunnels at rear of car. Photo by Tom Monroe. I
wheelbase of car (in.)
=
We = total weight 01 the car (lb) F, vertical force on (in.) both front tires (Ib) I == wheelbase of car force of onthe both F,, = =vertical W total weight carrear (Ib)tires (lb) FA = vertical aerodynamic downforce Ff = force on both front(lb) tires (Ib) f-t (coeflcient friction) tires F, == grip vertical force onofboth rear of tires (Ib) d = aerodynamic maximum deceleration FA downforce(g's) (Ib) M= b = from front axle to center p = distance grip (coeffcient of friction) of tires of pressure (in.) Xeg = maximum distance from front axle(g's) to CG (in.) deceleration dM = Y height offrom CG above ground (in.) of pressure (in.) b eg = -distance front axle to center Xcg = distance from front axle to CG (in.) Ycg - height of CG above ground (in.) [Xeg f-t Ye~ f.1. YegJ F, = We~ --1- + -I-J+ FAL + --I-
[b
,
2FFR
__-
-I
=
w,[-p + 'j++ F] FA[-:
_ _ Xcg _ _ _ _...... 1 We
I
I-
I
Fr = W,
.1
+ FA- Ff
I
FF = Friction Force On One Front Tire =~ LIL
FF
=
d M = ~ +FAP -
wc
f-t F,
Friction Force On One Rear Tire = - -
2
vFf
2
/JFr
FF = Friction Force On One Front Tire =FF =on Friction Forcetire On One Rear Tire =forces - are computed. If you can estimate or calculate all data shown on drawing, 2you can calculate forces tires. From forces, friction 2 Friction forces are then used to calculate brake torque during maximum deceleration. It is assumed FA is the only aer?dynamic downforce.
If you can estimate or calculate all data shown on drawing, you can calculate forces on tires. From tire forces, friction forces are computed. Friction forces are then used t o calculate brake torque during maximum deceleration. I t is assumed FAis the only aerodynamic downforce.
both front- and rear-tire forces. Maximum brake torque is calculatboth and rear-tire forces. ed byfrontthe following formulas: Maximum brake torque is calculatFront-brake torque = FFF r FT in ed by the following formulas: i nCh-pou nds Front-brake torque rFTtire in in FFF = Friction force = onF,front inch-pounds pounds Frictionradius force on front tire tire inin FFF r FT == Rolling of front pounds inches
,r = Rolling radius of front tire in Rear-brake torq ue = FFRr RT in inches
inch-pounds Rear-brake torque in in FFR = Friction force=onFF,rrear tire inch-pounds pounds F Frictionradius force on rear tire tire inin r,RT == Rolling of rear pounds inches
,,r = Rolling radius of rear tire in Rolling Radius - The rolling radius of inches
a tire is the distance from the center Rolling Radius rolling radills of of the wheel to -The the pavement wilh the a tire is the distance from the center of the wheel to the pavement with the
94
lire loaded. You cannot get an accurate rolling radius by measuring an unloadtire tire. loaded. Youtirecannot get an accurate ed The deflects when suprolling porting radius a car. by measuring an unloaded Rolling tire. The tire depends deflects on when radius the supload porting a car. on the tire, tire size, inflation pressure radius the load andRolling stiffness of depends the tire on casing. So on the tire, tire size, inflation pressure measure rolling radius with the car on and stiffnessMake of the the ground. suretirecarcasing. weight So is measure rolling radius with the on the same as yours will be. Also car check the ground.pressure; Make surecorrect car weight inflation it is if the same as yours will be. Also check necessary. inflation pressure; correct it if necessary. SELECTING & POSITIONING BRAKES SELECTING & Take the following into consideraPOSITIONING BRAKES tion before selecting brakes: following • Take Disc orthe drum brakes. into consideration before selecting brakes: Disc or drum brakes.
• Brake diameter. • Brake mounting-inboard or outBrake diameter. board. Brake mounting-inboard outEach decision must be madeorbefore board. a brake . selecting Each be made Theredecision are a must number of before brake selecting a brake. sources. Several manufacturers have Thereforarespecial a number of brake brakes applications. Or, sources. Several have you could use manufacturers standard road-car brakes for special applications. Or, brakes. Your choice depends primarily you could use standard road-car on the intended use. For instance, is brakes. choiceuse depends primarily your carYour for street or racing? If it's the intended Fordesigned instance,for is aonrace car, use use. brakes it's your for street or racing? racing.carBrakes fromuse a road car areIfusua racetoo car, heavy use brakes for ally for designed best racing racing. Brakes from a road car are usuperformance. And racing brakes on a ally too racing street car heavy may be foran best unnecessary performance. And racing brakes on a expense. street car may be an unnecessary expense.
Unloaded Radius of Tire Unloaded Radius Tire at Proper Inflation Pressure and Load Tire Under at Proper Inflation Pressure and Under Load
--~-----r--~~~~----~--~r---~----~Ground
While most road-car brakes are too heavy, some are worth considering for highperformance use. Cast-iron Corvette While most road-car brakes1984 are too heavy, sliding are caliper was designed more high some worth considering forforhighperformance thanCast-iron low cost.1 9It8 4may be a performance use. Corvette natural for road with 4-wheel sliding caliper was car designed more for disc high brakes. Photo than courtesy performance low Girlock cost. ItLtd. may be a natural for road car with 4-wheel disc brakes. Photo courtesy Girlock Ltd.
F = Vertical Force on Tire = Vertical Force on Tire from wheel center to ground with car weight on tire. Tire RollingF radius of tire is distance must be at correct inflation pressure. Rolling radius of tire is distance from wheel center to ground with car weight on tire. Tire must be at correct inflation pressure.
Disc Brakes or Drums? - Because disc brakes are usually superior to Disc Brakes Drums? -Because drum brakes, or most people choose disc brakes are usually superior to discs for high-performance applidrum brakes, mostthere people cations. For racing, is nochoose other discs for high-performance applichoice if you want to win. Drum cations. For racing, there is no brakes have many limitations. other You choice want to to win. will needif a you special reason use Drum drum brakes have many limitations. You brakes for racing-such as rules requir-
will need a special reason to use drum ingthem. requirbrakes racing-such as rules of On a for road car, a combination disc ing them. and drum brakes may be best. Drums Onbe a road car, aon combination of disc may standard the rear axle you and drum brakesroad may cars be best. mustDrums have will use. Also, may be standard on theare rearusually axle you parking brakes- drums set will use. Also, road cars must up for parking brakes. Although have disc parking brakes-drums are usually set brakes on the rear are good for a road up for parking brakes. Although disc car, they may introduce added combrakes rear Aaredisc good for athat's road plexity on andthecost. brake car, they mayforintroduce not designed a parkingadded brakecommay plexity andtocost. be difficult adapt.A disc brake that's notNow designed for posed a parking brake may that I've the disc/drumbe difficult to adapt. brake question, I'll assume you are Nowdisc that brakes I've posed discldrumusing on allthefour wheels. brake high-performance question, I'll assume Most cars you are are so using disc brakes on all four wheels. designed. If you choose drum brakes, Most high-performance cars areThe so the design procedure is similar. designed. Ifis you brakes, difference thatchoose you'll drum have to conthe design procedure is similar. The sider the servo action of a drum difference is that you'll have to conbrake. Servo action is discussed in sider the2. servo action of a drum Chapter brake. Servo action is discussed in Brake Diameter-Disc-brake diameChapter 2. outside diameter of the ter is the Brake Choose Diameter-Disc-brake diamerotor. the largest-diameter ter is the outside diameter the brakes that will fit in the wheels,ofif the rotor. Choose the inlargest-diameter brakes are mounted the wheels, not brakes that will98. fit The in theonly wheels, if the inboard, page exception brakes are mounted in the wheels, not inboard, page 98. The only exception
to this is on a very light car or one with large-diameter wheels. Most to this is on a very light car or from one high-performance cars benefit with large-diameter the largest possible rotorwheels. that will Most fit. high-performance benefit from Maximum rotor cars diameter is about the largest possible rotor that will fit. 3-in. smaller than wheel diameter. Maximum diameter is about For example, rotor a IO-in. rotor should go 3-in. than wheel diameter. inside smaller a 13-in. wheel or a 13-in. rotor For example, a 10-in. rotor should go in a 16-in. wheel. Caliper design deterinside a 13-in. wheel or a 13-in. rotor mines how big a rotor can be used for a 16-in. wheel. Caliper design deterwheel. aingiven mines how big a rotor canuse be used for For pavement racing, a largea given wheel. diameter wheel with a low-profile tire For than pavement racing, rather a smaller wheeluse andaa largehighdiameter wheel with a low-profile tire profile tire. With a given rolling rather than a smaller wheel and a highradius, the large wheel allows the use profile tire.brake Withrotor; a given of a larger and therolling lowradius, the corners large wheel profile tire better.allows the use of a larger brake rotor;- and the lowDisc-Brake Selection Rotors and profile tire corners better. calipers should be selected as a Disc-Brake and matched set. Selection By using -aRotors caliper and calipers shouldto be rotor designed workselected together,asyoua matched set.to By usingabout a caliper and don't have worry a dimenrotor designed to work together, you sional mismatch between the two. So don't have to worry dimenchoose the caliper andabout rotor aintended sional the two. So for themismatch same roadbetween car or from a racechoose the caliper and rotor intended car- brake manufacturer. forCalipers the same car or from a raceandroad rotors must meet the car-brake requirements: manufacturer. following and be rotors mustenough meet the • Calipers Rotor must massive to following requirements: absorb heat from at least one stop Rotor must be speed massive to from maximum at enough maximum absorb heat from at least one stop vehicle weight. from maximum speed and caliper mustatfit maximum mounting • Rotor vehicle weight. space on car. Rotor and caliperdeliver must fit maximum mounting • Brake must space car. required without excesbrake on torque
Brake must deliver maximum brake torque required without exces-
Although fixed, aluminum race-car caliper appears similar to Corvette caliper in above photo. APaluminum CP2751 race-car caliper was deAlthough fixed, caliper Signed forsimilar IMSA toroad racers using appears Corvette caliper13in in.-diameter above photo.rotors. AP C PThese 2 7 5 1 require caliper minimum was de14-in.-diameter inboard brakes. signed for IMSAwheels road or racers using 13Photo courtesy AP Racing. in.-diameter rotors. These require minimum 14-in.-diameter wheels or inboard brakes. Photo courtesy AP Racing.
Race cars generally use largest possible brake diameter. On this Indy Car, caliper almost rubs generally against inside wheel.possible Race cars use of largest brake diameter. On this lndy Car, caliper almost rubs against inside of wheel.
sive tl uid pressure. One-Stop Temperature Rise Roadsive pressure. weight must be Car fluid Rotors-Rotor One-Stop Temperature Roadhigh enough to absorb Rise all kinetic Car Rotors-Rotor weight must be energy stored in the moving car. The high enough absorb all worst conditiontois stopping a carkinetic travenergyatstored in thewith moving car.atThe eling top speed the car its worst condition is stopping a car maximum weight. Some road travcars eling at top that speedprobably with thedon't car at its have brakes meet maximum weight.This Some road cars this requirement. is probably be-
have brakes that probably don't meet this requirement. This is probably be95
Kinetic energy
Wc S2 =---
W,S2 29.9 Kinetic energy =in foot-pounds 29.9 We = Weight of car in pou nds Sin =foot-pounds Speed of car in miles per hour W, = Weight of car in pounds After calculating kinetic energy S = Speed of car inthe miles per hour of a car, determine how much energy After kinetic goes to calculating the front the brakes andenergy how of a car, determine how much energy much to the rears. A good guess is to goes to thekinetic front energy brakes according and how proportion much the torques. rears. A This goodrelationship guess is to to the to brake proportion kinetic energy is only approximate, but theaccording calculato the brake torques. This tion for rotor weight does relationship not have to is but the calculabe only exact.approximate, Use the following formula:
tion for rotor weight does not have to = KrTF K exact. be Use the following formula: F
Exception to the rule: Brake is considerably smaller than wheel allows on front ofI lu sprint car. Demands on Brake brakesisofconsideracar raced Exception to the rule: on are than muchwheel less allows than ifonraced bly dirt smaller front on of pavement. sprint car. Demands on brakes of car raced on dirt are much less than if raced on pavement.
Garage area or pits is best place to look at and photograph race-car brakes. Take advantage of oryears trialGarage area pits isof bestexpensive place to look at and-error development to select and photograph race-car brakes. Takerotor adsizes and of designs. the mechanics. vantage yearsTalk of toexpensive trialIf they have brake trouble, their and-error development to consider select rotor problems your Indy sizes and during designs. Talkbrake to thedesign. mechanics. Car brake wasbrake photographed at Phoenix InIf they have trouble, consider their ternational Raceway-one-mile problems during your brake design.paved lndy track that was putsphotographed high demands on brakes. Car brake at Phoenix InPhoto by Tom Raceway Monroe. -one-mile ternational paved
track that puts high demands on brakes. Photo by Tom Monroe.
cause some road-car designers think it's unreasonable to drive at the top cause some designers speed of a carroad-car at maximum weightthink and it's unreasonable drive at thethink top suddenly do a hardtostop. I don't speed of a car at maximum weightdrivand it's unreasonable, even though suddenly a hard think ing at topdo speed is stop. illegalI don't and unsafe it's unreasonable, even though on the road; but some people do it.drivingFrom at top speed 1, is the illegal and energy unsafe Chapter kinetic on the road; but some people do it. as of a moving car is determined From Chapter 1, the kinetic energy follows:
of a moving car is determined as follows: 96
(T F + T R)
KF = Kinetic energy to front brakes in foot-pounds KF = Kinetic energy to front brakes Kr = Total kinetic energy of car in in foot-pounds KT Total kinetic energyinofinch-pounds car in T F == Front brake torque foot-pounds T R = Rear brake torque in inch-pounds T, = Front brake torque in inch-pounds = Kr - KF T , KR = Rear brake torque in inch-pounds KR = Kinetic energy to rear brakes in K,= K T - K, foot-pounds K, = Kinetic energy to rear brakes in The kinetic energy calculated is for foot-pounds a pair of brakes-two front and two TheDivide kineticthe energy calculated for rear. answers by 2 tois get pair of brakes-two and two akinetic energy absorbed front by each brake. rear. Divide the answers by 2 to rise get Now, compute the temperature kinetic energy absorbed by each brake. of the rotor after one stop using Now, compute formula on page the 11 .temperature Use weightrise of of therotor rotoror after stop using single drum one for W s' This is formula on temperature page 11. Use of the average of weight the entire single rotor drumtemperature. for W,. This is rotor, not theor surface theIfaverage temperature of the entire the average rotor temperature is+ rotor, the surface near not lOOOF (538C) temperature. use a heavier If the average temperature rotor. This meansrotor a thicker rotor is if near lOOOF (538C) use a you have chosen the largestheavier rotor rotor. This means The a thicker rotor if diameter possible. type of brake you have the largest linings usedchosen will determine howrotor hot diameter The still type have of brake the rotor possible. can be and the linings used will determine how hot brakes work. the rotor Rotors-If can be andyou stillarehave the Race-Car designbrakes work. ing a race car, and the brakes are used Race-Car Rotors-If designmany times during a you race,are a calculaing a race car, and the brakes are used tion for one stop will not mean much. many times a race, a calculaBefore each during stop, brake temperature tion be formuch one stop willthan not mean much. will higher 100F (38C). Before each stop, brake temperature For a road racer, assume the rotors will much500F higher(260C) than 100F ( 3 8the 0. are be about when For a road racer, assume the rotors brakes are applied. Also, each brake are about is500F (260C)topwhen application not from speed the to brakes are applied. Also, each brake full stop as assumed in the previous application is not from top speed to calculations. fullRacers stop ashave assumed in the previous experimented with calculations. different-size and -weight rotors for Racers have experimented with years. Although some work, others different-size -weight for can overheat. and After years rotors of trialyears. Although others and-error, a brake some designwork, has been decan overheat. Afterracing yearsclass of trialveloped for each that
and-error, a brake design has been developed for each racing class that
works for most cars under normal conditions. Go to the track and look at works for on most under normal the brakes carscars similar to yours. If conditions. G o selected to the track and lookdifat the rotor you is greatly the brakes on cars to yours. If ferent in size andsimilar weight, you are the rotor you selected is greatly difprobably wrong. If in doubt, go larger. ferent size and weight, you onarea Use thisinmethod to select rotors probably wrong.your If incar doubt, go larger. race car, unless is unique. Use thisword method to selectIfrotors One of caution: other on carsa race car, unless your car is unique. in your class are using water-cooled One word of147 caution: other have cars brakes-page -they Ifeither in your classrotors are using water-cooled undersized or improper air brakes-page ducting. Water 147-they cooling is aeither crutchhave and undersized or unless improper air should not rotors be used larger ducting. Water cooling is a. crutch and brakes cannot be fitted In other should notthebecompetition used unlessis larger words, if using brakes cannot be In thicker other water cooling, go to afitted. larger or words, if they the use. competition is using rotor than water cooling, to ayou larger thicker While at the go track, canormake inrotor than observations they use. teresting about brakes. at the canoval make inIf While you are at atrack, flat, you paved track teresting about brakes. where hardobservations braking is used going into If youone areand at athree, flat, time pavedvarious oval track turns cars where hard braking is used going early in a long race and late in into the turns one time increase various cars same race.and If three, lap times on early in longnot race latechances in the some carsa and on and others, same lap times increase on are therace. cars Ifrunning slower near the some cars and not on others, chances end are "running out of brakes." See are carsvarious running cars slowerarenear the whatthethe doing end are "running out of brakes." See differently. what carslong arestraights doing At a the road various course with differently. followed by tight turns, such as turn Atata road course withthelong straights five Elkhart Lake, importance followed by tight turns, such turn of good brakes is evident. Walkasalong five at Elkhart the straight to Lake, where the theimportance cars start of good brakes is evident. Walkdeeper along braking and see how much the straight to where the cars start cars with good brakes go. Good braking andmean see ashow much brakes can much as a deeper 200-ft cars with going goodinto brakes Good advantage a slowgo. corner off brakes can mean as much as a 200-ft a fast straight. Imagine how much advantage a slowitcorner horsepowergoing and into handling takes off to amake fastupstraight. 200 feet!Imagine how much horsepower and handling it takescan to Race-ear-brake manufacturers 200 feet! make up be a big help when selecting rotors for Race-car-brake can a race car. They aremanufacturers aware of all applibe a big for helptheir whenproducts selecting and rotorswhat for cations a race car. aware of all aware appliworks best.They Theyare also are made cations for their their brakes productsdon't and work. what of it when works best. They also are made aware Manufacturers work with race-car deof it when brakes signers to their develop the don't best work. rotor Manufacturers work with design for each racing class.race-car designers to companies develop the rotor Contact suchbest as Hurst, design for each racing class. JFZ, Tilton, Wilwood or their dealers Contact suchyour as special Hurst, before you companies buy rotors for JFZ, Tilton, Wilwood or their dealers race car. before Area-Another you buy rotors for special Swept aid your in selecting race car. the proper rotor size is the swept area Swept aid on in selecting of the Areabrake. Another The chart page 28 swept cars. area the proper rotor sizefor is the shows swept area various of the brake. The chart on page 28 Consider using a swept-area-to-weight shows swept area for various cars. ratio for a car of nearly the same Consider a swept-area-to-weight power andusing speed as yours. If you are ratio for aa car nearly same designing raceofcar, use the a swept-
power and speed as yours. If you are designing a race car, use a swept-
area-to-weight ratio for race cars, not for road cars. In both cases, if long area-to-weight race cars, not lining life andratio fadefor resistance are for road cars. In both cases, if long more important than brake weight, lining life and use a higher sweptfade area. resistance are more important thanmeans brakeyou weight, Higher swept area must use swept area.rotor. This may use aa higher larger-di ameter Higher sweptusing area means you must mean larger-diameter also use a larger-diameter rotor. Thisrotor may wheels, if the wheels limit also meanIf you usingsimply larger-diameter diameter. cannot get wheels, if the area wheels limit ofrotor enough swept because the If you simply diameter. wheels, you can reso rt tocannot using get inenough swept page area 98. because of the board brakes, An inboard wheels, can resort to using inbrake isyou mounted inboard on the board or brakes, page transferring 98. An inboard frame transaxle, brakinboard onto the brake is through mounteda driveshaft the ing force frame or transaxle, transferring brakwheel. ing force a driveshaft the Vented or through Solid Rotors - When to lookwheel. ing at cars like yours, note whether Vented ororSolid vented solidRotors-When rotors are lookused. ing at cars likeweight yours,and note whether Usually, rotor cooling revented or solid rotors ifare vented used. quirements determine Usually, weight and cooling rerotors arerotor needed. Vented rotors are quirements determine if needed. vented rotors are used where heavier rotors needed. Vented are A very are thick solid rotor doesrotors not cool used where heavier rotors are needed. adequately. Because of this, it is A very thick solid cool unusual to see a rotor solid does rotor not thicker adequately. than 1/2 in. Because of this, it is unusual see needs a solidverotor If yourto car nted thicker rotors , than 112 in. refer to the rotor section in Chapter 3. If yourtypes car of needs vented rotors, Various vented rotors are 3. refer to theYour rotorbrake section in Chapter available. supplier will be Various types of rotors are able to compare thevented merits of one type available. Your brake be versus another. I supplier suggest will using able to compare thecurved merits vents of oneiftype vented rotors with you versus another. I suggest using can afford them. The cooling advanvented rotors with curved vents if you tages are worth the expense.
can afford them. The cooling advantages are worth expense. CALIPER SELthe ECTION Caliper
and
rotor
selection
go
CALIPER SELECTION together because they often come
Caliper and manufacturer. rotor selection go from the same He will together they works often with comea supply a because caliper that from the same manufacturer. will certain-diameter and -thicknessHerotor. supply a caliper that works with Make sure the caliper fits in thea certain-diameter andcalipers -thickness desired area. Some are rotor. more Make caliper fits in the compactsure thanthe others. Pay attention to desired area. You Somemust calipers more the details. not are machine compact others. Pay attention to metal off than a caliper to provide clearance the details. You must not machine to a wheel or suspension member. metal offuse a caliper to provide clearance Also, a caliper that will mount to a wheel suspension member. on your or suspension or chassis Also, use aSome calipercalipers that will components. aremount easily on your suspension or adapted to existing components.chassis Concomponents. calipers are sult a brake Some manufacturer. He easily may adapted to existing components. Conoffer a ready-made caliper mounting sult a brake manufacturer. He may bracket. offer a ready-made caliper mounting If you are also designing a new bracket. suspension, be sure to consider the If you and are also designing new caliper provide space a large suspension, be sure to consider enough for it. A proper caliperthe is caliper bit and asprovide spaceas large every important the enough for it. A proper caliper is suspension. every bit as suspension.
important
as
the
Don ' t buy a caliper that must use a flimsy mounting bracket. Make sure buy isa caliper thatand muststrong. use a theDon't bracket very stiff flimsy Extra "mounting beeP ' on bracket. this partMake helps sure the the bracket very stiffbracket and strong. braking. A ismounting that Extra "beef' onpoor this brake part helps the twists can cause performbraking. A mounting ance and uneven pad wear.bracket that twists cause poor delivered brake performThe can brake torque by a ance and uneven pad wear. caliper and rotor must be as great or The than brakewhat torque delivered by a greater is required for maxicaliper and rotor mustThe be as great or mum deceleration. maximum greater what is required for by maxipossiblethan brake torque is limited the mum deceleration. The maximum maximum operating pressure the calipossible torqueIfisthis limited by the per can brake withstand. maximum maximum the calipressure isoperating exceeded,pressure the caliper can per can withstand.theIf this flex excessively, seals maximum can leak pressure is exceeded, the caliper caliper can can and, in severe cases, the flex excessively, the seals can leak fail. Never design a brake system that and, in severe cases, the caliper can exceeds the manufacturer's recomfail. Never design a brake system mended maximum-pressure rating.that exceeds theRotor manufacturer's recomCaliper & Placement-When mended maximum-pressure rating. fitting brakes to a new car, it's imporRotor tant to position theP1aeement-when caliper in the best fitting to a the new rotor, car, it'sand imporpositionbrakes around the tant toand position theincaliper in the best rotor caliper the best lateral position around the rotor, and the position. rotor and caliper in the bestposition lateral First, let's consider caliper position. aro und the rotor. Assume you are First, let's consider caliper position looking at the left-front wheel from around the rotor. Assume you are the outside. Theoretically, the caliper lookinggoat at the any left-front wheel from1 could position from the outside. o'clock to 12Theoretically, o'clock. Therethe arecaliper many could go at any position things to consider, such as from existing1 o'clock to 12 o'clock.bleeding, There arespindle many mounting bosses, things to consider, such as and existing deflection, air-duct location, susmounting pension andbosses, steeringbleeding, clearances.spindle deflection, air-duct location, susIf you have an existing car,and mountpension and steering clearances. ing bosses on the spindles- or If you have uprightsmay an existing dictate car, mountcaliper ing bosses on isthebestspindles-or at 3 and 9 location. Bleeding uprights-may dictate positioned caliper o'clock. Usually, calipers location. Bleeding is best at 3 and 9 at 12 and 6 o'clock must be removed, o'clock. Usually, positioned rotated and have acalipers spacer inserted to 12 .and 6 o'clock be removed, at bleed Spindle and must axle-shaft deflecrotated and have a spacer can inserted to tion during cornering cause bleed. Spindle and axle-shaft defleccaliper-piston knockback with calipers tiontheduring cause at 12- andcornering 6-0'clock can positions. caliper-piston ktiockback with calipers This should not be a problem with at the 12- hubs and or 6-o'clock positions. full-floating sliding calipers. This shouldairnot be aenter problem Because ducts from with the full-floating hubs or sliding calipers. front of a brake, 3 o'clock is usually Because from can the best for theaircaliducts per soenter the ducts 3 o'clock is usually front of a brake, enter the center of the rotor at 9 best for the caliper suspension so the ductsclearcan o'clock. Although enter differ the center of tothecar,rotor ances from car thereatare9 o'clock. Although suspension usually ball joints and uprights clearat 12 ances differ from car to car, arms there are are and 6 o'clock. Steering usually ball joints and uprights at 12 either at 3 or 9 o'clock . Usually, when and 6 o'clock. Steering everything is considered , 3 arms o'clockare is either at 39 or 9 o'clock. Usually, when best and o'clock is second best, but everything considered, is any positionis will work. It 3allo'clock depends best and 9 o'clock is second best, but on what is best for your car. anyFor position work. It all lateral will positioning, thedepends things
on what is best for your car. For lateral positioning, the things
Caliper did not fit wheel correctly, so metal was removed from outboard edge. Don't do this to get a caliper to fit. Caliperso flexing, Caliper did not fit wheel correctly, metal cracking or other problems edge. may Don't result do if was removed from outboard excess metal is removed. Instead, flexing, select this to get a caliper to fit. Caliper calipers and wheels that clear without cracking or other problems may result if modification. excess metal is removed. Instead, select
calipers and wheels that clear without
to consider are eXistIng mounting bosses, and wheel and suspension to considerWith are anexisting clearances. existingmounting car, you bosses, and wheel and suspension may be able to use existing bosses and clearances. Withbut an you existing car, you hole locations, will probably may be able to use existing bosses have to fabric ate an adapter plate.and It hole but I/2-in. you will probably must locations, be rigid . I like steel plate. have to fabricate an adapter It Position each caliper so itplate. has at like 112-in.tosteel must be rigid. I clearance the plate. wheel least O.080-in. it has at Position and 114 in.each to caliper moving sosuspension least 0.080-in. clearance to the parts. Be sure to check the fron wheel t susand 114with in. the to steering moving atsuspension pension full lock, parts. and Be sure to check front posisusrightleft-turn. If nothe caliper pension with the steering at full lock, tion can be found that clears at full rightand left-turn. If nostops. caliperExcept posi'steering lock, consider tiondirt canoval-track be found cars, that few clears at cars full for race lock, as consider 'steeringangle stops.as Except need much steering a road for dirt oval-track cars, few race cars car. need much steering anglecaliper as a road RotorasOffset-Once lateral pocar. sition is found, the rotor position is Rotor Offset-Once caliper pofixed. Determine lateral rotor-hat offset sition is found, the rotor position is next. Hat offset is the distance from fixed. Determine rotor-hat offset the hub mounting surface to the rotor next. Hat offset the distance mounting surface.is Never order from hats the hubthe mounting the rotor until calipersurface and torotor are mounting order hats positioned. surface. Rotor Never hats with almost untiloffset the cancaliper and off rotor are any be supplied the shelf positioned. hats with byalmost or machinedRotor to specification your any offset canorbe supplied off the shelf brake dealer manufacturer. or machined to specification your, Rotor-Hat Holes-For some by reason brake dealer or manufacturer. many hats come with large holes Rotor-Hat Holes-For some reason, around their circumference. These many hats come with large holes holes help air flow to the outboard suraround These face of their solid circumference. rotors and ventilated holes help air flow to theairoutboard surrotors not using sealed ducts. With face ofducts solid rotors and ventilated sealed , these holes allow cooling
rotors not using sealed air ducts. With sealed ducts, these holes allow cooling 97
Sprint-car rear axle: Single inboard brake on solid axle is possible because of exposed axle rear shaftaxle: and Single locked inboard rear end. Not Sprint-car brake only is weight by because one-half,ofwhen on solid axle isreduced possible exone wheel a bump, brake rear moves smalposed axlehits shaft and locked end. Not ler distance than wheel,byreducing brake's only is weight reduced one-half, when effective weight. Improved hanone wheelunsprung hits a bump, brake moves srnaldling results. than Photowheel, by Tomreducing Monroe. brake's ler distance -
Inboard rear brakes are used on this Formula Ford. Brake COOling is excellent, rotor diameter is not limited by wheel size, and handling on rough surfaces is improved . Inboard brakes are not rear usedbrakes on ground-effects cars because they reduce tunnel width and resulting lnboard are used on this Formula Ford. Brake cooling is excellent, rotor diamedownforce. ter is not limited by wheel size, and handling on rough surfaces is improved. lnboard brakes
-
effective unsprung weight. Improved handling results. Photo by Tom Monroe.
are not used on ground-effects cars because they reduce tunnel width and resulting downforce.
Caliper mounts to quick-change side-bell and rotor-to-axle adaptor clamps to axle shaft: Actual sprint-car installation is at right. Note bearing housing- cage-with control-arm brackets at outer end axle. Photo at left courtesy AP Racing; photo at right courtesy Tilton.
Caliper mounts to quick-change side-bell and rotor-to-axle adaptor clamps to axle shaft: Actual sprint-car installation is at right. Note bearing housing-cage-with control-arm brackets at outer axle.allow Photo at left courtesy photo at right Tilton. air to escape from the center of the only doesend this larger rotors, AP Racing; such as those forcourtesy an independently
rotor before it flows through the
air to escape from the center the rotor. Consequently, these ofholes rotor before it flows through the should be plugged. When ordering rotor. Consequently, holes new hats, specify with these or without should depending be plugged. ordering holes, on When your rotor and new hats, specify with or without cooling system. If existing hats have holes, and depending rotor aluand you wishon to your plug them, holes cooling If existing hats have minum system. tape with high-temperature holes andworks you wish adhesive well.to plug them, aluminum tape with high-temperature Inboard Brakes-For one reason or adhesive works well. want to consider another, you might Inboard Brakes-For reasonNot or mounting the brakes one inboard. another, you might want to consider mounting the brakes inboard. Not
98
cooling is better because the brakes only not doesshrouded this allowby larger rotors, are the wheels. cooling is better because the Wheel-weight reduction alsobrakes imare not handling shroudedon byrough the surfaces wheels. proves Wheel-weight and brake torquereduction does not goalso into imthe proves handling on rough surfaces suspension. and brake torque doesbrakes not gomounted into the Why aren't many suspension. inboard? To begin with, they compliWhya aren't many . brakes mounted For example, cate car design inboard? To begin with, they mounting provisions must becomplimade cate a car For example, for the rotordesign. and caliper on the mounting provisions mustand be joints made, chassis. Then an axle shaft
for the rotor and caliper on the chassis. Then an axle shaft and joints,
sprung, driven wheel, must be used. such as the those for must an independently spindle rotate in the Finally, sprung, driven wheel, must be used. upright. All this increases complexity, Finally, the spindle must rotate the cost and weight. To top it off, inmost upright. All this increases complexity, front-wheel-drive cars don't have cost top it Race off, most roomand for weight. inboardTobrakes. cars front-wheel-drive cars don't have using ground effects need the narrowroombody for possible inboard brakes. cars between Race the side est using ground thethe narrowducts; inboardeffects brakesneed make body est the side andpossible reduce between the aerodynamic widerbody ducts; inboard brakes make the body downforce on the car. Use inboard wider and reduce the aerodynamic brakes if it makes sense , but keep in
downforce on the car. Use inboard brakes if it makes sense, but keep in
TOTAL PISTON AREA FOR EACH TYPE OF CALIPER AT = Total Piston TOTAL PISTON AREA FOR EACH TYPE OF CALIPER
Type of Caliper
Area (sq in.)
Fixed mount-one piston on each side of rotor Type of Caliper Fixed mount-two pistons on each side of rotor Fixed mount-one piston on on each side of rotor Fixed mount-three pistons each side of rotor Fixed mount-two pistons rotor Floating mount-one pistonononeach onlyside one of side of rotor Fixed mount-three of rotor Floating mount-twopistons pistonson oneach only side one side of rotor Floating mount-three mount-one piston on on only oneone side of rotor Floating pistons only side of rotor Floating pistons on only one side of rotor Ap = areamount-two of one piston (sq in.)
A, =Total Piston Area (sq in.) 2AP
4AP 6AP 2AP
4AP
Floating mount-three pistons on only one side of rotor GAP A, = area of one piston (sq in.) Chart gives total piston area for each type of caliper. Floating-sliding-caliper
has one piston doing job of two in a fixed caliper. If you don't know the type of caliper, remember that calipers piston(s) one Floating-sliding-caliper side. Area Ap of each piston in Chartfloating-mount gives total piston areahave for each typeon of only caliper. has is one square doing inches. Determine for your particular piston job of two inAp a fixed caliper. If youcaliper. don't know the type of caliper, remember
that floating-mount calipers have piston(s) on only one side. Area A, of each piston is in square inches. Determine Ap for your particular caliper.
mind the concept.
disadvantages
of
the
mind the disadvantages of the concept. DETERMINE HYDRAULIC-SYSTEM DETERMINEPRESSURE OPERATING HY DRAULIC-SY T E M torque is Once required Sbrake OPERATING PRESSURE known and you've made a caliper Once required braketo determine torque is selection, it's possible known and you've made caliper fluid pressure. Some brake a catalogs selection, it's possible to determine give the relationship between hydraufluid pressure. catalogs andSome brakebrake torque for a lic pressure give thecaliper relationship betweenHowever, hydraugiven and rotor. lic pressure and for a remember that brake the torque torque-vergiven caliper and rotor. However, sus-pressure relationship depends on remember that coefficient. the torque-verbrake-lining friction sus-pressure depends on fluid pressure required To find therelationship brake-lining friction coefficient. for your car, you need the following To find the fluid pressure required information: for your car, you needcoefficient. the following • Brake-lining friction information: • Total piston area for each caliper. Brake-lining friction coefficient. effective radius. • Rotor Total piston area for each caliper. • Brake torque at maximum decelerRotor effective radius. ation. Brake at maximum decelerIf you torque have the friction coefficient ation. for your linings, use it. Otherwise, If you it's have friction coefficient assume 0.3.the Most linings are this for your linings, it. by Otherwise, approximate value.use Start calculatassume it's 0.3. Most ing caliper-piston area: linings are this approximate value. Start by calculatArea of piston = 0.785 Dp2 in square ing caliper-piston area: inches Area piston = in square Dp = of Diameter of0.785 pistonDP2 in inches inches Total piston area is the area of one D p = Diameter of piston in inches piston multiplied by the number of Total piston area is the area of one pistons for a fixed-mount caliper. If pistonhave multiplied by caliper, the number of you a floating multiply pistons fixed-mount If the areafor of aone piston by caliper. twice the you have a floating caliper, multiply total number of pistons to get total efthe area of one mice the fective piston area.piston This by is illustrated total number of pistons to get total efabove. fective piston selected area. Thisa iscaliper illustrated If you've with above. non-circular pistons, such as those If you've selected a you caliper from Alston Industries, mustwith use non-circular pistons, as those an effective piston area insuch the formulas. from Alston Industries, must use piston area foryou each caliper Effective eJfective piston area in the formulas. an is given in the caliper manufacturer's Effective piston area for each caliper is given in the caliper manufacturer's
catalog. If you use a formula that requires using piston diameter, you catalog. If you use formula that remust compu te a effective piston quires diameter.using This piston is the diameter' diameter of a that has an area piston equal circular must piston compute effective diameter. Thisarea is the diameter of a to the piston of the non-circular circular piston that has an area equal caliper. All formulas requiring piston to the piston area using of thethis non-circular diameter will work method. caliper. formulas requiring piston Brake All effective radius is the distance diameter will work using this method. from the center of the rotor to the Brakeofeffective radiuspad. is the distance center the brake Once you from center ofradius, the rotor to folthe know the the effective use the center of the brake pad. Once you to compute fluid preslowing formula knowatthe effectivebrake radius, use the folsure maximum torque.
lowing formula to compute fluid presT sure at maximum torque. Maximum hydraulicbrake pressure = __ 8_ ,uLATrE
in pounds hydraulic per squarepressure inch Maximum
'8 =-
T 8 = Brake torque in inch-pounds PLAT'E in Dounds Der sauare inch of brake ,uL = Coefficient-of-friction T,' = rake torque in inch-pounds linings p Coefficient-of-friction of brake AT, == Total area of caliper pistons in linings inches square A, Total arearadius of caliper pistons in r E == Effective of brake in inches
square inches r, = Effective radius of brake in inches
Once maximum pressure is calculated, make sure the caliper can Once at maximum is operate this pressure .pressure Usually, the calculated, make sure the caliper can maximum operati;lg-pressure rating operate at thisis pressure. the of the caliper specified Usually, by the brake maximum operatiag-pressure manufacturer. It varies from rating about of the tocaliper specified by theonbrake 1000 1500 ispsi, depending the manufacturer. It varies caliper. The caliper cannot from safely about oper1000continuously to 1500 psi, above depending on the ate maximumcaliper. The caliper cannot safely operrated pressure because seal or caliperate continuously above maximumbridge fatigue failure may occur. rated pressure because seal or caliperHowever, an occasional locked-wheel bridgestop fatigue panic is OK. failure may occur. However, an occasional locked-wheel If calculated fluid pressure is too panic stop is OK. high for the caliper, the solution is If calculated fluiddopressure simple. You can one ofis too the high for the caliper, the solution is following: simple. can with do more one ofpiston the • Use a You caliper following: area - bigger pistons or more of them. a caliper withcaliper more onpiston • Use Use more than one each arearotor. bigger pistons or more of them. Use more than one on each • Use a larger rotorcaliper diameter, if
rotor. Use a larger rotor diameter, if
{
\--.-/ Effective radius of disc brake is measured from center of pad to center of rotor. Make sure you have correct combiEffective radius of discrotor/caliper brake is measured nationcenter to determine effective radius. from of pad to center of rotor. Make
sure you have correct rotor/caliper combination to determine effective radius.
there's space. • Use a caliper that has a higher there's space. operating pressure. Use caliper that one has caliper a higher If youause more than per operating pressure. rotor, each caliper supplies its rated If you Thus, use more one caliper per torque. twothan calipers on each rotor, doubles each caliper suppliesthat its brake rated rotor the torque torque. Thus, calipers on fluid each can deliver. Fortwo a given torque, rotor doubles the torque that brake pressure for a two-caliper disc brake can be deliver. Forfor a given torque, will half that a single caliper;fluid repressure fluid for a displacement two-caliper disc quired willbrake be will be half that for a single caliper; redouble. quired fluid displacement will you be Operating Pressure-In general, double. should use an operating pressure Operating general, you that's wellPressure-In below maximum-rated should operating pressure use for aancaliper. Leaks pressure and exthat's well below can maximum-rated deflection result from cessive pressurefluid for apressure. caliper. Leaks and exexcess If maximum cessive deflection resulthalf from operating pressure can is, say, of excess fluid pressure. If maximum maximum-rated pressure for the operatingthepressure is, say, half of caliper, extra margin of safety in maximum-rated pressure for the the brake system is sufficient.
caliper, the extra margin of safety in the brake&system is sufficient. PEDAL LINKAGE DESIGN After selecting and positioning the
PEDAL & LINKAGE DESIGN brakes and calculating maximum After selecting and positioning the hydraulic-system operating pressure, brakes calculating maximum the next and step is to design the pedals hydraulic-system operating pressure, and linkage. Various types of pedals the next step is to design the are discussed in Chapter 6. As pedals stated and linkage. types of pedals earlier, use Various a hanging pedal if 6. As stated are discussed Chapter possible . This in allows the master cylinearlier, a hanging pedal ders to beuse mounted high in the car forif possible. This allows the master cylinon easy servicing. Also, brake balance ders to be mounted in tothe car for balance-bar setups ishigh easier adjust. easy servicing. Also, of brake balance on The disadvantage hanging pedals balance-bar setups is easier to adjust. is the extra height required. On a lowThe disadvantage hanging profile race car, thereofmay not bepedals suffiis the extra a lowcient roomheight for required. hangingOnpedals. profile race car, there not be Consequently, you'llmay have to suffiuse cient room for hanging pedals. floor-mounted pedals. Consequently, you'll have to use floor-mounted pedals. 99
Hurst! Airheart 200X2 caliper is largest one offered by this manufacturer. Brake torque is rated2 0at brake Hurst/Airheart 0 x 223,000 caliperin-Ib is largest torque at 1200-psi hydraulic pressure. one offered by this manufacturer. Brake Double-piston caliper is popularin-lb for use on torque is rated at 23,000 brake racing stock cars. Photo courtesy Hurst torque at 1200-psi hydraulic pressure. Performance. Double-piston caliper is popular for use on Two calipers on rotor doubles brake torque for a given hydrauliC pressure-an easy and effective means of lowering pedal effort or fluid pressure. Smaller single-piston caliper is stiffer than a dual-piston caliper, too. torque Photo by Monroe. .TWO callpars u r i rudor doubles brake TorTom a ylven nyaraullc pressure-an easy and ef-
fective means of lowering pedal effort or fluid pressure. Smaller single-piston caliper is stiffer than a dual-piston caliper, too. Photo by Tom Monroe.
Ideal race-car brake- pedal setup; balance bar with remote adjuster. Remote - adjuster cable is routed to left of balance bar under clutch pedal. Floor-mounted pedals are necessary Idealbecause r,-- .,- of -.low-profile ,., .-,,, body height. d ; balance bar with remote adjuster. -r
,.,
.,.,.
,,,,.
cable is routed to left of balance bar under clutch pedal. Floor-mounted pedals are necessary because of low-profile body height.
Decide at this point what type of brake-balance method to use . There this point whatfortype of areDecide severalatchoices available a race brake-balance method to use. There car: are• several available for a race Balancechoices bar. car:• Adjustable proportioning valve. Balance bar. of the two. • Combination Adjustable proportioning Road cars usually don't use valve. balance thedifficult two. to inbars Combination because theyofare Road cars usually don'tpedals. use balance corporate into existing Also , bars are difficult to inbrakebecause balance they for road use is not as corporate existing predictableinto as for ~acing.pedals. This isAlso, bebrake road balance use istypes not as cause carsfor runroad on many of
predictable as for racing. This is because road cars run on many types of
100
surfaces. And, adjusting a balance bar while driving on the road is simply not surfaces. bar practical. And, On a adjusting race tracka, balance conditions while driving on the road is simply not are stable or reasonably predictable . practical. a race track, conditions Also, the On driver constantly uses the are stable reasonably brakes hardorand can sense predictable. the need to Also, the driver constantly uses the adjust balance. brakes hardbars and are can used senseon therace needcars to Balance adjust for twobalance. m ain reasons: are pedal used on carsa • Balance Provides bars stiffer fee race l than for two main reasons: proportioning valve . Provides master stiffer pedal feelare than cylinders easya • Separate proportioning to change to mvalve. ake large bra ke-balance
Separate master cylinders are easy to change to make large brake-balance
racing stock cars. Photo courtesy Hurst Performance.
changes. An adjustable proportioning valve has limited adjustment. changes. An adjustable If you plan on using aproportioning balance bar, valve has limited adiustment. consider using an adjustable proporIf youvalve, plan on a balance tioning toousing . A balance bar bar, can consider using an adjustable proporbe adjusted to accomplish the desired tioning valve, brake too. Abalance, balance but bar can front-to-rear the be adjusted to valve accomplish desired proportioning does itthe autom atifront-to-rear brake balance, but the cally over a limited range of tire-grip proportioning valve does it automativalues. The disadvantage of using a cally over a limited rangea balance of tire-grip proportioning valve with bar values. The disadvantage of using a is the added weight , cost, complexity proportioning valve with a balance bar and pedal travel. is Unless the added weight, cost, complexity you like climbing into a raceand pedal travel. car cockpit upside down on your back, Unless climbing make sureyou thelike balance bar into can aberaceadcar cockpit upside down on your back, justed from a convenient position. makemay sureaffect the balance bar canposition be adThis the mounting justed fromfora the convenient position. you choose pedals. But , pedal This may affect the mounting are position and balance-bar maintenance critiyou choose for the pedals. But, cal to keeping a. brake system inpedal top and balance-bar maintenance are critioperating condition. A balance bar cal a. brake system in and top withtoa keeping remote-adjustment cable operating condition. A balance bar knob may be the solution. with a remote-adjustment and Brake-pedal ratio and cable masterknob may be the solution. cylinder size (s) should be selected at theBrake-pedal same time.ratio The and objectmasteris to cylinder the size(s) shouldoperating be selected at achieve maximum presthe same time. The object is to sure you established with an acceptachieve the effort maximum presable pedal usingoperating the following sure you established with an acceptsteps: able pedal effort the following • Select pedal ratiousing . steps: • Select pedal effort at maximum Select pedal ratio. deceleration. pedal at maximum • Select Calculate forceseffort on master-cylinder deceleration. push rod (s) . Calculate forces on master-cylinder master-cylinder diameter(s) • Select pushrod (s) . that gives proper maximum operating Select in master-cylinder diameterk) pressure hydraulic system. that gives geometry proper maximum operating • Check of the pedal and pressure in hydraulic system. linkage at extremes of travel. of theandpedal and • Check Design geometry pedal bracket masterlinkage atmount. extremes of travel. cylinder
Design pedal bracket and mastercylinder mount.
MASTER-CYLINDER SIZE VS. PISTON AREA
Making under-dash brake-balance adjustment forces mechanic into this uncomfortable position. Hanging brake pedal with Making under-dash brake-balance adjustbalance bar and remote into adjuster more ment forces mechanic this is uncompractical.position. Hanging brake pedal with fortable balance bar and remote adjuster is more practical.
• Change anything necessary and start over. l Change anything necessary and Pedal Ratio- There is nothing Select start over. magic about the pedal ratio. Many Select Pedal Ratio-There is nothing values are possible. However, if you magic know aboutwhat the to pedal don't use, ratio. try a Many pedal values possible. However, if you ratio of are about 5.0. don't know try use a pedal If you buywhat a settoofuse, pedals, the ratio about 5.0.into them. Unless the pedalofratio built If you buy a set of pedals, use the resulting master-cylinder size(s) or pedal them. the linkage movement is incorrect, you resultinghave master-cylinder Size(S) or should a good design. Don't linkage amovement incorrect, you design new pedal isunless you have should a good design. Don't to. It is have time consuming and difficult design a new pedal unless you have to do correctly. to.Some It is time consuming and difficult points to consider when to do correctly. selecting a pedal ratio: Some a points given to pedalconsider ratio, iswhen the • With selecting a pedal ratio: master cylinder(s) mounted in a conl With place? a given pedal ratio, is the venient master cylinder(s) mounted in a con• Can you get master cylinder(s) with venient place? enough stroke so the pedal hits the l Can before you getthe master cylinder(s) with floor master cylinder(s) enough bottoms?stroke so the pedal hits the floor master cylinder(s) • Doesbefore the the pedal position feel bottoms? comfortable? D o e s the feel Pedal pedal Effort position at Maximum Selecting comfortable? Deceleration-Most people can stop a Selecting Pedal Effort Maximum car that requires 100-lbatpedal effort. Deceleration-Most stop for acan road car.a However, this is highpeople car that requires 100-lb pedal effort. And, it may not allow enough safety However,forthis is high road car. or margin brake fadefor fora street And, not allowthat enough racing.it Imay recommend you safety use a margin for brake street or 75-lb pedal effortfadeforformaximum racing. I recommend that you deceleration. If you use less use pedala 75-lb pedal effort for maximum effort, the brake pedal will feel less deceleration. If you less pedal rigid and will have moreuse travel. effort, the brake pedal will feel less Master-Cylinder Pushrod Force-If rigid and will have more travel. your car uses a tandem master cylinMaster-Cylinder Pushrod Force-If der or a single master cylinder, the your car tandem master cylinforce on uses the apushrod is found by
der or a single master cylinder, the force on the pushrod is found by
Nominal Diameter MASTER-CYLINDER SIZE VS. PISTON AREAArea Bore Size In. Sqln. Nominal Diameter Area 5/8 in. 0.6250 0.3068 Bore Sire In. Sq In. 11/16 in. 0.6875 0.3712 5/8 in. 0.6250 0.3068 19mm 0.7480 0.4394 11/18in. 0.6875 0.371 2 3/4in. 0.7500 0.4418 19mm 0.7480 0.4394 20mm 0.7874 0.4869 3/4 in.in. 0.7500 0.4418 13/16 0.8125 0.5185 20mm 0.7874 0.4869 21mm 0.8268 0.5369 13/16 in. 0.8125 D.5185 22mm 0.8661 0.5892 21 mm 0.8268 0.5369 22.2mm 0.8740 0.5999 22mm 0.8661 0.5892 7/8 in. 0.8750 0.6013 22.2mm 0.8740 0.5999 23mm 0.9055 0.6440 7/8 in.in. 0.8750 0.661 3 29/32 0.9063 0.6451 23mm 0.9055 0.6440 15/16in. 0.9375 0.6903 29/32 in. 0.9063 0.6451 24mm 0.9449 0.7012 0.9375 0.6903 15/16 In. 25.4mm 1.0000 0.7854 24mm 0.9449 0.701 2 1 in. 1.0000 0.7854 25.4mm 1,0090 8.7854 1~1/32 in. 1.0313 0.8353 1 in. 1.OOOO 0.7854 26.6mm 1.0472 0.8613 1-1/32 in. in. 1.0313 0.8353 1-1/16 1.0625 0.8866 26.6mm 1.0472 0.861 3 1-1/8 in. 1.1250 0.9940 0.8866 1-1/16in. 1.0625 28.6mm 1.1260 0.9958 1-1/E3 in. 1.7250 0.9940 1-1/4in. 1.2500 1.2272 28.6mm 1.f26Q 0.9958 31.8mm 1.2520 1.2311 1.2600 1.2272 1I-1/4 ~5/16In. in. 1.3125 1.3530 3?.8rnm 1.2520 1.231 I 1-11/32in. 1.3438 1.4183 1-5/16in. 1 3 125 1.3530 1-1/2in. 1.5000 1.7671 1-1 1/32 1.3438 1,4183 1-3/4 in. in. 1.7500 2.4053 1-1/2 In. 1.5000 1,7671 1.7500 2.4053 1-3/4 in. Listed are diameters of popular mass-produced master cylinders and their areas. Note that some metric sizes are close to standard inch sizes. Be careful to get correct sizes when buying replacement Many mass-produced cylinders have diameters marked and on them. Listed are diametersparts. of popular master cylinders their areas. Note that some metric sizes are close to standard inch sizes. Be careful to get correct sizes when buying replacement parts. Many cylinders have diameters marked on them.
multiplying the pedal ratio by pedal effort. multiplying the if pedal For example, pedalratio ratiobyis peda! 10.0 effort. and pedal effort is 75 Ib, force on the For example, pushrod if pedal isratio is 10.0 master-cylinder 750 lb. and pedal effort is 75 Ib, force on the the If you are using a balance bar, master-cylinder pushrod is 750 lb. force just calculated above is the pedal If you a balance bar, Itthe thatare actsusing on the balance bar. is force force justbetween calculated is the cylinpedal divided the above two master force that acts ontothethe balance bar. Iton is ders according formulas divided between the two master cylinpage 75. ders according to on I recommend thatthe youformulas assume the page 75. bar divides pedal force equally balance I recommend thatmaster you assume the between the two cylinders. balance bar divides pedal force equally This allows the maximum amount of between the adjustment two master incylinders. balance-bar either This allowsItthe maximum amount of direction. also makes the design balance-bar adjustment in either easier. If you do this, divide equally direction. It pushrod also makes design the resulting forcethe found by easier. If you do effort this, divide equally multiplying pedal by pedal ratio. the resulting by This gives thepushrod force onforce eachfound mastermultiplying pedal effort by pedal ratio. cylinder pushrod. If you do not center This gives the on each masterthe balance bar,force calculate the force to cylinder pushrod. If you do not center each pushrod. theNow balance the on force to that bar, you calculate have force each each pushrod. pushrod, you also have the force apNowto that have force onpiston. each plied eachyou master-cylinder pushrod, you also have the force apThe forces are the same.
plied to each master-cylinder piston. The forces are the same.
Master-Cylinder Size-Now that you know the desired maximum Master-Cylinder Size-Now operating pressure and force on that the you know the desired master-cylinder piston, it's maximum simple to operating the pressure and force on the the required area for calculate master-cylinder piston, it's simple to master-cylinder piston:
calculate the required area for the F master-cylinder piston: Master-cylinder-piston area
=
~ p
in square inches ~aster-cylinder-piston area - F M C FMC = Force on master-cylinder P piston insquare in pounds inches FMc Force onpressure master-cylinder piston P = = Hydraulic in pounds per square inch in Pounds = Hydraulic pressure in pounds per
inch
A list of piston areas for commonly available master-cylinder diameters is A listinof piston areas for commonly given the accompanying table. available master-cylinder diameters is Most cars use 3/4-1-in.-diameter given the accompanying table. master in cylinders. If your calculated Most cars use 314-1-in.-diameter area falls between two standard sizes, master the cylinders. If your calculated choose master-cylinder diameter area falls between two closest to the required standard area. Yousizes, can choose the adjustments master-cylinder make small later diameter with the closest balance to bar.the required area. You can make small adjustments later witharea the If the required master-cylinder balance bar. is smaller than what's available, go to the required master-cylinder numerical pedal ratio area or a Iflarger
is smaller than what's available, go to a larger numerical pedal ratio 101 or
Pedal
1
.-
Pedal
Centerline
F-;r;
/J Must Be Less Than 5° For All Positions Pedal 0 Must BeofLess
Than 5" For All Positions of Pedal
L
Pushrod Make a drawing to determine angle between pushrod and mastercylinder centerline. Angle must not be excessive, or binding and rapid wear will result.angle Limit between angle to 5° maximum. If angle Makecylinder a drawing to determine pushrod and masteris too large, increase length pushrod or shorten total pedal cylinder centerline. Angle mustofnot be excessive, or binding and travel.cylinder Angle should be result. nearly Limit zero angle with pedal in positionIfwhere angle rapid wear will to 5" maximum. maximum deceleration Onpushrod most cars hanging is too large, increase occurs. length of or with shorten totalpedals, pedal this occurs with pedalbe at nearly about 2zero in. from travel. Angle should withfloor. pedal in position where
I
Floor-mounted Neal pedal bracket ties master cylinder to pedal pivot in one assembly. Only forces on chassis are those delivered directly by driver's on master cylinder and Floor-mounted Neal foot. pedalLarger bracketforces ties master cylinder to pedal pedal pivot taken byOnly bracket. pivot in oneare assembly. forces on chassis are those delivered
directly by driver's foot. Larger forces on master cylinder and pedal pivot are taken by bracket.
maximum deceleration occurs. On most cars with hanging pedals, power brakes However, this occurs with .pedal at about 2don't in. fromuse floor. the pedals and seat. Position them as
power brakes on a race car unless abpower brakes. However, use solutely necessary. There don't are easier power brakes on a race car unless abways of avoiding this, unless your solutely race car isnecessary. extremely There heavy. are easier ways of avoiding unless your If you select a this, 5/8-in.-diameter race car is extremely heavy. master cylinder, be aware that you If you goselect cannot to a a 5/8-in.-diameter smaller size master cylinder, be aware that Ityou later-there are none available. is cannot go a to a orsmaller size better to use 3/4-in. larger cylinlater-there It is der so you are can none makeavailable. a change, if better to use a 314-in. or larger cylinneeded. For example, if new tires give der youthan canwhat make change,for,if moresogrip youa allowed needed. For example, if new give you'll need smaller master tires cylinders more grip than what you allowed for, to keep the same pedal effort for maxiyou'll need smaller master cylinders mum deceleration. So, leave yourself to keeproom the same pedalchanges. effort forTo maxisome to make inmum deceleration. So, leave yourself crease the master-cylinder diameter some room topedal make changes. inand maintain effort, use aTo larger crease the master-cylinder diameter pedal ratio. and maintain pedal effort, use a larger Pedal & Linkage Geometry-A pedal ratio. brake pedal must be designed to fit Pedal & As Linkage Geometry-A the driver. the driver pushes the brake pedal must be designed fit pedal, the ball of his foot shouldtostay the driver. As the driver pushes the in contact with the pedal pad. Measure pedal,foot the orball his foot should stay your theofdriver's-if the sizes in contact with the pedal pad. Measure are significantly different-and check your or the driver's-if the sizes pedal foot positions. areAlso, significantly check look for different-and a car with pedals in pedal positions. the "perfect" position for the driver's Also, look forthe a carrelationship with pedalsbein feet. Measure the "perfect" position driver's tween the floor, ped als for and[he seat. Copy feet. Measure bethe design of a the goodrelationship car if you find tween the floor, pedals and seat. Copy one that's suitable. There is no perfect if you find the of abecause good car pedaldesign design, each person's one suitable. There is nodifferent perfect bodythat's has slightly pedal design,So, because person's dimensions. designeach yourdifferent car to body has slightly suit the driver. dimensions. SO,doubts design about your car to If you have pedal suit the driver. position, make a full-size model of
If you have doubts about pedal position, make a full-size model of 102
they will be in the car and see how the and seat. as theypedals fit. Now's the Position time to them change they will be in the car and see how things that are not comfortable. they fit.theNow's thethetime to change Check pedal in extreme posithings comfortable. tions of that travel.areYounot should have no Check the pedal in the more than 6 in. of totalextreme travel atposithe tions pad. of travel. You should have no pedal Try it to be sure. of total travel of at the more than After you6 in. make a drawing the pedal pad. it to be sure. and Try its mounts, check the linkyouextreme make apositions. drawing of the ageAfter at the There pedal and the linkshould be its no mounts, binding.check Pay particular age at thetoextreme positions. There attention the angle the pushrod should be no binding. Pay particular makes with the master cylinder. If the attention to the angleextreme the pushrod pushrod goes through angles makes m ~ master s t e cylinder. r cylinder, If the to the with bore the of the it extreme severe angles pushrod goes This causes can bind. the bore of the t-naster cylinder, Ait problems, including breakage. longer bind. pushrod may causes be required to Can This severe reduce the misalignment angle. A problems, breakage. longer pushrod may be required maximum of 5° misalignment between pushrod the and master cylinder angle. is recomreduce misalignment A mended See maximumby brake manufacturers. between pushrod and master Vlinder recornthe accompanying drawing forisan illusmended manufacturers. See tration ofby thisbrake pro blem. for an the Pedal-Bracket &drawing Master-Cylinder Mount-On many cars the pedal Uation this problem. Master-C~linder bracket and master-cylinder mount Mount-On many cars the pedal are the same. This makes a strong, b r x k system e t and with master-cylinder mount rigid minimum of overall are the Race-car same. This a strong, weight. pedalmakes brackets manurigid system with minimum of overall factured by companies such as Tilton, weight. brackets manuNeal or Race-car Winters pedal use this concept. A factured by colnpanies as Tilton, pedal bracket is difficultsuch to design, so Neal Winters use this concept. A buyingor one of these sturdy, lightpedal bracket is difficult to design, So weight brackets makes sense. These of these sturdy,applicalightparts areone designed for racing weight tions andbrackets are easy makes to use. sense. These are designed for racing applicaparts pedal-bracket design in I discuss tions and are easy to use. Chapter 6. However, re member this
I discuss pedal-bracket design i n 6 . However, remember this
important point: The bracket must not deflect an excessive amount when important point: The hard. bracket must the pedal is pushed A pedal not deflect an excessive amount when bracket mounted in the center of a the is pushed thin pedal sheet-metal fire hard. wall A ispedal 1101 bracket mounted center pedal of a satisfactory. This, in or the a flexible tfor thin sheet-metal fire airwall is hybracket, is worse than in the satisfactory. This, or a flexible pedal draulic system. With a flexible pedal bracket, worse than pump air in the bracket, isyou cannot up hythe draulic With a flexible pedal orsystem. bleed the trapped air to pedal cure bracket, you cannot pump up the the problem' pedal or bleed the trapped air cure I f you stress-analyze the to pedal the problem! bracket, remember to use maximum If you normal stress-analyze load-not operatingthe load.pedal The bracket, remember to use maximum maximum load occurs during a panic load-not operating stop when normal the driver pushesload. withThe all maximum loadIf occurs duringis astrong panic of his might. the bracket stop when driver pushes withfine all enough forthethis, it will work of his might. If the bracket is strong during maximum deceleration. enough Design for this,Problem-Following it will work fine Sample during maximum deceleration. is a sample race -car brake-design Sample Problem-Following problem. Design The steps are in the same is a sample race-car brake-design order presented . problem. The steps are in thesystem same First select the disc- brake ordergives presented. that the requi red brake torque at select the disc-brake a First 500-psi operating pressure system at the that gives the required brake at front brakes and 400-psi at torque the rear. a 500-psi operating are pressure at the These calculations explained in front brakes the first part ofand this400-psi chapter.at the rear. These calculations explained in system has an A proven pedal are the first part of this 8.0-to-l pedal ratio.chapter. I wish to design proven pedal has an forAa pedal effort of 75system lb at maximum 8.0-to-1 pedal ratio. I wish to deceleration. The pedal force design acting for the a pedal effort lb at maximum on balance barofis 75 calculated:
deceleration. The pedal force acting Force balance = PE Rp in on the on balance barbar is calculated: pounds PE = Pedal pounds on effort inbar = R~ i n pounds Rp = Pedal ratio effortinbarpounds pE = Pedal = (75 Ib)(8.0) Force on balance R, = Pedal ratio bar = 600 lb. Force on balance
',
Force on balance bar Force on balance bar
= (75 lb)(8.0) = 6 0 0 Ib.
Accident waiting to happen: Steel brake line must be secured to frame with a bracket where the flexible hose attaches (arrow). With this waiting setup, steel line is subjected to line bending fatigue as Accident to happen: Steel brake must and be secured to the suspension moveswhere up and the line will frame with a bracket the down. flexibleEventually, hose attaches (arrow). fracture, brakeline failure. With this causing setup, steel is subjected to bending and fatigue as the suspension moves up and down. Eventually, the line will fracture, causing brake failure.
Brake-line mounting bracket is simple plate, located near suspension pivots (arrow). This minimizes hose bending and pulling as wheel moves. Line and hose attaches bracket using an suspenaircraft Brake-line mounting bracket is simple to plate, located near bulkhead fitting. Jam This nut clamps bulkhead to bracket. sion pivots (arrow). minimizes hose fitting bending and pulling as wheel moves. Line and hose attaches to bracket using an aircraft bulkhead fitting. Jam nut clamps bulkhead fitting to bracket.
Assuming the balance bar divides pedal force equally between the front Assuming the balance cylinders,barthedivides force and rear master pedal force equally between the front lb. on each pushrod is 300 andAlthough rear master cylinders, the force the master cylinders have on eachforces, pushrod is 300 lb. equal different size cylinders cylinders have rear brakes. areAlthough required the for master front and equal forces, different size cylinders This is due to the difference in the are requiredpressure for frontofand brakes. operating therear front and This is due to the difference in the rear systems. operating of page the front From thepressure formula on 101: and
rear systems. F ~ on page 101: Piston Fromarea the =formula P F master-cylinder M ~ FMC = Force piston Piston area =on P in pounds Force onpressure master-cylinder piston FMc P= = Hydraulic in pounds per in pounds square inches P = Hydraulic pressure in pounds per For theinches front brakes, master-cylinder square piston area is:
For brakes, master-cylinder . the front 300lb Piston area = 500 psi oiston area is: 300 Ib = 0.6 sq in. Piston area =
For the rear-brake master cylinder: = 0.6 sq in. .
300lb
Piston = 400 psi For thearea rear-brake master cylinder: = 0.75 sq in. 300 Ib Piston area =400 psi The closest standard-size master = 0.75 sq in.
cylinder is selected from the table on The101:closest standard-size master page
cylinder is selected from the table on : page 101 Front master-cylinder diameter = 7/8 in. (area = 0.601 sq in.) Frontmaster-cylinder master-cylinder diameter diameter == 7/8 Rear in.in.(area sqsqin.) 1 (area==0.601 0.785 in.). Rear master-cylinder diameter = 1 in. (area = 0.785 sq in.). Note that the front master cylinder
is almost perfect and the rear cylinder that large. the front master is Note a bit too I'll use the cylinder balance is perfect and the the rearsystem. cylinder baralmost in testing to fine-tune is Also a bit note too large. the balance that I'll the use smaller master
bar in testing to fine-tune the system. Also note that the smaller master
Custom-fabricated reservoirs are secured with hose clamps and rubber cushions in between. Reservoirs will slipare if secured clamps CUJLUIII-~dbricated reservoirs loosens. with hose clamps and rubber cushions in between. Reservoirs will slip if clamps cylinder is considerably larger than loosens.
Reduced diameters at centers positively locate fluid reservoirs in mounting clamps. Clamps have toatloosen considerably R e u u ~ awould uularnerers centers poslr~vely before reservoirs could in slip. locate fluid reservoirs mounting clamps. Clamps would have to loosen considerably to complete a could brake-system design. before reservoirs slip.
the minimum size. This is good in cylinder is considerably wrong at thelarger start ofthan the case I guessed the minimum size. This is good in design. I can easily change hydraulicwrong the startsmaller of the case I guessed system pressure byat using easilya change hydraulicdesign. I can cylinders. When problem occurs, system by using smaller cylinder is reusually a pressure smaller master cylinders. When a problem quired to reduce pedal effort. occurs, usually smaller master cylinder is re-I After a finishing the calculations, quireda side to reduce draw view pedal of theeffort. pedals to check After geometry. finishing the calculations, linkage Because I selectedI draw a side view of the pedals checka from a standard pedal design to I selected linkage geometry. Because manufacturer, this step is probably anot standard pedal sets design required. Pedal shouldfrom be de-a manufacturer, this step is probably signed to work without binding.
The major items remaining are: to complete brake-system • Route brakealines on chassis. design. The major items remaining are: • Attach flex hoses to chassis. Route brake lines on chassis. • Locate and mount remote masterAttachfluid flex reservoir hoses to chassis. cylinder (s) (if used). Locate and mount remote master• Locate proportioning valve (if cylinder fluid reservoir(s1 (if used). used) . Locate mounts proportioning valverotors (if • Design for calipers, used). and other brake hardware. Design mounts for calipers, rotors • Design cooling-duct system, if and other brake hardware. required. Design that cooling-duct bleeders aresystem, accessibleif • Confirm required. and mounted high. Confirmthethatcarbleeders are accessible After is completed, the and mounted high. brake system must be tested before After use, theChapter car is 10. completed, the serious
not required. Pedal sets should be designed to work BRAKE without binding. COMPLETE SYSTEM There are now other steps required
COMPLETE BRAKE SYSTEM There are now other steps required
brake system must be tested before serious use, Chapter 10.
103
78sting
10
...
Testing is required to get maximum performance n any car, but particularly race cars. This includes brake testing. George B.,..>tti and Tom Sneva discuss effects of changes to car between practice runs while tire engineer measures tire temperatures. Photo by Tom Monroe.
served brake while it George operates. BrakeAs any you car, now a great Testing is required to get maximum performance from butknow, particularly racedeal cars.of This includes testing. Bignotti and dynamometer testing done the brake-system design processmeasures is Tom Sneva discuss effects of changes to car between practice runs while tire engineer tire temperatures. Photo is by usually Tom Monroe.
Brake dynamometer, designed to run continuously, is driven by a 289-cu in. Ford V 8 through a gearbox. Power delivered to brake is equivalent to a sedan under a hard stop. Datsun drum brake is being tested. Brake dynamometer, designed to run continuously, is driven by a 289-cu in. Ford V8 through a gearbox. Power delivered to brake is equivalent to a sedan under a hard stop. Datsun drum brake is being tested.
based on assumptions. For this reason, a brake-test program is absolutely necessary. Often, when a new As car youisnow know,and a great of race designed built, deal testing the brake-system design process is is neglected in favor of getting the car based on assumptions. For this to its first race. This is false economy. reason, program absoTesting aatbrake-test a race takes a lotis longer lutely necessary. Often , when a new than at a planned private test session. race car is designed and built, testing I've seen many people use up a whole isracing neglected in favor of getting the car season to get a car working to its first race. This is false economy. properly when they could've sorted at in a race takes longe r Testing out the car one full day aoflot testing. than at a pl anned private test session. Brake testing falls into two I' ve seen many people use up a whole categories: laboratory testing and racing season to get a car working track testing. Laboratory testing inwhen they couldbrake ' ve sorted properly volves running a single on a out the car in one full day of testing. testing machine called a brake Brake testing falls on into two See photo the back dynamometer. andto categories: laboratory cover. This type of testingtesting is similar track Laboratory intestingtesting an . engine on testing an engine running a single brake on a volves dynamometer. Because a brake is out testing machine called a brake in the open, it can be studied and ob-
dynamometer. See photo on the back cover. This type of testing is similar to testing an engine on an engine dynamometer. Because a brake is out in the open, it can be studied and ob104
by the big brake manufacturers, but if you are so inclined you can make such a device for yourself. served it operates. BrakeMost while brake-testing time will be dynamometer testing is usually spent on the track. You take the done car to by the bigtest brake manufacturers but if a private track and test the ,brakes. you are so inclined can make such Measuring brake you performance and apushing device for yourself. them to the limit should be a Most brake-testing timethat will part of the test. Many tests canbe be spent on the track. You take the car to done very easily during track testing awould privateotherwise test track and test the brakes. be difficult or imMeasuring brake performance and possible during a race. Even a practice pushing them to the limit should be a session during a race weekend is not of the test. Many tests that can be part appropriate for testing. Other cars on done very easily during the track prevent you track fromtesting doing otherwise be difficult would what is needed for a good test. or impossible during a race. Even a pract ice during a race weekend is not session BRAKE-DYNAMOMETER appropriate TESTING for testing. Other cars on theBrake track manufacturers prevent you use from doing brake dywhat is needed for a good test. namometers for laboratory testing. A
single brake is mounted o n and driven
BRAKE-DYNAMOMETER TESTING Brake manufacturers use brake dynamometers for laboratory testing. A single brake is mounted on and driven
by the dynamometer. Instruments measure and record such things as DY Lne temperature, uy narnomeler. rpm, 1nsLrumenrs brake brake measure record such thingsand as pressure torque, and hydraulic brake temperature, rpm, brake stresses. The dynamometer is powtorque, and ered by anhydraulic engine or pressure electric motor. stresses. The dynamometer is powUsually, a large high-speed flywheel is ered used. by an engine or electric motor. Usually, a large high-speed is Dynamometer testing flywheel involves used. revving up the flywheel until there is testing ofinvolves a Dynamometer predetermined amount energy revvinginupit. the is Theflywheel driving until motorthere is disstored aconnected predetermined amount of energy and the brake is applied to storedthe in flywheel it. The driving motor is disto a predetermined slow connected and the brake applied of to rpm or to a dead stop. Theis amount slow theenergy flywheelinto the a predetermined stored flywheel is rpm or to a dead stop. The known. It is equivalent to a amount fraction of of stored energy in the flywheel is the kinetic energy stored in a moving known. It is equivalent to a fraction of car, or about one-third of the total the kinetic energy one stored in brake a moving front and energy for testing car, or about one-third of one-sixth for one rear brake. the total energy for testing one front brake and Dyno testing tests a brake's energyone-sixth for one rear brake. absorbing capaci ty for one or a series testing a brake's energyof Dyno complete or tests partial stops. The flyabsorbing capacity for one or a series wheel can be stopped slowly or of complete or partial The flyrapidly, depending on stops. how much hywheel be stopped slowly or pressure is applied to the draulic can rapidly, depending on how much hybrake. Sophisticated dynamometers draulic pressure is applied to the are computer controlled and can be brake. Sophisticated dynamometers programmed to duplicate brake are computerspeeds controlled and can be and decelerations applications, programmed to duplicate brake encountered in city traffic, a mountain applications, speeds anda race decelerations descent, or laps around track . encountered in city a mountain Another type of traffic, dynamometer apdescent, or laps around a race brake. plies constant power to thetrack. Another type of input dynamometer This steady-power can be atap-a plies constant power to brake. heats up, particular rpm. As the brakethe This steady-power can be its torque changes.input Torque can atbea particular the brake .heats up, measured rpm. with As instruments Friction its torque changes. Torque can be change with temperature at a constant measured instruments.with Friction rpm can with be determined this change with temperature at a constant setup. rpm can be Measuring-The determined withsecret this Temperature setup. of proper brake-dynamometer testing Temperature Measuring-The is the instrumentation. A good secret setup of proper testing will havebrake-dynamometer numerous temperatureis the instrumentation. A good setup measuring devices mounted in critical will have numerous temperaturelocations on the brake. Generally, measuring devices mounted thermocouples are used for this.in critical locations on the brake. Generally, is a joint of two A thermocouple thermocouples are used for this. wires with dissimilar metal. When the A thermocouple is a joint of two joint, or thermocouple junction, is wires with dissimilar metal. When the heated , it generates a small electrical joint, junction, is voltage.or Thisthermocouple tiny voltage can be measheated, it generates a small electrical ured and converted to indicate a voltage. temperature This tiny voltage be measwithcan a pyrometer. specific ured and converted to indicate If the thermocouple junction is in con-a specific a pyrometer.a the item towith be measured, tact withtemperature
If the thermocouple junction is in contact with the item to be measured, a
HOW MUCH HORSEPOWER GOES INTO THE BRAKES? HOW MUCHisHORSEPOWER Horsepower the rate at which GOES is INTO THE BRAKES? energy delivered. The heat energy
Horsepower = 0 .00268W ed M S We = weight of car in pounds Horsepower = 0.00268WCd,S decleration in g's d M = maximum W weight of of car pounds S, = = speed the in car in miles per Horsepower is brakes the rate at awhich d , = maximum decleration in g's hour. during stop received by the S = speed of the car in miles per energy delivered. The heat energy can be isexpressed as horsepower. hour. received by the a stop For example, if brakes a brakeduring is driven by Because the speed of a car canengine be expressed horsepower. an on a brakeasdynamometer, changes during a stop, power to the For example, if a brake brake is driventhe by Because speedDeceleration of a car power into the equals brakes also the changes. an engine on of a brake dynamometer, changes during a stop, to the power output the engine. In a car, during the power stop due to may change power intoenergy the brake brakes changes. and Deceleration kineic of the equals moving the car the this also changesalso in downforce, power output the engine. In a that car, may change duringtothethe stopbrakes. due to supplies the of power. However, changes power the kineic energy of the moving car changes downforce, and this also kinetic energy originally came from Obviously,inthe highest power is for a supplies changes to lots the ofbrakes. the engine.the power. However, that car with downfast, heavypower Obviously, theracing highest power is for a kinetic energy originally One horsepower equalscame 550 from ft-lb force and big tires. the energy engine. delivered each second, fast, heavy with lots of downof calculations Below arecarsample ft-lb force andexplain big racing One horsepower brakes The total power intoequals all four550 that may whytires. bra'k es are deof energy delivered Belowtheare during a stop is given each by thesecond. followsigned waysample they arecalculations for various The total power into all four brakes that explain why brakes are deing formula: typesmay of cars. during a stop i s given by the followslgned the way they are for various ing formula: types of cars. d M (g's) Power(HP) Ty,p eof Car We (lb) S (mph) 515 0.8 4000 60 Large sedan, street tires Type of Car W, (Ib) S (mph) d, (g's) Power(HP1 257 0.8 2000 Small sedan, street tires 60 51 5 4000 60 0.8 Large street tires tires 2573 1.2 Racingsedan, stock car, racing 200 60 0.8 257 Small sedan, tiresdownforce 2000 2680 200 2.5 Fast race car street with high 2573 4000 200 Racingrace stock tires 120 386 1000 1.2 Small carcar, withracing low downforce 2000 200 2.5 2680 Fast race car with high downforce 386 1000 120 1.2 Small race car with low downforce
remote temperature measurement is possible. remote temperature is Thermocouples canmeasurement be used on any possible. stationary brake part. To measure Thermocouples useda on any moving parts, suchcan as abe rotor, sliding stationary brake part. To measure contact or more-sophisticated instrumovingare parts, such. as a rotor, a sliding ments needed Often, rotor temcontact or more-sophisticated perature is measured with ainstrutherments are brought needed. Often, rotor temmocouple into contact with perature is measured with therthe rotor immediately after thea brake mocouple brought into contact with stops. theA rotor immediately after connected the brake hand-held pyrometer stops. to a thermocouple probe is a useful A hand-held pyrometer brakeconnected and tire device for measuring to a thermocouple probetrack. is a useful temperatures at a race When device for the measuring brake and they tire racers use term pyrometer, temperatures at a race track. When usually mean hand-held pyrometer or racers use the term pyrometer, they thermocouple. usually hand-held pyrometer or There mean are many interesting comthermocouple. parisons to make when dynamometer ThereHere are are many comtesting. someinteresting possible tests: parisons to make when dynamometer • Comparison of brake friction matetesting. some possible tests: rials forHere fadeareresistance , wear and Comparison of brake friction matetorque. rials for fade resistance, wear part and the most critical • Determining torque. of braking system when excessive Determining most critical part temperatures arethe reached. of braking system whentemperature excessive • Finding the maximum temperatures are reached. a brake can withstand without failure. the maximum temperature Comparison of brake-fluid perform• Finding a brake can withstand without failure. at high temperatures. ance
Comparison of brake-fluid performance at high temperatures.
• Testing different types of calipers, brake drums or other hardware. different of calipers, • Testing Comparison of types different ro tor brake drums or other hardware. designs . Comparison rotor • Testing effectof ofdifferent caliper-piston designs. insulators. effect oftorque caliper-piston Finding maximum the brake • Testing insulators. is capable of achieving without strucFinding torque the brake tural failuremaximum .
is capable of achieving without structural failure. .TESTING COMPONENT
Manufacturers do a lot of brakeCOMPONENT TESTING system-part testing. They test master Manufacturers do cylinders a lot of on brakecylinders and wheel test system-part testing. They test master rigs that automatically apply the cylinders andand wheel test brakes over over.cylinders This testsondurarigs that automatically apply the bili ty of the parts. brakes over over. cylinder This tests duraBy cyclingand a brake rapidly, bility parts. much less time than testingof the takes By testing. cycling aInbrake cylinder rapidly, track addition , components testing takes much less time subjected to internal pressure than are track In addition, components testedtesting. for bursting strength at pressubjected internalthanpressure sures muchto higher normal. are It tested for bursting strength must be proven that each itemathaspresthe sures much higher than It strength to withstand the normal. maximum must be proven that each item has the possible pressure and have a signifistrength withstand the maximum cant factortoofsafety. possible a signifiIf youpressure wish and to have pressure-test cant factor of safety. components, it is not difficult to set you You wishmustto getpressure-test upIfa test. a hydraulic i t is not difficult to seta components, pump or build a lever to operate
up a test. You must get a hydraulic pump or build a lever to operate a 105
Complete line of temperature-measuring instruments is offered by Omega Engineering, Inc. Digital meters shown are designed to be used with By combininginstruments a meter with a therComplete linethermocouples. of temperature-measuring is offered mocouple in a Inc. special probe, you shown C:ln custom-build your by Omega mounted Engineering, Digital meters are designed to own pyrometer. Such instrumentation is useful for testing on a be used with thermocouples. By combining a meter with a therbrake dynomounted or race car. courtesy mocouple in aPhoto special probe, Omega you canEngineering. custom-build your
own pyrometer. Such instrumentation is useful for testing on a brake dyno or race car. Photo courtesy Omega Engineering.
Handy pyrometer kit is manufactured by AP Racing and sold by Tilton Engineering. It comes with two probes; one for soft materials such as tires, kit andisone for hard materials as brake rotors. Handy pyrometer manufactured by APsuch Racing and sold by Instrument can be used to measure brake temperatures on mateopenTilton Engineering. It comes with two probes; one for soft wheel cars.asPhoto AP hard Racing. rials such tires, courtesy and one for materials such as brake rotors.
Instrument can be used t o measure brake temperatures on openwheel cars. Photo courtesy AP Racing.
Indicator Mount
---Force
! tp,,,, Caliper
Master Cylinder or High-Pressure Pump
Master Cylinder or Pressure High-Pressure Caliper pressure-test setup: gage Pump should have minimum 1S00-psi range; 2000 psi is preferable. If maximum pressure is exceeded, gage will be damaged. Spacer gives something for pads to push against. Notegage how should dial indicator is mounted: Bracket is attached Caliper pressure-test setup: Pressure have minimum 1500-psi range; 2000 to side of caliper and gagepressure is set square against oPPosite so it will read totalgives calipsione is preferable. If maximum is exceeded, gage willside be damaged. Spacer per deflection. Test to can alsoagainst. be performed on the if a pressure gage Bracket is installed in brake something for pads push Note how dial car indicator is mounted: is attached line. Remove before avoid excessive pedal travel. to one side ofgage caliper and driving gage iscar settosquare against opposite side so it will read total caliper deflection. Test can also be performed on the car if a pressure gage is installed in brake line. Remove gage before driving car t o avoid excessive pedal travel.
brake master cylinder. The lever can be operated by hanging weights on a brake pulley master system.cylinder. You can The then lever applycan an be operated by hanging weights on a exact load to the master-cylinder pulley You can itthen an pushrodsystem. and maintain so apply you can exact load to the master-cylinder make measurements . pushrod Deflections-It and maintain itis so you can System interesting make measurements. to test the deflection of hydraulicSystem components Deflections-It interesting system whileis the system to test the deflection of is pressurized . Of particular hydraulicinterest is system components while the deflects system how much a caliper is pressurized. Of particular interest is outwardly. You can measure this dehow much a indicator caliper mounted deflects flection with a dial
outwardly. You can measure this deflection with a dial indicator mounted 106
to the caliper. You must also measure either hydraulic pressure in the to the caliper. must also measure system or forceYou on the master-cylinder either hydraulic pressure in the be piston. System pressure can then system or force on the master-cylinder calculated. A hydraulic-pressure gage piston. System pressure can do then with a large-enough scale will it. be calculated. A hydraulic-pressure gage An engine oil-pressure gage won 't with a large-enough scale will do it. have enough capacity. Relatively inexAn engine gage psi won't pensive gages oil-pressure reading to 2000 are have enough Relativelystores. inexavailable at capacity. industrial-supply pensive gages reading to 2000' s psi are Marsh Instrument Company J4878 available at industrial-supply stores. pressure gage is a 2000-psi gage that Marsh Instrument Company's J4878 uses minimum displacement.
pressure gage is a 2000-psi gage that uses minimum displacement.
Put a tee in the hydraulic line and install the gage. Make sure air cannot a tee inin the the gage hydraulic line high and bePut trapped or other installinthethe gage. Make sure air cannot spot system. Pressurize the be trapped the gage or other high system and inrecord caliper deflection spotincremental in the system. Pressurize pressures. Drawthea at system recordversus caliper deflection pressure deflection . It graph ofand at incremental pressures. a Draw should be approximately straighta graph of pressure deflection. It line. If it's not, versus something in the should be approximately a straight system has slack, which is being taken line. it's not, issomething in the up, orIfsomething failing. Check to system has deflection slack, whichreturns is beingto taken see if the zero up, orpressure something is failing.If Check to when is removed. some desee if the deflection returns to zero flection remains without pressure, when pressure is removed. If some desomething has bent or crushed . flection remains without pressure, You can measure brake-hose and something has bent or crushed. These deflecline deflection as well. You can measure tions are small, but brake-hose you should and be line well. with These defleca dial inable deflection to measureasthem tions arewhile small,us ing but extremely you shouldhigh be dicator able to measure them with a dial insystem pressure. Take a number of dicator while just using extremely high measurements to be sure.
system pressure. Take a number of measurements just to be sure. THE TEST TRACK
The only way to get the most from a
THE brake TEST systemTRACK is to test it on the car. The only way to to get You don ' t have testthe on most a racefrom track.a brake to test itbrake on the car. Unlikesystem chassisis testing, testing You have tointest a race track. can don't be done a on straight line. Unlike chassis Therefore, youtesting, may brake have testing more can be done in a straight line. options. Therefore, havehasmore Each area you of themay country difoptions. ferent facilities and laws. List possible Each locations area of the country difdon'thas forget testing so you ferent facilities and laws. List possible any. Pick the one most suitable for testingpurposes. locationsDon't so you don'ttheforget your ignore legal any. Pick the oneas most for limitations, such noise suitable ordinances. your purposes. Don't ignore the legal People next to your " test track" may limitations, such noiseofordinances. not appreciate the as sound screeching People next to your "test track" may not appreciate the sound of screeching
~'mzo", Caliper Deflection (in) Caliper Deflection (in.)
When testing a race car's brakes, do it on the same type of track it will run on. This track is best for testing oval-track When testing a race car'sanbrakes, do itdirt on car. same It's not much good for testing a roadthe type of track it will run on. This racing is car. track best for testing an oval-track dirt car. It's not much good for testing a roadracing car.
Hydraulic Pressure (psi)
Hydraulic Pressure (psi) Use data obtained from caliper-deflection test to plot pressure-versus-deflection curve. Curve should be a straight line. If deflection increases at a faster rate at high pressure, something in the system failing. Don't risk test trouble brakes in the problem zone. Use data obtained from is caliper-deflection to by plotusing pressure-versus-deflection curve. Curve should be a straight line. If deflection increases at a faster rate at high pressure, something in the system is failing. Don't risk trouble by using brakes in the problem zone.
Stock car has pressure gage mounted on brake line next to each master cylinder. pressures, an Stock carBy hasrecording pressure gage mounted exact numerical record brake balon brake line next to of each master ance is available. Don't ,l eave pressure cylinder. By recording pressures, an gages numerical in hydraulic system because exact record of brake balthey increase pedal travel. ance is available. Don't leave Pressure pressure gages testing only. gages are in for hydraulic system because they increase pedal travel. Pressure gages are for testing only.
WARNING High-pressure testing is used WARNING only to find the limits of a design and High-pressure testing determine its safety factor.is If used you to finda the limits ofpump a design and onlyusing are hydraulic capable determine If you 3000 psiitsorsafety more, factor. you may be of are a items hydraulic pumpbecause capable to failure ableusing to test of 3000 psisystems or more,operate you may be most brake below able test itemsistosome failure because 1500topsi. There danger asmost brake systems operate so below sociated with such testing, be danger as1500 psi.Air There is some careful. trapped in the system sociated with such testing,force. so be explosive If can escape with careful. Air trapped theflying system parts break, they canin go at can escape with explosive force. If parts break, they can go flying at
tires, even if you think your testing is strictly legal. tires, even if you think your for testing is Some possible locations brake strictly legal. testing are: possible locations fortesting. brake • Some Road-racing track rented for
testing are: Road-racing track rented for testing.
high velocity. Isolate people from the items being tested, and make high tovelocity. from thesy.stem. sure bleed allIsolate air frompeople the items being tested,before and make Always relieve pressure looksure bleed all air from the system. ing attothe parts. Always pressure before lookIf yourelieve pressurize a part to three ing at the times its parts. maximum rated capacity If you pressurize to three and it does nbt fail aorpart distort, it is times its maximum rated .all capacity well designed. However, parts and it does fail or distort, it is tested to not excessive pressures well designed. However, all parts should not be used. They should be tested pressures marked permanently destroyedto or excessive should be used. TheyThere shouldmay be for easynotidentification. destroyed marked permanently be damageorhidden from view that for easy There makes the identification. part unsafe to use . . may beIf damage viewrig that you are hidden makingfrom a test for makes the part unsafe use. 3000to psi, go to an pressures up to If you are making a test rig Airfor aircraft-surplus shop for parts. pressures up tosystems 3000 psi, go to an craft hydraulic operate at aircraft-surplus shop for their parts.highAir3000 psi. Consequently, craft hydraulic systems operatecan at pressurehbses and fittings 3000 psi. pressure. Consequently, their take this Check withhighthe pressure andgetfittings can shop to be hoses sure you parts rated take3000-psi this pressure. Check the for pressure. Handwith pumps shop to bepressurize sure you get rated that can a parts system to for 3000-psi pumps 3000 psi arepressure. available.Hand You'll also that pressurize to 3000-psi need can pressure gages aforsystem 3000 psi are available. You'll also capacity. need pressure for lines 3000-psi surplus and Before using gages capacity.wash them throughly with fittings,. Beforeto using lines and alcohol removesurplus dirt, moisture fittings, them throughly with aircraft wash hydraulic fluid. Aircraft alcohol to remove dirt,different moisturefrom and brake fluid is totally aircraft hydraulic fluid. Aircraft start automotive brake fluid. Always brakeclean fluidcomponents. is totally different from with automotive brake fluid. Always start with clean components.
,
• Drag strip rented for testing. • Large parking lot. Dragairport, strip rented for testing. • An particularly one with Large parking lot. light air traffic or unused runways . An airport, one with, • Straight road particularly away from residences
light air traffic or unused runways. Straight road away from residences,
intersections and with little traffic. Race Tracks-Obviously, the best intersections with place to test and a race carlittle is atraffic. race track Race Tracks-Obviously, the best like the one you will compete on. place to test a race car is a race Even for testing a road car, a track race like one advantages you will compete on. track the has the of safety and Even testing road are car,available a race privacy.forSome race atracks track hasthetheweek advantages of safety fee and. during for a nominal privacy. Some race tracks are available You should be prepared to bring whatduring the week for a nominal fee. ever safety equipment the track You should be prepared to bring whatrequires, even if you consider brake ever equipment the track testing safety much safer than going flat-out. requires, even if you consider brake Chances are that track management testing much safer than going flat-out. and insurance companies won't make are that track management anyChances distinction between one type of and insurance companies won't they'll make driving and another. Usually, any distinction between one type of require the driver to wear a helmet driving another. Usually, and use and other standard racing they'll safety require the driver to wear a helmet equipment. You and all those inand use other standard racing safety volved may also have to sign a waiver equipment. and of all allthose that relieves You the track legal inrevolved may ifalso have tois sign a waiver sponsibility someone injured. that relieves the track of all legal car, reIf you are testing a road-racing sponsibility if someone is injured. you should test on a road course . The If you are testing same holds true fora road-racing other typescar, of you should test on course. The cars. Oval-track carsa road should be tested same holdstrack-dirt true for cars otheron types of on an oval dirt and cars. Oval-track cars should be tested pavement cars on a paved on an oval track-dirt dirt and and track-dragsters on a cars drag on strip, pavement on will aallow paved on down the cars line. This you track-dragsters on a or drag and to run the car around up strip, and down on down the line. This will allow you the track many times in succession to runtest thethe car brakes around for or up and down and temperature the track in succession and wear many undertimes simulated racing and test the brakes for betemperature conditions. This will not possible at and wear under simulated other types of test tracks. If youracing can't conditions. This will not be possible at test on a race track, you'll have to use other types tracks. If"you can't. actual racingof fortest "real-world testing test on a racea track, to use Although drag you'll strip ishave ideal for actual racing for "real-world" testing. testing a drag-car brake system, one is Although a drag strip is ideal also useful for testing other types for of testing a drag-car brake system, is cars. You can do one stop one from also useful for types of moderately hightesting speed other at a drag strip. cars. can allows do one stop Or, if You the track , you canfrom run moderately high speed at a drag strip. several stops in succession by running Or, the track you can run backif and forth. allows, Usually , there is
several stops in succession by running back and forth. Usually, there107 is
Drag strip can be used to test brakes at medium to high speeds. Dragster reaches top speed in quarter mile, so its brakes get a realistic workout. will only reach about two-thirds Drag strip can be Typical used toroad testcar brakes at medium to high speeds. of its maximum Regardless, dragmile, strips usually get safe Dragster reachesspeed. top speed in quarter so are its brakes a and handy for brake testing. realistic workout. Typical road car will only reach about two-thirds
Small airports are potential brake-test sites. However, you must first get permission from the airport manager.
Small airports are potential brake-test sites. However, you must first get permission from theairport manager.
of its maximum speed. Regardless, drag strips are usually safe and handy for brake testing.
plenty of room to bring the car to a safe stop. plenty room to of bring the strip car toarea The of advantages a drag safe stop. that it will be clean , smooth and level. The advantages of aconsiderations. drag strip are These are important that it will be clean, smooth and level. The problem with a drag strip is its These are important considerations. length. You usually can't get a car Tnear h e problem with speed a draginstrip is its its maximum a quarter length. You you usually get a a drag car mile, unless are can't running near its maximum speed in a quarter racer. Most road cars reach about twomile, you are running a drag thirds unless maximum speed in a quarter racer. Most road cars reach about twomile. This represents about one-half thirds maximum kinetic speed in a quarter of the maximum energy a car mile.deliver This represents about one-half can to the brakes. Thus, testof the maximum kinetic energy a car ing at a drag strip leaves some doubt can deliver the brakes. Thus, of test-a about the to ultimate capability ing at system. a drag strip leaves some doubt brake about thecan't ultimate of a If you rent capability the drag strip, brake system. enter the car in a drag race . You may you can't be Ifallowed to runrent time the only, drag wherestrip, you enter car in a drag competition. race. You may don't the engage in actual If be allowed to run time hard only,at where you apply the brakes the you end don't in actual competition. If of the engage strip, you can get some idea of you the brakes hard at the end how apply the brakes work at medium-high of the strip, you can get some idea of speeds. how the racing brakes will worklimit at medium-high Drag testing bespeeds. cause carrying an observer during Drag will be limit testingAlso, beeach runracing may not allowed. causewon't carrying observer during you be ableanto get as many runs each maytest notsession. be allowed. Also, as in arun private you won't be able to getlots as many runs Parking Lots-Parking are someas in a private test session. times available on weekends. The Parking is Lots-Parking lotsenough are someproblem finding a lot big for times available on weekends. The testing brakes. Most are too small. problem is finding a lot problems big enoughwith for Also, you'll run into testing brakes. too small. dirt, bumps and Most nearbyare people. And, Also, run into with it may you'll be difficult to getproblems permission to dirt, bumps and nearby people. And, use a really large lot because they are it may beowned difficult get permission to usually by to large corporations. use alarger reallythe large lot because they difare The company, the more
usually owned by large corporations. The 108 larger the company, the more dif-
ficult it will be to talk to the individual who makes the decisions. ficult it will talk to lot the to individual If you findbeatoparking run on, who makes the decisions. be aware of the legal and safety If you find aAlways parking run lot to run on, requirements. a muffled be aware of the legal and safety exhaust, unless you are really out in requirements. Always run a muffled the "sticks." Test during hours when exhaust, unless are really If outyou in people will not you be disturbed. the permission "sticks." Test when get to during use thehours lot, try to people not be disturbed. If you get it inwill writing. Invite the person in get permission to use the lot, to charge to attend your test session.tryNot get writing. Invite person in onlyitisinthis good PR, butthe if the police charge he to attend your testasession. Not come, can give them good story. only is athis good PR, but if the police Often, well-meaning bystander will come, he can give them a story. call the police, because he'sgood not aware Often, obtained a well-meaning bystander will you've permission . call the police,large because he'ssurface not aware Airports-A testing can you've obtained permission. be found at an airport. The runways Airports-A large testing surface can are always long and usually smooth, be found at an airport. The runways level and relatively clean. The best are smooth, placealways to try long is a and smallusually airport, which level and relatively clean. The best may be used occasionally by private place to try is a small airport, which planes. They may have a runway not may beorused occasionally private in use, possibly an accessbyroad that planes. They may have a runway not. can be closed temporarily for testing in use, or possibly an access road that It helps if the airport manager likes can closed temporarily forask testing. race be cars. Don't be afraid to . You It helps the airport manager likes might be if pleasantly surprised. race cars. Don't afraid to ask. You Airports havebethe advantage of might be pleasantly surprised. minimal noise problems and a lot of Airports havehave theto advantage of room . You may sign a waiver minimal and a lot of to releasenoise the problems airport management room. responsibility. You may have Also, to signthey a waiver from may to release the airport management want proof of insurance. If you are from responsibility. Also, they may professional in your approach to want insurance. If you are testing,proof it willofhelp a great deal. professional in you yourhave approach to Public Roads-If a road cat, testing, it will help a great deal. you can try a pu blic road as the last Public ItRoads-If you to have car,a resort. may be legal stopa aroad car in you can line try if a public as the last straight you do road it safely. If you
resort. It may be legal to stop a car in a straight line if you do it safely. If you
do not speed , make excessive noise or appear to be driving recklessly, you do excessive noise or maynot bespeed, able tomake convince a police offiappear to be driving recklessly, you cer to allow you to test. It helps to be mayfrom be able to convince police. offifar houses and other apeople cer to allow you to test. testing It helps while to be Race Testing-Brake far from houses and other people. running a race can be done as a last Race testing while resort. Testing-Brake If you do this, pick an event running a race can be done as atime last that offers maximum practice resort. If you do this, pick an event and mlntmum competition . For that offersa local maximum practice time example, drag event is much and minimum competition. better than a championship event. For For example, a local event is much road racers, try a drag solo-I or time trial better event. For rather than than a achampionship race. In solo-I events, road racers, try a solo-I or time trial the cars run one at a time. The practice rather than a race.quite In solo-I events, sessions are often long. Another the carsisrun at athe time. option to one enter carThe in practice. a racesessionsschool. are often quite driving But firstlong. , get Another permisoption is the to enter the car in a race-. sion from sponsoring organization
driving school. But first, get permission from the sponsoring organization. PLANNING BRAKE TESTS Plan your tests before you get to the
PLANNING TESTS If you track. Testing BRAKE time is valuable. Plantoyour testswork before the have do any on you the get car to other track. Testing time is planned, valuable. Ifyou'll you than what you've have to do on the car waste other probably runany outwork of time. Don't than what you've planned, you'll time trying to think up what to do probably out. Plan of time. Don't waste next at therun track ahead. time to thinkdown up what do Starttrying by writing yourto test Plan ahead. next at the track. plan. List what you'll be testing for. Start by writing down test Include a step-by-step planyour of how plan. List whattesting. you'll be testing for. you'll do the While writing Include step-by-step of how the test aplan , think of plan all the test you'll do the tools testing. writing instruments, and While parts needed the test plan, think of all the to do the job . List these separately.test A instruments, tools isand parts onneeded sample test plan shown page to doItthe List separately. A 109. willjob. give youthese an idea of what's sample test plan is shown on page needed . Determine exactly what's 109. It will giveplan. you an idea of what's needed in your needed. Determine exactly what's Data Sheets-In addition to the test needed in your plan. Data Sheets-In addition to the test
SAMPLE TEST PLAN
SAMPLE LIST OF BRAKE- TESTING EQUIPMENT
1. 2. 1.
Inspect brakes and record starting data . SAMPLE TEST PLAN Overall brake-performance test. lnspect brakes and record data. a. Record comments on starting performance. 2. Overall brake-performance test.as required. b. Inspect and adjust brakes a. Record comments on performance. 3 . Balance adjustment tests. b. Record lnspect deceleration and adjust brakes required. beforeassetting balance. a. 3. Balance adjustment b. Test brakes andtests. adjust balance. Record deceleration before setting balance. . a. c. Continue until maximum deceleration is attained. b. Test brakes 4. Cooling-duct testsand . adjust balance. c. Continue maximum deceleration is attained. a. Tuft tests until to confirm airflow in duct. 4. Cooling-duct b. Measuretests. brake temperature after one stop. a. tomeasured confirm airflow in duct. car for time and measure cooling effect. c. Tuft Run tests b. Measure brake temperature one stop. d. Modify ducts and test coolingafter again. c. Runlining car fortests, measured time and measure cooling effect. 5. Alternate d. Modify fluidducts tests.and test cooling again. 6, Alternate 5. Alternate liningtesting, tests. 7. Long-distance 6. Alternate fluid tests. a. Check temperature. 7. Long-distance testing. b. Check wear rate after test. a. Recordtemperature. driver comments and results of brake inspection, c, Check b. Check rate 8. Bed-in sparewear linings forafter nexttest. race . Record driverwith comments and results of brake inspection. balance wings adjusted to maximum downforce settings, 9 . Setc.brake 8. Wet Bed-in spare linings forrain nexttires, race.and balance brakes for wet. 10. down track, install
SAMPLE OF work on car. • Tool box LIST for general BRAKE-TESTING for driver, fire • Safety equipment EQUIPMENT Tool box for general work on car. extinguishers. Safety equipment driver, and fire • Spare parts for forengine extinguishers. chassis, parts for engine and • Spare Spare tires and wheels. chassis. • Brake linings, brake fluid, special Spare tires and wheels. brake-maintenance tools. Brake linings, brake fluid, special temperature~indicating • Pyrometer, brake-maintenance tools. labels, temperature-indicating paint. Pyrorneter, temperature-indicating • Stopwatch. labels, temperature-indicating paint. • Toppling.block setup. • Stopwatch. Yarn for tufts, tape, scissors. setup. • Toppling-block Video camera, still camera, portafor tufts, bleYarn TV and VCR. tape, scissors. camera, stilltank. camera, porta• Video Fuel, oil, water, air TV and VCR. ble • Jack,jack stands, creeper. oil, water, tank. Materials for air modifying brake • Fuel, Jack,racer's jack stands, ducts, tape, creeper. rivets and rivet Materials for modifying brake gun. ducts, racer's tape,pen. rivets and rivet • Notebook, paper, gun. Notebook, paper, pen.
plan, make several copies of the blank data sheet on this page for recording plan, make copies o f the blank test results.several Pertinent information data sheet on this page for recording about the exact brake-system setup test results. Pertinent should be included: type information of linings, about balance-bar the exact brake-system setup fluid, setting, and similar should be included: type o f linings, information. These will be valuable fluid, tobalance-bar and similar facts determine setting, what setting caused information. These will be valuable what to happen. facts to determine what on setting caused Recorded comments brake perwhat to happen. formance versus temperatures are Recorded comments brake pervital. If you are recordingo ndeceleration formance versus temperatures are rates, make a form for that, too. you are recording deceleration vital. I f test-data These forms can also be rates, make a to form for car that, too. useful at a race record settings These test-data forms can also be and compare them to actual performuseful a race ance onatthe track.to record car settings and compare them to actual ListsYou can never bringperformenough ance on the track. tools or parts to a test session. If you Lists-You cantool never bring you enough leave a part or at home, can you tools or it's parts a test session. be sure thetoone you'll need. IfMura part or tool at home, you can leave phy's Law always applies. beMake sure it's the one you'll need. Mand ura list of tools, supplies phy's Law always instruments. Addapplies. to these lists anyMake a list for o f car tools, supplies and thing needed maintenance or instruments. Add to these liststhings anyrepair. Bring spare parts for thing to needed car have maintenance or likely break.for If you room, also repair. Bring spare parts things bring everything that's notforlikely to likely break.to break. I f you have room, also bring everything not likelyinto to Organize parts that's and supplies break. sturdy boxes and label them. This will Organize and supplies into make taking parts everything much easier. sturdy boxes and label one them. pit Thiscrew will If possible, assign make taking everything much easier. member to keep track of things, and If possible, one pit after crew put everything assign back immediately member to keep track team o f things, and use . A well-organized is a must putsuccessful everythingtesting back immediately for and racing. after well-organized team is sheets, a must use. PutAyour test plan, test-data for successful testing and racing. and parts and supplies lists into a notePutconsisting your test plan, test-data sheets, book of a three-ring binder and parts and supplies lists into a notebook consisting o f a three-ring binder
9. 10.
Set brake balance with wings adjusted to maximum downforce settings. Wet down track, install rain tires, and balance brakes for wet.
HPBooks® BRAKE TESTING DATA SHEET Car _ _ _ Date _ _ 1, Brake System Specification, Date A, Balance-bar setting _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ __ _ _ 1 . Brake System Specification. B, Proportioning-valve setting _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ __ A. Balance-bar setting C. Lining material: Brand _ _ ___ (Front) _ _ __ ___ (Rear)
HPBooksmBRAKE TESTING DATA SHEET Car
I
B. Proportioning-valve setting
D. Brake fluid : _______ Brand _ ______ Type
C. Lining material: Brand
(Front)
I
(Rear)
E, Rotor diameter & thickness: _ _ _ _ _ _ _ (Front) _ _ _ _ _ _ (Rear)
D. Brake fluid:
Brand T
y
p
e
F, Caliper brand & type: _ _ _ _ _ _ (Front) _ _ _ _ (Rear) (Front) (Rear) 2, Brake performance , & type: (Front) -(Rear) F. Deceleration Caliper brandreadings, A. 2. Brake performance. B, Comments on each test. A. Deceleration readings. C. Tires used, size and brand _ _ _ _ _ _ _ (Front) _______ (Rear)
E. Rotor diameter & thickness:
B. on each test._ __ __ (Weather) _ _ _ _ __ _ _ D, Comments Road condition _ __ C. Tires used, size and brand (Front) (Rear) E, Comments _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ D. Road condition (Weather)
3. Temperature testing,
I I
(Front)
E. Comments Maximum caliper 3. A. Temperature testing.temperature
(Front)
(Rear)
.
(Rear)
B, Maximum rotor-edge temperature A. Maximum caliper temperature C. Maximum hub temperature
I I
B. Maximum rotor-edge temperature
D. Maximum lining temperature
C. Maximum hub temperature
I I 1
E, temperature D. Maximum lining temperature F, Comments _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ __ temperature E. testing. 4. Wear (Front) (Rear)
F. Comments
A, Lining thickness-beginning 4. Wear testing. B, Lining thickness-ending C, Wear (beginning/ending) B. Lining thickness-ending D, Test duration _ _ miles, _
C. Wear (beginning/ending)
1
I
(Front)
(Rear)
A. Lining thickness-beginning
_
laps, _ _ stops @ _ _ mph
E, Test track Conditions _ _ _ D. Test duration -miles, -laps, -stops @ -mph F. Comments _ _ _ _ _ __ _ _ _ _ __ _ _ _ _ _ _ _ _ _ __ E. Test track Conditions -
F. Comments or similar record-keeping system, Bring a clipboard to write on, Keep or similar record-keeping the notebook with you during system. all tests Bringraces; a clipboard write on. Keep and put all to technical informathe notebook with you during all tests and races; put all technical informa-
I
tion in it. The notebook will becomeI your "bible " after a year or so . Betion in test it. The will become cause datanotebook is valuable, make your after a year so. Becopies"bible" of everything whenor you '!et cause test data is valuable, make copies o f everything when you n_et 109
Pyrometer is used to measure brake temperature on open-wheel race car. This is difficult on full-fendered cars. When checking temperature, quickly hold pyrometer probe firmly against rotor until meter needle stops rising. Peakontemperature braking cannot be pyrometer is used to measure brake temperature open-wheelduring race car. This is difficult on full-fendered cars. When checkingbecause temperature, quickly will holdoccur. pyrometer probe firmly measured with hand-held pyrometer some cooling Peak temperature can only rotor be measured withneedle an on board or temperature-indicating label or paints. against until meter stopspyrometer, rising. Peak temperature during braking cannot be measured with hand-held pyrometer because some cooling will occur. Peak temperature can only be measured with an onboard pyrometer, or temperature-indicating label or paints.
Omega Engineering Inc. specializes in temperature-measuring devices. Some of their paint and Omegatemperature-indicating Engineering Inc. Specializes in labels are shown here.devices. Photo courtesy temperature-measuring Some of Omegatemperature-indicating Engineering. their paint and labels are shown here. Photo courtesy Omega Engineering.
0-800C (32-1472F) range. It is useful for checking both tire and (32-1472F) range. It is 0-800C brake temperatures. The liquid-crystal useful allows for checking tire ease and used with display it to be both brake temperatures. The liquid-crystal in the sunlight. There are two display allows it to be for usedtires withand easea probes-a sharp one in the There are flat one sunlight. for hard surfaces suchtwo as probes-a sharp oneI for tiresrecomand a brake components. highly flat surfaces suchserias mendone suchfor an hard instrument for the brake components. I highly recomous racer. I t can also be used fo r. mend such an instrument the seriengine tuning, such asfor checking ous racer. It can be used for. which exhaust pipe also is running hotter engine tuning, such as checking or cooler than the others. which exhaustwhen pipe using is running hotter Remember a hand-held or cooler thanthat the others. pyrometer the object being Remember whenrapidly. using aTherefore, hand-held checked will cool pyrometer that the object it must be measured quickly being after checked cool rapidly.isTherefore, maximumwilltemperature reached. it must be measured quickly after Unfortunately, it is impossible to maximum temperature is reached. measure the peak temperature of an Unfortunately, is impossible to iron brake rotorit with a hand-held measure peak of an pyrometer.theBut youtemperature can come close if iron work brake rotor with a hand-held you quickly. pyrometer. ButIndicators-You you can come close Temperature mayif you work quickly. find that it's easier to use temperature Temperature Indicators may indicators rather than a -You pyrometer. find that easiertypes to useof temperature There areit's several indicators. rather changing than a color pyrometer. indicators Some are paint, when There are several types of indicators. they reach a certain temperature . DifSome are color atwhen ferent colorpaint, paintschanging change color difthey reach a certain temperature. Different temperatures, so by using variferent color the paints change color at difous colors, peak temperature can ferent temperatures, so by using varibe found. ous colors, peak temperature can One line the of temperature-indicating be found. paint is available from Weevil Ltd . in One line of Tempil temperature-indicating Europe. Also, has a complete paint is available from Weevil includLtd. in line of temperature indicators,
ing Tempilaq temperature-indicating paint. Another is sold by Tilton ing TempilaqUsually, temperature-indicating Engineering. these paints are paint. Another is soldofby the Tilton brake applied to the periphery Engineering. Usually, these paints are rotor. They can be used on the caliper applied to the periphery of the brake body as well. rotor. They temperature can be used on the caliper Another indicator is a body as well. stick-on label. These are sold by Another temperature is a Tempil (Tempilabel) andindicator Omega Enstick-on label. These are sold by gineering Products (Omega Label), Tempil (Tempilabel) and Omega Enrespectively. gineering Products (Omega Label), These adhesive-backed labels have respectively. white spots that turn black at increThese temperatures adhesive-backed have mental , aslabels indicated white that turn black at on increnext tospots each spot: If some spots the mental as do indicated label turntemperatures, black and others not , a next each spot: If was somereached spots on the bepeak totemperature label turn black and others not, a tween the values of the dohighestpeak temperature wasandreached betemperature black spot the followtween thespot. values theturnhighestwhite If all of spots black , ing temperature black spot andonthethefollowthe highest temperature label ing white spot. spotsa turn case,black, you was exceeded. IfInallsuch the temperature on the label needhighest the next higher-temperature was case,black you, label exceeded. available. IfInnosuch spot aturns need the next higher-temperature the temperature of the lowest spot label available. If In no this spotcase, turnsgoblack, reached. to a was not the temperature oflabel. the lowest spot lower-temperature was not areached. In this go to a Have wide range of case, temperature lower-temperature label. indicators for your first test. You Have a have wide no range temperature idea ofwhat the temprobably indicators for your test. perature ranges will be.first Once youYou get probably have no idea what the temsome experience, you'll know which perature ranges will be.toOnce temperature indicators use . you get some experience, which If you want to be you'll able to know get accurate temperature indicators to use. peak and non-peak temperature readIf you want stopping to be able the to get accurate ings without car, you ' ll peak non-peakpyrometel; temperature readneed and a remote a multi-
home. Store the copies somewhere other than in the notebook. Notehome. get Storelost, the particularly copies somewhere books at the other than in the notebook. Noteraces. books get bring lost, particularly at the Finally, as many qualified races. helpers as possi ble, and all the equipFinally, bring you as ' llmany ment you think need . qualified Include helpers as possible, and all the equipthe required safety equipment. Even ment Include if you you are think testingyou'll in a need. straight line, the helmetequipment. and drivingEven suit. bringrequired a crash safety if you testing a straight line, never be tooincareful. You canare
bring a crash helmet and driving suit. You can never be too careful. BRAKE-TESTING INSTR UMENTS BRAKE-TESTING Certain instruments are needed to INSTRUMENTS get maximum benefit from a test Certain Of instruments are needed to session. primary importance is get benefit a test temperature. It can from be measured brakemaximum session. Of aprimary importance is with either hand-held pyrometer, brake temperature. It can be measured remote pyrometer or with temperature with either a hand-held pyrometer, indicators placed on the brake . remote pyrometer pyrometer or with temperature Pyrometer-The is a speindicators placed on Itthehas brake. thermometer. a probe that cial Pyrometer-The pyrometer is aTemspecan be placed against an object. cial thermometer. It has a probe perature is then read from a meter.that A can be placed against anused object. Tempyrometer is commonly to measperature is then from a meter. A ure race-car tire read temperatures. It can pyrometer is commonly used to measalso be used to measure brake temure race-car tirethetemperatures. can perature up to limit of the It meter also beThe used to measure brake temscale. pyrometer-probe tip must perature to contact the limitwith of the meter be held inupfirm the object scale. The pyrometer-probe tip into being checked so heat can soakmust be in firm contact with stabilizes, the object theheld probe. When the meter being checked so heat can soak into the reading is taken and recorded. theAnprobe. Whendual-purpose the meter stabilizes, excellent pyromethe taken and sold recorded. ter reading is AP's is CP-2650-8 by Tilton An excellentThis dual-purpose pyromeEngineering. instrument has a ter is AP's CP-2650-8 sold by Tilton Engineering. This instrument has a
110
Europe. Also, Tempil has a complete line of temperature indicators, includ-
ings without stopping the car, you'll need a remote pyrometel; a mirlti-
ap: RACinG Excellent temperature indicators are manufactured by Tempil. Tempil's Tempilaq paint meltstemperature when heated to rated Excellent indicators are temperature. Tempilabel spots turn black manufactured by Tempil. Tempil's Tempilaq when heated rated temperature. paint melts towhen heated to Photo rated by Tom Monroe. temperature. Ternpilabel spots turn black when heated to rated temperature. Photo by Tom Monroe.
position switch and thermocouples to put in contact with the test objects. A position thermocouples to full lineswirch of and remote temperatureput in contact with the test objects. A measuring equipment, including therfull line ofandremote mocouples leads, temperatureis available measuring equipment, including from Omega Engineering Productsther. mocouples and leads, is available Their 12-volt model 650K digitalfrom Omega Engineering readout pyrometers areProducts. relatively Their 12-volt digitalcompact and aremodel easy 650K to read . All readout pyrometers are relatively digital-readout pyrometers require excompact and are easy toseries-7000 read. All ternal power. Omega's digital-readout pyrometers pyrometers require exdial-readout are selfternal power. Omega's powered, compact and lessseries-7000 expensive dial-readout pyrometers areto selfthan digitals, but not as easy read powered, compact and less expensive accura tely. than digitals, butElectronic not as easySystems' to read Nationwide accurately.II digital-readout pyrometer Slimline Nationwide Electronic12-volt, Systems' IDT-7726 is compact, d-c I1 digital-readout pyrometer Slimline powered, and is easy to read. It reIDT-7726 is compact, d-c 12-volt, d-c quires a 100-0193-01 isolator powered, andsure is easy to read.type-K It remodule . Be to specify quires a 100-0193-01 d-c isolator thermocouples when ordering. Also module. Be sure to specify type-K specify whether you want a pyrometer thermocouples when ordering. Also that displays temperature in Fahrenspecify whether you want a pyrometer heit or Centigrade. that displays temperature in FahrenThermocouple Installation - Therheit or Centigrade. mocouple attachment is important. Thermocouple -Ther-be The thermocoupleInstallation junction must mocouple important. in contact attachment with the istest object. The thermocouple must be Otherwise , readings junction will be low. Highin contact with the test object. temperature epoxy works well for atOtherwise, readings will betolow. Hightaching thermocouples calipers. temperature epoxy works well for atThermocouples can be pinched under taching thermocouples to calipers. the head of a screw. Or, silver solderThermocouples be pinched under ing works well oncan some metals. Whatthe head solderever you of usea, screw. be sureOr, thesilver attachme nt ing worksinsulate well on some Whatdoesn't the metals. thermocouple ever you use,object. be sure the attachment from the test doesn't insulate the isthermocouple Rotor temperature difficult to from the test measure withobject. a thermocouple. The
Rotor temperature is difficult to measure with a thermocouple. The
As with other temperature-indicating paints, AP Racing's indicators can be used to check rotor or brake-drum temperature. Temperature indicators will tell you the highest tempera·· ture reached, you use the right range paints, of paints. Racing. can be used to check As with other iftemperature-indicating APCourtesy Racing's AP indicators rotor or brake-drum temperature. Temperature indicators will tell you the highest temperature reached, if you use the right range of paints. Courtesy AP Racing.
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Drawings show how to install thermocouple plugs in disc and drum-brake linings so brake temperatures can be monitored while running. For this purpose, you can make your own type-K thermocouples twisting chromel and alumel and linings silver soldering Drawings show how to by install thermocouple plugs in discwire andtogether drum-brake so brake the twisted end a copper tube. You running. can get For this this wirepurpose, from companies Omega temperatures canin be monitored while you can such makeas your own Engineering. Reprinted with permission © 1984 Automotive type-K thermocouples by twisting chrome1 andSociety alumel of wire together Engineers, and silver Inc. soldering the twisted end in a copper tube. You can get this wire from companies such as Omega thermocouples must be silverin the lining material close to Inc. the fricEngineering. Reprinted with permission 0 1984 Society of Automotive Engineers,
soldered or crimped into a small Oat thermocouples be springsilverprobe, insulated must and lightly soldered or crimped into a small flat loaded against the rotor friction probe, insulated and lightly springsurface. Brake manufacturers who loaded against the rotor with friction measure rotor temperature rubsurface. Brake manufacturers who bing thermocouples make their own; measure rotor with rubthey are not for temperature sale. bing thermocouples make their A practical alternative used by own; most they are not brake for sale. American and lining manuA practical used by most facturers is to alternative install the thermocouple
American brake and lining manufacturers is to install the thermocouple
tion surface. Temperatures measured
in closelower to the than fricin the thislining way material are slightly tion actualsurface. rotor Temperatures temperature . measured However, in way are slightly lower the this difference is consistent and thethan inactual rotor temperature. However, stallation is much easier and more the difference and the indurable thanis consistent the rotor-rubbing stallation is much easier and more thermocouples. durable than the end rotor-rubbing The thermocouple is stripped thermocouples. back approximately 0.500 in ., twisted , The thermocouple is stripped inserted into a end 3/16-in.-long, back approximately 0.500 in., twisted, inserted into a 3116-in.-long, 111
HOLE MUST BE
OPE: ~
A r..O FRE E
>R O'..', SOLD ER SO .0.5 NC T TO
/
.I
,T STRlcr FLUI O FLOW WHEN
BLEE D' NG *OLE MUST BE WEll ClliD FREE FROM SOLDER SO 1 5 N O T TO RESTRICT FLUtD FLOW W H E N
i
I
L
L5·cvE~
SO LDER SECURELY
SECTI ON A- A
GRIN D O ~ F EXCE SS SOLDER F LUS H WIT H SU RFACE SHOWN
SECURELY
SECTION A-A
RIND OFF EXCESS SOLDER
SURFACE SHOWN thermocouple for measuring brakeFLUSW WITH Drawing shows bleed-screw fluid temperature. The screw is first drilled through, then twisted thermocouple is bleed-screw silver-soldered in place. Reprinted with permisDrawing shows thermocouple for measuring brakesion © 1984 Society of screw Automotive Engineers, Inc. fluid temperature. The is first drilled through, then twisted
thermocouple is silver-soldered in place. Reprinted with permission 0 1984 Society of Automotive Engineers, Inc.
1/8-in.-OD X 0.086-in.-IO copper tube and silver-soldered in place to 118-in.-OD copper form a plug. XThe0.086-in.-ID plug is installed in tube and silver-soldered in place to the friction material. Typical disc- and form a plug. installations The plug isare installed drum-lining shown in in the friction material. the drawing, page Ill.Typical disc- and drum-lining are shown in If the pluginstallations hole is drilled through the drawing, 11with 1 . a number-31 the lining andpage shoe If the plug hole drilled (O.IOO-inJ drill, theisplug can through be reset the lining andtheshoe withwears a number-31 easily when lining down to (0.100-in.) drill, the plugthermocouple can be reset the plug surface. If the easily when the lining wears to plug is not reset, readings willdown fluctuthe plug surface. If the thermocouple ate between rotor and lining plug is not reset, readings will fluctutemperature. ateThebetween lining drawing atrotor top of and page shows temperature. how to install a thermocouple on a Thescrew drawing at top of page shows bleed for measuring brake-fluid how to installin a athermocouple on a temperature caliper or wheel bleed screw for measuring brake-fluid cylinder. temperature in a caliper or wheel With a mUlti-positio n switch, many cylinder. thermocouples can be connected to a multi-position theWith pyrometer so they switch, can be many read thermocouples When can berunning connected to individually. therthe pyrometer so they can be read mocouple leads from the brakes to the individually. Whento the running chassis, band them flexibletherhymocouple leads from the brakes to the draulic line with plenty of slack so chassis, them to the hythey donband ' t break when the flexible suspension draulic line with plenty of slack so moves. they don't Gage-Brake-tluid break when the suspension Pressure pressure moves. can be measured with a simple presPressure sure gage .Gage-Brake-fluid Marsh Instrument pressure Compacan be measured with simple presny's 14878 gage has lowa displacement sure isgage. Compaand usedMarsh widely.Instrument Another pressure ny's J4878 gageavailable has low displacement gage is also from Hurst and is used widely. Another pressure Performance . gage is also available Hurst used in the A pressure gage can befrom Performance. shop or at the track . If used at the A pressure canthe bedriver used or in obthe track, mount itgage where shop orcan at see the ittrack. usedtheatgage the server easily.If Fill
track, mount it where the driver or observer can see it easily. Fill the gage 112
U-tube decelerometer is made by AM MCO Tools Inc . It's calibratin feet per second per second (ft/sec/sec) rather than g's (1 gI = 32.2 ftlsec/sec) . Instrument reads down Tools scale Inc. for deceleration U-tube decelerometer is made by AMMCO It's calibratandinup scale acceleration. Deceleration scale is used brake (1 g ed feet perfor second per second (ft/sec/sec) rather thanfor g's testing; accelerationlnstrument scale can be useddown for engine and shift= 32.2 ft/sec/sec). reads scale tuning for deceleration pointupdetermination. Instrument can be mounted to windshield and scale for acceleration. Deceleration scale is used for brake with suction cups or scale bolted to be instrument panel. tuning Photo and courtesy testing; acceleration can used for engine shiftAMMCO Tools Inc. point determination. lnstrument can be mounted to windshield Ied
with suction cups or bolted to instrument panel. Photo courtesy AMMCO Tools Inc.
with fluid before mounting it. And always put a valve at the gage so it can with fluid beforenot mounting be shut off when in use andit.soAnd the it can always won't put a valve the gage gage lose at its bleedso when be shut offThe when nottointhe usegage and can so the removed. line be gage won't lose its bleed bled by loosening the valve jamwhen nut removed. The line to the gage can be while applying slight pressure to the bled bypedal. loosening valvebegins jam nut brake Whenthefluid to while applying slight pressure to the leak, retighten the nut to complete brake pedal.. When fluid begins to the bleeding leak, retighten the nut relates to complete pedal Hydraulic pressure the bleeding. effort to actua l force on the brakes. Hydraulic pressure relates pedal When used with a decelerometer, the effort to actual force on pressure gage can be usedtheto brakes. deterWhen used with a decelerometer, mine brake-system effective ness , the or pressure gage can be versus used to vehicle deterto plot pedal effort mine brake-system effectiveness, or deceleration. to plot pedal effort vehicle Camera-Photos are a versus good source of deceleration. test data. Use a camera that provides Camera-Photos are a good of instant prints. Photograp h thesource car just testthe data. Useslams a camera thatbrakes provides as driver on the at a instant prints. Photograph the car prescribed braking point. You mayjust be as the driver slams on the brakes able to detect whether the front or at thea prescribed be rear wheelsbraking lock uppoint. first.You It's may someable detecttowhether thelocks frontuporfirst the timestotough tell which rear wheels lockTouphelp, first.paint It's asomeby observation. large times tough to tell which locks first X on the wheels and tires with up waterby observation. To help, paint a large soluble white paint. X Even on the better wheels and with awaterthantires using still soluble white paint. camera to detect brake lockup is a Evencamera. better It than still video can beusing playeda back camera to detect immediately after brake makinglockup a shot.is Aa video be be played video camera. camera It cancanalso usedback to immediately after making a shot. Aa record instruments in the car during video Tocamera be must used be to stop. do this,can thealso camera record instruments during mounted securely in in the a car bracke t. Aa
stop. To do this, the camera must be mounted securely in a bracket. A
camera is an accura te data recorder-much more so than a person camera is an accurate data reusing his eyes. corder-much more decelerometer so than a person Decelerometer-A is using his for eyes. valuable testing the stopping capaDecelerorneter-A decelerometer is bility of a car. One can be as simple as valuable for testing the stopping capatoppling blocks or as complex as a bility of a car. One can as simple as recording g-meter. See be accompanying toppling blocks as complex and or photos. Buy the as besta illustration recording g-meler. See accompanying decelerometer you can afford. Use the illustration and inphotos. the besta Tapley meter a car Buy in which decelerometer you along can afford. Use the passenger can ride and observe. Tapley in a can car in whichthea Perhaps meter a camera replace passenger ridecare alongto and passenger can if you· rig observe. one up . Perhaps a camera can replace the The Tapley meter indicates actual passenger if you rig one deceleration ratescareasto the car up. is The Tapley meter indicates actual stopping. deceleration the car7350 is AMMCO rates Tools' as model stopping. U-tube decelerometer is easy to install AMMCO Tools' well.model 7350 and adj ust. It works This instruU-tube decelerometer is easy to install ment is used widely by the American and adjust. well. This instruautomob ile Itanworks d brake industries, and ment is used widely by the American many state vehicle-inspection stations automobile in the U.S. and brake industries, and many vehicle-inspection The state simplest decelerometerstations is the in the U.S. toppling blocks. Set up a tray with recThe simplest decelerometer is the tangular blocks as shown. The blocks toppling Seta up a tray recare lined blocks. up along ledge on with the tray. tangulartheblocks as shown. The blocks When car stops, the taller blocks are lined up atalong ledge on the rates tray. topple over lowera deceleration When the car stops, the taller blocks than the shorter ones. Deceleration toppleis over at lower rate between the deceleration tallest block rates that than the shorter ones. Deceleration toppled and the shortes t one that rate is between the tallest block that didn't. toppled andblocks the shortest that Toppling can be one knocked didn't.by bumps or vi brations, so make over
Toppling blocks can be knocked over by bumps or vibrations, so make
Forward Motion of Car Forward
X1 =~ = 067 H1 1.5 . 9
X2=~=090 H2
1.0
.
9
Motion of Car
0.9 x3 - 0.8 0.679 1.339 x2 =-= 0.90g HI 1.5 H1 1.0 H3 0.6 Dimensions of toppling blocks determine maximum deceleration they can take before toppling. Blocks dimensions don't have to be precise as long as they are square. Measure height and width, of each block determine and calculate its toppling deceleration as shown. Each Dimensions of toppling blocks maximum deceleration they can take before block is positioned against adon't thin have ledgetoonbea precise flat trayastolong allow to topple whenMeasure the car toppling. Blocks dimensions as it they are square. decelerates. Tray can be angled toand compensate angle. height and width, of each block calculatefor itsvehicle-dive toppling deceleration as shown. Each block is positioned against a thin ledge on a flat tray to allow it to topple when the car decelerates. Tray can be angled to compensate for vehicle-dive angle.
XI
=-
=
at least three runs to verify the results. If you don ' t get consistent reat least runs definitely to verify work the sults and three the brakes results. If you rethe same eachdon't time,get tryconsistent another test sults and the brakes definitely work method. However, be aware that varithe same time, ations in each results cantrybeanother caused test by method. However, be aware that varibrake-temperature changes or other ations in results can be caused by changes. brake-temperature changes or other Tire-Test Instruments-Don't forchanges. get that tire grip affects braking. Thus, Tire-Test Instruments-Don't forto test brakes, also test the tires. You get tiretogrip affectstires braking. Thus, maythat wish try other during the to testbalance the tires. testtest andbrakes, changealso brake to You suit may wish to trytires. otherBring tires during the the different along the test and change brake balance to suit extra tires and instruments needed to the tires. Bring and along the test t1:different em. A tire pyrometer an airextra tiresgage andare instruments needed to pressure the usual minimum test tkem. A tire pyrometer and an airinstruments for tire testing . pressure gage Gages-One are the usuallast minimum Air-Pressure instruinstruments for tire ment to consider is testing. a gage for measurAir-Pressure Gages-One last instruing low air pressures in brake-cooling ment to consider is a gage for air ducts and at the exterior measursurfaces ing the low car. air pressures in brake-cooling of These pressures are not air ducts and exterior surfaces measured in at psi,thebut in inches of of the (in.Hp). car. These are not water Forpressures comparison, the measured butwater in inches pressure 27inin. psi, below surface of is water (in.H,0). For comparison, the 27 in.Hp, or 1 psi. pressure below water is Gages 27 for in. measuring low surface pressures 27 in.H20, or 1 psi. are very useful for developing brake Gages for measuring low pressures ducts , engine-induction ducts, waterare very usefulairfor developing brake and oil-cooler ducts, driver-cooling ducts, engine-induction ducts, waterducts and even car body-surface and oil-cooler air ducts,manometers driver-cooling aerodynamics. U-tube are ducts and even car body-surface used often for measuring low air aerodynamics. manometers pressures, but U-tube a dial gage is easierare to used often for measuring low air read and install in a car. pressures, but a dial gage is easier to 2010 MagneDwyer Instruments' read helic and gageinstall readsinupa car. to 10 in. Hp . This Dwyer 2010 small 5-in.Instruments' round gage can be Magnemount10 in. H,O. This helic gage reads up to ed temporarily on an instrument small gage of canthe be steering mountpanel 5-in. or in round the center
ed temporarily on an instrument panel or in the center of the steering
wheel of a cramped formula car. Dwyer also carries all types of wheel of a cramped formula car. manometers.
Dwyer also carries all types of manometers. BRAKE-PERFORMANCE TESTS
There are a few basic-performance BRAKE-PERFORMANCE TESTS tests that can be made without much Thereorare a few basic-performance trouble expensive instruments. All tests can beshould made without brakethat systems deliver much minitrouble or expensive instruments. All mum performance regardless of the brake car type.systems should deliver minimum performance regardless of the To run a basic brake-performance car type. test, pick a distance between stops, To as run0.4a mile, basic or brake-performance such a time between test, pick between stops, stops, suchaasdistance one minute. Accelerate such asrest 0.4atmile, or a time between from wide-open throttle to stops,best suchspeed-to as one minute. your 55 mphAccelerate for a road from wide-open throttlerace to car orrest 80 atmph for a small your best maintain speed-to that 55 mph foruntil a roadit car-and speed car or for 80 the mph a Distance small race is time nextfor stop. or car-and maintain that speed until toit time between stops can be adjusted is time fororthedecrease next stop. Distance or increase test severi ty. time stops firmly can be so adjusted to the brakes the car Applybetween increaserapidly or decrease severity. stops without test locking the Apply the brakes so the car wheels. After the firmly car stops, record stops rapidly without locking the some comments on your data sheet: wheels. carwheels stops,lock? record front the or rear • Did theAfter some on yourordata • Didcomments the car swerve pullsheet: to the Did the front or rear wheels lock? side? Did there the car swerve inor deceleration pull to the a change • Was side? as the car slowed? change in deceleration Was there • Were there anoises from the brakes? as the car slowed? • Was the pedal firm? there noises fromor thewas brakes? • Were Was the stop smooth there the pedal firm? anyWas vibration? Was the stop repeat smooth the or was Immediately test there and any vibration? record your comments. Do this until Immediately repeat the performtest and you notice a change in brake recordoryour this have until ance untilcomments. about tenD ostops you notice a change in brake performbeen completed . It's important to be ance or until ten so stops consistent with about each stop yourhave test
been completed. It's important to be consistent with each stop so your test
Dwyer's 2010 magnehelic gage is easier to install and use than manometer for measuring air pressure. Dwyer's 2010 magnehelic gage is easier
to install and use than manometer for measuring air pressure.
is repeatable for later comparisons. After you finish testing, carefully is repeatable for where later comparisons. touch the wheel it bolts on. After you finish testing, carefully Record the following comments: touch the wheel where it about bolts on. • Are front and rear wheels the Record the following comments: same temperature? rearthe wheels aboutBoth the • Are Can front you and smell brakes? same temperature? sets? youblack smell Both dustthe on brakes? the outside of • Can Is there sets? the wheels? black dust on the outside of • Is Is there grease leaking from the front the wheels? hubs? Is grease leaking from the front The comments you've recorded are hubs? for comparison with other cars or with Thetests. comments recorded beare other There you've are no numbers, for comparison withusing otherinstruments. cars or with cause you are not other tests.you There no numbers, beHowever, canare record your comcause you are not using instruments. ments about specific parts of the However, youperformance. can record your combrake-system The effect ments about specific parts of the of brake-system. changes should be brake-system performance. Thehow effect of learning to recorded as part of brake-system. should be maintain and adjustchanges a brake system. recorded as part ofperformance learning howtest to The overall maintainbeand adjust abybrake system. should followed some work on overall performance test theThe brakes. Usually, there'll be one should be followed by some work on aspect of performance that you wish the brakes. Usually, there'll be one to improve. See the trouble-shooting aspect of performance that12you section following Chapter for wish sugto improve. gestions on See howthe to trouble-shooting correct specific section following Chapter 12 for sugproblems.
gestions on how to correct specific
problems.TESTING TRACK A race car or high-performance TRACK road carTESTING should be track tested . A race car time or high-performance However, the and effort that road car testing shouldat abe goes into tracktrack is nottested. worth However, the timetransportation and effort that it for the ordinary car. goes into testing a track is not worth Performance testsatjust described done it for the ordinary on a country road transportation should suffice.car. In Performance just described done this section, tests I discuss track testing on a country roadtheshould suffice. In highest possible aimed at getting this section, I discuss track testing performance from a brake system.
aimed at getting the highest possible performance from a brake system. 113
Pushrod
Pushrod
Pushrod
Balance-Bar Adjuster Balance-Bar
Measure lining thickness with dial caliper or micrometer before and after each test session determine wear Brake Measure to lining thickness with rate. dial caliper wear can be related toand number stops or or micrometer before afterofeach test laps; particularly important session to determine wear for rate.planning Brake strategy racing. Be sure wear canfor be long-distance related t o number of stops or to measure pads in same place for eachplanning time. laps; particularly important strategy for long-distance racing. Be sure to measure pads in same place each time.
-
Torque Force Wrench Position A Torque Wrench Position A
Torque Wrench Position B
.- ~. o r---
o
.
o~
I
(!)
Force
Center of Wheel Force Wheel Lug Nut Center of Wheel
w heel Lug Nut To measure torque about wheel center, put torque wrench in position B. Wrench in position A willtorque read about low because distance To measure wheel center, put from wrench to wheel center is torque wrench handle in position B. Wrench in pogreater length wrench. Don't sition A than will read low ofbecause distance exceed torque capacity lug nutscenter or bolts. from wrench handle toof wheel is greater than length of wrench. Don't exceed torque capacity of lug nuts or bolts.
Locked wheels is indicated by the smoke. Excessive wheel locking can flat-spot tires, testing Locked making wheels is brake-balance indicated by the smoke. expensive. takes locking a sensitive and Excessive Itwheel can driver flat-spot careful observation to keep from testing ruining tires, making brake-balance tires. expensive. I t takes a sensitive driver and careful observation to keep from ruining tires.
114
\.'-..--Jr--1 I I
o
o
I ~ Reference
r-
Distance
When making brake-balance changes with a balance bar, make a reference measurement so you know where you started. With this measurement, you can quickly return to your starting balance, if required. changes with a balance bar, make a reference measurement When making brake-balance so you know where you started. With this measurement, you can quickly return t o your starting balance, if required. Recommended track tests are as If you are unfamiliar with the race
follows: Recommendedadjustment. track tests are as • Brake-balance follows: • Deceleration. Brake-balance adjustment. • Effectiveness. Deceleration.measurements. • Temperature Effectiveness.comparisons. • Brake-lining Temperature measurements. Lining Thickness-Before you start Brake-lining testing, check comparisons. brake lining thickness. Lining Thickness-Before you their start Remove the linings and measure testing, check brake lining thickness. thicknesses with a micrometer. It's Remove the alinings andcaliper. measure their OK to use vernier Record thicknesses a micrometer. It's on your data each lining with thickness OK to use a vernier caliper. Record sheets. Also indicate where on the each lining thickness onwasyour data lining each measurement taken. sheets. Also indicate where on so Disc-brake pads wear on a taper,the lining eachthem measurement was taken. measure in the middle and at Disc-brake pads wear on a taper,linso each corner. Measure drum-brake measure them in the middle and at ings at each corner and at the inside each corner. Measure drum-brake linand outside edges of the center. Measings the at each corner and at the of inside ure combined thickness the and outside edges of the center. Measlining and shoe plate. Subtract shoeure the combined of the plate thickness to get thickness lining thickness. lining and shoe plate. Subtract shoeThe purpose of these measuremen ts plate thickness get lining is to check for to lining wear. thickness. By recordof these measurements ingThe thepurpose total number of hard stops is to check for wear. By recordduring testing, lining you can calculate the ing the total number of hard amount of wear per stop. Youstops can during testing, about you can calculate the then calculate how long your amount of wear per stop. You can brake linings will last. then aboutthehow longareyour Brakecalculate Balance-If linings not brake linings will last. bedded in, do it before testing. This Brakealso Balance-If are and not will warm upthe thelinings engine bedded in, do it before testing. This chassis. Check page 40 for details will also upbrakes. the engine and about how warm to bed in chassis. Check page for car, details If you are testing 40 a race it about how bedadjustable in brakes.balance bar. should havetoan a race car, init you are A Ifbalance bar testing is usually mounted should have an adjustable balance bar. the pedal and is adjusted from one A balance bar is ausually mounted in end by loosening jam nut and turnthe the pedal and aisscrewdriver. adjusted from one ing bar with
end by loosening a jam nut and turning the bar with a screwdriver.
car, you may not know where to set you are bar. unfamiliar with the theIf balance Start setting it at race the car, you may not know where to seta center of its adjustment and perform the balance bar. Starttest. setting at the simple brake-torque Jackit up the center of its adjustment and perform car and put it on jack stands so thea simple brake-torque Jack upHave the tires are off the test. ground. car and put it on jack stands so the someone sit in the car and lightly tires are off the With ground. Have the brakes. the helper apply someone sit in the car and lightly holding the brake pedal, turn a front, apply helper then athe rearbrakes. wheel With usingthe a torque holding the brake pedal, turn a front, wrench on a lug nut as shown in the then a rear wheel usingRecord a torque accompanying drawing. the wrench a lugcan't nut asmeasure shown in the results. on If you brake accompanying drawing. Record the torque with a torque wrench, use your If you can't measure brake results. hands and estimate it. torque wrench,torque use your Start with witha torque front-brake at hands and estimate it. about 50% greater than rear-brake Start ifwith front-brake torque at torque, the car has 50-60% of its about 50% greater than rear-brake weight on the rear wheels. If the car is torque, if the car has 50-60% of its extremely nose-heavy, set front-brake weight the rear wheels. the car is torque on at about 100% moreIfthan rearextremely nose-heavy, set front-brake brake torque. But if it is extremely tailtorque at about than rearheavy, start with100% front-more and rear-brake brake torque. But if it is extremely tailtorques approximately equal. This heavy, start with frontand rear-brake also confirms that both front- and torques approximately rear-brake systems work. equal. This also confirms that both isfrontand If front-brake torque less than rear-brake work. rear, adjustsystems the balance bar. is less than If front-brake The tricky part torque of balance testing is rear, adjust the balance bar. figuring out which end locks up first. The tricky part ofhelpers balancetotesting is You'll need some do this. figuring out which end locks up first. As suggested, this is the time to use a You'll need or some helpers to With do this. still camera video camera. an As suggested, this is the time to use instant-replay video camera, you cana still camera or video With an observe at leisure whatcamera. happened. instant-replay can A driver willvideo have camera, difficultyyou telling observeend at leisure what happened. which of a car locks up without A driver will telling flat-spotting the have tires. difficulty Instead, he has which end of a car locks up without to ease off the pedal the moment a flat-spotting thelock tires. he has wheel starts to up.Instead, If he doesn't,
to ease off the pedal the moment a wheel starts to lock up. If h e doesn't,
White spot on tire is cord showing through where rubber was worn off. Locking brakesspot risks tires and also White on flat-spotting tire is cord showing through going through cord.worn Tire is and where rubber towas off.ruined Locking must be risks replaced. brakes flat-spotting tires and also
going through to cord. Tire is ruined and must be replaced.
he can grind right through the tires. Flat spots can ruin a tire. Be careful! heDo canthe grind through thetest tires. firstright brake-balance at Flat spots can ruin a tire. Be careful! moderate speed-about 40 mph . If DO test to at you gothe too first fast, brake-balance the car will be hard moderate speed-about observe safely. If yo u're 40 not mph. using Ifa you too fast,position the car people will be on hard to both videogocamera, observe safely. If you're not using sides of the track . Use two observersa video camera, on both on each side ifposition possible.people Tell them to sides of the twoorobservers try and see track. if the Use front the rear on eachlock sideupif first. possible. them to Don Tell 't lock up all wheels try and see if the front or the rear four wheels. The test will then mean wheels up first. Don't lock up all nothing,lock so don't brake too hard. four wheels. test lock will first, then adjust mean If the frontThe wheels nothing, so don't brake too hard. the balance for more braking. Make If the lock first, sure youfront turn wheels the adjuster in theadjust corthe forRecord more braking. Make rect balance direction! the number of sure adjuster the data corturnsyou on turn the the adjuster in in your rect direction! Record the number of sheet and retest. Continue testing turns on the adjuster in your data until you are satisfied with brake sheet balance.and retest. Continue testing until are wheels satisfied should with brake The you front lock balance. before the rears. Rear-wheel locking The instability. front wheels should lock causes If the car is turning before Rear-wheel or has the any rears. side forces on it, locking it will causesFront-wheel instability. If locking the car iscauses turninga spin. or has any side forces on it, it will car loss of steering control, but the spin. Front-wheel locking causes usually goes in a straight line. Thea loss of steering control,onbut final setting will depend the the typecar of usually goes in 's a preference. line, l-he car and the driver final setting the type of If your carwill has depend wings oronaerodynamcar and the driver's preference. ic downforce from ground effects, If your car has or aerodynambrake balance maywings be different at high ic downforce effects, rear speeds. A rearfrom wing ground loads the brake balance mayincreases. be different Onatahigh car wheels as speed A rear wing loads thebrakes rear speeds. that has only a rear wing, if the wheels as speed increases. On a the car are evenly balanced at 40 mph, that has only will a rear wing, front wheels lock first ifatthe 100brakes mph. areis evenly balanced at 40 the mph, the impossible to balance brakes It 100 mph. front wheels will lock first at for all speeds on such a car. It is impossible Compromise . to balance the brakes forRace-car all speeds such more a car. brakes on are used at Compromise. high speed than at low speed. The Race-carbraking brakes speed are used more at minimum on the track high speed at lowturn. speed. is going into than the slowest PickThe an
minimum braking speed on the track is going into the slowest turn. Pick an
rear of sports racer improves rear-tire traction for improved handling and braking IatWinghighat speed. -*. As speed drops, so does wing downforce, increasing the chance of rear.-
I
wheelat lockup when braking tight corners. -.id braking Wing rear of sports racerfor improves rear-tire traction f-. ....,. at high speed. As speed drops, so does wing downforce, increasing the chance of rearwheel lockup when braking for tight corners.
Ground effects and rear wing provide maximum aerodynamic downforce. Wing also increases drag dramatically. NACA ducts optimize airflow to brakes with minimum drag.
Ground effects and rear wing provide maximum aerodynamic downforce. Wing also increases drag dramatically. NACA ducts optimize airflow to brakes with minimum drag.
average braking speed for the particUlar track and set the balance for that average speedstrongly for the particuspeed . Ifbraking the driver prefers lar track set theover balance for that one type and of balance another, the speed. thebedriver strongly prefers brakes If may balanced perfectly at one type of over another, the top speed andbalance increasingly unbalanced brakes perfectly at speedmay dropsbe. Abalanced lot of experimenting as top speed and increasingly is needed to arrive at unbalanced the best as speed drops. compromise . A lot of experimenting is Remember needed tothatarrive the isbest bra ke at balance afcompromise. fected by the foJ]owing: Remember that brake balance is afchanges-could be caused • Tire-grip fected by the following: by either track-surface changes or tireTire-grip changes-could be caused temperature changes. by either track-surface changes tire• Aerodynamic-force changes,or such
temperature changes. Aerodynamic-force changes, such
as a wing-angle change. temperature-fade may • Brake as a wing-angle change. at one end of the car before the occur Brake may other end . temperature-fade occur at one end of the car before the • Change to different-size or -comother end. pound tire. Change to to different-hardness different-size or -cornbrake • Change pound tire. lining. Change toto different-hardness brake the car weight distri• Change lining. bution. Change intomaster-cylinder the car weight size.distri• Change bution. Because it is difficult for a driver to Change in master-cylinder detect small brake-balance size. changes, Because it is difficult for a driver to don ' t be concerned about small detect small However, brake-balance adjustments. if youchanges, make a
don't be concerned about small adjustments. However, if you make a 115
Severe changes in track conditions is why brake balance needs to be adjusted by the driver. If Geoff Lee's Formula Ford was set up for the dry, front wheels would lock in the wet. To changes correct, in balance is is changed to give more needs rear-wheel and Severe track adjuster conditions why brake balance to bebraking adjusted by less the front. During testing, can deliberately wet to find correct rain settings. driver. If Geoff Lee's you Formula Ford was set upthe fortrack the dry, front wheels would lock Photo in the by Steven Schnabel. wet. To correct, balance adjuster is changed to give more rear-wheel braking and less
front. During testing, you can deliberately wet the track to find correct rain settings. Photo by Steven Schnabel.
~A
A
1.0
1.0--
---
0.81--====::::::-=---
0.8 Average Deceleration
-
-
(g) Average Deceleration
A.
(g)
o
40
80
~c 120
I I Speed When Brakes Are Applied (mph)
40
I
80
B
yc I
I
0
---- B
120
balance-bar, master-cylinder valve problems later.TESTS DECELERATION
160
I
problems-it has lift at high speed. Most road cars have less deceleration at higher speeds, but not as severe as curve B shows.
only a few laps, make only one and then discuss with the ob-
change, 116
and
A verage Deceleration - This test is
I I
160
Average deceleration tests will tell you When something about car's aerodynamic downforce. If Speed Brakes Are aApplied (rnph) deceleration increases with higher-speed stops, stopping is improved with downforce, asI I shown bydeceleration curve A. Curve B will reflects a car with littleabout or noadownforce. Curve Cdownforce. is a car with Average tests tell YOU something car's aerodynamic If problems-it has lift at high Most road cars have lessisdeceleration at higher speeds, deceleration increases withspeed. higher-speed stops,-stopping improved with downforce, as but not by as curve severeA.asCurve curve BB reflects shows. a car with little or no downforce. Curve C is a car with shown
big adjustment, brake balance should be checked by testing. The most imbig adjustment, balance should portant factor is brake tire grip, caused by be checked by testing. The most either changing track conditions orimby portant tire grip, by the tires.factor Tiresis often lose caused grip with either changing track conditions by age , wear or temperature change.orTest the tires. Tires often lose grip with the car with the setup you will be runage, temperature change. Test ning wear in theorrace. theIfcar with you will be runyour carthe hassetup a cockpit-adjustable ning in the balance bar,race. check it during a test sesIf your has aThe cockpit-adjustable sion at thecartrack. driver should balance bar, check it during seschange balance to see howa test it feels. sion the track.should The driver Also, atobservers recordshould what change see braking. how it feels. happens balance during tohard Run Also, observers should only a few laps, makerecord only what one happens and during change, then hard discussbraking. with theRun ob-
deceleration. Remember, as deceleration increases, so must front-wheel deceleration. Remember, as decelerabraking. tion increases, must front-wheel If your car has so well-balanced brakes braking. and you want to change a master cylinyour cara has well-balanced brakes derIf or go to different type of proporand you valve, want tothis change tioning can abemaster done cylinwithder or go to a different of proporout changing balance. type However, you tioning valve, this be pressure done withmust measure and can record in out you bothchanging hydraulicbalance. circuits However, before changmust measure and be record in ing parts. This can donepressure by installboth hydraulic circuits before changing pressure gages downstream from ing This can be doneand by proporinstallthe parts. front master cylinder ing pressure from or downstream the rear master tioning valvegages the front Amaster cylinderplace and isproporcylinder. convenient at the tioningandvalve or thebleed rearscrews. master frontrear-caliper cylinder. A convenient place is at the by Modify two spare bleed screws frontand rear-caliper bleed screws. brazing the cross-hole shut, drilling Modifythe twocenter spare hole bleedand screws by through brazing brazing the cross-hole shut, drilling an adapter fitting to the end of the through the center hole and brazing screw . Install one modified screw in a an adapter to inthea rear end caliper. of the front caliperfitting and one screw. Install one modified in a Connect a gage to each screw modified front caliper and one in a rear caliper. screw with flexible brake hose or steel Connect a gage modified tubing and bleed to theeach gages. While screw withapplies flexible the brakepedal hose to or steel someone give tubing and the gages. 800-psi frontbleed pressure, read theWhile rear someone pedalmake to give pressure . applies You canthenow the 800-psi front pressure, rear system changes. Withread thethegages pressure. You can make the now balance bar the or installed, adjust system changes. theandgages proportioning valve With so front rear installed, read adjustthethe balance bar the or pressures same as before proportioning valve so front and rear change. Be sure to keep this gagepressures read the same before itthe and-bleeder-screw setup as because is change. Be sure keepsorting this gagean excellent toolto for out and-bleeder-screw setup because itand is balance-bar, master-cylinder an excellent tool for sorting out valve problems later.
servers what they saw. If you make more than one change before testing, servers whatbe they If you make won't able saw. to pinpoint what you more than one change before change to the brake system testing, caused you be able change to pinpoint what whichwon't observable in brake change to the brake system caused performance. which brakea If theobservable track surfacechange is dirty in or wet, performance. balance test will be useless unless you If the dirty orsurface. wet, a plan to track race surface on a is similar balance test willa be useless unless Instead, make crude attempt at you setplan to raceif on similar surface. ting balance the abrakes were never Instead, make a crude deceleration attempt at setset. Record maximum so ting if the never you balance can judge howbrakes muchwere to change set. deceleration so the Record balance maximum when traction improves. you can judge how much to change After a few brake-balance tests, you'll the balance when balance traction settings improves. be able to relate to
After a few brake-balance tests, you'll be able to relate balance settings to
DECELERATION used to determine TESTS how rapidly a car Average is stops. TheDeceleration-This test can be done withtest miniused to determine how rapidly a car mum effort using a stopwatch. If you stops. test can be done withtominiknow The the time it takes a car stop mum effort using a speed, stopwatch. If you calculate from a known know the time it takes a car to stop deceleration: from a known speed, calculate Average deceleration = :2t in g's deceleration: Average deceleration = stop in g's S = Car speed before the in miles
&
per hour S Car speed theinstop in miles t ==Time it takesbefore to stop seconds
per hour do itthis testtoyou know the t =ToTime takes stopmust in seconds speed of the car. If the car has a To do this test youthemust know the speedometer, have speedometer speed of the car. If the car has a calibrated at a speedometer-repair speedometer, the speedometer shop. If there ishave no speedometer, have calibrated at ashop speedometer-repair a speedometer put the car on shop. there is no speedometer, have machine, their Ifspeedometer-testing aandspeedometer shop put the car on record the miles per hour that cortheir speedometer-testing machine, respond to various tachometer and recordMake the miles hour that correadings. sureper you record the respond to various tachometer gear ratio , driving-wheel tire size and readings. record the what gear Make the carsure is inyou when making gear ratio, driving-wheel tire size and what gear the car is in when making
this test. Speedometer and tachometer calibrations are necessary because this Speedometer tachometer they test. usually read in and error, causing calibrations are necessary because errors in calculations. they usually read in error, When stopping from verycausing high errors indeceleration calculations. changes during speed, stopping from high theWhen stop. Therefore, averagevery deceleraspeed, deceleration changes during tion must be compared to other stopthe decelerapingstop. tests Therefore, done at the average same speed. tion must be compared to other stopit Bring the car up to speed and hold ping tests done at the same speed. steady. Start the stopwatch the instant theare carapplied; up to speed it theBring brakes stopand the hold watch steady. Startthe thecar stopwatch the instant stops. Timing can the instant the brakes applied; in stop be done by are a passenger thethe carwatch or by the instant the car stops. Timing an observer. Several tests should can be be done by a passenger in the by run to minimize errors, butcar letorthe an observer. Several tests. tests should be brakes cool between If you are run to minimize but leteach the about the errors, same results getting brakes cool testing between tests. Ifareyou are. time, your methods good getting about the same results each However, it's difficult to do this test time, your testing methods are good. be surprised if accurately, so don't However, it'sconsistent difficult to do this test you can't get results. accurately, don't begin be surprised if your stops To reducesoerror, you can't get consistent results. from a higher speed. Start the stop To reduce error, begin reaches your stops watch as the speedometer the from a speed. higher Ifspeed. Start observer the stop a trackside desired watch as the speedometer the is timing, you'll need to reaches signal him desired speed. If a trackside observer when to start timing. is It's timing, you'll toneed to signal him interesting measure the averwhendeceleration to start timing. when braking from age It's interesting measure avervarious speeds. Iftoyour test the methods age deceleration when braking from are consistent, you can plot a graph of various speeds. If your methods deceleration versus car test speed. This are you can plot aof graph of will consistent, indicate the amount aerodeceleration versus car speed. This dynamic downforce . If average decelwill indicate the amount of aeroeration increases with stops from dynamic downforce. If average decelhigher speeds, the car has increasing eration increases stops downforce at higher with speeds. Mostfrom cars higher speeds, the car has increasing have less deceleration at high speed downforce higher The speeds. Mostrotatcars for several at reasons. wheels have deceleration high speed ing atless high speed takeat away some for several reasons. Thethe wheels rotatdeceleration the instant driver hits ing at high speed take away the brake pedal. Also, many cars some have deceleration the the driver aerodynamic liftinstant at high speed, hits so the Also, . many cars have theybrake have pedal. less traction aerodynamic lift at highdeceleration speed, so While performing they have less traction. tests, also measure stopping distance performing forWhile each speed . Providingdeceleration you know tests, alsoand measure stopping distance car speed stopping distance, decelfor each speed. Providing you know eration can be calculated from the folcar speed and stopping distance, decellowing formula:
eration can be calculated from the folS2., · lowing formula: A d I t verage ece era Ion
=
29.9d
In
9s
a S2
Average deceleration = in g's S = Car speed before the stop in miles per hour S = Distance Car speedit before theto stop ininmiles takes car stop feet d= per hour Distance takes harder car to stop feet d= This test is itmuch thaninusing
a stopwatch because it's difficult to hit testatis amuch harder using theThis brakes certain spot. than Observers a stopwatch becausethat it's braking difficult really to hit can help confirm the brakes a certain Observers starts whereatthe driver spot. intends.
can help confirm that braking really starts where the driver intends.
Toppling Block
\J Z + ; ---y Toppling Block
Wedge~ wedge
M
/rTra
Floor
Forward Direction
Forward Direction
To compensate for nosedive during a toppling-block test, first photograph car from the side hard braking. From photo, measure dive angle A of car as shown. Make a wedge atI this angle and place it under during toppling block tray. Usetest, a protractor/level to car check tray To compensate for nosedive a toppling-block first photograph from theangle side in car. hard braking. From photo, measure dive angle A of car as shown. Make a wedge at during
Iduring
this angle and place it under toppling block tray. Use a protractor/level to check tray angle in car.
Again, accelerate the car to a constant speed and make several practice Again, accelerate the car a contests. If you do both time andtodistance stant speed andon make practice measurements eachseveral test, compare tests. If you If doyou bothmeasured time and the distance the results. time measurements on each test, compare and the distance accurately, you the results. you same measured the time should get If the deceleration and distance methods. accurately, using the the different On you the should get errors the same deceleration other hand, in measuring will using inconsistent the different methods. On the give results. Because other hand, errors in measuring will speed is squared in the stoppinggive inconsistent Because distance formula, theresults. speed measurespeed squared in the stoppingment is is critical. distance formula, the speed If you are having troublemeasuregetting is critical. ment accurate deceleration measurements, youMark are ahaving tryIfthis: line ontrouble the roadgetting or set accurate deceleration measurements, up markers where braking should try this:Start Markthe a line on the road or car set begin. stopwatch as the up markers where braking should crosses the line. To apply the brakes begin. Start theline, stopwatch as the car approach it with exactly at the crosses theoff line. apply the your foot theTothrottle andbrakes posiexactly at the approachpad. it This with tioned over theline, brake-pedal your foot off the throttle and posireduces driver-reaction time. It takes tioned 1/2 oversecond the brake-pedal pad. This about to move your foot reduces time.pedal. It takes from the driver-reaction throttle to the brake about second to read movethe your foot Have112 a passenger speedfrom the throttle to the brake pedal. ometer or tach. It may be necessary to Have a passenger read the the instrument for speedeasier reposition ometer It may to reading. orOr,tach. if you havebea necessary camera that reposition the instrument for easier can be tripped electrically - necessary reading. Or, if you have a camera with a single-seater-you could that use can tripped electrically the be brakelight switch to-necessary trip the with a and single-seater-you could use camera take a photo of the speedthe brakelight switch to trip ometer the moment the brake pedalthe is camera and take a photo of the speedhit. ometer thethe moment brake pedalthe is To get speed the right when hit. brakes are applied, run some tests
To get the speed right when the brakes are applied, run some tests
without hitting the brakes. Back off the throttle at a mark on the road without hitting the the line brakes. off and Back observe before crossing the throttle at a mark on the road the speed as you cross the line. Adjust before crossing the line so you crossand theobserve line at initial speed the speed as you cross the line. Adjust the desired speed. initial speed so youto cross line of at If you are going run a the number the desired speed. deceleration tests, you should invest you are going to run a number of in If a decelerometer. deceleration tests, you should invest Maximum Deceleration Tests-You in a decelerometer. can measure maximum deceleration Maximum Deceleration You can alsoTests-You test decelduring a stop. can measure maximum deceleration eration at particular speeds without during a stop. test decelstopping. To doYou this,can usealso a deceleromeration at particular eter or toppling b10cks.speeds without stopping. To do use athe deceleromDecelerometer-this, Follow instruceter toppling tionsorthat comeblocks. with the instrument. Decelerometer-Follow the a instrucMost decelerometers require passentions that come with the ger to take readings . On ainstrument. single-seat Most require a passenracer, decelerometers this is not practical. Instead, use ger to take readings. On ainsingle-seat a video camera mounted the car to racer, is not practical. Instead, use recordthis decelerometer readings. aToppling video camera mounted in the car to Blocks-The toppling-block record decelerometer readings. method doesn't require a passenger. Toppling Blocks-The blocks-see toppling-block drawing-can Toppling method doesn't require a passenger. be built in a home workshop. Make a Toppling blocks-see drawing -canA flat surface for the blocks to rest on. be built in a can home Makeina be workshop. mounted firmly flat tray that flat the blocks restthe on.car A yoursurface car is for ideal. Don't to use flat tray that can be mounted firmly in floor. Chances are it's not flat enough youraccurate car is measurements. ideal. Don't use the car for floor. are it's gradually not flat enough Set Chances up the blocks, bring for the accurate car up tomeasurements. speed and hit the brakes. Set upwillthe blocks, bring You topple gradually the blocks the car up to speed and hit the brakes. immediately, so you don't have to You will speed. toppleWiththe blocks lose much the blocks, immediately, so you ordon't to you'll find maximum peak have deceler-
lose much speed. With the blocks, you'll find maximum or peak deceler117
Temperature-indicating paint is best way to measure rotor temperatures. Paint can be applied to outer edgepaint of rotor and way obTemperature-indicating is best served after rotor test run. ExperimentPaint with difto measure temperatures. can ferent temperature to rotor get good be applied to outerranges edge of and test obdata. an test open-wheel car, a pyrometer servedOn after run. Experiment with difcan be temperature used, but youranges must act fastgood to avoid ferent to get test having rotor off before data. On an cool open-wheel car,measurement a pyrometer is taken. can be used, but you must act fast to avoid
having rotor cool off before measurement is taken.
ation during that range of speed when the brakes were applied . By running a ation during that, you rangecan of plot speed when number of tests a graph the brakes were applied. By running of deceleration versus car speed.a number of tests, can plot graph Again, this is an you indication of avehicle of deceleration versus car speed. If deceleration is higher at downforce. Again, is an aerodynamic indication of vehicle higher this speeds, downdownforce. If deceleration is higher at force is present and vice versa. higher speeds, aerodynamic downEach block falls over at a certain force is present vice versa. deceleration . Mand aximum deceleration Each a block fallsbeover at a certain during stop will indicated by the deceleration. Maximum deceleration shortest block that fell over. The during acan stop tell will be indicated bywhat the driver immediately shortest block that fell by over. The deceleration he is getting looking driver can tell immediately what the blocks. at deceleration he iserror getting lookingThere is some in thebytoppling at the blocks. block test. If the car nosedives while There isthe some errorwill in the topplingblocks tend to fall stopping, block the car nosedives while more test. easilyIf than if the car stopped stopping, the blocks will tend to fall level. Most race cars don't nosedive more easily than if the car stopped enough to matter, but the error may level. Most race don't nosedive on cars a high-CG, softly be significant enough to matter, but the error may sprung road car. beTosignificant on for a nosedive, high-CG, take softlya compensate sprung road car. photo of the car from the side while it compensate for nosedive, take a is To stopping at maximum deceleration. photo car from the side while of it thethe photo, measure the angle Using of is stopping at maximum deceleration. tilt of the body. Compare it to a photo Using the photo, measure of taken from the same anglethe ofangle the car tilt of the body. Compare it to angle a photo Once the dive is sitting level. taken from , the samethe angle the the car determined adjust trayof for sitting Once dive up angle is topplinglevel. blocks. Tip the the tray at the determined, adjust the tray for the front , at the same angle the car toppling blocks. tray up at the nosedives. This Tip willthe compensate for front, at caused the same angle theOncara the error by nosediving. nosedives. Thisnosedive, will compensate for car with little position the the error caused by nosediving. On toppling-block tray level on the cara car with little nosedive, position the floor.
toppling-block tray level on the car floor. 118
Check Changes-When making deceleration tests , now's the time to Check making deceleration is affected by check howChanges-When deceleration tests, now's the time to changes other than to the brakes. For check how deceleration is affected by example, you can combine the decelchanges other than to the brakes. eration test with aerodynamic testsFor to example, can combine decel-. see how you downforce affectsthe braking eration test this with aerodynamic tests to Combine with brake-balance see how downforce affects braking. changes to achieve maximum Combine with brake-balance deceleration.thisRemember, maximum changes achieve maximum decelerationto occurs when brake baldeceleration. maximum ance is set soRemember, all four wheels lock deceleration occurs when brake balsimultaneously. ance is set so wheels Although tire all gripfour is the most lock imsimultaneously. portant item affecting deceleration , it tirebygrip is theinmost imis Although also affected a grade the road portant item affecting deceleration, it or the wind. So test in both directions is also affectedthebyresults a gradetoineliminate the road and average or the effects. wind. So in bothday, directions these Ontest a windy a large and average the results to eliminate error is introduced . Wind forces vary these a windy day, a On largea the effects. square On of the wind speed. as error isday, introduced. Wind will forces vary change windy drag forces as the squaresignificantly. of the wind speed. On a deceleration
windy day, drag forces will change deceleration significantly. EFFECTIVENESS TESTS
Brake-system effectiveness is the EFFECTIVENESS TESTS amount of deceleration obtained for a Brake-system effectiveness the particular pedal effort. A isbrake amount of deceleration obtained for system that is more effective stops aa particular effort. A brake car with less pedal pedal effort. system that is more stopsfora Effectiveness testseffective are useful car with less pedal effort. comparing brake systems and also for Effectiveness tests are tests usefulmust for comparing linings. These comparing brakea systems and also for be run with continuous-reading comparing linings. tests must decelerometer, suchThese as aU-tube debe run with a continuous-reading celerometer or reco rding g-meter and such With as a U-tube deadecelerometer, line-pressure gage. a recording celerometer or tests recording g-meter, these can beg-meter run by and the adriver line-pressure With aa recording alone. gage. With U-tube g-meter, these tests be run by the decelerometer, ancan observer is driver alone. With a U-tube required. decelerometer, an observer is To run an effectiveness test, dri ve required. the car at a predetermined speedTo as run60an effectiveness drive such mphand applytest, the brake the car at a predetermined speedpedal until a 100-psi pressure is such as 60 the brake reached. Atmph-and that point ,apply deceleration is pedal and untilrecorded. a 100-psi is read Thenpressure accelerate reached. At that is the car back to 60point, mph deceleration and repea t the read and recorded. Then accelerate test in increasing 100- or 200-psi the car backuntil to 60lockup mph and repeat the increments is reached. Be test to in allow increasing 100-time or between 200-psi sure sufficient increments lockupfor is reached. Be each pedal until application the brakes sure to allow sufficient time between to cool. each pedal application for the brakes Following each test , calculate pedal to cool.required for each pressure . Plot effort Following each paper test, calculate pedal with decelerathis data on graph effort required for each pressure. tion in g's on the vertical axis Plot and this on graph paper with deceleraon the horizontal axis. pedaldata effort tion in g's comparison, on the vertical axis and For easy if you test pedal effort thedifferent horizontal axis. another car oronwith lining on For easy car, comparison, if you the same plot the second testtest on another or with lining on the samecar graph. Fordifferent a quick comparithe same plot, the on son and nocar, graphs run second the teststest at just
the same graph. For a quick comparison and no graphs, run the tests at just
Effect of scoop on brake temperature can be tested by enlarging scoop. If you make scoop larger andontemperature drops, use Effect of scoop brake temperature can this information to design improved be tested by enlarging scoop.anIf you make scoop. larger Use theand smallest scoops drops, to give use acscoop temperature ceptable brake temperatures because big this information to design an improved scoops increase air drag.scoops to give acscoop. Use the smallest
ceptable brake temperatures because big scoops increase air drag.
one line pressure decelerations.
and
compare
one line pressure and compare decelerations. BRAKE TEMPERATURE TESTS Brake temperature is important to
BRAKE the brakes get TESTS too hot, know . IfTEMPERATURE Brake temperature is important to cha nges may be necessary. By measurknow. the brakes get can too check hot, ing the Iftemperature , you changes mayofbeanecessary. By ally, measurthe success ch ange. Usu iming the temperature, you can check proved airflow to the brakes will be the most success of a change. the effective change. Usually, improved airflow to temperature the brakes will Measure brake withbea the most effective change. hand-held or remote pyrometer. You brake temperature with a temperature-indicating canMeasure also use hand-held or remote paint or labels. The pyrometer. hand-held You pycan also gives use the temperature-indicating rometer temperature at the paint The hand-held The pytime or of labels. the . measurement. rometer gives the temperature at the remote pyrometer with thermocoutime gives of the 'measurement. ples continuous temperatuThe res. remote pyrometer with give thermocouTemperature indicators maxiples gives continuous temperatures. mum temperature experienced at a Temperature indicators give maxispecific location. m uThe m disadvantage temperature of experienced a hand- heldatpy-a specific rometerlocation. is it takes time to stop the of aand hand-held pycar,The getdisadvantage to the brake, make the rometer is it takes time to stop the measurement. By that time, temperacar, to the brake, and make the turesgethave dropped . Therefore, the By that time, temperameasurement. hand-held pyrometer will be useful tures ifhave dropped. Therefore, only you can get fast access to the the hand-held pyrometer will useful spot to be measured . For be example, only if you get fast race access to but the it'll work on can open-wheel cars, spot to beimpossible measured.on For example, is almost full-fendered it'll work on open-wheel cars, but cars that don't have largerace openings in is almost impossible on full-fendered the wheels. cars that are don'tmany haveways largetoopenings in There determine the wheels. Whatever you do, plan temperature. are and many waysthetowritten determine theThere test first follow plan. temperature. Whatever you You must have good recordsdo,to plan get the firstinformation. and follow theIt written plan. doesn't do any test useful You must have good records to get any useful information. It doesn't do
any good to say, "My brakes get to lOOOF." You must know how many any good say, "My get to stops weretomade, from brakes what speed, 1000F." how many and how You muchmust time know elapsed between stopsstop. wereAlso, made, from speed, each a car thatwhat sits still beand how much elapsed than between tween stops is a time lot different if it each stop. Also, a car thatfor sitsthe still bewas moving at 100 mph same tween stops is a lot different than if it time period. was at 100 same If moving you don ' t mph have fora theremote time period. pyrometer, use the next best If you don't have aindicators remote thing-apply temperature pyrometer, the and nextlabelbest to your brakes.use The paint inthing-apply dicators go on temperature the edges of indicators the brake to yourand brakes. Thebody, paint respectively. and label inrotor caliper dicators on temperature the edges of gets the brake Usually, go rotor twice rotor and caliper body, respectively. that of the caliper. Usually, rotor temperature gets twice Accelerate to a predetermined that ofand the caliper. speed make one full stop. Check a predetermined theAccelerate temperaturetoindicators and record speed and make one full temperature. stop. Check the maximum-indicated theyou temperature indicatorsasand record If have a pyrometer well, use theTemperature maximum-indicated temperature. it. rise in one stop can If have a topyrometer as well, use be you compared a calculated number it. Temperature rise in one stop can using the formula on page 11. The difbe compared to a calculated number ference between calculated-tempusing therise formula on measured page 11. The erature and the risedifis ference between calculated-tempthe energy-heat-Iost elsewhere, erature and caliper, the measured is such as rise to the wheel, rise brake the energyheat-lost elsewhere, hats and air drag. such as to thea caliper, wheel, If you have road-racing car, brake make hats and air drag. a number of fast laps around the track you have a road-racing at Ifracing speed. After aboutcar, 10 make laps, abring number the brake track the of carfast in laps and around measure at racing speed. Afterthis about 10 laps, laps, temperature. After many bring the car in and measure brake brake temperature should stabilize. temperature. many laps, To check this, After make this several multilap brake temperature should after stabilize. tests, checking temperature each To this,Eventually, make several multilap set check of laps. you'll find tests, checking temperature after each how many laps it takes for the brakes set laps. maximum Eventually,temperature. you'll find to of reach how many laps get it takes the brakes They will not any for hotter unless to reach maximum temperature. there's a major track , car or driver They nota get any pyrometer hotter unless change.will With remote and there's a major linings, track, car driver thermocoupled thisorcan be change. With a remote and done easily in one seriespyrometer of laps. thermocoupled be Pay particular linings, attentionthisto can caliper done easily innear one series of laps. temperature the piston (s). If the Pay particular to caliper temperature gets attention close to the braketemperature near the piston(s). fluid dry boiling point, watchIf the for temperature gets close to theatbraketrouble. A caliper running over fluid dry boiling point, watch for. SOOF (260C) will experience trouble trouble. caliper running at ifover The sealsAeventually leak even the 500F doesn't (260C) boil. will experience trouble. fluid So try to limit caliThe seals eventually leak even if the per temperature to 3S0F (177C) or fluid doesn't boil. So less, to give longer sealtry life.to limit caliperTotemperature to 350F (177C) or evaluate differences between less, to give longer seal life. different components or setups, such evaluate as Tocool ing-duct differences systems orbetween rotor different setups, such types, it iscomponents best to test or one configuraas or right. rotor tion cooling-duct on the left andsystems one on the types,, switch it is best to and test rerun one configuraThen sides the test. tion on the left and one the right. Caution: When runningontests with Then, switch sidesonandeach rerun theoftest. different setups side the
Caution: When running tests with different setups on each side of t h e
Temperature-indicating labels are for use on disc-brake calipers. Note the word CAUTION starting at 320F (160C). Temperature-indicating labels are forTemuse perature indicates fluid may on disc-brake calipers. Note be the boiling word inside caliper. Photoatcourtesy AP Racing. CAUTION starting 320F (160C). Tern-
perature indicates fluid may be boiling inside caliper. Photo courtesy AP Racing.
.'" ,
Temperature-indicating paint at different locations on caliper : Paint on outboardpiston housing is most important because Temperature-indicating paint at different it indicateson fluid temperature cooling locations caliper: Paint where on outboardair is minimal. not because exceed piston housing Caliper is most should important 350F (177C) at temperature this point. it indicates fluid where cooling
air is minimal. Caliper should not exceed 350F (1 7 7 C ) at this point.
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+ L27 L FL1 Wear = = La - LF Wear
Wear =top Lo -= LFNo. of Stops Wear/S Wear 1000 x Wear Stops of Stops Wear /1000 = Wear/Stop No. =of No. Stops 1000 x Wear Wear/1000 Stops = No, of Stops
LO
Wear per stop can be calculated using simple formulas shown. If pads weQr in a taper, use I average final thickness T f to compute wear. Usually, wear per 1000 stops is more usefulI than per can stop.beLining-wear calculations very important for long-distance racing. Wear wear per stop calculated using simple are formulas shown. If pads wear in a taper, use Wear perfinal lap or wear per T, hour be most important pad per changes be planned fuel average thickness to may compute wear. Usually,so wear 1 0 0 0can stops is more at useful stops.wear Have make quick calculations lining checks during tire changes to double-check than per crew stop. Lining-wear are very important for long-distance racing. calculations. Wear per lap or wear per hour may be most important so pad changes can be planned at fuel
stops. Have crew make quick lining checks during tire changes to double-check calculations.
car, watch out for uneven braking. The driver can lose control! car, for careful uneven you braking. Nowatch matterouthow are, T h e driver lose control! there are can always test-to-test difNo matter howeliminated careful you are, ferences that are by runthere are always test-to-test difning both configurations at once. ferences that are eliminated by runRerunning a test with the configuraning both configurations once. tions switched and averagingat results Rerunning side-to-side a test with differences the configuraeliminates . tions switched and parts averaging results When evaluating designed to eliminates run in oneside-to-side direction differences. only, such as When evaluating to curved-fin rotors, beparts suredesigned to switch run in oneyou direction only, such as parts when switch sides. curved-fin rotors, be sure to can switch Brake-Wear Test-Brake wear be parts when you switch sides. tested only after many stops. Earlier
Brake-Wear Test-Brake wear can be tested only after many stops. Earlier
in this chapter 1 suggested measuring lining thickness befo re testing. If you in this suggestedlining measuring do this,chapter you canI measure thicklining afterward thickness before testing. you ness to judge wear.If The do this, you can measure lining But thickamount of wear is interesting. to ness afterward judgeto wear. The be useful, you toneed determine amount wear is interesting. But to wear per of SlOp. beTouseful, you wear need per to determine calculate stop, you wear stop. the number of stops or must per know Tooncalculate stop, you laps the pads.wear You per should be able must know the number of stops or to find this in your records if you laps on the pads. Youin should be able recorded everything your notebook to suggested. find this in your records if you as recorded everything your notebook After you finish in testing, measure as suggested. brake-lin ing thickness. Measure the
After you finish testing, measure brake-lining thickness. Measure the
119
,r /
pad Backing Plate
/
Plate
Riveted Lining
Bonded Lining
Lining
When measuring lining thickness to compute wear rate, take several measurements and them. Because brake Whenaverage measuring lining thickness to shoes comand weartake unevenly, rates are pute pads wear rate, severalwear measurements based on average over the lining. To and average them.wear Because brake shoes compute lining thickness, look are for and padsminimum wear unevenly, wear rates thinnest based onspot. average wear over the lining. To
compute minimum lining thickness, look for thinnest spot.
linings in the same places as before and compare thicknesses to the origilinings in the sameWear places is as the before original measurements. and compare thicknesses to the original thickness minus the thickness nal measurements. is theatorigiafter testing. Look Wear carefully the nal the onthickness liningthickness to see if minus it is worn a taper. after testing. Look carefully Make a diagram to recordat the the lining to see if it is worn a taper.. information, as shown in theondrawing
Make a diagram to record the Lining-wear per stop = in ~ the drawing. information, as shown Lining-wear stop in inches perper stop
=r W
W = Total amount of lining wear in in inches per stop inches W Total amount of lining wear in N = =Total number of stops inches The answer from this formula will N= Total number of stops
be very small. So, multiply it by 1000 answer this formula will This figure to The get wear per from 1000 stops. it by 1000 be very small.toSo, will be easier use multiply . to Once get wear 1000 stops. This figure you per have wear per stop, calcuwill be easier to use. late the number of stops it takes to Once have wear completely. per stop, calcuoutyouthe linings To wear late this, the number stops it takes to lining do find theof minimum wear out the linings completely. To thickness allowed. Your car manudo this, find lining facturer or the brakeminimum manufacturer thickness allowed. Your car manushould be able to supply this facturer or Obviously, brake manufacturer information. you shouldshould able to to wear supply this n't allow be the lining so much information. Obviously, you shouldthat the metal backing plate contacts n't to wear much the allow rotor.the Or,lining if you havesoriveted that the it's metal contacts the backing distance plate the rivets are linings, the rotor. into Or, the if you havethat riveted recessed lining you linings,be it'sconcerned the distance should with.the rivets are recessed the lining give that miniyou Most carinto manufacturers
should be concerned with. Most car manufacturers give mini-
120
--1 __
pad Backing Plate k:king Plate
Rivet Head
Minimum Lining Thickness
+Minimum Lining
--11---c
1I
-t
Minimum Lining Thickness
Minimum Lining Thickness
To compute number of stops available from a new lining, you must know its minimumThickness I allowable lining thickness. This is different for riveted and bonded linings. Use depth-gageI
endcompute of dial caliper to measure lining.you More wear will result in rotor To number of stops available availablewear fromofa riveted new lining, must know its minimumor drum scoring. allowable lining thickness. This is different for riveted and bonded linings. Use depth-gage end of dial caliper to measure available wear of riveted lining. More wear will result in rotor or drum scoring.
mum lining thickness in their shop manual. If you can't find this figure, mum thickness in their shop assumelining you can wear the linings to manual. If you can't find this figure, within 1/16 in. of the plate or rivets. assume youminimum can wearlining the linings to Subtract thickness withinthe 1/16 in, of theofplate or rivets. from thickness a new lining to minimum liningwear. thickness getSubtract maximum allowable You from the thickness of a new lining to can then calculate the maximum get maximum number of stops: allowable wear. You
can then calculate the maximum W number of stops: Number of stops allowed
=_M_
Ws
WM Number of stops allowed = W M = Maximum lining wear w allowed in s inches W, Maximum wearinallowed Ws == Lining wearlining per stop inches in inches per stop W, = Lining wear per stop in inches perRemember stop that brake wear in-
creases with temperature. And, if you Remember that horsepower, brake wear the inincrease engine creases with temperature. And, if you brakes will get hotter because you'll increase horsepower, the be stoppingengine from higher speeds. Wear brakes willwill get also hotterincrease. because Aeroyou'll per stop be stopping from higher Wear dynamic changes also speeds. affect lining per stop will also increase. Aerotemperature and wear. Therefore, dynamic changes alsothickness affect lining keep records of lining each temperature and the wear.brakes. Therefore, time you inspect Also keep records of lining each record the number of thickness stops between time you inspect the brakes. Also inspections so you can keep track of record thewear number stops track between changing ratesof from to inspections so you can keep track of to setup. track and setup changing wear from track to Wear rates willrates change dramatically track and setup to setup. from track to track. One with long Wear rates dramatically straights and will tightchange flat turns is much
from track to track. One with long straights and tight flat turns is much
harder on brakes than one with short straights and high-banked turns. harder on brakes than one are withimporshort Lining-wear calculations straights and high-banked turns. tant in long-distance road racing. If Lining-wear calculations are aimporyou wear out linings and ruin rotor, road inracing. If of long-distance time will be lost the pits atant lot in you wear out linings and ruin a rotor, changing it. By determining lining awear lot during of timepractice will besessions lost in and the calpits changing it. number By determining of stops orlining laps culating the wear during sessions calallowed, youpractice can predict howandmany culating the number of stops or laps laps you can run before changing allowed, you can predict how sets many to have enough of pads. Be sure laps can run pads you bedded-in to before go the changing distance pads. have enough sets of thesure race to starts. beforeBe pads bedded-in to go the isdistance This sort of calculation useful before the race starts. only for race cars. Usually, you can This sort both of calculation useful determine wear rate isand the only for race of cars. Usually, can exact number possible stopsyou before determine wear rateTheand the is necessary. brakes a pad changeboth exact number of possible stops before are always used as hard as possible, so athepadwear change TheOn brakes rateisisnecessary. predictable. the are always as hard as possible, so street, the used number of stops depends the wear rate is predictable. On the on the type of driving . City driving street, stops depends takes the morenumber stops of than freeway on the type of driving. driving driving. Fast driving in theCity mountains takes more stops than freeway is a lot different than taking the family driving. Fast driving in the calculating mountains Therefore, to the drive-in. is a lot different than taking family wear per stop is impossiblethe . So, for to the drive-in. street use, keepTherefore, a record calculating of the car wear per each stop is impossible. So, are for mileage time the brakes street use, keep a record of the car inspected. This, along with a record of mileage each time the you brakes are lining thickness, will give an idea inspected. This,miles alongyour with brakes a recordwill of of how many lining thickness, will give you an idea last.
of how many miles your brakes will last.
Maintenance Proper maintenance is essential for brake-system safety and performance. maintenance essential for If Proper you have a good is maintenance brake-system safety and performance. program, you can usually find a probIf have a good serious. maintenance it becomes Don't lemyou before program, can usually find a occur probwait untilyoubrake problems lem before becomes serious.may Don't enbefore doingitsomething-you wait until brake problems occur counter a life-threatening situation. before doing system something-you maymost enThe brake is one of the counter a life-threatening situation. critical parts of a car. Luckily, brakes brakereliable, system iseven one of the most areThe very with poor critical parts of a car. Luckily, maintenance . Brake trouble can brakes usualarebe very even poor ly sensedreliable, at the pedal , sowith the driver maintenance. Brake trouble usual-, knows it immediately. For can example ly sensed at the pedal, the driver and so lower if the thebepedal gets lower knows it immediately. For brakes need adjusting. Andexample, it goes the pedal getsinto lower lower if the theand system through soft if air gets brakesseals. need Worn-out adjusting. linings And it make goes bad soft if air gets into the system through horrible noises as metal contacts bad seals. liningsevident make Most Worn-out problems become metal. horrible noises as metal contacts before a total brake failure occurs. metal. problems become evident One Most of the most dangerous probbeforeisa total brake occurs. This a line or failure hose failure. lems One of problem the mostcan dangerous probpotential go unnoticed lems is a line or hose failure. This, until the brakes are used hard . Then problem can can go occur unnoticed apotential line or hose rupture with until the brakes are used hard. to Then, the pedal suddenly dropping the afloor. line If or the hosecar rupture occur dualwith has a can modern the pedal suddenly dropping to the braking system , the driver can usually floor. If the modern car. car But,hasif athe systemdualhas stop the braking driver can andusually is in only twosystem, wheelsthebraking stop car. But, if the system has of maintenance, it may be imneed the only twoto wheels brakingOnly anda is in possible stop quickly. good need of maintenance, it may impreventive-maintenance effortbe will possible to stop quickly. Only a good prevent such problems. preventive-maintenance effort plan will Schedule-A good maintenance prevent problems. If the car is raced, requires such a schedule. Schedule-A goodbrake maintenance plan maintenance always do some requires a schedule. If the car is raced, before each race. Inspect the system always some brakeAlso maintenance for weardoand damage. bleed the beforebefore each each race. event. InspectIf the fluid yousystem fail to for this, wearbrake and performance damage. Alsowill bleed the suffer. do fluid before each event. If you fail to On a race car, major brake-system do this, brake performance will suffer. maintenance is done each season - or On often a race ifcar, major brake-system more problems occur. Major maintenance doneinclude each season-or maintenance ismay replacing more oftenand if problems Major the seals surfacing occur. or replacing maintenance may include replacing the rotors. Wheel-bearing lubrication theusually seals done and at surfacing is this time.or replacing theOnrotors. Wheel-bearing lubrication a road car, your shop manual is usually done at this time. will give a recommended brakeOn a road schedule. car, yourUsually, shop manual maintenance it sugwill give a recommended brakethe fluid level and gests inspecting maintenance schedule. it sugchecking the linings for Usually, wear after cergests inspecting fluid level You and tain mileage has the accumulated. checking the linings for wear after cercan modify this schedule if you find tain mileagebuthasthe accumulated. You manufacturer's problems,
can modify this schedule if you find problems, but the manufacturer's
II
Brake maintenance on race car should be done after each time car is raced. Mechanic prepares to disassemble and inspect brakes on this Indy Car after a practice session. He is using cleaningonfluid remove Cleanliness when workingpreon Brakebrake maintenance racetocar shouldcontamination. be done after each time carisisvital raced. Mechanic brakes.to disassemble and inspect brakes on this lndy Car after a practice session. He is pares
using brake cleaning fluid to remove contamination. Cleanliness is vital when working on recommendation is a good place to BRAKE ADJUSTMENT brakes.
start. Here is my brake-maintenance
recommendation a good place to schedule for a roadiscar: start. Here is my brake-maintenance Every 5000 miles: Inspect hoses schedule a road car:level. and lines;for check fluid Every 10,000 5000 miles: Inspect linings hoses Every miles: Inspect andwear. lines; check fluid level. for Every year: Every 10,000 25,000 miles: miles Inspect or everylinings for wear. Replace brake fluid . Every 25,000 or every year: Every 50 ,000miles miles: Overhaul Replace brake fluid. calipers; wheel cylinders, master Every 50,000 miles: Overhaul cylinder. calipers; wheel cylinders, This maintenance schedulemaster does cylinder. not cover everything. It just outlines schedule does theThis mostmaintenance common items and approxinot cover everything. It just outlines mates brake-maintenance needs. the most items and approxiYour car'scommon needs depend on its design mates and how brake-maintenance it's used . If the car needs. is not Your needs its design drivencar's often, youdepend shouldoninspect the and how used. If the the car is not fluid andit'soverhaul hydraulic driven often, inspectthan the system at you lowershould mileage fluid and overhaul thelining hydraulic recommended . Although wear system not at belower mileage than should a problem, corrosion recommended. Although lining wear and seal leakage may be, because time should be ofa aproblem, corrosion becomesnot more factor. and seal leakage may be, because time becomes more of a factor.
Brake adjusting is not needed with BRAKE ADJUSTMENT many cars. Disc .brakes are self adjustBrake adjusting is notbrakes needed with usually ing and modern drum many cars. Disc,brakes are self adjusthave automatic adjusters. If your car ing such and modern has features,drum forgetbrakes brake usually adjusthave automatic adjusters. If yournew car ment except when installing has such features, forget brake adjustdrum-brake linings. Often, a drum ment exceptbe when installing brake must adjusted manuallynew to drum-brake linings. adjuster Often, ato drum the automatic work allow brakefirst musttime. be adjusted manually to the Automatic adjusters allow the automatic adjuster to work only maintain clearance-they don't the first Automatic adjusters make largetime. adjustment changes. only clearance-they don't On maintain drum brakes without automatic make large adjustment changes. adjusters, periodic adjustment is On drum brakes wear, without automatic needed. As linings clearance beadjusters, periodic adjustment is and drum increases. tween the shoes needed. As linings wear, pedal clearance beThis results in more travel. tween theparking shoes and drum increases. brake requires more Also, the This results in more pedal travel. travel. You can usually tell when the Also, parking brakebyrequires more brakesthe need adjusting the increase travel. can However, usually tellifwhen the in pedalYou travel. you wait brakes need adjusting by the increase too long, the pedal may go to the floor in pedal fade travel. However, if youadjust wait if brake occurs. Therefore, too long, the pedal may go to the floor the brakes often; don't take risks.
if brake fade occurs. Therefore, adjust the brakes often; don't take risks. 121
>i~ Torn I nner Lining Restricts Flow, Acts as Valve.
Torn Inner Lining Restricts Flow,
Fitting Leakage Seeps Out or Forms Bubble.
Fitting Leakage Seeps Out or Forms Bubble.
Although duo-servo brake uses automatic adjuster, brakes must be manually adjusted after brake-lining replacement. Although duo-servo brake usesBlade-type automatic tool is used to turn adjuster through slot in adjuster, brakes must be manually adjusted backing plate (arrow). after brake-lining replacement. Blade-type
tool is used to turn adjuster through slot in backing plate (arrow).
Inspecting and changing brake fluid is an important part of brake maintenance. Race car is getting filling of brake AP Racing fluid. Inspecting andachanging fluid is an Note reservoir cap withmaintenance. rubber bellows. It important part of brake Race isolates fluid from the of airAP when cap fluid. is in car is getting a filling Racing place, but allowscap fluid to rise and bellows. fall. Note reservoir with rubber It
isolates fluid from the air when cap is in place, but allows fluid to rise and fall.
Most modern road-car brakes are discs on the front and drums in the Most modern road-car brakes are rear. With this dual-braking system, discs on the front and drums in the only the drum-brake system can go rear. this dual-braking system, out ofWith adjustment. Typically there is a only the drum-brake switch system in can the go brake-warning-light out of adjustment. Typically there is system that senses excess movementa brake-warning-light switchWhen in the of the rear-brake fluid. the system that senses excess movement brakes need adjusting , more displaceof the is rear-brake fluid. the When the ment required than master brakes need adjusting, more displacecylinder can supply; the brake ment is required the on master turns the warning-light switchthan cylinder can This supply; thewillbrake warning light. switch also warning-light switch detect fluid loss causedturns by a on leakthe in warning light. This switch will also either system. detect fluid loss caused by agenerally leak in the rear brakes Adjusting either system. requires jacking up the car, supporting theunderneath rear brakes generally it, Adjusting and getting . There are
requires jacking up the car, supporting it, and getting underneath. There are
122
Bottom : Blistered brake hose is ready to fail. Replace such a hose immediately! Top: Hidden brake-hose failure restricts Bottom: Blistered brake hose is ready to flow to or fromsuch brake. Thin layer of inner fail. Replace a hose immediately! lining Hidden can lift off surface and restrict flow Top: brake-hose failure restricts of fluid This may to flow to to or brake. from brake. Thincause layer brake of inner apply laterliftonoffone side, and causing carflow to lining can surface restrict swerve. brake hoses shouldbrake be reof fluid toOld brake. This may cause to placed later as aonsafety precaution. apply one side, causingDrawing car to courtesy Bendix Corporation. swerve. Old brake hoses should be re-
placed as a safety precaution. Drawing courtesy Bendix Corporation.
many types of brake adjusters. One is a square bolt head projecting from the many types of brake adjusters. Onead-is backing plate. Most domestic-car a squarerequire bolt head projecting from justers inserting a tool intothea backing plate. Most domestic-car adslot in the backing plate and turning justers require inserting a tool into the star wheel. There may be one ora slot the backing plate and dependturning moreinadjusters on each brake, the on starthewheel. ing design.There may be one or more adjusters each brake, dependthe on shop-manual instrucFollow ing on the design. tions for brake adjustment. Be sure the shop-manual notFollow to overtighten the brakes. instrucA dragtions brake for brake adjustment. Because sure will overheat and can ging not to overtighten the brakes. A dragdamage, excess wear, lower mileage ging brake will overheat and can cause. or fade . damage, excess lower mileage Make sure the wear, parking brake is not or on fade. when adjusting rear brakes. Make sureyou thewon parking braketo.isThe not Otherwise, ' t be able on when adjusting rear brakes. parking brake is applied to the rear Otherwise, youare won't be able to. The brakes, which usually drums. You parking brake is applied to the rearif will think the brake is fully adjusted brakes, which are usually drums. You you try it with the parking brake on. will think the fool brake is fully adjusted if Don't let this you. you try it with thedrum-brake parking brake on. Normally, rear adjustDon't let this fool you.of parking-brake ment will take care Normally, rear drum-brake adjustment. Except on some adjustfourment will take care of wheel, disc-brake cars,parking-brake you should adjustment. on the someparking fournever need Except to adjust wheel, disc-brake cars, you should brake unless it won't work ajteradjustnever to adjust the parking ing the need rear brakes. Parking-brake adbrake unless it won't work afteradjustjustment is discussed on page 135.
ing the rear brakes. Parking-brake adjustment is discussed on page 135. HYDRAULIC-SYSTEM INSPECTION HY DRAULIC-SYSTEM Besides brake adjustment, the most INSPECTION common maintenance item is checkbrake adjustment, ingBesides the hydraulic system . To the be most safe, common maintenance item is check the fluid level about everycheck5000 ing the Fluid hydraulic system. be safe, miles. leakage can To cause total check the fluid about every 5000 brake failure onlevel a single brake system. miles. Fluidcause leakage can cause It can also problems on a total dual brake failure on a single brake system. It can also cause problems on a dual
system . If you discover that fluid level has dropped each time you look at it, system. If you discover level problem andthat fixfluid it. Fluid locate the has dropped each time you look at it, shouldn't leak from a brake system. locate the aproblem it. Fluid Typically, leak canand be fix traced to a shouldn't leak from a brake defective wheel-cylinder seal, system. caliper Typically, a leak canOr,be atraced or master-cylinder. leak to maya defective wheel-cylinder seal, caliper occur at a fitting or hole in a line or or master-cylinder. a leak brake hose. Look forOr,drips and may wet occur near at a the fitting or holesystem. in a line or areas hydraulic Fluid brake hose. Look for drips and wet be fixed immeleaks should areas near the hydraulic system. diately-procrastination can Fluid be leaks should be fixed immedangerous! diately-procrastination can , you be In addition to fluid level dangerous! should check all brake hoses and In This addition to done fluid while level,youyou lines. can be ' re should check all brake hosesunder and performing other maintenance lines.car, This canasbeadjusting done while the such the you're brakes performing other maintenance or doing a lube job. Inspect the under brake the car, as adjusting theLook brakes both ends of the car. for hoses at such or doingchafe a lube job. Inspect brake. cracks, marks, or otherthe damage hoses at both the car. Look for on aends hoseofindicates failure. A lump cracks, chafe marks, or other damage. Fluid can seep through the first few A lump a hose indicates layers of on reinforcing cord and failure. form a Fluid can seep through the If first few lump or blister on the hose. a hose layers reinforcing cord and form Don'ta blisters,ofreplace it immediately. lump orsudden blister brake on the hose. If a hose chance failure. blisters, replace it immediately. Occasionally, a pinhole in a Don't brake chance sudden brake failure. hose can allow air to get into the brake Occasionally, pinhole a brake fluid . The hole acan be theintype that hose can allowwhen air to get the brake leaks only the into brakes are fluid. The drawing hole can in be the that released, air, type creating leaks when the brakes are bubblesonly . When pressurized , this leak released, drawing not let in fluidair, out. creating If your can seal and bubbles. When this leak brake hoses arepressurized, old and weathered, can seal and not let fluid out. If your replacing them may cure a recurring brake hoses are old and weathered, spongy pedal. replacing them may a recurring can cure fail because of Brake hoses spongy pedal. improper installation. If a hose is Brake or hoses can fail of twisted installed in because the wrong improper installation. If a hose is position, it can break. Or, if a car is twisted onor rough installed in large the wrong driven terrain, wheel position, it can if a car is movements can .break. strain Or, a brake hose. driven on rough terrain, large wheel Also , hoses can be damaged by rocks movements can strain or road debris throwna brake up byhose. the Also, damaged by rocks I've can seenbebrake-hose damage wheels.hoses or roadbydebris thrown over up bydebris the caused a car running wheels. I've seen brake-hose damage that gets tangled in a wheel and caused a car running over debris wrappedby around the brake hose. that getscause tangled in damage a wheelis and Another of hose letwrapped aroundcaliper the hang brakefrom hose. ting a disc-brake its Another cause of hose damage lethose during maintenance: Use ofis corting disc-brake caliper hang fromwill its procedures rect a maintenance hose during of coravoid such maintenance: potentially Use dangerous rect maintenance procedures will situations. avoid potentially Check such Clearances - If yourdangerous car has situations. wide wheels, fat tires , or other suspenCheckmodifications, Clearances-If look yourforcarchafe has sion wide fat tires, other. suspenmarkswheels, on the brakeorhoses A tire sion modifications, look for touching a hose eventually can chafe wear marks on the brake hoses. tire through it. Even something Aminor touching a large-diameter hose eventuallyheavy-duty can wear like a set of throughcanit.cause Evensimilar something minor shocks problems.
like a set of large-diameter heavy-duty shocks can cause similar problems.
To check clearances, turn the front wheels to full right and left lock and To check the sides. front check them.clearances, Check atturn both wheels to full right and left lock the Clearances may not be exactly and check Jack them.upCheck at and bothlook sides. same. the car at Clearances with may the not wheels be exactly the clearance at full same. at Next, up jacktheup car oneand rearlook wheel. droop. Jack clearance with the wheels at full This will compress the diagonally droop. jack suspension. up one rear wheel. Check oppositeNext, front This will compress thethediagonally clearances, then jack up opposite oppositeandfront suspension. Check corner recheck. Conditions and clearances, then jack up the opposite clearances change a great deal as the corner and recheck. Conditions wheels travel up and down as they and are clearances great deal as the steered. Trychange every apossible combinawheels up Although and down front as they are tion to travel be sure. hoses steered. Try every possible combinahave the most clearance problems, tion to be sure. hoses particularly whenAlthough turning, front check the havehoses the as most rear well.clearance problems, particularly turning, the If your carwhen has been usedcheck off road, rear hoses as well. check the condition of the steel brake If your car the has car. beenIt's used off road, lines under possible to check the condition of the steel brake pinch a line when going over a rough lines under It's possible to If youthe findcar. a damaged line, resurface. pinch a line when going over a rough place it. Look closely. A crack or a surface. a damaged thin spotIfisyou veryfind hard to see. line, replace it. Look closely. A crack or a If your car is older, check the steel thin hard to Rust see. can eat linesspot foris very corrosion. If yoursteel car is older, check the steel even though they through lines, lines for corrosion. Rust eat are about as corrosion-proof ascan science through steel lines, even though they can make them. The likelihood of are about as corrosion-proof science having rusty brake lines is as greater if can make them. T h e likelihood of you drive where salt is used on the havinginrusty greater if roads the brake winter.lines You iscan expect you drive where salt is used on the trouble from salt-water spray. Older roadsfrom in the Youand canMidwest expect cars the winter. Northeast trouble from salt-water spray. Older are likely to require brake-line cars from the Northeast and Midwest replacement. Rusty brake lines is a are to require brake-line usual likely problem on vintage cars. replacement. Rusty brake lines is a most restorers replace Consequently, usual problem on vintage cars. them without bothering to check . Consequently,the most restorers Remember, inside rustsreplace from them without bothering water in the brake to fluidcheck. as Remember, the inside rusts check from well-something you can't water visually. in the brake fluid as
well-something you visually. BRAKE BLEEDING
can't
check
Bleeding is important to proper
BRAKE BLEEDING brake-system maintenance. It is usualBleeding is important to trapped proper ly done to remove air bubbles brake-system maintenance. in the system. Bleeding isIt isa usualmust ly donetime to remove air bubbles trapped every the hydraulic system is in the system. Bleeding opened up for any reason is . Ita ismust imevery hydraulic is possibletime to the prevent some system air from opened uptheforsystem any reason. It is imentering if a fitting is possible prevent some from loosened. toMost systems haveairnumerentering system a fitting is ous high the spots whereif air will be loosened. Most systems have numertrapped . ous highbleeding spots can where air will be Brake be frustrating or trapped.depending on the system easy, Brake Some bleedingbleeders can be frustrating or are reached design. easy, depending on the system easily on the inboard side of the design. Someunderneath. bleeders are brakes, from On reached others, easily on bethe inboard of the they may tucked insideside the suspenbrakes, from underneath. On others, they may be tucked inside the suspen-
Someone previously installed wide wheels on myoid Ford truck, but didn't check brake-hose clearanceinstalled with front wheels at Someone previously wide wheels full my lock.old After some use,but wheel-rim edge on Ford truck, didn't check rubbed through line,with causing a leak. brake-hose clearance front wheels at Fortunately, was discovered full lock. Afterdamage some use, wheel-rim edge during maintenance, rather athan by rubbed brake through line, causing leak. "accident." Fortunately, damage was discovered during brake maintenance, rather than by "accident!'
sion where they are real "knuckle busters" to get at. Some systems also sion theyother are real have where bleeders than"knuckle at the busters" to get at. Some also the master wheels, such as on systems have bleeders at the cylinder. Consultother your than shop manual wheels, such bleeders. as on the for any hidden If youmaster miss cylinder. Consult your shop manual one, you will wonder why your pedal for any hidden bleeders. If you miss is spongy even after bleeding. one, you will wondercan whyusually your pedal Bleeder screws be is spongy even after bleeding. turned with a small Six-pOint box-end BleederA void screwsusing can anusually be wrench. open-end sk-point box-end turned with a small wrench to prevent rounded-off bleedwrench. using knuckles. an open-end er screwsAvoid and bloody For wrench to prevent rounded-off bleeddifficult-to-get-to bleeders, special er screws and bloody knuckles. For bleeder wrenches are available at autodifficult-to-get-to bleeders, special parts stores. These look like a box-end bleeder wrenches available at autowrench with a hugeare offset. parts look like box-enda that there is ausually Be stores. aware These wrench with a huge offset. bleeder at each brake, but some sysBe use aware that there usually tems a single bleederis to servicea bleeder each brake, but some sysboth rearatbrakes. tems use anormally single bleeder to at: service Bleeders are found both rear brakes. • Each drum-brake wheel cylinder. normally are found two at: or caliper• Bleeders Each disc-brake Each drum-brake wheel more bleeders may be used.cylinder. or Outlet disc-brake port at caliper-two some master • Each more bleeders may be used. cylinders, particularly those mounted O an u t angle. l e t port at some master at cylinders, those mounted combination valves used • On someparticularly at an angle. with disc brakes. On some combination used • On accessories, such valves as trailer with disc brakes. brakes. On accessories, as trailer Don't forget to looksuch for bleeders on brakes.sides of a disc-brake caliper. both Don't forget to look for bleeders bleeders on Some fixed calipers have on both sides where of a you disc-brake caliper. the inside would expect, Some fixed calipers have bleeders plus another on the outside hidden on by the inside where you would expect, the wheel. If you don't remove the plus another on the by wheel, you'll missoutside the hidden outboard the wheel. If you don't remove the bleeder. wheel, you'llto miss replacethetheoutboard rubber Be sure
bleeder. Be sure to replace the rubber
When brake line rusts, fittings can seize on steel tube. This can happen when seized fitting brake is turned with a wrench. When line rusts, fittings canAlthough seize on such tube. a lineThis maycan nothappen leak, it should be steel when seized replaced. fitting is turned with a wrench. Although such a line may not leak, it should be replaced.
Brake bleeding can be awkward and messy. Consequently, it's easy to do the job wrong or miss a bleeder. Take your Brake bleeding can be awkward and time, the job right, messy.plan Consequently, it'sand easyuse to correct do the tools. Startorbymiss jacking up theTake car your and job wrong a bleeder. removing wheels to improve access. time, planthe the job right, and use correct tools. Start by jacking up the car and removing the wheels to improve access.
bleeder-screw caps if your brakes have them . They protect the bleederbleeder-screw caps if from yourmoisture brakes screw seat and threads have them. They protect the bleederand prevent corrosion seizure. These screw seat andcan threads from moisture caps, which be purchased from and prevent dealers, corrosionareseizure. Volkswagen a goodThese addicaps, cancar.be purchased from tion towhich any road Volkswagen dealers, are involves a good addiAnother frustration the tion to any road car. metering valve used on some road Another frustration involves the to hold this cars. A special clip is used metering on can some road valve openvalve so theused brakes be bled.
cars. A special clip is used to hold this valve open so the brakes can be bled. 123
Note that caliper has a bleeder on each side. Forget to remove the wheel and you'll miss bleeding outboard side. This can result in a spongy pedal. Photo Note that caliper hascourtesy a bleederAP onRacing. each side. Forget to remove the
wheel and you'll miss bleeding outboard side. This can result in a spongy pedal. Photo courtesy AP Racing.
Pressure bleeder is used in most repair shops because of its speed. Huge can of fluid is used to fill pressure bleeder. Because most racers fear possible of oldrepair or contaminated fluid, of presPressure bleeder is used use in most shops because its sure bleeders areofnot popular. road cars, they offerBecause speedy speed. Huge can fluid is usedFor to fill pressure bleeder. low-cost brake bleeding in ause shop. most racers fear possible of old or contaminated fluid, pres-
sure bleeders are not popular. For road cars, they offer speedy low-cost brake bleeding in a shop.
If it's not held open , the brakes can't be fully bled. If Consult it's not held brakes the open, shop the manual forcan't the be fully bled. correct information on your car. If Consult the shop thea you don ' t have a shopmanual manual,for visit correct information on your It's car.too If car dealer and ask a mechanic. you don't have a shop manual, dangerous for guesswork in thisvisit area.a car a mechanic. too Youdealer may and also ask have to buy a It's special dangerous for guesswork in this area. tool from the dealer. This tool is often may also have to to buy special aYouspring designed flex awithout tool from the often damaging thedealer. valveThis as tool fluidis flows athrough springit. designed to flex without damaging the as fluid flows Sequence of valve Bleeding - Bleeding throughbe it. done in a specific sequence should Sequence to avoid the of need Bleeding to double-Bleeding back and should be done in specific sequence rebleed . Follow athis sequence if to avoidbleeding the need double you're onetowheel at aback time:and rebleed. this itsequence if • Master Follow cylinder-if is bleeder you're bleeding one wheel at a time: equipped. l Master cylinder-if • Combination valve. it is bleeder equipped. • Bleeders on intermediate hardware l Combination valve. in system. l Bleeders on intermediate hardware • Wheel farthest from master in system.usually the right rear wheel. cylinder, W h e eIfl wheel farthest from have master Note: cylinders two cylinder, the one rightfirst; rear if wheel. bleeders, usually do upper a caliNote: wheel cylinders have one two per hasIftwo bleeders, do inboard bleeders, do upper one first; if a califirst. If it has more, follow the manuper has two recommended bleeders, do inboard one facturer's bleeding first. If it has more, follow the manusequence. facturer's recommended bleeding • Bleed other brake at that sequence. end - usually left rear. e e d next otherwheel brake at from that •B lBleed farthest end-usually left rear. right front. master cylinder-usually Bleed next farthest from •l Bleed wheel wheel remaining-usually master cylinder-usually right front, left front. l Bleed wheelbleeding remaining-usually After the process is left front. check the system by presscomplete,
After the bleeding process is complete, check the system by press-
124
ing hard on the pedal to be sure it stays firm. If the pedal is spongy, reing on or thecheck pedalfortoa leak. be sure it bleedhard system stays firm. If the pedal is spongy, reTo check for air in the brake bleed system or check for a leak. system, have someone pump the To several check times, for airthenin hold the it brake pedal down system, have the firmly while yousomeone remove thepump reservoir pedal several times, then hold it down cap. Watch the fluid surface while firmly helper while you remove the reservoir your slides his foot off the cap. the pedal fluid snaps surface pedal Watch pad so the backwhile and your slidesdrops his immediately. foot off the systemhelper pressure pedal apad so the pedal snaps back With well-bled system, there willand be' system pressure drops immediately. a little turbulence at the surface of the With system, there will1/4 be' fluid. aIfwell-bled fluid boils up more than ain.little turbulence at the surface of the above the surface, there's probably fluid. If fluid boils up more than 1/4 air in the system. in. above the surface, there'scommonly probably Bleeding Methods - Three air in the system. for brake bleeding used techniques Bleeding Methods-Three commonly are: used techniques for brake bleeding bleeding. • Pressure are: • Manual bleeding. l Pressuremethods, bleeding. such as gravity • Special l Manual bleeding. bleeding or vacuum bleeding. l Special suchargue as gravity These allmethods, work. People which bleeding or vacuum bleeding. method works better. All good arguTheseare all so work. People that arguenothing which ments complex method better. good arguwill everworks be settled . So,All I suggest that ments are so complex that method, nothing if you have trouble with one will ever beuntil settled. try another youSo, findI suggest the one that that if you best havefor trouble with one method, works your car. tryI'll another until you of findthe theproblems one that explain some works best for your car. with each method. Then I'll explain I'lleach explain how job issome done. of the problems with each method. Then requires I'll explaina Pressure bleeding how each job is done. pressure-bleeder tool. The pressure Pressure bleeding requires bleeder pressurizes the fluid in thea pressure-bleeder tool. The you pressure reservoir. Once pressurized, open bleeder pressurizes fluid innoted the each bleeder in the the sequence
reservoir. Once pressurized, you open each bleeder in the sequence noted
until no air is left in the system. The advantage of pressure bleeding until is leftand in the is thatnoit air is fast onesystem. person can do The advantage of pressure the job. But, there are bleeding several is that it is fast and one person can do disadvantages: The tool is expensive the ajob. But, are several and lot of fluidthere is wasted. If you disadvantages: The toolbleeder is expensive don't use the pressure often, and a lotin of fluidcontaminated, is wasted. If even you the fluid it gets don't use the pressure bleeder often, though it' s in a sealed container. theFluid fluid flow in it gets contaminated, in the lines is higheven if a though a sealed container. bleeder it'sis inopened too far during Fluid flow the cause lines isbubbles high if toa bleeding. Thisin can bleeder is opened too far turbuform within the system from during bleeding. Thisas can causeflows bubbles to lence created the fluid around form within system fromtheturbusharp corners.theThis defeats purlence created as the Conversely, fluid flows around pose of bleeding. rapid sharp corners. This defeats the purfluid flow flushes out air trapped in pose bleeding. rapid high of spots in the Conversely, system . Bubbles fluid flow trapped in the wallsout of air rough compoclinging to flushes high spots in the system. Bubbles nents will be washed away by the flow. clinging to the the pros wallsand of rough With all cons, itcompois not nents if willpressure be washed away byis the flow. clear bleeding good or With all the pros and cons, it is bad . Most auto-repai r garages usenot it clear if pressure or because pressure bleeding bleedingis isgood fastbad. use it most Most racers,auto-repair don't duegarages to potential because pressure bleeding fluid-contamination problems.is fastmost racers,bleeding don't due to advantage potential Pressure has an fluid-contamination problems. on an older car which has had little Pressure bleeding The has an advantage brake maintenance. master cylinon older which hasstroked had little der an does notcar have to be to brake maintenance. Thesystem master cylinpush fluid through the . This is der does have to be stroked to unlike thenot manual-bleeding method push fluid through the system. is that requires full strokes of theThis brake unlike theanmanual-bleeding older car, there method may be pedal. On that requires themaster brake corrosion andfull dirtstrokes insideofthe pedal. On an older car, there may be cylinder. Stroking the pedal to the corrosion andthedirt inside theinto master floor moves piston deep the cylinder. Stroking the itpedal the master cylinder, where would to other-
floor moves the piston deep into the master cylinder, where it would other-
Most racers prefer manual-bleeding method : One person opens and closes bleeders while helper operates brake pedal. Although optional, it's helpful for third person to watch reservoir add fluid when needed. Method is reliable, but success on communication Mostand racers prefer manual-bleeding method: One person opensdepends and closes bleeders while between those doing job. helper operates brake pedal. Although optional, it's helpful for third person t o watch reser-
voir and add fluid when needed. Method is reliable, but success depends on communication between those doing job.
wise never travel. Corrosion and dirt would likely damage the seals, causing wise travel. Pressure Corrosion bleeding and dirt them never to leak. would likely damage the seals, causing avoids this. them to leak. Pressure bleeding Manual bleeding is cheaper, but reavoids this. quires at least two people; while one Manualthe bleeding cheaper, reoperates pedal, isthe other but opens quires at least two people; while one and closes the bleeders. The fluid operates the other opens reservoir the has pedal, to be topped up during and closes the bleeders. the bleeding process. FluidThe flowfluid can reservoir has todepending be toppedonuphow during be fast or slow, fast the process. and Fluidhow flow can the bleeding pedal is pushed much be fast or slow, depending on how fast each bleeder is opened. Manual bleedthe pedal is pushed better and how ing can be controlled thanmuch preseach bleeding bleeder is, so opened. Manual bleedsure most racers prefer it. ing be job controlled Andcan , the wastes better little than fluidpresand sure bleeding, most racers prefer it. doesn't requireso expensive tools. And, the job wastes little fluid and Gravity bleeding can be done only doesn't require expensive tools. with certain brake systems. As you Gravity beforms done bubonly know, air inbleeding the brakecan fluid with certain brake systems. As bles that float to high points in you the know, thehigh brake fluid bubsystem.airIfin the point is forms the master bles that float high points the cylinder, air to will come in out system. If the high point is the master automatically. cylinder, air will out Gravity bleeding is notcome used often automatically. because it takes too long. Also , in Gravity bleeding not used thereoften are almost every brake is system, because takesmake too itlong. Also, . in high spotsit that impossible If almostareevery brake system, are you designing a brakethere system high spots that you makemay it impossible. If from scratch, be able to you system make areit designing possible toa brake self-bleed by from scratch, yousystems may be to gravity, but most are able not demake it possible to self-bleed by signed that way. gravity, but most systems aredone not deVacuum-bleeding can be by signed that way. one person. A small hand-operated
Vacuum-bleeding can be done by one person. A small hand-operated
eTA Manufacturing's bleeder hose, available at many auto-parts stores, makes it possible for one person to manually bleed CTA Manufacturing's bleeder hose, availabrakes. Hoseauto-parts is slipped over makes bleeder, ble at many stores, it bleeder is and free end is put in possible foropened one person to manually bleed catch canHose or bottle. Fluid orover air can only brakes. is slipped bleeder, flow out isofopened hose. When pedal bleeder and free endcomes is putup, in one-way closes. This air catch canvalve or bottle. Fluid or prevents air can only from out entering hose. Using hose requires flow of hose. When pedal comes up, getting in valve and out of carThis to check for air one-way closes. prevents bubbles in hose andUsing fluid hose in reservoir. from entering hose. requires Photo byinRon getting andSessions. out of car t o check for air
bubbles in hose and fluid in reservoir. Photo by Ron Sessions.
Master Cylinder
-
1
t'.
To 0 Reservoir To o
Master Cylinder
-
Reservoir
-
Gravity Bleeding or Caliper
Master Cylinder
I
-
.
Trapped Bubbles
Master Cylinder
-
No Gravity Bleeding Possible or Caliper
Gravity Bleeding Bleeding If brake system is free of high spots that trap No air,Gravity bleeding can be Possible done automatically by gravity. Air bubbles rise to reservoir. If system has high spots in lines, as shown at right, system not gravity If brakewill system is freebleed. of high spots that trap air, bleeding can be done automatically by gravity. Air bubbles rise t o reservoir. If system has high spots in lines, as shown at right, system will not gravity bleed.
vacuum pump is attached to a jar-or plastic bottle-with a closed top. The vacuum is attached to ableeder. jar-or jar has a pump hose that goes to the plastic bottle-withfrom a closed the jartop. and The the Air is evacuated jar has a ishose that goes the bleeder. bleeder opened. The to vacuum pulls Air evacuated from the the jar hydrauand the air bubbles from fluidisand bleeder is opened. The vacuum pulls lic system and into the jar. fluid and airbleeding bubbles sounds from theneat, hydrauVacuum but
lic system and into the jar. Vacuum bleeding sounds neat, but
it has a potential problem. Brakecylinder cup-type seals are meant to it haswith a potential problem. Brakework fluid pressure greater than cylinder cup-type seals are With meant the to the outside air pressure. work with fluid fluid pressure greater than vacuum pump, pressure is below the outside air. air This pressure. Within the the outside may draw air vacuum is below past the pump, seals, fluid unlesspressure your hydraulic the outside may drawI in system has air. cupThis expanders. donair 't
past the seals, unless your hydraulic system has cup expanders. I don't 125
Vacuum bleeder sucks fluid or air into container through tube connected to opened bleeder. Although tool is easy to use and requires only one person, I don't recommend it. Seals in brakes allowsucks air to be drawn if vacuum is applied totube brake fluid. Vacuumcan bleeder fluid or airininto container through connected to opened bleeder. Although tool is easy to use and requires only one person, I don't recommend it. Seals in
brakes can allow air to be drawn in if vacuum is applied to brake fluid.
Master Cylinder Bleeder Hose -Glassor Clear-Plastic Jar
Pressure Bleeder
Clear-Plastic Jar
Pressure bleeder setup: Pressure-bleeder tank is charged with compressed air, which pushes fluid into brake system. Adapter clamps to reservoir, sealing fluid entering system. Drawing courtesy Pressure bleeder Bendix setup: Corp. Pressure-bleeder tank is charged with compressed air, which
pushes fluid into brake system. Adapter clamps to reservoir, sealing fluid entering system. Drawing courtesy Bendix Corp.
Master Cylinder
1 3
Press slowly on brake ~ e d a l .
Bleeder Hose
,--1''-<-- G lass or Clear Plastic Jar
Glass or Clear Plastic Jar Setup for manual bleeding: It takes two people, one at the brake pedal and another at the bleeder. Person operating bleeder should give instructions to person operating the pedal. Bleeder openedbleeding: only whenItpedal being pushed is closed pedal is Setup foris manual takesistwo people, onedown; at thebleeder brake pedal andbefore another at the returned. Drawing courtesybleeder Bendix should Corp. give instructions to person operating the pedal. bleeder. Person operating
Bleeder is opened only when pedal is being pushed down; bleeder is closed before pedal is returned. Drawing courtesy Bendix Corp. 126
recommend the vacuum-bleeding method, although some people use it. recommend theroadvacuum-bleeding Many modern cars are vacuum method, some people use it.is filled at although the factory . The system Many modern roada cars are vacuum pumped down to nearly perfect filled at through the factory. The system is vacuum the master cylinder pumped down to a nearly perfect by a very large vacuum pump. Then, vacuum through master fluid is forced in atthe about 100 cylinder psi. Beby a very large all vacuum Then, cause virtually the airpump. is removed fluid is forced in at about 100 psi. Bebefore the fluid is put in, no bleeding cause virtually all the air is removed is required. Systems filled like this before the fluid put in, no bleeding must have cup is expanders, but no is required. Systems filled like this residual-pressure valves. must have and cup manual expanders, but are no Pressure bleeding residual-pressure valves. detailed in the following pages. Before Pressure and manual bleeding starting, consult your shop manualare to detailed in theprocedures following pages. Before see if special must be folstarting, yourI'llshop manual to your car. describe what lowed forconsult see if special procedures must be folis done for a typical car, but be aware lowed for your car. I'll describe that it may not be correct for yourwhat paris done for a typical car, but be aware ticular model. that it may not be correct for- your parHow to Pressure Bleed Pressure ticular model. bleeders are used to save time by How to Pressuremechanics. Bleed-Pressure most professional It is a bleeders are used to savefastest timeway by one-man job. It is also the most professional mechanics. It is to bleed brakes . You must have a pres-a one-man job. Itto isdo alsothe thejob, fastest waya sure bleeder plus to bleed of brakes. You mustair. have a pressource compressed Pressure sure bleeder to do the job, amount plus a bleeding also requires a large source of compressed air. Pressure of brake fluid to fill the pressure bleeding bleeder. also requires a large amount of Abrake fluidbleeder to fillhasthe pressure pressure a tank conbleeder. taining brake fluid, plus an air comA pressure bleeder has tank conpartment to pressurize thea fluid. The taining plus anormally n air comfluid andbrake air arefluid, separated by to pressurize fluid.moisThe apartment rubber diaphragm to the prevent fluid and separated normallythe by ture in theairairare from contaminating a rubber to prevent fluid. Thediaphragm fluid outlet connectsmoisand ture intothe from contaminating the seals theairmaster-cylinder reservoir fluid. The fluid outlet connects and with an adapter that fits in place of the seals to the reservoir onlymaster-cylinder works on a master cylincap. This with an adapterwith that fits in placeintegral of the der designed a sturdy cap. This only works on acylinders master cylinSome master with reservoir. der designed with a sturdy integral remote reservoirs cannot be pressure reservoir. Some master cylinders with bled. Again, check the shop manual. remote reservoirs cannot be connectpressure With the pressure bleeder bled. checkcylinder, thz shoppressure manual. is ed to Again, the master With the pressure bleeder connectapplied to the hydraulic fluid from the ed to the master pressure is pressure in thecylinder, tank. About 30 psi air applied the hydraulic from dethe is used. to Follow bleedingfluid sequence air pressure in the About 30 psi bleeding, scribed earlier. To tank. do the is used. Follow bleeding sequence each bleeder is opened about de1/4 scribed do the bleeding, turn - noearlier. more.ToOtherwise, excess each flow bleeder is opened about 114 fluid results, allowing air and turn-no more. Otherwise, excess fluid to escape. When only fluid fluid results, allowing comesflow out, the bleeder is shut. air and fluid to escape. When only fluid Each pressure bleeder comes with comes out, theAlso bleeder is shut. instructions. supplied are adapEach bleeder comes with ters thatpressure fit popular master-cylinder instructions. Also supplied are adap-a reservoirs . Bled fluid flows through ters that fithose popular master-cylinder pushed on the bleedclear plastic reservoirs. fluid flows er and intoBled a container. Oldthrough fluid ora clear plastic hose pushed on the bleedany fluid bled through a hydraulic er and into a container. Old fluid or system should never be reused.
any fluid bled through a hydraulic system should never be reused.
A pressure bleeder is convenient for changing all the fluid in a brake A pressure bleeder is convenient system. It allows the whole system to for changing all the fluid in atobrake stop be refilled without the need system. the master whole system to and topIt allows up the cylinder. be refilled without stop However, if you the haveneed theto fluid and top byupsomeone the master cylinder. else, you may changed However, if you have the fluid not get to choose the fluid that goes in changed bysystem. someone else, you your brake Whatever is inmay the not choose that goes in tankget is to what you the get,fluid no matter what your brake system. is inThe the is best Whatever for your car. you think tank what get, or no itmatter fluid is may be you the best may bewhat the you think is best for your cheapest the shop could buy.car. AndThe , it fluid maynew be or theold. bestThis or itismay the whybemost may be cheapest theuse shop could buy. And, it racers won't a pressure bleeder. may be new or old. This is why most How to Manual Bleed-Manual racers won't use a pressure bleeder. bleeding is simple, but takes at least How to Manual Bleed-Manual one helper, as mentioned earlier. The bleeding is simple, but takes at some least equipment needed includes one helper, as mentioned earlier. The clear plastic tubing to fit the bleeder, equipment includes jar to some catch and a glass orneeded clear-plastic clear plastic tubing to fit have the bleeder, the bled fluid. You must a quart and a glass or clear-plastic jar to youcatch are or two of fresh fluid, unless the bled fluid. have a quart changing the You fluid.must Then, you may or two of fresh fluid, unless you are about one gallon. need changing fluid. Then, you may Bleedingthesequence remains the need about one gallon. same. Pedal pressure forces fluid and remains Push the bubbles sequence out the bleeder. airBleeding same. Pedal forces and down on thepressure pedal and hold fluid it. Open air bubbles Fluid out should the bleeder. the bleeder. flow outPush the down on the pedal and hold it. Open bleeder, through the tube, and into the Fluid should the bleeder. jar. If the jar-end of flow the out tubethe is bleeder, through tube, covered with fluid,theyou ' ll beand ableinto to the air jar.bubbles If the come jar-endout.of the tube is see covered with fluid, be ablethe to is opened, After the bleeder you'll see airshould bubblesbecome out. slowly until pedal go down After against the bleeder is oropened, the it stops the floor stop . Close pedal should be go down slowly until the bleeder before the pedal is it stops against the the floorpedal or stop. released. Usually, will Close have the before times the to pedal is to be bleeder pumped several " bring released. Usually, the the pedal will have opening next bleeder it up" before to be pumped in the sequence.several times to "bring it up" before theatnext Watch the opening reservoir all bleeder times. in thetosequence. Plan add fluid at least once while Watch each the reservoir times. bleeding wheel. If at the all reservoir Plan to add fluid at least once while runs out of fluid, air will be drawn bleeding wheel. If theand reservoir into the each master cylinder you'll runs to outstart of bleeding fluid, airallwill drawn have overbeagain. It into the master cylinder and you'll helps if a third person watches the have to start bleeding again.the It fluid reservoir while all oneover pumps helps and if athethird the pedal otherperson bleeds watches . fluid the the one hosepumps off the As reservoir you pullwhile pedal and the other bleeds. bleeder, fluid in the hose will run out. As you you bleed pull the the next hosewheel, off the the When bleeder, fluid in hoseairwill first bleeding willthepush outrun of out. the When you bleed wheel, the hose. This makesthe lotsnext of bubbles in first bleeding will push air out of the jar. So don't assume this is the air hose. the This makes lots of bubbles in bleeder. from theOnjar.a So don't this is the air don't pump road car, assume from bleeder. brake the pedal with the bleeder open , On though a road the car,hose don'tis filled pump with the even brake pedal with the bleeder open, fluid and submerged in fluid in the jar. even though hose iscontaminatfilled with There's a risk the of drawing fluid and submerged in fluid in .the jar. ed fluid back into the system Fluid
There's a risk of drawing contaminated fluid back into the system. Fluid
Not a good setup for bleeding brakes : Hose should be clear and free end immersed in fluid in clear or jar. BubNot a good setup for bottle bleeding brakes: bles can then be andand mess is avoided. Hose should beseen clear free end im-
mersed in fluid in clear bottle or jar. Bubbles can then be seen and mess is avoided.
must always be pushed out the bleeder, never drawn in. On a race must be pushed the fluid is usually clean, out so drawcar, thealways bleeder, drawn in. On a race less risky because it ing in oldnever fluid is car, thebe fluid is usually clean, so drawshould relatively fresh. ing in old fluid is less risky because it Simultaneous should be relatively fresh. bleeding is BleedingSimultaneous Simultaneous another manual-bleeding method Bleeding bleeding is sometimes Simultaneous used on race cars with dual another manual-bleeding method master cylinders. With this method, a sometimes raceare carsbled withatdual rear on brake the front and a used master time. cylinders. With this method, same Simultaneous bleedinga front a rear brakeofareeach bled master at the allowsand a full stroke same time. Simultaneous bleeding cylinder and a straight motion of the allows full To stroke balance a bar. do of this,each youmaster need cylinder helper and a and straight another tube motion andjar. of the balance bar. To do this, you need simultaneous bleeding, To perform another helper and tube and jar. partially fill the jars with fresh brake To. perform bleeding, Connect simultaneous one end of each tube to fluid jars withthefresh bleederfill andthe submerge otherbrake end apartially fluid. Connect oneBleed end ofthe each tubeand to in a jar of fluid. front arear bleeder and submerge the other end wheels farthest from the master in a jar of fluid. Bleed the front cylinder first. If the calipers have and two rear wheels farthest from the first. bleeders, bleed the inboard side master cylinder first. Ifpressure the calipers have two With gentle on the pedal, bleeders, bleed the inboard side first. simultaneously open both front and With gentle pressure the pedal, rear bleeders. Air will on bubble from simultaneously open both front and the hoses and some fluid will follow. rear bleeders. Air will bubble from With the bleeders open, slowly pump the pedal hoses up andand some fluiduntil willbubbles follow. the down With Then, the bleeders open, slowly Go pump stop. close the bleeders. to the pedal up and down until bubbles the other side of the car-inboard stop. Then, close thethem bleeders. o to bleeders if you have - and Gbleed the other side of the car-inboard those brakes. Remember, always and bleed bleeders you have them -level keep theif reservoir-fluid high those brakes. Remember, always enough to prevent running out of keep during the reservoir-fluid high fluid the bleeding. Iflevel you suck enough to master preventcylinder, runningyouout of air into the must fluid over. during the bleeding. If you suck start
-
air into the master cylinder, you must start over.
Plastic bottle and clear plastic hose is handy for brake bleeding. Note that bottle is supported wireclear looped over hose bleeder Plastic bottlebyand plastic is screw. for Bottle each wheel minimizes handy brakeatbleeding. Note that bottle mess and brake-bleeding Clear is supported by wire looped chore. over bleeder plastic bottle shown. screw. Bottle isat better each than wheelone minimizes Photo by Tombrake-bleeding Monroe. mess and chore. Clear
plastic bottle is better than one shown. Photo by Tom Monroe.
Once both sides are bled, test the action of the balance bar. With the Once sides bled, the tubes stillboth in the jars,are open one test bleeder action of the thepedal balance bar.to With the and push slowly the floor. tubes simulates still in the jars, open This failure of one onebleeder set of and push the pedal slowly to the floor. brakes. The balance bar shouldn't This failurebottom. of one IfsetOK, of bind, simulates nor the pedal brakes.theThebleeder balanceandbarrelease shouldn't the close bind, bottom. If OK, pedal. nor Test the the pedal other brake system by close the bleeder and release opening a bleeder at the other endthe of pedal. thetests other system the car.Test This thebrake balance bar by at opening a bleeder the master other end of its maximum angle.atOne cylinthe is car. Thiswith tests theunder balance bar at der filled fluid pressure; its maximum angle. One master cylinthe opposite one has no pressure at der is filled with fluid under pressure; all. If everything is properly des igned the has no at and opposite built, theone balance barpressure should be all. If everything is properly designed free at either . extreme angle. If it and barremedy should the be outbalance why and bindsbuilt, , find the free at either, extreme angle. If it problem. binds, find out why and remedy the Simultaneous bleeding is not problem. recommended for road cars. Unlike a Simultaneous not race car, brake fluidbleeding in a road is car gets recommended for road bled infrequently, so it cars. will Unlike be dirtya race contaminated. car, brake fluidDon in a'troad gets and risk car pulling bled infrequently, so it will be dirty old fluid back into the system by and contaminated. risk bleeder pulling pumping the pedal Don't with the old fluid back into the system by open. pumping the pedal with the bleeder Eliminating Bubbles-Brakes are open. sometimes spongy after manual EliminatingSlowBubbles are movement bleeding. pedal-Brakes sometimes spongy after manual avoids fluid turbulence that would bleeding. form Slow bubbles. pedal movement otherwise But, slow avoids fluid turbulence fluid flow will not dislodgethat smallwould bubotherwise form tobubbles. But, slow rough surfaces. If bles that cling fluidtap flow not dislodge smalla plasbubthewill calipers gently with you blesmallet that cling rough surfaces. If tic whileto bleeding, this will you tap the calipers gently with a plashelp dislodge those stubborn bubbles. tic mallet while bleeding, thisbleedwill Bleeder Problems-Sometimes help dislodge those stubborn bubbles. ers cause trouble. A common problem
Bleeder Problems-Sometimes bleeders cause trouble. A common problem 127
To Master Cylinder With Fluid Being Bled Out.
To Master ~ylinder'with Fluid Being Bled Out.
Penetrating oil is sprayed around studs before removing stuck brake drum. Before using penetrating make sure adjuster is penetrating oil isoil,sprayed around studs loose, parts are stuck clean,brake and drum. all attaching before removing Before clips screws are removed. usingand penetrating oil, make surePenetrating adjuster is oil mustparts be removed after and use. all attaching loose, are clean,
Pedal
Master cylinder being bled strokes its piston forward until pedal hits stop. Other cylinder piston doesn't travel as far. As a result, balance bar assumes extreme angle when one master bled. bled Balance bar must not bind at thisuntil angle, or breakage result. Master cylinder cylinderisbeing strokes its piston forward pedal hits stop.may Other cylinder
piston doesn't travel as far. As a result, balance bar assumes extreme angle when one master cylinder is bled. Balance bar must not bind at this angle, or breakage may result. Caution: Be careful to avoid spraying brake fluid. Do not hold face Caution: Be careful to directly above reservoirs. avoid spraying brake
fluid. Do not hold face directly above reservoirs. Press in and release several times. Press in and
release several
Bleeder Tubes
Bleeder Tubes Dry master cylinder should be bled as shown. This can be done off the car. Bleeder tubes can be made of copper or steel brake tubing. When reinstalling master cylinder, transfer lines quicklycylinder to minimize fluidbeleakage. courtesy Bendix Dry master should bled asDrawing shown. This can be doneCorp. off the car. Bleeder tubes
can be made of copper or steel brake tubing. When reinstalling master cylinder, transfer lines quickly to minimize fluid leakage. Drawing courtesy Bendix Corp.
is a rusted bleeder that seizes. It must be loosened with care with the correct is a rusted bleeder that seizes. It must wrench-no open ends. A broken-off be loosened with care with the bleeder screw means you'll havecorrect to rewrench-no open component-wheel ends. A broken-off place the entire bleeder means you'll cylinder have to recylinder,screw caliper, master or place the entire whateverbecausecomponent-wheel it is almost imcylinder, caliper, master cylinderhalf or remove the broken possible to whatever-because is almost without damaging theitdelicate seat. impossible the broken Loosentoa remove stuck bleeder screw half by without damaging the delicate seat. cleaning the area around it with a wire Loosen stuck bleeder by brush. Try a turning it after screw cleaning. cleaning area try around it with a wire resort a good grade of As a lastthe brush. Try oil. turning it aafter cleaning. penetrating This is last resort beAs a oil lastcan resort a good grade of get try inside and contamicause penetrating oil. This is a last resort benate the brake fluid. After using cause oil canoil, get inside penetrating removeandit contamiby disnate the brake fluid. After using the component and cleanassembling penetrating oil, remove it by dis-
assembling the component and clean-
128
ing it completely with brake-cleaning fluid or alcohol. ingThe it completely with brake-cleaning best penetrating oil I have fluid or alcohol. found is called Kroil. Available from The best penetrating I have Kano Laboratories in oil Nashville, Kroil. in Available found is called Tennessee, it comes a sprayfrom can Kanoa plastic Laboratories Nashville, tube that in attaches to the with Tennessee, comesyou in toa spray nozzle. Thisitallows direct can the with a plastic tube that attaches to less the oil exactly where you want it with nozzle. allows you to direct the of This contaminating other brake risk oil exactly where you want it with less parts. Be careful! If penetrating oil risk on of brake contaminating othermust brake linings, they be gets parts. Be careful! If penetrating oil replaced. gets linings, they corrosion must be prevent internal To on helpbrake replaced. and sticking, install rubber bleederTo help screw caps. prevent internal corrosion and sticking, rubber bleederFilling Dryinstall Tandem Master screw caps. Cylinders-Fill a dry tandem master
Filling Dry Tandem Master Cylinders-Fill a dry tandem master
clips and screws are removed. Penetrating oil must be removed after use.
cylinder with care. It's not good practice to pour in fluid and pump the cylinder with air care.trapped It's not inside, good pracpedal. With the tice to pour in fluid and pumpcause the piston will bottom and possibly pedal. air trapped inside, the internalWith damage. piston bottom and possibly If thewill master cylinder is off thecause car, internal damage. fill it at the workbench. Remove interthe master cylinder itisasoffshown the car, nalIfbubbles by bleeding in fill at the workbench. Remove interthe itaccompanying photographs. The nal bubbles by bleeding shown of in tubes illustrated can itbeas made the accompanying photographs. The copper or steel. They install in the tubes illustratedoutlet canports. be made of master-cylinder copper steel. They in the After or bleeding all theinstall bubbles, inmaster-cylinder outlet ports. stall the master cylinder on the car. After connecting bleeding all the the brake bubbles, inWhen lines, stall the them master cylinder on the car. transfer quickly to avoid losing When brake makes lines, fluid. Thistheprocess all the connecting transfer them quickly to avoid losing bleeding easier, because no small buball process makes the master bles the get fluid. trappedThis inside bleeding easier, because no small bubcylinder. bles trapped inside master A get master cylinder usedthewith disc cylinder. brakes usually doesn't have a resid ualA master cylinder with disc Thus, used bench-bleeding pressure valve. a residualbrakes usually haveand will only movedoesn't fluid back forth in pressure Thus, bench-bleeding the tube. valve. To prevent this, hold a will only move fluidofback in the end the and tubeforth during finger over the tube. To prevent this, hold the return stroke of the piston. Thisa finger over thefrom end of the tube prevents fluid being drawnduring back the return stroke piston.stroke. This into the tube on of thethe return prevents fluid from being drawn back The drum-brake side of a tandem into the may tubehave on the returnpressure stroke. cylinder a residual The of flow a tandem reverse of the valve drum-brake that preventsside cylinder maythe have a residual pressure fluid below residual-pressure setvalve reverse flow of the the prevents valve. ting ofthat
fluid below the residual-pressure setting of the valve. DRAINING BRAKE FLUID When changing brake fluid, drain
DRAINING FLUID This the hydraulic BRAKE system completely. Whenbe changing brakethe fluid, drain cannot done through bleeders. the hydraulic completely. This is due to system the basic function ofThis the cannot beBleeders done through the bleeders. bleeder. are designed to let This is due the basicsystem, functionsoofthey the air out of a tohydraulic bleeder. Bleeders arehigh designed let spot into the are located at each air out of After a hydraulic system, so they system. draining from the are located at each high spot in the system. After draining from the
bleeders, fluid remains in all low spots. Some people think that pumpbleeders, fluid in the all fluid low ing the pedal willremains push all of spots. Some people think that pumpout. Although this gets most out, ing the pedal push all of the fluid some fluid willwill remain. out. Although this gets most out, To get all new fluid, one method resome fluid will remain. quires refilling and pumping out the To getmany all new fluid,This oneforces method system times. all reof quires and the pumping out the the oldrefilling fluid from low spots by system manythe times. of mixing with cleanThis fluid.forces This all procthe old fluid from the low spots by ess is better than nothing at all, but it mixing with the proc-a is expensive to clean do it fluid. right This because ess of is better than nothing at all, but it fluid is wasted. And, it never lot is expensive to do it right because a gives 100% clean fluid. lotThe of fluid is wasted. And, never correct way to drain olditfluid is gives 100% clean fluid. to open up the system at every low TheThis correct way tomeans drain old fluid is usually disassemspot. to open up the system removing at every low or bling wheel cylinders, spot. This usually means disassembling calipers, and disassemunscrewblingfittings. wheel The cylinders, or master removing cylinder will ing disassembling calipers, and unscrewalso have to be removed and drained. ing fittings. masteras cylinder will involves much work Because thisThe alsoa have to be removed and drained. as hydraulic-system rebuilding job, Because as all much it makes this senseinvolves to replace the work seals as a hydraulic-system rebuilding job, at the same time. it makestoSense to replace all changing the seals Glycol Silicone-When at the asame time. from glycol-based fluid to silicone ~ l to silicone-when ~ draining ~ ~is a must. changing l To fluid, complete from a glycol-based fluid to silicone take full advantage of the properties fluid, complete is a must. of silicone fluid,draining drain every drop To of take full advantage of the properties the old fluid, flush the system with of siliconeand fluid,rebuild drain every dropthe of alcohol, all of the old fluid, flush the system with cylinders.
alcohol, and rebuild all of the cylinders. HYDRA ULIC-CYLINDER REBUILDING HY LINDER InDRAULIC-CY time, the seals in a wheel REBUILDING master cylinder or caliper cylinder, time, the seals in a wheel willIn leak. Contamination or corrosion cylinder, master cylinder or caliper makes this happen sooner. Caliper will leak. Contamination or corrosion subjectseals that are old or have been makes thistemperature happen sooner. Caliper also lose their ed to high seals that are old or have been subjectelasticity and limit piston retraction. ed to highalltemperature also lose their Usually, brake-system cylinders elasticity and limit piston retraction. need rebuilding. Usually, all abrake-system cylinders cylinRebuilding wheel or master need rebuilding. der should start with getting your Rebuilding a wheel or master cylincar's factory shop manual. There are der should startbrake withdesigns. getting Some your many different car's factory manual.procedures. There are require specialshop rebuilding many different brake designs. Some Most wheel or master cylinders can be require special rebuilding procedures. rebuilt, but some are impossible beMost wheel or masterare cylinders be cause bore surfaces usually can pitted rebuilt,corrosion. but some The are impossible becylinder then from cause bore surfacesTherefore, are usually before pitted cannot be honed. from corrosion. The cylinder then buying rebuilding kits, disassemble cannot be honed. Therefore, the cylinders and inspect them.before Even buying your rebuilding kits, though cylinders can disassemble theoreticalthe cylinders and inspect them. Even ly be rebuilt, they may be too damaged though to allow your it. cylinders can theoretically To be rebuilt, may an be too damaged entire cylinbe safe,they replace to allow it. der if it leaks. For older cars for which Tocylinders be safe, are replace an entire acylinnew not available, mader if it leaks. For older cars for which new cylinders are not available, a ma-
Cleaning brake parts should be done with special brake-cleaning fluid. CRC Brakleen is used at start of brake-maintenance job. Petroleum products should never be used on brake parts, as brake is easily courtesy CRC Chemicals. Cleaning brakefluid parts shouldcontaminated. be done with Photo special brake-cleaning fluid. CRC Brakleen is used at start of brake-maintenance job. Petroleum products should never be used on brake parts, as brake fluid is easily contaminated. Photo courtesy CRC Chemicals.
chine shop can bore out the old cylinder and press in a stainless-steel or chine shop can bore Post out the old cylinWhite Restorations brass sleeve. der and press in a stainless-steel of White Post, Virginia, specializes or in brass sleeve. White Post Restorations sleeving collector-car brake cylinders. of Brake-cylinder White Post, Virginia, in rebuildspecializes kits usually sleeving collector-car brake cylinders. include rubber seals, dust boots and, Brake-cylinder rebuild kits or usually sometimes, internal springs seal include rubber seals, dust boots expanders. Often, an older designand, will sometimes, internalseals springs or seal have newer-style in the kit. expanders. Often, ancup-type older design will Many replacement seal kits have newer-style seals add in reliabilithe kit. include expanders. These Many replacement cup-type seala kits ty to the seal. Rebuild kits are lot include expanders. These add reliabilicheaper than a new cylinder, particty to the seal. Rebuild are a lot if you have to buy akits caliper. ularly cheaper than a new cylinder, particDisc-brake calipers usually must be ularly if you have buyfor a caliper. removed from theto car rebuilding. Disc-brake caliperswheel usually cylinders must be Some drum-brake removed from the car for rebuilding. can be left in place on the backing Some drum-brake cylinders plates for rebuilding,wheel providing you can reach be left in with placea hone. on the backing them can plates rebuilding, providing you Wheel for Cylinders & Master can reach them with a hone. Cylinders- The first task is disassemWheel Cylinders & Master completely. If it is bling the cylinder Cylinders-Theclean firstup taskthe is disassemrebuildable, cylinder bling the cylinder completely. If You it is bore with a brake-cylinder hone. rebuildable, clean up the cylinder can buy a hone at an auto-parts store. bore awith brake-cylinder You Get honea with three smallhone. replaceacan buy a hone an auto-parts store. Theyatlook like a miniature ble stones. Get a hone with three engine-cylinder hone.small Usereplaceabrake ble stones. They look like a miniature fluid-the type you'll be using in the engine-cylinder Use brake brake system-ashone. a lubricant while fluid-the typeuse you'll be or using the solvent any in petrohoning. Never brake system-as a lubricant while leum product on brake parts. Never use or anyapetrohoning. If a cylinder cansolvent be rebuilt, light
leumproduct on brakeparts. If a cylinder can be rebuilt, a light
Wheel-cylinder rebuilding kit typically contains cup-type seals, boots and spring. Make sure wheel cylinder rebuildable Wheel-cylinder rebuilding kit is typically conbeforecup-type buying kit.seals, boots and spring. tains Make sure wheel cylinder is rebuildable before buying kit,
honing is required to remove surface imperfections. After honing, check honing is required remove surface bore diameter with to a feeler gage. If a imperfections. narrow 0.006-in.After feeler honing, gage can check be inbore diameter feeler and gage.bore, If a serted betweenwith the apiston narrow 0.006-in. feeler gage can be inyou should replace the cylinder. You serted pistonmicrometer and bore, can alsobetween use an the outside you replacegage the cylinder. You and should telescoping to measure can also use an outside micrometer piston and bore diameters. If the difand telescoping gage two to measuremeasure ference between the piston bore in. diameters. If the difments and is 0.005 or more, replace ference between the two measurethe cylinder. ments is 0.005 seal in. is or used more, If a cup-type in areplace cylinthe cylinder. der that has excessive clearance beIf a cup-type useda in a cylintween the pistonseal andisbore, condition der that has excessive clearance beknown as heel drag can occur. The seal tween the piston and bore, a condition gets pinched in the space between the
known as heel drag can occur. The seal gets pinched in the space between the
129
@ Cylinder
Cylinder
-
Pushrod
Seal
Seal
Motion Piston
Cup-Type Seal Pinched Between Cylinder Piston andSeal Cup-Type
Pinched Between Piston and Cylinder
Two types of brake cylinder hones: Upper hone one is made for a specific cylinder diameter; lower one is more expensive, but will adjust to different bore sizes. Buy the adjustable hone, it will cylinder be cheaper in theUpper long run. Two types of asbrake hones: hone one is made for a specific cylinder
diameter; lower one is more expensive, but will adjust t o different bore sizes. Buy the adjustable hone, as it will be cheaper in the long run.
If bore-to-piston clearance is too great, rubber seal may wear excessively and can inhibit piston movement. The cause heel If bore-to-piston clearance is too isgreat, drag-seal gets pinched betweenand piston seal may wear excessively can and Honing beyond inhibitbore. piston Thefactory cause islimits heel causes this condition. drag-seal gets pinched between piston
and bore. Honing beyond factory limits causes this condition.
Wheel-Cylinder Clamp
Wheel-Cylinder Clamp
Hone is driven by drill motor while brake fluid lubricates hone and keeps stones from loading up with metal particles. Never use oil or solvent for honing brake parts, as it will damage seals. Hone is driven by drill motor while brake fluid lubricates hone and keeps stones from loading
up with metal particles. Never use oil or solvent for honing brake parts, as it will damage seals.
piston and bore. This causes the piston to retract very slowly or stick. piston andheel bore. A voiding dragThis is acauses must the for piston to retract very slowly or stick. proper braking. Avoiding heelreplace drag the is aseals, mustwash for When you proper braking. all of the parts with clean brake fluid, When you wash blowout with replace clean drythe air,seals, and lubriall of with the parts cleanfluid. brakeAgain, fluid, cate cleanwith brake blow out with dry same air, andtype lubriremember to clean use the as cate brakeinfluid. Again, what with you ' llclean be using the system. remember to use thecleaner same type as Use only brake-part for the what you'll be using in the system. first cleaning, but use only new brake Use for onlylubricating brake-part cleaner for thea fluid . Don't assemble first cleaning, but and use only new brake grease must be cylinder dry. Grit fluid for of lubricating. kept out the brake Don't systemassemble as well. a cylinder and greasea must be If youdry. areGrit rebuilding master kept out of the brake system as well. cylinder, fill it with the exact type of If you are rebuilding master fluid you plan to use and a bleed it cylinder, fill it with the the exactcar.type of before installing it on This
fluid you plan to use and bleed it before installing it on the car. This
130
will make brake bleeding much easier later. Bench-bleeding a master cylinwill brakeon bleeding much easier der ismake discussed page 128. later. Bench-bleeding a master cylinWheel cylinders don't have to be der is discussed on page 128. filled with fluid, only lubricated with cylinders to be it. Wheel They will fill easilydon't duringhave bleeding. filled fluid, with Youwith may findonly a lubricated wheel-cylinder -it. Theyhandy will filltoeasily bleeding. clamp holdduring in the pistons You installing may find a wheel-cylinder while a wheel cylinder. The clamp handy to hold in hold the pistons dust boots don't always in the while installing a wheel cylinder. Thea The wheel-cylinder clamp, pistons. dust boots always the simple tool don't available at hold most ingood pistons. The wheel-cylinder clamp, auto-parts stores, keeps the internala simple tool pushing available out at the mostpistons good spring from auto-parts and seals. stores, keeps the internal spring from Rebuildingpushing out Disc-brakethe pistons Caliper and seals. caliper rebuilding is more complicated Caliper Rebuilding-Disc-brakethan rebuilding a master cylinder or caliper rebuildingYou is more complicated wheel cylinder. usually have to
than rebuilding a master cylinder or wheel cylinder. You usually have to
Wheel-cylinder clamp is used to keep pistons inside wheel cylinder while shoes are removed. Once clamp shoes isand return springs Wheel-cylinder used to keep pisare reinstalled, clamp is removed. Drawing tons inside wheel cylinder while shoes are courtesy Bendix removed. Once Corp. shoes and return springs
are reinstalled, clamp is removed. Drawing courtesy Bendix C q p .
disassemble the caliper to remove the pistons. Don' t get brake fluid on the disassemble to remove pads if you the plancaliper to reuse them . the On pistons. Don't get brake fluid on the some calipers it is hard to remove the pads youSpecial plan tocaliper-piston reuse them. On pistonif(s). resome calipers is hard to remove the moving tools itare available. Another piston(s). caliper-piston remethod is toSpecial use compressed air at the moving tools are available. Another hole where the hose installs. If you method is to use compressed air at will the use compressed air, the pistons hole where installs. If you come flying the out.hose Be careful! Flying use the or pistons will partscompressed can cause air, injury damage! come flying out. Be careful! Flying Wrap rags around the caliper and trap parts can And causedon't injuryuseortoo damage! the parts. much Wrap rags Be around the caliper andwhen trap pressure. especially careful the parts. And don't use too much removing plastic pistons. They are pressure. Be especially careful when easily chipped and scratched . removing plasticbores pistons. are Some caliper can beThey cleaned easily chipped andothers scratched. up with a hone; cannot. Check Someshop calipermanual bores canforbe cleaned your specific up with a hone; Check thosecannot. that can be instructions. Forothers your manual isforsimilar specific honed, shop the operation to
instructions. For those that can be honed, the operation is similar to
Caliper
Caliper
v
Usually, disc-brake piston can be removed with low air pressure applied through brake-hose hole. Make sure in front Usually, disc-brake piston canarea be removed of piston we"pressure padded to preventthrough piston with low isair applied from flying hole. out and your brake-hose Makebouncing sure areainto in front face. Don't apply air pressure until you of piston is well padded to prevent piston cover flying everything with bouncing a rag. When from out and intopiston your comesDon't out, brake-fluid spray will follow! face. apply air pressure until you Job can be dangerous, be careful. Drawcover everything with so a rag. When piston ing courtesy Bendix Corp.spray will follow! comes out, brake-fluid
Job can be dangerous, so be careful. Drawing courtesy Bendix Corp. Wooden or Plastic Stick
Removing piston seal from Chrysler floating caliper: Seal is installed in groove in caliper bore. Use seal a plastic woodenfloattool Removing piston from or Chrysler to damaging edges. Such in a ingavoid caliper: Seal isgroove installed in groove tool should also to or install sealstool on caliper bore. Usebea used plastic wooden pistons. courtesy to avoidDrawing damaging grooveBendix edges.Corp. Such a
tool should also be used to install seals on pistons. Drawing courtesy Bendix Corp.
honing a wheel cylinder or master cylinder. Usually, caliper bores are honing ato wheel cylinder or master limited O.002-in. oversize. Any cylinder. boresOnarea larger, andUsually, the seals caliper won't work. limited that to cannot 0.002-in. oversize. Any caliper be honed, the bore larger, and the seals work. can be refinished withwon't crocus cloth.On a caliper cannotis benot honed, the bore If itsthat bore(s) scratched or can be refinished withbecrocus cloth. pitted, a ca liper can rebuilt. When If its bore($ is notthescratched or corrosion has pitted bore, you pitted,replace a caliper can be or rebuilt. must the caliper sleeveWhen it. corrosion has pitted bore, you Caliper bores on oldthe Corvettes are must replace caliper or damage. sleeve it. In suscepti ble tothecorrosion Caliper bores old aCorvettes are fact, this has beenonsuch problem that susceptible to corrosion damage. a company has come up with In a fact, this has been such aCorvette problem calithat solution. Stainless-steel a company has comeStainless up with pers are avai lab le from Steela
solution. Stainless-steel Corvette calipers are available from Stainless Steel
Retracting caliper piston on Honda with a screwdriver. Some manufacturers recommend using their special tool or a C-clamp. See your shop manual for specifics.
Retracting caliper piston on Honda with a screwdriver. Some manufacturers recommend using their special tool or a C-clamp. See your shop manual for specifics.
Brakes Corp., in Clarence, New York. These stainless-steel calipers miniBrakescorrosion Corp., in damage, Clarence, particularly New York. mize These stainless-steel calipers on cars using glycol brake fluid. minimize corrosion Some two-piecedamage, calipers particularly can be dison cars usingfor glycolrebuilding. brake fluid. Others assembled Some even two-piece cal~pers be discannot, though it maycan appear to assembled rebuilding. be possible.for Consult your Others shop i t may appear to cannot, manual even beforethough disassembling the calibe body. possible. Consultcaliper yourwith shop per A two-piece an manual disassembling thewhere caliinternal before fluid passage has seals per body. A two-piece caliper with an the caliper splits. Make sure these internal fluid passage has seals where seals are replaced before reassembling the caliper. caliper The splits. sure the boltsMake holding thethese caliseals are replaced reassembling per body togetherbefore are high-strength the caliper. bolts holding caliand require The a specified torque. the Be sure per body together are high-strength to tighten these bolts to the specified and require a specified sure torque to avo id potentitorque. al catasBe trophic to tightenlater. these bolts to the specified problems torque to avoid potential catastrophic Removing or installing the seals on problems later. some calipers can be tricky. They fit Removing or which installing the be seals on into a groove, must clean some calipers can be tricky. They and free of burrs. Be careful not to cufitt into a age groove, which must when be clean or dam the seal or groove inand free of burrs. Be careful not to cut stalling seals. Use pl astic tools to or damage the sealcritical or groove when in-, avoid damaging parts. Also stalling seals. plastic don't ignore the Use rubber pistontools boot. to It avoid damaging critical parts. keeps moisture and dirt out of theAlso, calidon't ignore theboot rubber piston boot. It per bore. If the is torn, water and keeps moisture dirt out of the calidirt will ruin theand caliper quickly, parper bore.onIf athe boot ticularly road car.is torn, water and dirt will ruin the quickly, Before installingcaliper calipers on a parcar, ticularly onthey a road make sure arecar. perfectly clean and Before calipers on isa parcar, free of dirtinstalling and corrosion . This make sure they are perfectly clean and ticularly important on sliding calipers. free of are dirtcontacting and corrosion. parThere partsThis that ismust ticularly important on sliding slide while under load. Thesecalipers. sliding
There are contacting parts that must slide while under load. These sliding
surfaces should be cleaned and lubricated with high-temperature brake surfaces be friction cleanedand andresist lugrease to should minimize bricated with high-temperature brake corrosion. Your shop manual will progrease to minimize friction and resist vide specific instructions . corrosion. Your shop manual proCaliper-mounting bolts will typical ly vide instructions. are specific high-strength and should be Caliper-mounting torqued to specificationbolts using atypically torque are high-strength and shouldbolts be wrench . If the caliper-mounting torqued to specification using a torque loosen, serious problems can result. wrench. there caliper-mounting So, makeIf su the correct boltsbolts are loosen, serious can result. used, they are inproblems good condition, and So, sure the correct are they make are torqued to the value bolts specified used, they are in good condition, and in the shop manual.
they are torqued to the value specified in the shop manual. LINING REPLACEMENT
The most frequent brake job is LINING REPLACEMENT replacing friction material. Before The most frequent brake job for is starting thi s job, check the brakes replacing friction material. Before roughness by driving the car at highstarting this ajob, brakes th fore way speed nd check lightly the applying roughness by driving the car at highbrakes. If the brakes shudder or the way speed and lightly the applying the pedal pulsates , repeat test using brakes. If the brakes shudder or the parking brak e -if the brakes the are pedal repeat thepresence test using on thepulsates, rear whee ls . The or the parking brake-ifwill the are absence of shudder tell brakes you which on the wheels. The . presence or pair of rear brakes is rough Be careful absence of shudder will tell you which while apply ing the rear brakes. pair of rear brakes is rough. Becar careful Locked brakes make the very while applying the rear brakes. unstable . Always have the release Lockedorrear brakes make the button handle activated so car you very can unstable. Always have the release release the parking brake quickly. button handle activated so you can Whenorreplacing linings, you should release the parking brake quickly. also inspect the rotor or drum surfaces linings, should andWhen otherreplacing brake parts, andyou check for also inspect the rotor or drum surfaces sea l leakage. and other brake parts, and disc-brake check for Pad Replacement-Most
seal leakage. Pad Replacement -Most
disc- brake 131
Rotor is being surfaced with tool mounted on car. Rotor can be rotated by engine with this front-wheel-drive car. Tool machines both sides of rotor simultaneously, ensuring that surfaces be parallel. Rotors be on surfaced on car andengine done on a speRotor will is being surfaced with that tool cannot mounted car. Rotor canare beremoved rotated by with this ciallathe. front-wheel-drive car. Tool machines both sides of rotor simultaneously, ensuring that sur-
faces will be parallel. Rotors that cannot be surfaced on car are removed and done on a special lathe.
pads are easy to change. They can be removed on many cars simply by pads are easy to change. They removing a wheel, pulling a can pin be or removeddevice on many cars simply by locking , and sliding the pads removing a wheel, a pinonly or Sometimes thispulling job takes out. locking device, and sliding the pads about fiv e minutes per wheel. The out. Sometimes this job takes only only effort required is pushing the about five into minutes per wheel. The piston back the caliper cylinder so only effort required is pushing the the new thicker pad can be inserted piston back the caliper cylinder so between theinto piston and rotor. Your the new thicker inserted shop manual will pad tell can you be how to do between the piston rotor. Your not to and damage a piston this. Be careful shop manual will tell you how to do by prying on it. this. Be careful not to damage a piston With the pads out, inspect the rotor by prying on it.for cracks or scoring. Check face. With the pads out, inspect the rotor but Minor imperfections are OK, face. Check for cracks or scoring. large imperfections must be machined Minor imperfections arebe OK, but out. Rotors usually must removed large must berotors machined to do imperfections this. Take damaged to a out. Rotorsbrake usually must removed reputable shop for be resurfacing. to do this. Take damaged rotors If you resurface one rotor, do tothea reputabletobrake for resurfacing. same theshopopposite rotor. If you resurface one may rotor,pull dountil the the brakes Otherwise, same to surfaced the opposite rotor is rotor. worn the newly Otherwise, the brakes may pull until smooth. theAnnewly rotor that is worn easily surfaced made mistake can smooth. when replacing disc-brake pads occur can is An thateasily manymade pads mistake can be that installed occur when replacing disc-brake pads backward. Although it seems is that many canfriction be installed obvious, make pads sure the matebackward. it rotor. seems rial is installedAlthough so it faces the If obvious, the friction mateyou put amake pad insure backward, the brakes rial is installed so it faces If won't work correctly andthe therotor. rotor you put a pad in backward, the brakes will be destroyed. won't correctly and pistons the rotor Whenwork retracting caliper to
will be destroyed. When retracting caliper pistons to 132
install the new pads, make sure the fluid reservoir isn't full. Otherwise, install thespill neworpads, surevent. the fluid will squirtmake out the fluid will reservoir isn'tYou full.may Otherwise, This be messy. find out fluid will glycol-based spill or squirt outworks the vent. how well fluid as a This will be messy. You may out paint remover. A void this by find opening how well glycol-based fluid works as the bleeder on the caliper before re-a paint remover. AvoidFluid this by opening come tracting the piston. will the bleeder on the caliper before reout the bleeder rather than being' tracting the piston. Fluid will come pushed back to the reservoir. Run a out than tobeing' hose the into ableeder jar fromrather the bleeder prepushed back onto to the Run a vent spillage the reservoir. floor. hose a jar from bleeder to preAs into a policy, mostthe brake shops survent spillage onto the floor. face rotors whenever pads are As a policy, most brake shops surreplaced . This results in good braking face rotors whenever are is done pads properly. if surfacing replaced. This results in good braking However, many times the job may not if surfacingTo is done this, properly. be required. determine careHowever, manythetimes the job not fully inspect rotors for may damage be required. and runout. To determine this, carefully the cars, rotorstheforpads damage On inspect most road wear and runout. out long before any rotor work is On most roadsurface cars, the pads wear needed , Small scratches and out long before any are rotor workpreis scores of little concern always needed. Small surface scratches and sent on a used rotor. And shops with scores little concern arecan always poorly of maintained lathes ruin prepersent a used rotor.orAnd shops witha drums . As fectlyongood rotors poorly, maintained lathes can ruin perresult avoid machining unless the fectly good rotors or drums. parts are scored heavily or As youra result, machining unless the brakes avoid are rough. Roughness is parts scoredrunout heavily or your caused are by rotor or thickness brakes are Roughness is variation, and rough. drum runout or ovality. caused by rotor runout or thickness Consult your factory manual for variation, and drum runout or ovality. specific information. Consult your factory manual discfor Since 1971, all U.S.-made
specific information. Since 1971, all US.-made disc-
Checking rotor runout is done with dial indicator clamped to a jack stand. Runout of 0.005 in. isrotor considered upper most Checking runout is donelimit withfor dial incars. dicator clamped to a jack stand. Runout of
0.005 in. is considered upper limit for most cars.
brake rotors have a dimension cast into them. This is the minimum-wear brake rotors have acalled dimension cast thickness, sometimes the discard minimum-wear into them. This is the thickness. A rotor is considered unsafe thickness, sometimes called discard if it's machined thinner. So, the never use is considered athickness. rotor thatAisrotor machined to or lessunsafe than if machined thinner.discard So, never theit'sdiscard thicknessit! use aRotor rotor Runout-Rotor that is machined runout-wobto or less than discard it! the discard bling of thethicknessrotor friction surface-is Rotor critical,Runout-Rotor particularly on runout-woba race car. It bling of be the checked rotor friction should everysurface-is time the critical, particularly on a race It brakes are serviced. Runout can car. cause should every timepedal, the roughness in the vibrationbeorchecked brakes are serviced. Runout can direct cause excess pedal travel, or can even vibration or roughness in the pedal, air into the caliper past the seals. excess travel, or can even direct Rotorpedal runout is usually caused by air into the caliper the seals. overheating. You past can expect it if you is usually hard. caused by It can useRotor your runout brakes extremely overheating. You can expect it if you also be caused by overtorquing the use your brakes extremely hard. repair It can wheel-mounting nuts. Many also by wrench overtorquing the shopsbe usecaused an impact to tighten wheel-mounting repair wheels. Don't letnuts. them Many use one on shops use impact wrench to tighten your car. anUsed incorrectly, impact wheels. them usetorque one on wrenchesDon't apply letexcessive to your car. lugs, Used possibly incorrectly, impact the wheel warping the wrenches apply flange. excessive torque to rotor-mounting theCheck wheelrotor lugs,runout possiblywith warping the the rotor rotor-mounting flange. mounted on the car. Before checking, Check runoutbearings with thearerotor make surerotor the wheel admounted on the preload. car. Before justed to proper Setchecking, up a dial make suresotheitswheel square are to adthe indicator tip isbearings justed to proper preload. Set up a dial rotor surface near the outer edge of indicator its tip Make is square the frictionsosurface. sure to the the tip rotor surface near the outer edge of is on the friction surface. theTurn friction surface. Makeyou sure the the tip the rotor until find is on the friction surface. minimum indicated reading on the Turn the rotor untila grease you find the indicator. Mark it with pencil,
minimum indicated reading on the indicator. Mark it with a grease pencil,
Special puller is designed to remove brake drums. Thin jaws grasp back of drum. Handle is then turned carefully by hand-not with a wrench lever. Excess force will break ordrums. distortThin drum or puller. Special or puller is designed to remove brake jaws grasp Tapping drum lightly a plastic mallet is OKbytohand-not assist removing back of drum. Handlewith is then turned carefully with a a stubborn drum. Excess force will break or distort drum or puller. wrench or lever. Tapping drum lightly with a plastic mallet is OK to assist removing blueing, or masking tape. each side. Never cut amachinist stubborn drum.
Zero the indicator dial. Now, turn the machinist blueing, or masking tape. rotor and find the maximum reading. Zero the indicator dial. Now, turn the This is called total indicated runout rotor and find the maximum reading. (TIR), or simply runouf. Mark it, too. This called total indicated runout runout Theistolerance for maximum runout. it, too. (TIR), or should be simply specified in theMark factory shop The tolerance for maximum runout manual. If not, make sure the runout should be specified is less than 0.005 in. in the factory shop manual. not, make the runout can sure be reduced by Rotor Ifrunout is less than 0.005 in. one of two methods-resurface the Rotoror runout by rotor shim itcanat beits reduced mounting. one of two should methods-resurface the Resurfacing be used if the rotor or shim isit scored at its or mounting. rotor surface deeply Resurfacing should be used if the scratched. If the rotor surface is rotor surface is scored or deeply smooth, shimming can be used. scratched. If the rotor surface is Before shimming a rotor, make smooth, shimming cancaused be used.by outsure wobble is not Before shimming a is rotor, make of-parallel surfaces. This commonly sure wobble is not caused by outcalled thickness variation. Measure of-parallel surfaces. is commonly rotor thickness withThis a micrometer at variation. Measure called the highthickness and low spots you found with rotor thickness withThe a micrometer at the dial indicator. rotor should the high and low spots you found with have a constant thickness at all points. thethedialwobble indicator. The rotor should If was caused by varying have a constant thickness at all points. thickness, the rotor must be surfaced. If On the road wobble was caused by varying cars, thickness variation is thickness, the rotor surfaced, the biggest causemust ofbe disc-brake On road cars, thickness variation is roughness. Maximum thickness variathe biggest cause of disc-brake tion on new rotors is 0.0005 in. If a roughness. Maximum variarotor has 0.0010 in. or thickness more variation, tion new rotors is roughness 0.0005 in. and If a it willonprobably cause rotor has 0.0010 in.ororreplaced. more variation, must be machined Rotors it will be probably roughness must turned cause on a lathe with and two must be machined or replaced. Rotors cutting tools simultaneously-one on
must be turned on a lathe with two cutting tools simultaneously-one on
Brake-spring-removal tool is a must when working on brakes. Bloody fingers or damaged springs can result from pry bars or screwdrivers-springs be dangerous. Brake-spring-removal tool is a can must when working on brakes. Bloody fingers or damaged springs can result from pry bars or screwdrivers-springs can be dangerous.
rotors one side at a time. This will cause thickness each side. Never rotorsrotors one side at variation. Most cut racing with aremovable time. This will cause thickness hats can be ground using a variation. grinder. Most racing rotors with Blanchard removable can will be ground Shimminghats a rotor work if:using a Blanchard • Rotor is grinder. flat and mounted on a tilt. Shimming rotoronwill if: You can see athis thework indicator. A Rotor is flat tilt. tilted rotor has and one mounted high spot on anda one You can see this 180 on 0 the indicator. A low spot exactly apart. Multiple tilted rotor has one high spot and one high and low spots on a rotor require low spot exactly 180" apart. Multiple machining. high and low spots ontoa rotor require • Rotor is bolted a machined machining. surface. Some rotors are riveted on or is bolted a machined areRotor integral with theto wheel-bearing surface. Some rotors are riveted on or housing or axle. Such rotors cannot are integral with the wheel-bearing be shimmed. housing or aaxle. Such To shim rotor, yourotors must cannot deterbe shimmed. mine the location of the high and low To shim must already deterspots. Youa rotor, shouldyouhave mine thethe location of the high and low marked two spots. Roughly calcuspots. already late the You shim should thicknesshave required to marked thethetwo spots. Roughly calcurotor. straighten late the should shim thickness required to Shims be made from steel or straighten rotor. available in hardbrass shimthestock, Shims should made from steel or ware stores in be various thicknesses. brass shim stock, available in Make sure you buy O.OOl-in. or hardthinwarematerial. stores Otherwise, in various you thicknesses. ner may not Make sure buy the 0.001-in. be able to you adjust rotor or in thinfine ner material. Otherwise, you may not enough increments. beSpecial able totapered adjust the in fine rotorrotor shims are enough increments. available for Corvette rotors from Special Steel taperedBrakes rotor Corp. shims This are Stainless available for Corvette rotors from shim was developed to allow adjustStainless Steel which Brakesare Corp. This ment of rotors, made as an
shim was developed to allow adjustment of rotors, which are made as an
drum using drum using
assembly with the mating part. Normally, Corvette rotors cannot be assembly with the mating part. shimmed. Normally, Corvette be If you put shims rotors only atcannot the low shimmed. spot, shim thickness should be about If you putofshims at the low one-fourth total only runout. Install spot, shimonthickness should be about shim (s) the proper bolt. Place one-fourth of total runout. Install shims one-eighth of total runout on shim(s) on the proper bolt. the two adjacent bolts. Install Place rotor shimstorque one-eighth runout on and boltsof tototal specification. the two adjacent bolts. Install rotor Remeasure rotor runout and adjust and torque bolts to specification. shim thickness as needed. More than Remeasure rotor runout and adjust one try may be required. shim thickness as needed. than Don't worry about runoutMore less than one try may be required. 0.002 in. It's all but impossible to Don't worryzero. aboutAnd, runout less than make runout surprisingly, in. It's of all runout but impossible to can actually a0.002 tiny amount make runout zero. And,thesurprisingly, help braking! It keeps pads from a tiny amountrubbing of runout canrotor actually continuously on the surhelp braking! It keeps the pads from face by pushing them back a small continuously amount from rubbing the rotor.on the rotor surface by pushingReplacement-To them back a small Brake-Lining reamount from the rotor. place drum-brake shoes, you must Brake-Lining refirst remove theReplacement-To drum. Some drums place drum-brake you ismust come off easily aftershoes, the wheel refirst remove the are drum. Somedifficult. drums moved-others more come off easily after the wheel is reYou may have to use a special puller moved-others are more difficult. to remove a stubborn brake drum. You maythe have to useshop a special puller Consult factory manual for to remove a stubborn brake specific instructions before youdrum. start Consult the factory shop manual for working. specific youeasily start If the instructions drum shouldbefore come off working. but doesn't, don't use a prybar beIf thethedrum come off easily tween drumshould and backing plate. If don't use a prybar bebut doesn't, you pry against the backing plate,
tween the drum and backing plate. If you pry against the backing plate, 133
Parking brake is at output shaft of transmission on this front-engine, rear-drive car. Brake adjustment compensates for Parking brake is at output shaft of translining wear. brakes rear-drive are rarely mission on Such this parking front-engine, foundBrake on late-model cars. compensates for car. adjustment Installing brake springs requires same tool used to remove them. End of tool is simply hooked over anchor pin and spring is popped on. Doing this any other way invites injury to yourself the springs. Installingand brake springs requires same tool used to remove them. End of tool is simply
hooked over anchor pin and spring is popped on. Doing this any other way invites injury to yourself and the springs.
Lubricate the shoes with a dab of high-temperature brake grease where Lubricate a dab they rub on the the shoes backingwith plate and of at high-temperature brake grease where . pivots. Always use brake grease, not they ruboronwheel-bearing the backing plate and Be at chassis grease. . careful pivots. Always useabsolute brake grease, not to use an minimum chassis or wheel-bearing grease. Be amount of grease. It's critical that you careful to use an absolute minimum keep grease off the linings. amount of grease. It's critical that you Assembly-Drum-brake assembly is keep grease off linings. Installing the opposite of the disassembly. Assembly-Drum-brake is the automatic adjuster andassembly putting the the opposite of disassembly. Installing brake springs on are the only tricky the automatic adjuster the parts. Here, you must and use putting the special brake areinstallation the only .tricky brake springs tool for on safe The parts. Here, you must special springs sometimes canuse be the mixed up brake tool for safe installation. The and installed in the wrong place. springs be mixed up Refer tosometimes the shop can manual and your and installed in notes the wrong place. sketch, photos or to be sure. If Refer to the adjuster shop manual and operyour an automatic was used, sketch, photos ortonotes to beitsure. If ate it manually be sure works an automatic adjuster wasthe used, operproperly before installing drum. ateToit install manually to be you suremay it works the drum, have properly before installing the drum. to run in the adjuster to allow the To install drum, have drum to fitthe over the you newmay linings. to run run in the allow necthe Don't it adjuster in moreto than drum to fit enough over the newthelinings. essary-just to get drum Don't run goit too in far, more than necon. If you you'll have to essary-just enough to get the drum adjust the shoes back out from under on. If you go too far, you'll have to the car. adjust shoes backare outon,from Oncethe both drums you under must the car. adjust their clearances before driving on, automatic you must theOnce car. both Evendrums brakesarewith adjust theirmust clearances driving adjusters be set before close or they the car. Even brakes automatic won't work . Your shop with manual will inadjusters must be set close or they dicate the correct procedure.
won't work. Your shop manual will indicate the correct procedure.
PARKING-BRAKE-LINKAGE SERVICING PARKING-BRAKE-LINKAGE Usually, a parking brake requires SERVICING little servicing. All that's needed is an Usually, greasing a parking brake requires occasional of the linkage. On little All that's needed parkis an some servicing. cars, however, a separate occasional of the linkage. On ing brake greasing needs adjusting or other some cars, however, a separate parkserVICIng. Others have a parking ing brake needs adjusting or other brake on the drive shaft. Typically, servicing. Others drum have brake, a parking this is a simple often brake an on external-band the drive shaft. Typically, with drum brake this is to a wheel simplebrakes drumused brake, often similar on an anwith an external-band drum brake tique car. The shop manual should similar wheel brakes used onforan seranprovidetospecific instructions tique car. The shop manual should vicing this type of brake . provide specific serParkingbrake instructions linkages are for adjustvicing this type ofgenerally brake. this is not able , although Parking-brake linkages required . However, if are the adjustcable able, although generally this is not stretches, you may have to adjust it. required. the cable Do not use However, the "MickeyifMouse©" Ustretches, you adjuster. may haveIt to bolt-type slack canadjust breakit.a D o notInstead, use the "Mickey Mouse@" buy a new cable ifUit cable. bolt-type slacktoo adjuster. It can breakora has stretched far to be adjusted cable. Instead, a new And, cable only if it if it has brokenbuy strands. has stretched toobrake far to after be adjusted or the wheel adjust a parking if it has strands. And, only brakes are broken operating perfectly. the wheel adjust brake affer. One aofparking the biggest problems with brakes are operating perfectly. parking brakes on cars driven in One of problems with winter salttheis biggest cable corrosion and parking brakes carscandriven in sticking. A stuck on cable burn up winter salt is cable corrosion and brakes because it won't release , or sticking. stuck cable burn up makes theA parking brakecanimpossible brakes it won't release, or to apply.because If you have a sticking cable, makes parking brake impossible replace the it. Don't bother with lubricatto you havecables a sticking cable, ingapply. them. IfEnclosed are difficult
replace it. Don't bother with lubricating them. Enclosed cables are difficult
lining wear. Such parking brakes are rarely found on late-model cars.
to lubricate and will probably stick again anyway. to Some lubricate willfour-wheel probably stick cars and with disc again anyway. brakes have a drum brake inside the Some cars four-wheel disc rear-wheel discwith brakes as a parking brakes have is a drum brake the adjusted andinside serviced brake. This rear-wheel disc brakes as a parking the same as a normal drum brake.
brake. This is adjusted and serviced the same &asLINKAGE a normal drum brake. PEDAL MAINTENANCE
PEDAL Except& LINKAGE for periodic inspection, MAINTENANCE lubrication is about all a brake pedal Except periodic inspection, and linkage for needs. Make sure there is lubrication is about all system. a brakeExampedal no slop or failure of the and linkage needs. Make sure there ine the pedal pads and replace them is if nthey o slop failure of or thecoming system.apart. Examareorworn slick A ine pedal pads replace if off aand pedal canthem be as footthe slipping they are worn coming apart. A dangerous as a slick brakeorfailure. foot o.ff acan pedal can be for as Theslipping brake pedal be adjusted dangerous as a brake failure. free play. A brake pedal has a lot less Theplay brake pedal can adjusted for free than a c1u tchbepedal. There brakea pedal a lot less free play.beA only should slighthas amount of free than a between clutch pedal. There pedalplay movement its fully reshould be only and a slight amount of tracted position the beginning of pedal movement between movement. its fully remaster-cylinder-piston tracted position and manual the beginning of Consult your shop for exact master-cylinder-piston movement. specifications. Usually) free play Consult your shop manualunless for exact never needs adjusting, the specifications. Usually, free . play master cylinder has been replaced never needs adjusting, unless the master cylinder has been replaced. BRAKE-BOOSTER CHECK If
power
brakes
are
causing
BRAKE-BOOSTER problems , first checkCHECK the hydraulic If power system . This brakes includes are the causing master problems, first check the hydraulic cylinder and wheel cylinders. If the system. This includes theproperly, master system operates basic brake cylinder wheel cylinders. If the check theand booster. basic system operates properly, Thebrake following trouble-shooting check the booster. procedure is for a vacuum booster: The following trouble-shooting procedure is for a vacuum booster: 135
disassembled correctly. Often, a pressure of 1500 psi is involved. There's also a very strong spring behind itl If you don't have the proper instructions, leave the unit alone. Take the car to a mechanic knowledgeable of your type of car.
NOISY BRAKES
C~C Disc Brake Quiet compound is applied to backside of brake pads to reduce brake nOise. CRC r~commends uSing compound on outboard pads. They can be reassembled on the carDisc following 1 O-minute curing is time. Photo CRC Chemicals. CRC BrakeaQuiet compound applied tocourtesy backside of brake pads to reduce brake
noise. CRC recommends using compound on outboard pads. They can be reassembled on the car following a 10-minute curing time. Photo courtesy CRC Chemicals.
• With the engine off, press the brake pedal several times. This bleeds off all the engine pressand thethe brake theWith vacuum in the off, booster repedal several sulting power times. assist. This bleeds off all the vacuum in on the the booster theand re• Press lightly brakeand pedal sulting power assist. start the engine. The pedal should Press lightlyunder on theyour brakefoot pedal drop slightly if and the start theis working engine. properly. The pedal should booster If there is drop slightly under your if the no drop, the booster is notfoot working. booster isthe working properly. If there is Without booster, pedal effort will no drop, the booster is not working. be much higher than normal. Without booster, effortmake will • Before the replacing thepedal booster, be much sure it's higher getting than the normal. correct supply of Before Check replacing booster, make vacuum. all the vacuum lines for sure it's getting the correct supply of leaks and kinks. A vacuum leak often vacuum.like Check lines for sounds a hissallasvacuum the engine idles. leaks and kinks. A vacuum leak with oftena Check intake-manifold vacuum sounds like a hiss as the engine vacuum gage and compare it toidles. the Check specs intake-manifold in your shop vacuum manual. with Poora vacuum vacuum gage andmay compare to the engine mean it burned specs in your shop manual. Poor valves, hose or intake-manifoldengine vacuum may mean burned gasket leak or some other engine valves, problems.hose or intake-manifoldgasket or supply some isother engine • If the leak vacuum OK, correct problems. the booster. Most boosters are reIf therather vacuum supply is OK, correct than overhauled due to placed the Most boosters are retheir booster. low cost and critical construction. placed overhauled duethe to • Makerather a finalthan check, if you found their low cost and critical construction. vacuum booster to be at fault. A Make a final if you found the common causecheck, of vacuum-booster vacuum isbooster to be at fault. A failure automatic-transmissioncommon of vacuum-booster modulator cause failure. This allows failure is automatic-transmissionautomatic-transmission fluid (ATF)
modulator failure. This allows automatic-transmission fluid (ATF)
136
to be drawn into the engine and, subsequently, the vacuum booster. to be ATF drawn attacks into the the engine and, The booster subsequently, the vacuum booster. diaphragm, causing it to fail The ATF Transmission-modulator attacks the booster eventually. diaphragm, it toin the fail failure shows causing up as fluid eventually. Transmission-modulator vacuum hose from the manifold to failure shows white up assmoke fluid out in the the the booster, vacuum the manifold to exhaust, hose or a from malfunctioning transo the booster, white smoke out the mission . Replace the modulator if it is exhaust, at fault. or a malfunctioning trans: is mission. Replace booster the modulator If a hydraulic is used,if itthe at fault. troubleshooting process is similar : If a hydraulic booster used, the • With the engine off, ispump the troubleshooting process is similar: brake several times to bleed off all hyWith pressure the engine pump the draulic in the off, accumulator. brake several times to bleed hy• Push on the brake pedal off andallstart draulic pressure in the accumulator. the engine. The pedal should drop Pushyour on foot, the brake pedal and start under usually followed by a the engine. should slight surge. The This pedal confirms thatdrop the under your foot, usually followed by a booster is working. slight This confirms that test, the • If thesurge. booster doesn't pass this boosterthe is working. check power-steering pump. ConIf the test, sult yourbooster shop doesn't manualpass for this specific check the power-steering pump. Conchecks. A slipping belt or low powersult your shop for specific steering fluid maymanual be the cause. checks. A slipping belt or low • If there's pressure from the powerpowersteering fluid may consult be the cause. steering pump, your shop If there's fromonthe powermanual for pressure instructions servicing steering pump, consult your your booster. Be sure to read theshop inmanual for carefully. instructions on servicing structions High pressure your booster. Be sure to read instored in an accumulator can the be exstructions carefully. High pressure tremely dangerous if the unit is not
stored in an accumulator can be extremely dangerous if the unit is not
Disc-brake squeal can be very annoying on a road car, particularly if the rest of the car is quiet-running. Usually, squeal is caused by vibration of the front brake pads against the rotor. Some manufacturers use anti01 tne rront paas devices against detne squeal shims DraKe or other rotor. Some manufacturers use antisigned to damp these vibrations. squeal deWhen ashims car or getsother old, devices anti-squeal signed to damp vibrations. devices can becomethese ineffective. ReWhen a car placement of gets parts old, may anti-squeal eliminate devices can become ineffective. Renoise. Consult your factory shop placement of maintenance. parts may eliminate manual for this noise. Consult linings your factory High-friction tend toshop be manual for this maintenance. noisier than low-friction linings. And, High-friction linings linings generally tend to are be asbestos-filled noisier than linings. And, quieter than low-friction those without asbestos. asbestos-filled linings are This is the main reasongenerally why manuquieter than those without asbestos. facturers have taken so long to develThis is the mainlinings. reason why manuop asbestos-free facturers have taken socompounds long to develThere are anti-noise deop asbestos-free linings. signed to be applied the pad backing There are anti-noise plate as shown at left. compounds One of thesedeis signed to be applied pad Quiet. backing CRC Chemicals' Discthe Brake It plate as shown left. One of these is is a thick paste, atsimilar in appearance CRC Chemicals' Disc Brake It to RTV sealer or bathtub calkQuiet. . When is a thick paste, similar in appearance correctly applied, it can quiet squealto RTV sealer orBefore bathtub calk. ing disc brakes. using thisWhen type correctly applied, canthe quiet squealof material, make itsure brakes are ing disc usingcondition. this type clean andbrakes. in goodBefore operating of material, surebythe brakesmalare Noise can bemake caused serious clean and or in wear good in operating functions a brake. condition. Noise can be caused serious malSanding lining and byrotor surfaces functions or wear in a brake. will quiet noise temporarily. Usually , lining rotor surfaces theSanding ends of the and linings vibrate, so will quietchamfers noise temporarily. Usually, grinding on the leading and the endslining of the linings so trailing edges will vibrate, sometimes grinding chamfers on the leading and eliminate noise. trailing lining edges willassometimes If drum brakes squeak you apply eliminate noise. and release the pedal, it's probably brakes you apply theIf drum edge of the squeak shoes as rubbing the and release the pedal, it's backing-plate shoe ledges. probably Apply a the of high-temperature the shoes rubbingbrake the thin edge film of backing-plate shoeledges ledges. Applythea grease to the shoe to quiet thin of high-temperature brake noise film . Be careful not to get grease on grease to the shoe ledges to quiet the the lining. noise. Be iscareful not to get for grease on There no sure cure brake the lining. noise. If one existed, the manufactursure ersThere would is be no using it. cure for brake
noise. If one existed, the manufacturers would be using it.
Modifications
12
Grand Prix cars have some of the best-designed brakes. Mechanics modify brakes to suit course and temperature conditions on race day. Lightest brakes that work are used to avoid excess weight. Smallest-possible cooling scoops are used to reduce aerodynamic drag. As with engines in highly-competitive racing, brakes must be pushed to their performance or youand don't win! Grand Prlx cars have some of the best-designed brakes. Mechanics modify brakes to limits, suit course temperature conditions on race day.
Lightest brakes that work are used to avoid excess weight. Smallest-possible cooling scoops are used to reduce aerodynamic drag. AS with in highly-competitive racing, brakes must be pushed to their performance limits, or you don't win! If engines your brake system is not working
as desired, consider modifying it for If yourperformance brake system or is notreliability. working better as desired, consider modifying it for Modifications are often the result of better performance or reliability. testing, either on the road or the Modifications are don't often the resultany of track. However, attempt testing, either onyou: the road or the modification until track. However, don'ttheattempt brakes any so • Inspect and repair modification until you: they operate properly. Inspect repair brakes so • Test the and brakes and the record the rethey operate properly. know what aspects of sults so you'll Testperformance the brakes need and improving. record the retheir sults so you'll know what aspectsthe of • Analyze your car to determine their performance need improving. forces and pressures in the brake Analyze your the system. Also, testcar thetocardetermine to determine forces and pressures in the brake brake temperatures. You may have system. test the car to determine done thisAlso, already. brake You may before have The temperatures. first step is necessary done can this already. you justify spending time and The first step is necessary money on modifications. Mostbefore new you can justify spending and cars have well-engineeredtime brakes. money will on modifications. new They work fine ifMost properly cars have well-engineered maintained. However, jf the brakes. car is
They will work fine if properly maintained. However, if the car is
./ Numerous components are available to help improve a brake system. Trick is learning how to I choose and apply them. Some products available from AP Racing include: steel-braided I hoses, various size master vacuum boosters, and fluid reservoirs. courtesy Numerous components arecylinders, available to help improve a brake system. Trick Photo is learning how Racing.and apply them. Some products available from AP Racing include: steel-braided tAP o choose
hoses, various size master cylinders, vacuum boosters, and fluid reservoirs. Photo courtesy AP Racing. 137
Before you begin modifying a car's existing brakes, first make sure they are in top condition and test them. Modification may be unnecessary. Don't fix something that doesn't need fixing. race track is ideal for testing. BeforeAyou begin modifying a car's existing brakes, first make sure they are in top condition and test them. Modification may be unnecessary. Don't fix something that doesn't need fixing. A race track is ideal for testing.
driven beyond its design limits or if it is highly modified to different driven beyond its if it specifications, thedesign brakeslimits may orneed is highly modified to different modifying. specifications, brakes may To do an theintelligent jobneed of modifying. first identify what needs modification, To do The an next intelligent job out of modifying. step is to find modification, first identify what needs exactly what's wrong with brake modifying. T h e next step is list to findthese out performance. If you exactly with tobrake problems,what's you arewrong less likely lose performance. If you list these track of them during the modification problems, you are less likely to lose process. track of them during the modification Be specific when listing the process. problems. Don't just say, "The Be are specific listing say the brakes lousy."when For example, problems. Don't just say, "The "The brakes fade after two stops from brakes are lousy." For example, say 100 mph," or "Temperature reaches "The brakes two stops 600F after fade threeafter stops from from 100 100 mph," or "Temperature reaches mph." The more specific you are, the 600F after three stops from 100 easier, cheaper and more effective mph." T h e more you are, the modifications will specific be. easier, cheaper and inmore effective Use the formulas Chapter 9 to modifications will be. calculate internal brake-system forces the formulas to andUse pressures. These in canChapter be found9 by calculate internalif brake-system measurement, you prefer. forces You and These canhow be found by mustpressures. understand clearly and why measurement, if you prefer. You you're modifying the brakes before mustcan understand clearly Temperatures how and why you do it properly. you're the brakes before must modifying be measured by testing you can d o i t properly. Temperatures modifications, including cooling must be measured by testing changes. modifications, including cooling Following are some brake modificachanges. tions and objectives to consider: are s obrakes m e brake • Following Install bigger to modificaincrease tions and objectives to consider: brake torque and reduce brake Install bigger brakes to increase temperatures. brake torque and reduce brake • Improve cooling. temperatures. • Eliminate fade. Improvepedal cooling. effort. • Reduce Eliminate fade. life. • Increase lining pedal effort. Add brakebalance-adjustmen t • Reduce Increase lining life. features. Add brake-balance-adjustment deflections. • Reduce
features.
Reduce 138
deflections.
• Improve stability.
ImproveBRAKES stability. BIGGER Bigger brakes almost always imBIGGER BRAKES prove brake performance. The addiBigger brakes always imtional weight of a almost bigger disc or rotor prove brake performance. h e addireduces temperatures. If Tdrum or tional weight of aisbigger disc or pedal rotor rotor diameter increased, reduceswilltemperatures. If drum effort also be reduced. And, or if rotor diameter is increased, pedal swept area is increased, the linings effort willwillalso reduced. And, if probably wearbelonger. swept area is increased, the linings The disadvantage of bigger brakes probably will wear longer. is the adverse effects added weight T h e on disadvantage bigger brakes have accelerationof and handling. is t h e adverse effects added weight More weight slows acceleration. Addihave on acceleration and handling. tional rotating weight makes it even More weight slows acceleration. Addiworse. Also, added unsprung weight tional rotating weightdown makeswith i t even bouncing up and the worse. reduces Also, added unsprung weight wheels traction in bumpy corbouncing up accelerating and down orwith the ners and when braking wheels reduces traction in bumpy coron bumpy surfaces. So, don't install ners and when brakes accelerating the heaviest you or canbraking find. on bumpy So, the don't install Select brakesurfaces. size to suit performthe heaviest brakes ance needs of the car. you can find. Select brake Prix size to suitthe thebrakes performOn Grand cars, are ance needs of the sized closely to car. the performance of Grand Prixare cars,nothebigger brakesthan are theOncar. They sized closely to the performance of what's needed to do their job. On the car. are on n o brakes, bigger either than tracks thatThey are hard what's needed o their per job.rotor On bigger rotors or to twodcalipers tracks that are hard o n brakes, either are used. On tracks with less braking bigger rotors orbrake two weight calipersisper rotor requirements, reduced are used. Oncomponents. tracks with This less braking with lighter may be requirements, brake carrying things tooweight far is forreduced most with lighter components. This maywith be applications, but serious racers carrying things too far for most unrestricted funds do it to win in applications, but serious racers with tough competition. unrestricted do it application, to win in Regardless funds of the tough competition. always use the largest-diameter brakes Regardless of the application, possible. A large-diameter drum or always use the pedal largest-dic1n7eler rotor reduces effort and brakes makes possible. A large-diameter d r uelimim or braking easier. You can perhaps rotor reduces pedal effort and makes nate power assist by installing larger-
braking easier. You can perhaps eliminate power assist by installing larger-
Formula Ford brake is small, light and simple. It works great on a light race car with 110 HP. If allowed, bigger brakes may stop car faster, but lap times might be slower due to added weight. Always use a brake that's big enough, but not too big. Extra weight hurts in racing. brake that's big enough; but not -too big. Extra weight hurts in racing.
diameter brakes. Thicker rotors are not necessarily required when rotor diameter brakes. ThickerRemember: rotors are diameter is increased. not necessarily required when rotor Add brake weight only if required to diameter is increased. Remember: cure a severe cooling problem. If a Add brake only ifwell required to light, solid weight rotor cools enough, cure a use severe cooling problem. If a don't a heavier, vented rotor. light, solid rotortocools enough, When changing largerwell drums, condon't use a heavier, vented rotor. sider reducing weight by switching W h e n iron changing to larger drums, confrom to aluminum. Aluminum sider reducing weight by switching drums cool better than iron drums of from iron size. to aluminum. Aluminum the same And they are lighter. dThey r u m sare cool better than iron drums of well worth the expense. theSeparate same size. And they are lighter. cooling problems from They are well worth the expense. pedal-effort problems. If the brakes Separate cooling problems from have both high pedal effort and excespedal-effort problems. Ifthethe needed brakes sive temperatures, have bothare highobvious. pedal effort exceschanges Yourandcar will sive temperatures, the needed benefit from both larger-diameter and changes are obvious. Yourproblems. car will heavier brakes to cure both benefit from both larger-diameter and However, if pedal effort is the only heavier brakes t o cure bothrotors, problems. problem, stay with lighter caliHowever, if pedal effort is the only pers or drums. problem, stay with lighter rotors,larger caliIt's easy to predict the effect pers orordrums. rotor drum diameters will have on It's easy predict the effect larger pedal effort.to Because pedal effort is rotor or d r u m diameters will have on related directly to brake torque, use pedal effort. given Because pedal effort is the formulas in Chapter 9. Calrelated the directly to brake torque, use culate new brake torque and comtpare h e formulas in Chapter 9. Calit to thegiven old brake torque. The culate t h e new brake torque and comnew pedal effort will be the indirect pare of it to brake torque. The ratio thethe twoold numbers. Pedal effort new pedal effort with will increased be t h e indirect always decreases brake ratio of t h e two numbers. Pedal effort diameter. always decreasesrise withper increased brake Temperature stop can be diameter. calculated if you know the weight of per Because stop cantembe theTemperature old and new rise rotors. calculated if per you stop know the weight of perature rise is related directthe old and new rotors. Because tem1y to brake weight, doubling rotor or perature rise per stop reduce is related directdrum weight should temperaly to rise brake weight, doubling rotor or ture by one-half. The weight of an diron r u mdrum weight should temperaaffects the reduce temperature rise ture rise by T h e You weight an the same as one-half. rotor weight. canofpre-
iron d r u m affects the temperature rise t h e s a m e as rotor weight. You can pre-
Small caliper on solid disc works well on front of sprint car run on dirt. Photo courtesy AP Racing. Small caliper on solid disc works well on
front of sprint car run on dirt. Photo courtesy AP Racing.
dict how many stops from a certain speed it will take to reach a certain dict how many stopsthefrom a certain temperature from formula for speed it will rise, take page to reach certain temperature 11. Ita doesn't temperature from the formula for, indicate anything about cooling temperature rise, page 11. It doesn't however. indicate about cooling, is thing nearly unchanged with Cooling any however. brake-size changes. Improve cooling Cooling is nearly or unchanged with aerodynamic with air ducting brake-size changes. Improve cooling changes to the car. with air ducting or aerodynamic Installing Bigger Brakes - Finding changes to the for car. a road car can be a bigger brakes Installing Bigger Brakes-Finding problem . You may find a bolt-on conbigger brakes for a road car can be ifa size version that increases brake problem. You may find a bolt-on conyou have a popul ar performance car. version increases Or, you that may find biggerbrake brakessize on ifa you have a popular performance car. station wagon that will bol t on. Often Or, you may find bigger brakes on these brakes will have wider drums ora station bolt on.diameOften heavier wagon rotors, that but will sometimes these brakes willlarger. have Look widerfor drums or ter may also be largerheavier rotors, but sometimes diamedi ameter wheels to go with la rge rter may also be larger. Look for largerdiameter brakes. diameter wheels to manuals go with for largerBy studying shop difdiameter brakes. ferent model years for your car, you By discover studyingthat shopthemanuals for difmay brake-drum or ferent model yearsforfor your car, you rotor size is larger a certain year. If may discover discover that brake-drum you this the situation, go to ora rotor size is larger certainwhether year. If yardfor anda check dealer or junk you discover this situation, go the brake will bolt on. It may be to thata dealer yardofand the sizeororjunk design thecheck brake whether mountthe also brakechanged, will bolt eliminating on. It may be ing thethat inthe size or design of the brake mountterchange possibility. Another possiing changed, inis that someeliminating cars could the be orbilityalso terchangewith possibility. possidered optionalAnother heavy-duty bility is Sometimes that some cars be are orbrakes. thesecould brakes dered with optional heavy-duty larger. Study the parts books for brakes. Sometimes are options. Your dealerthese can brakes help with larger.Look Study for for the Police,parts Taxi,books or Heavy this. options. Yourin the dealer help with Duty listings partscan book . this. Police, Taxi, to or bigger Heavy On Look a raceforcar, changing
Dufy listings in the parts book. On a race car, changing to bigger
Porsche Can-Am car under hard braking: Because nose is so low to track surface, underbody airflow is blocked. Ducts route cooling air to brakes, page 141 .
Porsche Can-Am car under hard braking: Because nose is so low to track surface, underbody airflow is blocked. Ducts route cooling air to brakes, page 141.
brakes usually is easier than on a road car. First off, special brakes typically brakes is easier thanthey on genera road usedusually on a race car, and are car. Firstavailable off, special brakessizes. typically ally are in various The are used onpattern a race for car,aand they genermounting rotor is usually ally are available in variousit.sizes. The when ordering A rotor specified mounting pattern for a rotor is usually I-in. or so larger in diameter may specified it. A rotor accept thewhen same ordering caliper. Check with I-in. manufacturer or so larger or in diameter may the dealer before accept the same caliper. Check with assuming they will work. If you the manufacturer or either dealer the before change rotor thickness, caliassuming they work.or If to bewill changed the you linper will have change rotor thickness, either the calithinner. Companies ings machined per will have Tilton to be changed or the and linlike Hurst, Engineering ings machined thinner. Companies JFZ can help with either approach .
like Hurst, Tilton Engineering and JFZ can helpIMPROVEMENTS with either approach. COOLING
Modifications to improve cooling COOLING commonIMPROVEMENTS on race cars . Some road are Modifications to improve cooling cars can also benefit from cooling are common on but race your cars. Some improvements, choicesroad of cars cando also benefit from cooling what to are limited. improvements, but ways your to choices of There are several improve what do are limited. braketo cooling: several ways toto brakes. improve Add or are enlarge air ducts • There brake cooling: • Change or modify wheels for inAdd orairflow enlarge ducts to brakes. creased to air brakes. or modify inChange from solid towheels ventedfor rotors • Change creased airflow to brakes. on disc brakes. Change from solid to orvented rotors • Change to finned aluminum on disc brakes. drums. to mOdify finned dust or shields aluminum • Change Remove or on drums. disc brakes. Removebacking or modify dust on shields on • Vent plates drum disc brakes. brakes. Vent water-cooling backing plates on drum • Install system. brakes. • Change car-body aerodynamics for Install water-cooling system. increased airflow to brakes. aerodynamics AirChange Ducts -car-body The easiest and most for efincreased airflow to brakes. fective way to improve brake cooling
Air Ducts-The easiest and most effective way to improve brake cooling
Vented rotors in place of solid rotors will improve brake performance if temperatures are too inhigh. Scoops modified Vented rotors place of solidorrotors will ducting tried first . improveshould brakebeperformance if tempera-
tures are too high. Scoops or modified ducting should be tried first.
is to add air ducts . These start with scoops or holes in the body on most is to add airrace ducts. start with full-bodied cars.These On open-wheel scoops holescan in be thescoops body attached on most cars, theorducts full-bodied race cars. On open-wheel to the brakes, uprights or axle. cars, the ducts attached A brake duct can mustbebescoops designed careto thetobrakes, uprights or axle. fully get the most air for the least A brake must beThe designed amount of duct added drag. most carecritifully to get the most air for the localeast cal parts of a duct are its entrance amount of added drag. The most critition and where air exits the duct at the cal parts of aconstant-diameter duct are its entrance locabrakes . A tube to tion and air exits thebetween duct at the the carry thewhere air is often used brakes. A constant-diameter tube to duct entrance and exit. carry the air is often used between When installing a brake duct, the be duct and faces exit. forward and is sure entrance its entrance installing area. a brake in When a high-pressure Theduct, verticbe al
sure its entrance faces forward and is in a high-pressure area. The vertical 139
Dual master cylinders are used in place of stock tandem master cylinder on this dualpurpose car. Aftermarket spoiler has holes for brake-cooling ducts. High pressure exists in front of spoiler, making ideal spot for brake ducts. Spoiler without ducts adversely affects brake cooling. On a race car, tubes should be used to route air directly to brakes. Dual master cylinders are used in place of stock tandem master cylinder on this dualpurpose car. Aftermarket spoiler has holes for brake-cooling ducts. High pressure exists in front of spoiler, making ideal spot for brake ducts. Spoiler without ducts adversely affects brake cooling. On a race car, tubes should be used to route air directly to brakes.
This may help front-brake cooling, but not looks. Neat brake scoops under bumper or behind grille would do same job and not require cutting torch.
front surface of a car-body nose is always a high-pressure area. So is an This may help not air dam. A topfront-brake surface ofcooling, a body but is usulooks. brake scoopsarea, under bumper or ally aNeat low-pressure so avoid behind grille would do same job and not rethese areas unless you have quire cutting torch. aerodynamic-test data that shows otherwise. Almost any duct that profront a the car-body nose beis trudessurface forward of into air stream always high-pressure area, area. but So itisalso an comes aa high-pressure air dam. Adrag. top surface of a body is usuincreases A protruding duct will ally area,way so toavoid work;a itlow-pressure may be the only cool these areasHowever, unless try you have rear brakes. other ideas aerodynamic-test that shows before resorting to data a protruding scoop otherwise. any duct that profor the ductAlmost entrance. trudes forward into the engine-coolant air stream beA front-mounted comes but it also radiatora high-pressure is always in aarea, high-pressure duct duct will increases drag.into A protruding area. Tapping it with a brake work; it may be the only way to cool for the front brakes will not add drag, rear brakes. However, try other ideas before resorting to a protruding scoop for the duct entrance. A front-mounted engine-coolant radiator is always in a high-pressure area. Tapping into it with a brake duct for the front brakes will not add drag,
140
Brake ducts on McLaren Can-Am car are simple holes in body with tubes attached. Forward surfaces of sloping front fenders are in high-pressure areas.
but will reduce engine cooling known as a NACA duct, is often used slightly. Engine-induction plenums for rear-brake-duct entrance. If you on Can Am and sports-racing cars have a wind tunnel or do serious aerowith large overhead air scoops are dynamic track testing, you can find a Brake on McLaren Can-Am arebe simple holes in body with tubes attached. Forward alwaysducts at high pressure. Theycarcan suitable high-pressure area in which surfaces of sloping front fenders are in high-pressure areas. tapped for rear-brake cooling without to locate such a duct. A NACA duct increasing drag. Testing should be may flow some air in a mediumbut willcheck reduce engine cooling cooling known a NACA oftenmuch, used done to that reduced or pressureasarea, but itduct, won'tis flow slightly. for rear-brake-duct entrance. If plenum Engine-induction pressure does notplenums cause if any, in a low-pressure area. If you you on Can overheating Am and sports-racing have windattunnel engine or reduce cars top must aguess a spotorfordoa serious duct, ataeroleast overhead air scoops are with dynamic tracktest testing, speed,large respectively. try a wool-tuft first. you can find a always at high pressure. They can be suitable high-pressure in which Wool-Tuft Testing-A area wool-tuft test NACA Duct-A flush duct entrance, tapped for rear-brake cooling without increasing drag. Testing should be done to check that reduced cooling or plenum pressure does not cause engine overheating or reduce top speed, respectively. NACA Duct-A flush duct entrance,
to locate such a duct. A NACA duct may flow some air in a mediumpressure area, but it won't flow much, if any, in a low-pressure area. If you must guess at a spot for a duct, at least try a wool-tuft test first. Wool-Tuft Testing-A wool-tuft test
<8>= Possible High-Pressure Area 9= Possible Possible Medium-Pressure Area @= High-Pressure Area
(0= Low-Pressure Area @= Possible Possible Medium-Pressure Area
(&
High-pressure areas on car body exist atLow-Pressure nose leadingArea edge and base of windshield. Low Possible pressure always exists behind tail. Accurate wind-tunnel tests or pressure measurements must be used toareas find other areas suitable fornose ductleading entrances. High-pressure on car body exist at edge and base of windshield. Low
pressure always exists behind tail. Accurate wind-tunnel tests or pressure measurements must be used to find other areas suitable for duct entrances.
Cooling duct on March Indy Car maximizes airflow and minimizes drag. Rather than projecting intake airstream, Cooling ductduct on March lndyinto Car maximizes which would increase drag, advantage airflow and also minimizes drag. Rather than is taken of existing high-pressure area at projecting duct intake into airstream, front tire. Duct directs air fromadvantage intake at whichofwould also increase drag, front of tire, through high-pressure duct, and into area center is taken of existing at of suspension brake rotor. front of tire. Ductupright directsand air from intake at Photo bytire, Tomthrough Monroe.duct, and into center front of
of suspension upright and brake rotor. Photo by Tom Monroe.
Wool tufts are installed on car body before aerodynamic testing. Bits of yarn are taped in even rows. Assuming body is symmetrical, tufts on one side of car are sufficient.
Wool tufts are installed on car body before aerodynamic testing. Bits of yarn are taped in even rows. Assuming body is symmetrical, tufts on one side of car are sufficient.
requires driving the car. Tape short lengths of yarn-tufts-on the body a requires driving car. transparent Tape short apartthewith few inches lengths of yarn-tufts-on thecontrast body a tape. The yarn strips should few inches apart with transparent with the body color so you can see tape. .The stripsabout should5-in. contrast them Cut yarn the yarn long with tape the each bodypiece coloracross so you canwith see and the car them. yarn about 5-in. the tapeCut in the the middle. When thelong car and each piece across car awith motion, the yarn willthe form Uis intape the tapepointing in the middle. the car shape in the When direction of Uis in motion, yarn will formtoa the airflow. If the the flow is attached shape the directionyarn of body-itpointing is not in turbulent-the airflow. If the flow is attached to the will lie flat and straight with little body-it is not turbulent-the yarn wiggling. will lie the flat duct and straight withonlittle Place in an area the wiggling. most forward-facing surface where Place the ductisinindicated an area. on the smooth airflow If the most forward-facing surface where yarn points rearward and wiggles
smooth airflow is indicated. If the yarn points rearward and wiggles
slightly, such an area is a second choice. This is turbulent attached flow, slightly, such an area second and usually is found near isthea rear of a choice. is turbulent body. IfThis the yarn wiggles attachedflow, violently and and usually found near theis rear of a in all is directions, this separatpoints body. If the yarn wiggles violently ed air. It is low pressure and not and the points this is separatplace in foralladirections, duct entrance. You'll ed air. find It is separated low pressure andbehind not thea always airflow place for a duct You'll blunt entrance. protrusions, and body, behind always find separated airflow behind often, all over the tail end. Regardlessa body, blunt anda of the behind indicated flowprotrusions, , never install often, all over the tail end. Regardless duct entrance on any rearward-facing of the indicated surface, even ifflow, it is never only install slightlya duct entrance on any rearward-facing rearward-facing. surface, even if ittheis ducts, only slightly After installing retest rearward-facing. with wool tufts. Put tufts in and After the installing the entrance ducts, retest around brake-duct and with wool tufts. Put tufts in and check that air actually flows into the
around the brake-duct entrance and check that air actually flows into the
Brake ducts on Porsche Can-Am car use different designs at front and rear of body. Front direct airflow; rear Brakeducts ductsface on Porsche Can-Am carducts use use flush designs NACA-type ducts. different at front andEffectiveness rear of body. of rear ducts be confirmed by Front ducts faceshould direct airflow; rear ducts testing-pressure on top of body can't be use flush NACA-type ducts. Effectiveness determined by simple observation. of rear ducts should be confirmed by
testing-pressure on top of body can't be determined by simple observation.
opening . Some duct entrances have air coming out of them because presopening. entrances sure at theSome exit duct is higher than athave the air comingSo out of them because presentrance! , test the duct entrance sure atand thewith exit the is higher the alone entire than brakeatduct entrance! So, test the duct entrance installed. There may be critical alone and with the entire brake duct differences.
installed. There differences.
may
be
critical
141
Tuft test was to confirm that air flows smoothly over body at radiator-duct exit. Highpressure areas are indicated by tufts laying flat on body surface. Flow is somewhat disturbed, but intoproper direction. Tuft test was confirm that air flows smoothly over body at radiator-duct exit. High-
pressure areas are indicated by tufts laying flat on body surface. Flow is somewhat disturbed, but in proper direction.
Brake ducts on this stock car are mounted under front bumper. A flexible hose leads cool air to front brakes. This type duct is easily modified to change brake cooling . Brake ducts on this stock car are mounted under front bumper. A flexible hose leads cool
air to front brakes. This type duct is easily modified to change brake cooling.
A well designed duct is simple and neat. Ducts sealed to center of rotor such as this are much more efficient than those that just point at center of rotor. Flex hose used for air ducts cars is duct available in auto surplus stores. Noticeofboth A well on designed is simple andparts neat. or Ducts sealed to center rotorends suchofashose this are securely attached with hose clamps. much more efficient than those that just point at center of rotor. Flex hose used for air
ducts on cars is available in auto parts or surplus stores. Notice both ends of hose are securely attached with hose clamps. 142
Air-Pressure Gage-An air-pressure gage that measures in inches of water Air-Pressure Cin .Hp), pageGage-An 113, can air-pressure be used to gage that measures inches find high-pressure in areas andoftowater im(in.H20), pageMount 113, can be used to prove ducting. the gage so the find areas and ortovinyl imdriverhigh-pressure can see it. Run rubber prove the want gage to so test the tubing ducting. from theMount area you it. Run rubber or vinyl driver can see to the high-pressure port on the gage. tubingthe from the area wantPosition to test body. Tape tubing to theyou to high-pressure portofon gage. thethe tube on the surface thethe body so Tape theacross tubingthe to ends, the body. Position air flows not into it. theIf tube the the surface of the bodyport so you on leave low-pressure air flows across the ends, not into it. disconnected, the gage will measure you leavedifference the low-pressure theIf pressure between port the disconnected, gage will test area andthewhere the measure gage is the pressure difference between the located. However, you can run a tube test area and where the gage is from the low-pressure port to the area located. you can a tube of the However, car you want therunduct to from the low-pressure the gage area pressurizethe brake port rotor.toThe of the car you want the duct to will then measure the pressure difpressurizethe brake The gage ference between the rotor. test area and will then measure the pressure brake-rotor area. Before running difthe ference between the test areaofand test, blow velY lightly at the end the brake-rotor area.area. Before the tube in the test If therunning gage readtest, very lightly at the end of the ing blow increases, it is hooked up tube in theRun test area. readcorrectly. the If cartheatgage constant ing increases, is read hooked up pressure. speed, say 80 mph,it and correctly. carzero, at constant If the gage Run reads the below the duct speed, 80 .mph, and read will notsay work Air flows frompressure. high to If gage reads below zero,the thehighduct lowthepressure only. Tape will not work. Air flows from high to pressure tube to different locations low pressure only.until Tape around the body youthe findhighthe pressure tube toarea different highest-pressure that is locations practical around the body until you find the to accept a duct inlet. highest-pressure areaexit thatthat is practical If you have a duct seals to to ductyou inlet. theaccept rotor aand want to improve it a ductfewer exit that seals If you have with larger tubing, bends or toa the rotor and you want to improve it different inlet location, drill a hole in with larger tubing, fewer bends or the rotor plenum close to the rotor.a different drill a holeport in Connect inlet it to location, the high-pressure the rotorgage. plenum close to the on the Disconnect the rotor. lowConnect to the port Run a constantpressure it gage port.high-pressure on the gage. Disconnect the lowspeed test before and after modifying pressure port. Run a constantthe duct. gage If pressure increases after speed test before, and the modification the after duct modifying will flow the If pressure increasescan after moreduct. air. The same procedure be the modification, the duct will flow used for optimizing engine-induction more air. The and sameradiator-inlet procedure can be ram-air-scoop sizes. used for optimizing engine-induction Just be sure the high-pressure gage ram-air-scoop and of radiator-inlet pickup is in front and close tosizes. the Just be sure the high-pressure gage item being pressurized. pickup in front and close to the Thereis are some ofcomplex methodS item being pressurized. to determine the exact dimensions of some complex a There NACAare duct. The easiest methods way to to determine dimensions of design a ducttheis exact to copy one from a NACAcar.duct. easiest waytestto another A lotThe of wind-tunnel design a duct is to copy one from ing and track testing has been done on another car. Arace lot ofcars wind-tunnel no factory-built . There'stesting and track testingtheir has been done on reason to repeat work. They factory-built no can't hide therace duct cars. shape,There's so go into reason to repeat their work. They the pits with a camera and photograph can't duct shape, so go into ducts hide on the winning factory-designed the pits with a camera and photograph cars. Enhance the information you'll
ducts on winning factory-designed cars. Enhance the information you'll
.
get with with the the photo photo by by measuring measuring the the get the car car owner owner will will allow it. it. duct, ififthe duct, repeat, the front of of a car car body body or To repeat, spoiler-air dam-is dam-is an ideal nose spoiler-air nose place to to install install a duct entrance entrance for the the place front brakes. brakes. Make Make aa round, round, smoothfront of the the duct. hole the the size of edged hole the entrance miniRounded edges at the Rounded mize turbulence turbulence inside the the duct. duct. Use mize a round round tube or duct to route air to to the brake. Use smooth tube for straight ducts and corrugated heater-type ducting for curves. Mount the duct securewon't fall off. Check wheel and ly so it won't suspension clearances in all turn and wheel-travel extremes: bump, droop and steering lock. Exit-The duct exit should be Duct Exit-The at a specific location. On a drum brake, direct the exit at the drum so air hits both the drum edge and backIf tlie the backing plate is ing plate. If vented, make sure air blows into the vents. All race cars that use drum brakes should have vented backing plates-assuming rules allow plates-assuming them - bu t road cars may not. If there them-but are no vents, point the duct more at the drum and less at the backing plate. The accompanying drawing shows how to locate a cooling-duct exit for drum brakes. A disc brake with a solid rotor should have the duct pointing at the forward edge of the rotor so both sides of the rotor are cooled. cooled. This is not a suitable duct-exit location for a vented rotor. rotor. I discuss ducting vented rotors later. later. It's difficult to cool both sides of a solid rotor equally. equally. A duct pointed to the inboard side side of the rotor will take care care of that side side very well. However, However, the outboard side side of the rotor gets little little or no air if it is close close to the the wheel. Consequently, Consequently, the the duct should be designed to force force air between the the wheel and the the outboard outboard side side of the the rotor. rotor. If the the rotor has has one one hot side side and one one cool cool side, side, it may may warp. warp. A warped rotor rotor will will adversely adversely affect braking. braking. The The nearby drawing shows shows a duct duct dedesigned signed to cool cool both sides sides of a discdiscbrake rotor. rotor. This This may may be easy or or impossible, impossible, depending depending on on the the specific specific configuration. configuration. A duct duct design design must must be be proven by by testing. testing. This This isis because brake brake cooling cooling isis complicated complicated by by other other factors. factors. For For example, example, wheel wheel design design also also affects affects cooling cooling of of the the outboard outboard side side of of the the rotor. rotor. Measuring Measuring temperature temperature on on both both sides sides of of the the rotor rotor and and caliper caliper will will concon-
I
T JI Drum Drum
Vented Vented 8ackingBackingPlate Plate Scoop Scoop
I
I
I
I I
Backing Plate Vented Backing
Drum
I
Non-Vented Non- Vented Backing Backing Plate
-
Cooling Cooling duct should be pointed pointed as shown depending on backing-plate design. design. If there are cooling holes or scoops in backing backing plate, duct should point toward backing backing plate and drum. drum. holes in backing backing plate, point pOint duct entirely toward drum. If there are no holes
Rotor~
~DiVider
Duct
I
Hot Side HotSide~~1 I
I
I
I
, Cool Side
LJ
~
Original Shape Shape Original
It is is essential essential to to get cooling cooling air to both both sides sides of a solid solid rotor. rotor. Divider Divider in in duct will will split split airflow airflow so so it it can can be be directed to to each each side side of rotor. rotor. Some Some experimenting experimenting with with dividers and and duct duct locations locations may may be be necesnecesdividers sary sary to to get it it right. right.
rotor is is cooled cooled more more on on one one side side than than If aa rotor the other, other, it it can can warp warp as as shown shown here. here. Hot Hot side expands expands more more than than cold cold side side and and rotor rotor side takes the the shape shape of a saucer. saucer. Braking Braking is is not not good good on on aa warped warped rotor. rotor. Equal Equal cooling cooling on on each side side prevents prevents this this situation. situation. each
firm firm how how successful successful aa duct duct design design is. is. A disc disc brake with a vented rotor should should have have the the cooling air directed to to the the center of the the rotor. rotor. As As itit turns, turns, the the rotor rotor acts acts as as an an air air pump, pump, although although not an an efficient efficient one. one. Air isis drawn drawn into into the the center center of of the the rotor and and isis thrown out out the the edge. edge. Vented-rotor ducts ducts can can be sealed sealed to to the the center center of of the the rotor. rotor. be much more more efficient efficient than than This isis much This merely merely pointing pointing the the duct duct at at the the rotor rotor center center because because air air isis forced forced through through the the rotor. rotor. See See the the drawing drawing for for how how aa vented vented rotor rotor should should be be ducted. ducted. If If more more cooling cooling isis required, required, seal seal the the duct duct to to the the center center of of the the rotor. rotor.
Area-The ideal air-duct crossDuct AreaThe ideal sectional area area should should be at at least least as as sectional large as as the the rotor cooling-passage-inlet cooling-passage-inlet large area. To To determine determine this this area, area, measure measure area. the distance distance between the the inboard inboard and and the outboard rotor rotor side side plates. plates. Also Also measoutboard ure the the inner inner diameter diameter of of the the inboard inboard ure rotor side side plate. plate. Calculate Calculate the the area area rotor this formula: formula: using this Inlet area area == (3.14) (3.14)(inboard-plate Inlet (inboard-plate ID)(distance between plates) plates) 10) (distance between
For aa rotor rotor with with aa 6.25-in. 6.25-in. inboardinboardFor plate 10 ID and and 0.63 0.63 in. in. between between plates: plates: plate Inlet area area == (3.14) (3.1 4 )(6.25 ( 6 . 2 5in.l(O.63 in.I(O.63in.) in.) Inlet 1 2 . 3 6sq sq in. in. == 12.36
143
o o o
~Rotor
D
Rotor
= 0 0
Fiberglass scoop on this Indy Car brake is sealed to front upright. Air is ducted directly to centerscoop of vented rotor. This was Fiberglass on this lndy Carduct brake is obviously designed with of the car, sealed to front upright. Air rest is ducted directand merely added on This afterduct brakes ly to not center of vented rotor. was overheated. Photo bywith Tom Monroe. obviously designed rest of the car,
and not merely added on after brakes overheated. Photo by Tom Monroe.
Common duct diameters and areas are as follows:
Common duct diameters and areas Diameter/Area 19.6sq in . are5-in. as follows: 4-in. Diameter/Area 12.6 sq in . 5-in. Diameter/Area 7.1 19.6sqsqin.in. 3-in. 4-in. Diameter/Area 12.6sq in. IdealDiameter/Area duct size for this rotor 3-in. 7.1 sq in. is 4 in. If there isn't enough room to package duct duct size for 4 in, theIdeal correct in this yourrotor car, isget as Iff there isn't enough room to package close as you can. The exit adaptor that the correct ductto intheyour car, of getthe as seals the duct center close as you can. The exit adaptor that rotor should almost touch the rotor. seals duct1/16-in. to the clearance. center of Ifthe Allow the about it rotor should almost touch the rotor. rubs, the adaptor will make noise and Allow the about 1116-in. If it wear excess away,clearance. but it won't rubs, the adaptor will make noise and hurt the rotor. Be sure the adaptor wear the excess away, but it won't does not restrict airflow. hurt rotor. Be sure adaptor Thethe cross-sectional area the of the adapdoes not restrict airflow. tor should be as large as the duct. The cross-sectional areareduces of the adapSqueezing a tube oblong area. tor should be as large as Start with a cone and formthe theduct, exit Squeezing tube oblong reduces end to the aproper shape. It shouldarea. seal Start with acenter cone and form the The exit the entire of the rotor. end to the proper shape. It should seal adaptor should blend to a round secthe center The tion entire to which the of ductthewillrotor. connect. adaptor should blend a round secMake provisions for tomounting the tion to which duct orwill connect. adaptor to the the spindle suspension Make mounting the upright.provisions It must befor secure and move adaptor the spindle or suspension with the to wheel. upright. must be secure and move If yourIt car already has ducts, but with the wheel. brake temperatures are too high, duct If your car may already hasPerhaps ducts, but modifications help. the brake entrances temperatures tooare high, duct or are exits in duct the modifications may test help.them Perhaps wrong place. Tuft to seethe if ductis entrances or exits are duct. in the air really flowing into the If wrong place.looks Tuft good test ,them to see if everything try installing air is really flowing If larger-diameter ducts.into Testthe theduct. brakes everything looks good, try the installing with the new ducts under same larger-diameter ducts. Test the conditions as the old ones and brakes see if with the new ducts under they made any difference. the Yousame can conditions as the old ones and see if they made any difference. You can 144
Vented rotor needs cool air directed at its center. Air from duct is picked up by rotor and sucked vents. Best cooling Vented rotor through needs cool air directed at its ducts duct exit center.are Air deSigned from ductwith is picked up bysealed rotor against rotor center. and sucked through vents. Best cooling
ducts are designed with duct exit sealed
This brake duct directs air to center of vented rotor. Rotor motion sucks cool air in and out the vents. duct also This blows brakeitduct directs airThis to center of puts cold air Rotor on rubbing of rotor, vented rotor. motionsurface sucks cool air in but only on itinboard ThisThis could lead to and blows out theside. vents. duct also uneven of thesurface two of rubbing puts coldcooling air on rubbing rotor, surfaces, and may cause rotor to warp. A but only on inboard side. This could lead to baffle be added to upright to seal unevenshould cooling of the two rubbing gap between braking and surfaces, and inboard may cause rotorsurface to warp. A upright. This would force air collected baffle should be added toall upright to seal by through rotor-cooling passages. gapscoop between inboard braking surface and
upright. This would force all air collected by scoopthrough rotor-cooling passages.
always flow more cooling air through a bigger hole, but it always adds drag. always cooling through The carflow will more lose top speed air with larger aducts. bigger hole, but it always adds drag. The car willtolose top speed with larger Changing Vented Rotors-Solid ducts. rotors are cheaper and lighter than Changing to Vented t o r sget - s o ltoo id' vented rotors, but they~ ocan rotorsVented are cheaper hot. rotors and are lighter better than for vented rotors, they are can heavier, get too several reasons.butThey hot. Vented rotors are better for thus have less temperature rise per several reasons. They are heavier, stop. They also have four surfaces inthus have less temperature Per. stead of two to provide rise cooling stop. They also have Finally, vented rotorsfour alsosurfaces pump inair stead to Vented providerotors cooling. throughofthetwo brake. usuFinally, vented rotors air ally are necessary on a also heavypump race car through brake. such as a the stock car. Vented rotors usuallyThe arebest necessary a heavy car ventedon rotors haverace curved such as a stockcar. vents. Curved-vent rotors pump The air best than vented rotors have curved more straight-vent rotors, vents. Curved-ventrotors rotors plus curved-vent are pump more more air tothan straight-vent rotors, resistant cracking . However, this plus curved-vent makes rotors used rotors on the are rightmore and resistant to the cracking. However, left sides of car different. They this are makes usedaironas the designedrotors to pump theyright rotateand in left sides of the car different. They are one direction only. designed pump afford air as they rotate in If you tocan't curved-vent one direction only. rotors , use straight-vent rotors . They youconsiderably can't afford curved-vent willIf run cooler than solid rotors, use straight-vent rotors. rotors. RegardJess of which wayThey you will run considerably cooler than go, remember that vented rotorssolid are rotors. thicker Regardless which way. The you much than ofsolid rotors
go, remember that vented rotors are much thicker than solid rotors. The
against rotor calipers willcenter. have to be replaced or modified if you change to vented calipers will most have of to the be time, replaced or rotors. But, you'll modified if you change to vented need a different caliper. On some tworotors. But, most of the you'll piece calipers, spacers can time, be installed need a different caliper. Ontosome two-. to allow the thicker rotors be used piece calipers, spacers can be installed Longer bolts are required to make this to allow the thicker rotors to be used. modification. Longer are required to make this If youbolts change to vented rotors, modification. change the brake ducts to supply air to you change to vented rotors, theIf center of the rotor. This will prochange the brake ducts to supply to vide a constant supply of cool air air to be the centerthrough of the rotor. This will pumped the interior of prothe vide rotor.a constant supply of cool air to be pumped the interior of help the Modified through Wheels-Some wheels rotor. brake cooling by providing a place for Modified wheels help cooling airWheels-Some to exit the wheel well. This brake cooling by providing a place can happen by the wheel acting as for an cooling air or to the exitwheel the wheel well. This air pump, merely having can happen the wheel acting an enough ventbyholes in it to allowashot air to pump, or the wheel merely having air escape. enough holes in it to allow hot When vent I was .developing the first air to escape. monocoque split-rim racing wheels, I Whensome I was ,developing the from first found interesting effects monocoque split-rim racing cars, wheels, wheel centers. On some theI found interesting effects from brakes some ran much cooler if vent holes wheeldriJled centers. Onwheel some cars, The the were in the centers. brakes ran much cooler if vent holes outside of the wheel would be covered were drilleddust i n the wheel The with black from the centers. brakes. This outside of the wheel be covered indicated that airwould really flowed with black theOnbrakes. This through thedust ventfrom holes. other cars, indicated that air really flowed vent holes did not affect brake cooling. through the vent holes. other cars, After some study, weOnlearned that vent holes did not corners affect brake cooling. the shape of the of the body After some we learned that nose made the study, difference. As air flows the shape of the corners of the body around the corners of a rounded nose, made the difference. As airatflows anose low-pressure area is created the around the corners a rounded front wheel wells.of This drawsnose, air athrough low-pressure areaand is created at the the wheels helps cool the front wells. draws brakes.wheel On cars with This flat sides andaira through the wheels cool the square-edged nose, and this helps low pressure brakes.notOnexist. cars Airflow with flat through sides andthea does square-edged nose, this low pressure wheels had to be supplied entirely by does not exist. Airflow through the the brake-cooling ducts.
wheels had to be supplied entirely by the brake-cooling ducts.
This brake duct suffers from too many bends and tight clearances. Designing brake cooling ducts with rest of car can help avoid these problems. Best duct nearly with large, smooth This brake duct suffers from istoo many straight bends and tight clearances. bends. Designing brake cooling ducts with rest of car can help avoid
Angled vent and grooved rotors are directional. Left-side rotor must turn counterclockwise for maximum cooling.
Angled vent and grooved rotors are directional. Left-side rotor must turn counterclockwise for maximum cooling.
these problems. Best duct is nearly straight with large, smooth Because of the large area of a wheel bends.
well compared to an air duct, suct ion of the wheel large area we ll of cana wheel move at Because a low-pressure well compared to an air duct, When much more air than an air duct.suction at a low-pressure wheel well canvented move low-pressure wheel wells with much more air than an air duct. When wheels and sealed air ducts are low-pressure wells with vented combined, thewheel results are dramatic for wheels and sealed air moving air through a ventedducts rotor. are combined, the try results are wheels, dramaticfirst for Before you vented moving through a vented rotor.wool test the airnose of the car with Before you flows try vented wheels, first tufts. If air out of the front test the nose of the car with wool wheel wells, vented wheels will probatufts. If air brake flows cooling. out of the bly improve Thisfront will wheel vented wheels will roundprobaoccur ifwells, th e nose of the car has bly corners, improvealbrake Thiseasily will ed lowingcooling. air to flow occur if the nose of the car has roundaround the sides of the car. The air ed corners, air tothe flowcorners easily speeding upallowing as it rounds around the sides of athesuction car. The air of the body causes at the i t rounds the corners speeding up as front wheel wells . This flow can be obof the body a suction at the in served when causes watching cars run front wheel wells. This flow can be obheavy rain . If air flows out of the served whena great watching run will in of spray wheel wells, deal cars If air flows out of the heavy rain. come out too; you can see it. wheel a great of spray will Manywells, racing anddealstreet wheels come out too; you can see it. come with vent holes. If the wheels designedandto street act as wheels an air areMany also racing come with vent holes. the greater. wheels pump, the effect willIf be are also designed to act fans as anhave air Hubcap-like lightweight pump, the effect will be greater. been fitted to wheels to help pump air Hubcap-like fans have out. Chevroletlightweight Corvair cooling fans been fitted to wheels to help pump air have been used for this . out. Corvairaspect cooling fans of ventTheChevrolet most important have been used for this. ing air through a wheel is the total The most important aspect of ventamoun t of cut-out area. As this area ing air through a wheel is the increases , airflow increases. A total few amount of are cut-out thissmalarea large holes betterarea. thanAs many increases, airflow increases. few yo u may not haveAmuch ler ones, but large holes arewheels better than choice. Most must many have smalsmall ler ones, but you may not have much holes for structural reasons. choice. Most wheels must Another item that helps have brake small coolholes for structural reasons. ing is wheel material. An aluminum item that brake coolor Another magnesium wheelhelps conducts heat
ing is wheel material. An aluminum or magnesi~~rn wheel conducts heat
Hurst! Airheart caliper is available with or Iwithout a spacer between caliper halves:I With spacer, caliper be usedwith on or a Hurst/Airheart caliper can is available 0 .810-in.-thick rotor. Without spacer, caliwithout a spacer between caliper halves: per is suitedcaliper for can a O.375-in. rotor With spacer, be used on a thickness. If converting to thicker 0.81 0-in.-thick rotor. Without spacer,rotors caliand you have unspaced calipers, merely per is suited for a 0.375-in. rotor add spacers. Photo tcourtesy Hurst thickness. If converting o thicker rotors Performance. and you have unspaced calipers, merely
add spacers. Performance.
Photo
courtesy Front Tire
Centerline wheels were originally a solidcenter construction. As need to direct cooling airwheels through wheels became Centerline were originally a solidevident,construction. these vented versions were center As need t o direct created. Because this wheel is so deep, cooling air through wheels became duct should be used to take advantage of evident, these vented versions were cooling holes. created. Because this wheel is so deep,
duct should be used to take advantage of cooling holes.
Hurst Air From Brake
From
\
I
I
1
1
\ Airflow
\
~ \
----f--.----F-.Jr o nt Airllow
of Body
Shape of front corner of body determines how much air is pulled out through holes in wheel. This drawing shows two different body shapes, looking down on top of body. Car on left has a square with little suction on front wheel well.air Rounded-body on right holes drawing tends Shape of nose, front corner of body determines how much is pulled out through in wheel. to pull a lot ofshows air through front wheel. This drawing two different body shapes, looking down on top of body. Car on left has
a square nose, with little suction on front wheel well. Rounded-body on right drawing tends to pull a lot of air through front wheel. 145
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Although this
This Porsche race car has cooling fans mounted outside of each wheel. At high speed, fan sucks cool air out through wheel. Cool air is ducted to brake through car nose.
This Porsche race car has cooling fans mounted outside of each wheel. At high speed, fan sucks cool air out through wheel. cool air is ducted t o brake through car nose. -
Aluminum brake drums were used on large Buicks before they changed to disc brakes. Aluminum drumswere are great for large cars Aluminum brake drums used on requiring drum brakes. cooling Buicks before they Often, changed t o probdisc lems canAluminum be eliminated brakes. drums by arechanging great for from cars iron to aluminum drums.Often, cooling probrequiring drum brakes.
lems can be eliminated by changing from iron t o aluminum drums.
better than a steel wheel. The wheel conducts heat from the brake and better than steel wheel. wheel hub. aAlthough the The wheelwheel and conducts heat from the brake and tire will run hotter, the brake runs wheel hub. Although the wheel and cooler. tireAluminum will run hotter, the brakewheels runs or magnesium cooler. are used in racing because of generally Aluminum or magnesium wheels their lower weight. However, imgenerally are usedand in racing of proved cooling betterbecause handling their lowerracing weight. However, imresult with wheels. The lighter proved also cooling and acceleration. better handling weight improves result with racing wheels. The lighter Changing Brake Drums - Finned weight improves acceleration. brake also drums improve cooling over Changing Drums-Finned drums that Brake don't have fins . If your brake drums improve coolingtryover brake drums are not finned, to
drums that don't have fins. If your brake drums are not finned, try to 146
Wally Edwards improved braking on his vintage sports car by adapting Buick aluminum drums to early Fordbraking brakes.on Many old Wally Edwards improved his vinstreetsports rods car canby be improved this tage adapting Buickbyalumimodification. aluminum drums num drums toFinned early Ford brakes. Manylook old good on a show car, street behind rods wire can wheels be improved by this too. modification. Finned aluminum drums look
good behind wire wheels on a show car, obtain some. It is not a simple too.
modification , generally because few obtain is not simple cars offersome. finned Itdrums as a amodificamodification, generally because fewa tion or as optional equipment. On cars finnedwith drums a modificaro ad offer car, check yourasdealer to see tion or asdrums optional if special are equipment. offered. On On earlya road car, check with your dealer to see Corvettes, for example , optional if special drums are offered. On early heavy-duty brakes used finned Corvettes, for the example, optional drums. However, entire drum was heavy-duty brakes an used wider. This required entire finned brakedrums. However, assembly change. the entire drum was wider. This required entire brakeIf you change drumsan , use aluminum assembly change. drums in place of iron ones, if If you . change use aluminum possible They drums, are lighter and cool drums in place of iron ones,haveif better. Most aluminum drums
possible. They are lighter and cool better. Most aluminum drums have
optional
finned
Corvette
1drum is same diameter as standard drum, itI is 1/2-in. wider. Thus, it isfinned not possible to Although this optional Corvette merely finned drumsasonstandard in place drum, of nondrum isslip same diameter it finned Corvette drums.i t is Entire brake asis 1/2-in. wider. Thus, not possible to sembly slip must be drums replaced. careful to merely finned on inBe place of nontake allCorvette dimensions when converting to finned drums. Entire brake asheavy-duty brake sembly must be drums. replaced. Be careful t o take all dimensions when converting to heavy-duty brake drums.
fins for maximum cooling area . For years , Buicks and some Lincolns used fins maximum cooling area. For. large,for finned aluminum brake drums years, Buicks some You may find and some in a Lincolns wrecking used yard large, finned aluminum brake that can be adapted to your car.drums. Also, You may find some in a wrecking yard many foreign cars have aluminum that canonbetheadapted drums rear. to your car. Also, many foreign carscars have aluminum On some sports equipped with drums on the rear. drum brakes, optional aluminum On some with drums were sports offeredcars by equipped the factory or drum brakes, houses. optionalIf you aluminum from specialty have a drums by theas factory or car thatwere had Aoffered I-Fin drums an option from specialty houses. If you have and are lucky enough to find some,a car drumsmodification as an option. theythat arehad a Al-Fin worthwhile and enough to findcooling, some, Not are onlylucky do they improve they are great a worthwhile modification. they look behind wire wheels! Not only do Dust they improve cooling, Modifying Shields-Discthey look great behind wire wheels! brake dust shields block cooling air. If Dust Shields-DiscaModifying road car is modified for racing , the brake dust shields block air. to If dust shields should be cooling removed aallow roadcooling car is modified for racing, the air to hit the brake rotor. dust isshields shouldmodification be removed to This not a good if the allowis cooling air to the brake car driven on thehitstreet. The rotor. rotor This is not from a goodroad-dirt modification if the will suffer and grime car is driven on the street. The contamination , and wear rotor will will suffer from road-dirt grime increase. The manufacturerand wouldn 't contamination, will install them if theyand weren'twear necessary. increase. I'll qualifyThe this :manufacturer wouldn't install them if theytheweren't necessary. If you remove dust shields, reI'll qualify strict use tothis: racing only, unless you live
remove thedirt dustroads shields, in Ifanyou area with no and reno strict use to racing only, unless you live snow. Then , if it is a dual-purpose car, in an area to with no dirt roadsbetween and no you ' ll have make a choice snow. Then, if it is a dual-purpose car, improved brake cooling and more you'll to make afrom choice between brake have maintenance st reet use. improved brake cooling andcarmore This depends on the speCific and brake maintenance from street the conditions under which ituse. is This depends thetospecific carkeep and driven. You ' ll on have test and the conditions which is records to make under sure you madeit the driven. You'll have to test and keep right choice. records to make sure you made the right choice.
ltilt:anl ~----<
Backing plate on this car is modified by drilling holes in low-stress areas. Scoops are addedplate to direct cool interior by of Backing on this carairistomodified brake drum. racing rules allow it, this is a drilling holesIf in low-stress areas. Scoops desirable for air drum are addedmodification to direct cool to brakes interiorFor of street drum. use, Ifscoops and allow drilledit, backing brake racing rules this is a plates willmodification make brakes to desirable formore drumsensitive brakes For wet-weather street use, driving. scoops and drilled backing Ultimate in vented backing plates are found on this old oval-track racer. Entire backing is cut away except for small Ultimateplate in vented backing plates are tab holding wheel cylinder. Onracer. most Entire cars, found on this old oval-track however, the isbrake shoes will for notsmall be backing plate cut away except retained andwheel will possibly tab holding cylinder. become On most misacars, ligned sideways. A more normal however, the brake shoes will backingnot be plate modification is drillingbecome cooling misaholes retained and will possibly in it or adding air scoops. ligned sideways. A more normal backing-
plate modification is drilling cooling holes in it or adding air scoops.
Vented Backing Plates- Drumbrake backing plates should be vented Vented Plates-Drumfor racing .Backing This involves cutting a brake backing plates should hole in the front and rear ofbe thevented backfor plracing. This air involves cutting ing ate to allow to flow in and outa holethein drum. the front and rear ofa the backof Sometimes, scoop is ing plate to allow air to flow in and added to the front hole to direct out air of is intothe thedrum. drum.Sometimes, Venting can abescoop a large added front hole to direct air cut-outtoorthe a number of drilled holes. into the drum. Venting be abut large A large cut-out works can best, is cut-out or a number of drilled holes. structurally weaker. A screen can be A cut-out works but is usedlarge to keep rocks out. best, However, if structurally weaker.theA screen screen will can not be the track is clean, used to keep rocks out. disc However, if be necessary. Before brakes the track is clean, the screen will not became popular, for ma ximum be necessary. Before cooling, stock cars ran disc 12 Xbrakes 3-in. becamebrakes popular, for in maximum drum with brackets place of cooling, backing plstock a tes. cars ran 1 2 X 3-in. drum brakes with brackets in place of When modifying backing plates, backing plates. don't weaken the ba cking-plate When modifying structure. Brake shoesbacking mount plates, to the don't backing weaken pl ate , sotheall backing-plate the braking structure. Brake shoestomount to the torque is transmitted the suspenbacking plate, so all the braking sion through the sh oe anchor points torqueconsequently, is transmitted the suspenand, thetobacking plate. sion the through thepl shoe anchor points Cut backing ate only in areas far and, consequently, backing plate. from where these thehighly stressed Cut the points backingattach plate. only in areas far anchor If you are not from how where highly stressed sure to dothese this, turn the job over anchor pointsr or attach. If you race-car are not to an enginee experienced sure how to do this, turn the job over technici an . to an engineer or experienced race-car Water Cooling-One of the latest technician. tricks for cooling brakes is water Water Cooling-One of the latest cooling. A device is used to spray
tricks for cooling brakes is water cooling. A device is used to spray
plates will make brakes more sensitive to wet-weather driving.
water into the brake-cooling ducts . The water vaporizes in the duct and water brake-cooling ducts. cools into the the incoming air. Squirting The water vaporizes in the duct and water directly on the rotor has been cools the incoming air. Squirting used for years with varying degrees of water directly the with rotor this has been success. The on idea new used forisyears with varying degrees of system not to squirt water directly success. The idea with this new on the brake. Steam formed will not systemtheis brake not to as squirt water directly cool efficiently as air. on theit brake. Steam will not Also, may cause theformed rotors to crack. cool the the brake as efficiently Instead, water is strictly as an air. air Also, it may cause the rotors to crack. cooler. Instead, water is Cooling strictly anis air Brake the Evaporative an cooler. water-cooling system availaaccessory Evaporative Cooling an bleBrake from Tilton Engineering. It is is simic accessory water-cooling system availalar to a windshield-washer system, ble from Tilton Engineering. is simi: with a water reservoir and anIt electric lar to Water a windshield-washer system, pump. is fed to the spray nozwithwia th water zles smallreservoir hoses . and an electric pump. Water the is fed to the spray nozTo operate brake water-cooling zles with small hoses. system, the driver turns on a switch To operate theinstrument brake water-cooling mounted on the panel. Be system,thethe driver turns on a switch cause driver can't measure brake mounted on ,the panel. Betemperature he instrument must run the system cause the driver can't measure brake throughout the race or just when he temperature, he must thinks he needs it. Inruna the longsystem race , throughout race just , when he wate r supplythe may be or critical so planthinks he needs it. In a long race, ning should be done. Huge amounts water supply mayshouldn be critical, planof extra water ' t be socarried ning should be done. Huge amounts unless necessary. of Use extrawater water shouldn't be carried cooling as a last resort. unless necessary. Water is heavy and the system reUse water cooling as a last resort. quires constant maintenance. First, Water is heavy the issystem remake sure the airand ducting sized and quires correctly, constant and maintenance. First, sealed the inlets are in a make sure the area. air ducting is sized high-pressure Also , be sure and the sealed correctly, and the inlets in a wheels are vented correctly. If are all this high-pressure Also, be cooling. sure the is not enough, area. then try water wheels are vented correctly. If all this Because the water-cooling system is is not enough, then try water cooling. meant to cool the air in the brakeBecause the the water-cooling system is cooling duct, system only works meant cool well on to hot, drythe days.airIf in thethe air brakeis cool
cooling duct, the system only works well on hot, dry days. If the air is cool
J
Hose Tilton water-COOling system includes a reservoir with a small electric pump. Spray nozzles and fittings complete System Tilton water-cooling system kit. includes a is designed sprayelectric coolingpump. waterSpray into reservoir withtoa small brake ducts lowercomplete temperature coolnozzles and to fittings kit. of System ing designed air directed at brake. This system is to spray cooling, water into works ducts best to onlower hot, temperature dry days. Drawing brake of coolcourtesy Tilton Engineering. ing air directed at brake. This system -
-
works best on hot, dry days. Drawing courtesy Tilton Engineering.
and damp , little extra cooling is done . On a hot dry day, water co oling can and little extradifference. cooling is done. makedamp, a considerable On a hot dry day, water cooling can Modifying Body Aerodynamicsmakesubject a considerable The of brakedifference. ducts has been Modifyingpreviously. Body Aerodynamicsdiscussed If you've done The subject of brake ductspreviously has been all of the modifications If you've d~ne discussed previously. mentioned to improve duct performall theyoumodifications anceofand still find thatpreviously the ducts mentioned to improve the ductjob, performare not accomplishing or airance and you still find that the flow from the front wheel wells isducts low , are not accomplishing job, Before or airconsider changing thethe body. flow from the this frontpotentially wheel wellsdifficult is low, you attempt consider changing body. job, test the car withthe wool tuftsBefore to esyou attempt this potentially tablish a baseline. Take difficult photos , job, test orthevideo car with tuftstufts to esmovies tapeswool of the so tablishcan a review baseline. photos, you whatTake happens as movies orarevideo tapesFirst of the tuftsthe so changes made. check you review for what turbulent happens or as duct can entrances changes are made. First check the reverse airflow . duct entrancesrearforbrake turbulent or Frequently, ducts are reverse in airflow. located turbulent air. Typically, turFrequently, brake ducts bulence on anrear open-cockpit car are is located in turbulent air. Typically, caused by objects , such as turthe bulence on rollbar, an open-cockpit car is windscreen, or the driver's caused objects, the. head, in byfront of thesuch duct as intake windscreen, rollbar, or the driver's Some fairings or resh aping of parts head, in front the duct intake. can greatly affectofairflow over the car. Some fairings or areshaping of ,parts Consider adding streamlined tacan greatly airflow over thehead car. pered fairingaffect behind the driver's Consider a streamlined, tato reduce adding turbulence over the rear pered fairing behind the driver's head body. This will also reduce total drag to reduce on the bod y.turbulence over the rear
body. This will also reduce total drag on the body. 147
Rotor, below, was drilled with a few large holes. Above rotor is typical; it has many smaller holes.was Most drilled have Rotor, below, drilled with rotors a few large more themis and smaller ones. A holes. holes Aboveinrotor typical; it has many 3/8-in.-diameter hole is probably an aversmaller holes. Most drilled rotors have age but in I have fromones. 1/4- in. moresize, holes themseen andthem smaller A to 1 /2-in. diameter. 3/8-in.-diameter hole is probably an average size, but I have seen them from 1 /4-in. to 1/2-in. diameter.
If you have a Chevrolet sedan, you may wish to install 1984 Corvette disc brakes. Problem with this conversion is finding a way to mount calipers on your suspension, and resulting caliper clearance problems. If you pedal effort too high, could disc possibly useProblem master If you have a Chevrolet sedan, may wishgets to install 1 9 8 4you Corvette brakes. cylinder booster from the Corvette. modification as this can be difficult and will with thisand conversion is finding a way to Amount caliperssuch on your suspension, and resulting take a lot of planning. Photo courtesy Ltd. too high, you could possibly use master caliper clearance problems. If pedal Girlock effort gets cylinder and booster from the Corvette. A modification such as this can be difficult and will take a lot of planning. Photo courtesy Girlock Ltd.
FADE REDUCTION
the calipers. A caliper is often a diffi-
Brake fade is usually the direct FADE REDUCTION result of high temperature, so first Brake fade is usually the direct consider cooling modifications and result of high temperature, so first harder linings. Other modifications to consider cooling help reduce fade aremodifications also possible. and harder linings. Other modifications Converting from Drum Brakes to to help reduce fade are also possible. Disc Brakes-There will be a reducConverting from Drum from Brakes to tion in fade by converting drum Disc Brakes-There will Unless be a reducbrakes to disc brakes. you tion inanfade drum have old by carconverting that uses from four-wheel brakes to disc brakes. Unless drum brakes, drums will be usedyou on haverear an old car only. that uses the wheels On afour-wheel road car, drum brakes,problem drums with will be used on the biggest converting the wheels only.isOnretaining a road car, rear rear brakes to discs the the biggest problem with converting parking brake. rear brakes disc to discs is retaining the Although brakes reduce fade, parking there is brake. usually only a small gain to be Although disc brakesonly reduce made in converting the fade, rear there is usually only a small gain be brakes. Because front brakes do to most made in converting reara of the work, rear-brakeonly fade the is not brakes. Because brakes do most serious problem.front Consequently, you of the work, rear-brake fade is notthea should also consider modifying seriousbrakes problem. Consequently, you front with larger rotors, highshould also linings, considercooling modifyingthe performance improvefront with larger rotors, highmentsbrakes or other changes. performance cooling Convertinglinings, from drums to improvediscs can ments or other changes. be difficult. Major problems include Convertingclearances from drums discs can maintaining andtomounting
cult item to place in the wheel and
be difficult. Major problems include maintaining clearances and mounting
148
the calipers. Before A caliper is oftenupa diffisuspension. throwing your cult item to place in the wheel hands in despair, study brakes and on suspension. Before up your other cars made by throwing the manufacturer hands brakesthere on of your in car.despair, On somestudy road cars, otherhigh-performance cars made by theversions manufacturer are using of your car. on On the some there disc brakes rear.road Forcars, example, are high-performance versions using the Thunderbird, Lincoln and Cordisc rear. For vettebrakes used on discthebrakes on example, the rear, the Thunderbird, Lincoln and year while other models of the same vette used disc brakestheonwheel-stud the rear, used drums. Because while other models of the same year pattern is the same, rotor mounting used drums.may Because wheel-stud problems be the solved easily. pattern is caliper the same, rotor may mounting However, mounting not. problems may be solved easily. Mounting calipers usually requires However, mounting may not. a special caliper bracket, available from Mounting calipers usually requires racing-brake manufacturers. The abracket special bracket, from usually is for available drag- or stockracing-brakeapplications manufacturers. The car-racing using racing bracket usually is for dragstockbrakes. This bracket may or work on car-racing applications usingcarracing your car, even though your may brakes. This bracketrotors. may work on use passenger-car Contact your car, even though your car may racing-brake suppliers for information useyour passenger-car rotors. Contact on car. racing-brake suppliers for for information If you have a mount the rear on your car. calipers, the jo b isn't finished yet. BeIf you have a mount for theaction rear cause drum brakes have servo calipers, the job isn't finished yet. Beand disc brakes don't, brake balance
or-
cause drum brakes have servo action and disc brakes don't, brake balance
no doubt will be wrong. Refer to Chapter 9 for how to calculate the no doubt be wrong. Refer to forces in an will all-disc-brake system. 9 for calculate Chapter I suggest you how use atobalance barthe or forces in an all-disc-brake system. proportioning valve to balance your I suggest a balance bar or new system. you Also,use if you don't change proportioning valve to your the master cylinder, youbalance can expect new system. you don't because change pedal effort Also, to ifincrease, the master cylinder, yourequires can expect drum-brake servo action less pedal effort to increase, because pedal effort. Make sure you can live drum-brake servo action requires less pedal effort before with the increased pedal effort. Make sure you can live starting this modification. If your car with the has increased pedal pedal effort before already excessive effort, starting this modification. If your car changing the master cylinder or going already excessive to powerhasbrakes may pedal be theeffort, only changing the master cylinder or going answer. to power brakes may be the only Rotor Drilling or Grooving-Drilling answer. holes or cutting grooves in rotor sur-
Rotor Drilling or Grooving-Drilling holes or cutting grooves in rotor sur-
Grooves on this rotor run in same direction as cooling vents. This rotor turns clockwise as viewed in photo. Notice how each Grooves on this rotor run in same direction groove lines up This with rotor metalturns webclockwise between as cooling vents. cooling vents. This reduces of as viewed in photo. Notice chance how each cracks forming at ametal groove. in groove lines up with web Trend between racing-brake toward cooling vents. development This reduces ischance of grooves away at from holes.in cracks and forming a cross-drilled groove. Trend
racing-brake development is toward grooves and away from cross-drilled holes.
faces can help reduce fade . Holes or grooves allow gas and dust from the faces help reduce Holes or liningscan someplace to fade. go instead of grooves allow gas and dust from wedging between the linings and the the linings someplace to go instead of rotor surfaces. wedging between linings and the However, rotorsthetend to crack at rotor surfaces. the holes or grooves because of inHowever, rotorsat tend to crack at creased stress these points. the holes or grooves because inspect of inConsequently, frequently creased these points. drilled or stress groovedatrotors for cracks. Consequently, frequently inspect Replace them if they start to fail. Imdrilled grooved rotors for cracks. proved or fade resistance comes at the Replace them if they start to fail.rotor Imprice of more-frequent proved fade resistance comes at the replacement. price of more-frequent rotor Cross-dri lling a brake rotor appears replacement. to be a simple job. It isn't. The probCross-drilling a brake appears lem is maintaining rotorrotor balance. It ' s to be a simple job. It isn't. The prob-a almost impossible to come up with lem maintaining rotor balance. It's that doesn't affect rotor hole ispattern almost balance.impossible to come up with a hole pattern that doesn't affect A disc-brake rotor is heavy androtor robalance. tates at moderately high speed. Rotor A disc-brake is heavy and rounbalance will rotor be noticeable, partictates highhigh speed. Rotor ularlyatonmoderately a lightweight -speed car. unbalance will be wish noticeable, particTherefore, if you to cross-drill ularly on a lightweight high-speed the rotors, have a machine shop docar. it. Therefore, if you awish to cross-drill They can layout symmetrical hole the rotors, a machine shop it. pattern on have a rotary table and drilldothe They can lay outwith a symmetrical holes concentric the cente r ofhole the pattern rotor. on a rotary table and drill the holes withtothe of the It isconcentric also possible millcenter grooves in arotor. rotor to produce the same effect as It is also possibledoesn to mill grooves as in ' t remove holes. Grooving amuch rotorweight, to produce the same effect as so balance is less of a holes. Grooving doesn't as the job problem. However, to doremove much weight, balancemachine. is less ofIt ' as properly, use asomilling problem. to do the you job back to theHowever, machine shop , unless properly, use a milling machine. It's can do it in your home workshop. back to the machine shop, unless you Grooves should not run radially on a
can do it in your home workshop. Grooves should not run radially on a
If removing a solid rotor for modification, you may want to machine a groove in the edge. This removes someforweight from a If removing a solid rotor modification, solidmay rotor, slightly increases its surface you want to machine a groove in the area, and not change edge. Thisdoes removes some swept weightarea. fromDoa not this slightly if rotor increases temperatures are too solidtryrotor, its surface high. more rotor weight, area, You and may doesneed not change swept area. not Do less. not try this if rotor temperatures are too This rotor has many cracks due to thermal stress. Notice how holes seem to attract cracks. If you drill the rotor, you can expect cracking to holes be worse if left stress. Notice how seemthan t o attract undrilled. IfThis have you cracked cracks. you rotor drill would the rotor, can anyway, cracking but cross-drilling makes it worse. expect t o be worse than if left Cross-drilling weight, rotor undrilled. This removes rotor would have so cracked can't absorb much heat. makes it worse. anyway, but as cross-drilling
high. You may need more rotor weight, not less.
Cross-drilling removes weight, so rotor can't absorb as much heat.
rotor-they should have a diagonal slant to them. Such a design is used rotor-they should on havemany a diagonal the rotors new for slant to them. Such a design is used motorcycles. The exact dimensions of for the rotors many new the grooves aren ' t on critical-O.06-in. motorcycles. Thedeep exact of wide by O.03-in. willdimensions work . theAsgrooves aren't holes critical-0.06-in. with cooling in a vented wide 0.03-in.should deep will work. rotor,by grooves be cut different: As with cooling holes Iy from one side of the incara vented to the rotor, should be cut different: other. grooves According to rotor rotation, the ly from should one side of away the car the grooves slope fromtorotaother. to rotor rotation, tion asAccording they extend outward from the the grooves should slope ID. away from rotarotor friction-surface The purpose tion they asextend outward from the is theassame rotor vents. Gas should rotor friction-surface ID. through The purpose be pumped outward the is the same as rotor Gas grooves to the rotorvents. OD as theshould rotor be pumped outward through the rotates. grooves the rotor OD as rotor After todrilling holes or the milling rotates. deburr the edges of each cut. grooves, drilling or milling A After sharp edge acts holes like a cutting tool grooves, deburr the edges of cut. and will wear away the liningseach quickly. A sharp edge acts like a cutting tool Use an abrasive stone or fine file to and will all wear away the linings quickly. smooth of the edges. Go over them Use an abrasive twice to be sure. stone or fine file to smooth all of the in edges. Go over Drilling holes a brake drumthem has twice to be sure. more effect on reducing fade than Drillinga holes in a brake has drilling disc-brake rotor. drum Perhaps more effect ondrum reducing than this is because brakes fade fade more drilling a disc-brake rotor. Perhaps easily than disc brakes. Therefore, this is because drum brakes fade more any improvement is more effective. easily than disc Therefore, Few vehicles comebrakes. with drilled brake any improvement is more effective. drums, so some experimentation is Few vehicles come with drilled required . You probably won't brake find drums, some experimentation is anythingso to use as an example.
required. You probably won't find anything to use as an example.
Drilling holes in a brake drum is tricky. Never drill through reinforcing lip at edge of drum. holes Hole location chosen here near Drilling in a brake drum is istricky. center of lining, where it will do Never drill through reinforcing lipthe at most edge good. Holes drums chosen should here be experiof drum. Holeinlocation is near mented carefully center ofwith lining, wheretoit avoid will dodangerous the most drum failure. holesshould after drilling. good. Holes Debur in drums be experi-
mented with carefully t o avoid dangerous drum failure. Debur holes after drilling.
Drilling a brake drum also has its negative side. Drilling weakens a Drilling a brake drum also tohashigh its drum. A drum is subjected negative side. Drilling weakens tension loads each time the brakes area drum. drum is from subjected to high applied,A resulting the outward tension brakesThe are pressureloads of each the time braketheshoes. applied,expanding resulting infrom the outward shoes a drum tend to pressure of the brake shoes. burst it. Holes at the inboard edge The of a shoes expanding in a drum drum can cause cracks to start. tend to burst it. Holes at the inboard of a Because correctly drilling edge a brake drum can cause cracks to start. drum involves a knowledge of what a brake theBecause stressescorrectly are, it's drilling very difficult to drum involves a knowledge of what determine the proper hole size and
the stresses are, it's very difficult to determine the proper hole size and 149
Disc-brake pads often come with one groove cut in radial direction. Cut second groove for improved fade resistance. Disc-brake pads often come with one groove cut in radial direction. Cut second groove for improved fade resistance.
pattern. The stress on a brake drum is determined by the design of that parpattern. The stress on a brake drum is ticular drum. Therefore, start by drilldetermined by the design of that paring a few 1/4-in. holes. Drill the holes ticular start by drillin the drum. center Therefore, of the friction surface. ing anot fewdrill 1/4-in. holes. Drill the holes Do holes at the inboard lip. in the centeredge of the friction surface. The inboard is the weakest area D oa not drillAfter holesdrilling at the inboard lip. of drUli'. the drums, The inboard edge is the weakest area test to see if the holes help reduce of a dIfr uthere m After drilling drums, fade. is still a fadetheproblem, test to see if the holes help reduce drill more holes. Run another test. By fade. If there is still a fade problem, doing a number of identical backdrill more holes. Runbeanother By to-back tests, you'll able totest. deterdoing how a number of identical backmine many holes are required. to-back tests, you'll able to deterDon't drill more than be necessary. mine how many holes are required. Use drilled brake drums only for Don't drill morethem than necessary. racing. Inspect for cracks after Userace. drilled drumsstarting only for each If youbrake find cracks at racing. Inspect them for cracks the edge of the holes, replace after the each race. you find cracks starting at drum. TheIfreplacement drum should the of thedrilled holes,in replace the the holes a different have edge drum. h e replacement drum lasted shoulda pattern Tunless the other drum have the holes drilled in a different long time before cracking. Find areas pattern unlesstothe drum Experilasted a of low stress drillother the holes. long time before areas mentation is the cracking. only wayFind to deterof low stress to drill the holes. Experimine this. mentationLinings-Grooved is the only way to linings deterGrooved mine this. have the same purpose as drilled Grooved Linings-Grooved rotors or drums. Gas and dustlinings from have the same purpose as drilled the linings will enter the grooves inrotorsoforbuilding drums.up Gas and dust from stead a lubricating layer the linings entersurfaces. the grooves inbetween thewill friction stead of building up a lubricating Grooving linings has no affectlayer on between friction balancing.theAlso, it issurfaces. easier than cutGrooving no affect can on ting an iron linings drum orhas rotor-you balancing. Also, it is easier than cutdo it with a hand saw grinder. ting iron drum of or grooved rotor-youlinings can A an disadvantage do withthey a handwear saw grinder. is itthat faster. Reduced A disadvantage groovedwear. linings lining surface area of increases So
is that they wear faster. Reduced lining surface area increases wear. So 150
don't get carried away with the amount of lining you cut. Again, testdon't get carried away how withmuch the ing is needed to determine amount of lining you cut. Again, testgrooving is needed. ingOn is needed determine drum to brakes, cut how the much slots grooving shoe. Don't cut through across theis needed. drumA brakes, cutis the slots theOnlining. small slot all that's across the shoe. Don't cut through needed, or 1/8-in. wide, about half the lining. small slotBeiscareful all that's way throughAthe lining. not needed, 1/8-in. about to cut theorlining so it wide, will come offhalf if it way through thea lining. careful not cracks through groove.BeLeave a patto cut the lining so it will come off if it tern of at least four rivets in each cracks through a For groove. Leavelinings, a patuncut segment. bonded tern at least four there of should be no lessrivets than 2inin.each beuncut segment. For bonded linings, tween grooves.
there should be no less than 2 in. between grooves. WARNING
When cutting linings, wear a respiraWARNING tor to avoid inhaling potentially When cuttingasbestos linings, wear a respiradangerous dust. Also, tor togetavoid inhaling potentially don't the dust on your clothing dangerous asbestos or hands. Finally, clean dust. up the Also, dust don't get the dust on your when finished. If you have clothing a shop or hands.use Finally, cleancutting. up the Then dust vacuum, it while a shop when finished. you of have you won't have Ifmuch a mess to vacuum, use later. it while cutting. Then contend with you won't have much of a mess to contend with later.
On disc-brake pads, most linings already have a groove running across disc-brake linings altheOn center of the pads, pad inmost a radial direcready have a groove running across tion relative to the rotor. If yours are the centercut of the pad in a radial grooved, another groove 90°directo it tion relative to the rotor. If yours are through the center of each pad. grooved, another groove to ita However, cut if your pads don't90" have throughgroove, the center radial put oneof in.each Test pad. the However, if your pads don't have a pads before cutting the second radial groove, putenough one in. Test the groove. If there's fade reducpads before cutting thedon't second tion with a radial groove, cut groove. If there's enough fade reducanother groove.
tion with a radial groove, don't cut another groove.
REDUCING PEDAL EFFORT If your car has excessi ve pedal REDUCING PEDAL EFFORT effort during hard braking, it must be If your car has excessive reduced. I'm not talking about pedal fade effort during only hard braking, it mustthe be here-fade occurs when reduced. talking about isfade brakes areI'm hot. not If the pedal effort exhere-fadewhenonly the cessive the occurs brakes when are cool, brakes are hot. If the pedal effort is exother modifications are needed. I discessive themake brakes are cool, cuss herewhen how to modifications other modifications to reduce pedal effort.are needed. I discuss here how to make modifications reduce pedal effort, use: toTo reduce pedal effort. • Softer brake-lining material. reduce pedal effort, use: • To Smaller-diameter master cylinder. Softer brake-lining material. • Power-brake booster. cylinder. • Smaller-diameter On drum brakes,master larger-diameter Power-brake wheel cylinders.booster. On disc drumbrakes, brakes,more larger-diameter • On total piston wheel cylinders. area. On disc brakes, more • Smaller-diameter tires. total piston area. • Larger-diameter brakes. Smaller-diameter tires. servo action. • On drum brakes, more Larger-diameter brakes. • Increased pedal ratio. On drum servo action. Some of brakes, these more modifications are Increased pedal easy to figure out ratio. and do. Others are Some ofandthese modifications are expensive require testing. I listed easy to figure out and do. Others them in the order you should are try expensive I listed them, withand the require easiest testing. and less-costly them in first. the order you should try methods them, with theLinings-As easiest and less-costly Softer Brake discussed methods first. in Chapter 4, different friction mateSofterhave Brakedifferent Linings-As discussed rials friction coefin Chapter different friction mateficients. To 4,review, linings with the rials different friction coefhighesthave friction coefficient are called withpedal the ficients. To review, soft linings. You canlinings reduce highestmerely frictionby coefficient area called effort changing to softer soft linings. You can reduce pedal lining. It is inexpensive and simple to effort merely by changing to a softer make the change. If it doesn't work lining. is inexpensive and simple to becauseIt of fade, excessive wear or make the you change. If it doesn't whatever, can easily change work back because of fade, excessive wear or linings. to the original whatever, you can easily change back Of course, the problems with going to to the softoriginal liningslinings. are that fade usually Of course, t h etemperature problems with andgoing wear occurs at lower to soft linings are that fade usually increases. So, if you already have fade occurs at lower and wear problems, don'ttemperature use softer linings. In increases. have fade fact, you So, mayif you havealready to use harder problems, don't use linings. In linings, which will softer increase pedal fact, you may have to use harder effort. The same goes for wear. If linings, which will don't increase pedal wear is high already, use softer effort. same goes wear. If linings. The However, if it'sfor acceptable, wear high already, use softer try theis softer linings, don't but check wear. linings. However, if it's acceptable, There's no way to predict wear withtry the softer linings,inbut check out trying the linings actual use.wear. There's n o way to linings predictmay weargive withAlthough softer reout trying the linings in actual use. duced pedal effort, it will be difficult softer linings The may give reto Although predict the change. friction duced pedaloften effort,depends it will beondifficult coefficient tempto predictAnd, the you change. friction erature. can't The predict the coefficient often depends on temptemperature. Softer linings will inerature.temperature And, you because can't predict the crease the front temperature. will and inbrakes will doSofter even linings more work crease the reartemperature brakes less. because the front brakes willpedal do even work and If high effort more was preventing the rear brakes less. If high pedal effort was preventing
you from stopping at maximum deceleration, softer linings will indeceleration. On a race car, this crease deceleration. means higher friction-surface temperature. The temperature at the friction surface determines the fade characteristics and friction coefficient of If your brakes were balthe lining. If anced properly before you changed to higher-friction pads, you may have to rebalance your brakes. To repeat what I said in Chapter 4, people talk about hard and soft linings without knowing the designations to describe how hard or how soft a lining is. Only brake-lining manufacturers and, perhaps, race-car engineers numbers-and they won't won't know these numbers-and tell. It would be ideal to have curves showing coefficient of friction versus temperature for the various lining materials. If you could measure the temperature of your brakes, you could then predict what pedal effort would be. Because you don't have this information, you must test to see how the linings perform. Soft linings are a practical modification for street use. However, on a race car, softer linings usually result in fade or excessive wear. wear. If soft linings don't solve your high pedal-effort further. problems, let's look further. Changing a Single or a Tandem Master CylinderCylinder- This modification is usually inexpensive and easy. Also, the results can be calculated quickly. quickly. Pedal effort is reduced if you use a smaller-diameter master cylinder, and balance will not be changed. changed. Use the following formula to calculate new pedal effort: effort: New pedal pedal effort
P P
= = -inEO
°
D 22 2N
Do Do2
in pounds pounds
P,, EO == Old Old pedal pedal effort in in pounds ON D, = = New master-cylinder diameter in in inches inches Do Do = = Old Old master-cylinder master-cylinder diameter in in inches inches
As an an example, assume assume you are are changing a 1.00-in.-diameter 1.00-in.-diameter master cylinder to a 0.75-in.-diameter 0.75-in.-diameter cylinder. cylinder. Assume the old pedal effort with the 1.00-in. 1.00-in. master cylinder was was 100 100 lb lb at maximum deceleration. deceleration. PutPutting these these numbers into the formula gives: gives: (0.75 inJ2 New pedal pedal effort effort == (100 (1 00 Ib) lb)(-~~:6g :~:l~ New
New New pedal pedal effort effort == 56 56 Ib Ib
300 --
250 --
200 -Pedal Effort (lb) (I b)
150 150 --
~
100 - 100
1OO-Ib Pedal Effort I-in.-Diameter Using a 1-in.-Diameter Master Cylinder
50 - -
-
I 0 O~-------+--------~-------+--------~-------+ I I I
0.50 0.50
0.75 0.75
1.OO 1.00
1.25 1.25
1 .50 1.50
1.75 1.75
Master-Cylinder Diameter (in.)
has a 100-lb pedal pedal effort using using a 1.0-in.-diameter 1 .O-in.-diameter master master cylinder, cylinder, this curve curve If your car has shows how master-cylinder diameter can can change change pedal pedal effort. Plot a curve like this using using shows formula in in text relating relating pedal pedal effort to master-cylinder diameter. diameter. This curve is is handy handy for formula picking picking a new single single master-cylinder or tandem tandem master-cylinder size. Remember, Remember, as pedal pedal effort is reduced, reduced, pedal pedal travel travel increases. increases.
At the same deceleration, deceleration, pedal effort dropped from 100 100 lb to 56 lb. lb. This would be true for any car changing from a 1.00-in. 1.00-in. master cylinder to a 0.75-in. 0.75-in. master cylinder. cylinder. It does not depend on any other factors. factors. This formula does not work for a brake system with dual master cylinders unless you are making the same modification to both master cylinders. cylinders. Before changing master-cylinder diameter, diameter, find out if a smaller one exists that is interchangeable. interchangeable. Some companies manufacture differentdiameter master cylinders that have the same mounting-bolt patterns. patterns. Reread what to look for for when buying a new master cylinder beginning on page 46. 46. Make sure sure you get a master cylinder with the correct features, features, such as as with or without a residual prespressure valve. valve. When master-cylinder diameter is reduced, pedal stroke increases. increases. The The amount of fluid fluid displaced to apply the brakes-move friction brakes-move friction material in contact with rubbing surrubbing surfaces-depends faces-depends on clearances in the the
system. Displacement is not afafbrake system. fected by changing changing the master fected cylinder. If 0.5 0.5 cu in. in. of fluid fluid is discylinder. placed to take up all the clearances, 0.5 cu in. in. of fluid will have to be dis0.5 placed with either the old master one. cylinder or the new one. fluid disdisBecause the volume of fluid equals the piston area times its placed equals stroke, there will be a larger stroke stroke, with a smaller-diameter master cylinder. The new movement can be cylinder. as follows follows for for a single calculated as master cylinder or tandem master pistons: cylinder with equal-diameter pistons:
°
2 New piston piston movement == Mo--%Mo- Do2 New ON DN2 in inches inches in
M o == Old Old piston piston movement in in inches inches Mo Do == Old Old master-CYlinder master-cylinder diameter in in Do inches inches D, == New New master-cylinder diameter in in ON inches inches
at the If you measure movement at master-cylinder pushrod, the answer movement at at the the pushrod. pushrod. will be movement 151
1-in.-Dia. Master Cylinders ::linders
-
7/8-in.-Dia. New New Cylinder
300Ib(382-psiPressure) 300 ~b(382-psi Pressure)
r 2 in. in. Right I--~,-o" ~ Right Ib on on Cylinder '--"4---1 500 Ib Cylinder 500 . t Balance Balance Left /-<:,..-I---j I-----l~ ~ Bar Left Cylinder r----l_'=_' L Cylinder 200lb 200 Ib '3 3 in. in. (255-psi (255-psi Pressure) Pressure)
l
2.52 in. 3971b 2.48 in. G
--r-
200 lb (255 psi) 1-in. Dia.
79-lb New Pedal Pedal Effort Effort
"--100-lb Pedal Effort 500-lb 500- lb Force Force On Balance Bar Bar
O
Pedal With With ~pedal
Pedal Pedal Ratio Ratio of of 5.0 5.0 397 Ib ---
0
o Old Old System System
New New System System
Drawing Drawing shows shows example example problem problem described described in in text. text. Changing Changing right-hand right-hand master master cylinder cylinder from IS-in. diameter from 1-in. 1 -in. to to 77/8-in. diameter reduced reduced pedal pedal effort effort from from 100 100 to to 79 7 9 lb. Ib. In In addition, addition, balance balance bar bar is is nearly nearlycentered centered in in its its adjustment adjustment with with new new master master cylinder. cylinder.
Make sure sure the the new master master cylinder Make can can supply supply the required fluid displacedisplacement without without bottoming. bottoming. First, First, be be sure sure that that the the pedal pedal will will fully stroke stroke the the master master cylinder cylinder withwithfully out bottoming on on the the floor. floor. Do Do this this out before you connect connect the the lines. lines. If If the the before pushrod bottoms, increase increase pushrod pedal bottoms, length until until the the master master cylinder cylinder botbotlength toms the the same same time time as as the the pedal. pedal. Be Be toms sure to to adjust adjust the the return return stop stop so so the the sure master cylinder cylinder will will return return fully. fully. After After the the lines lines are are connected connected and and the system system isis bled, bled, drive drive the the car. car. Heat Heat the the brakes brakes by by making making aa few few hard hard the stops, then then try try to to lock lock the the brakes. brakes. If If stops, the pedal pedal bottoms bottoms before before wheel wheel the lockup, lockup, the the new new cylinder cylinder doesn't doesn't have have enough travel. travel. If If this this isis done, done, the the enough may be be out out of of position when when pedal may retracted, requiring requiring pedal, pedal, pedal pedal retracted, and cylinder cylinder modification. modification. bracket and If If pedal pedal movement movement is is already already excesexcessive sive or or the the pedal pedal isis too too high, high, reducing reducing the the master-cylinder master-cylinder diameter diameter is is not not aa good idea. idea. However, However, if if pedal pedal travel travel isis good excessive excessive because because there's there's too too much much deflection deflection in in the the brake brake system, system, that that can be be corrected. corrected. If If you you are are troubled troubled can with with both both long long pedal pedal travel travel and and high high pedal pedal effort, effort, first first try try modifying modifying the the system system to to eliminate eliminate excessive excessive deflection. deflection. Then, Then, you you may may find find that that reducing master-cylinder master-cylinder diameter diameter reducing will will now now work. work. There's There's another another thing thing to to consider consider when reducing reducing master-cylinder master-cylinder diamdiamwhen 152
eter: eter: Fluid pressure is is higher with a smaller smaller cylinder. cylinder. Usually, Usually, brakebrakesystem system components have a maximum maximum safe 000 -1500 safe operating operating pressure pressure ofl of 10001500 psi. psi. If If the the safe safe operating operating pressure pressure isis exceeded, exceeded, the the system system can can be be dangerdangerous ous and and unreliable. unreliable. The The maximum maximum operating operating pressure pressure isis troublesome, troublesome, particularly particularly on on special special cars cars with with lightlightweight weight calipers. calipers. Some Some racing racing calipers calipers cannot high aa pressure pressure as as roadroadcannot take take as as high car car calipers. calipers. If If calculated calculated operating operating pressure pressure isis too too high, high, do do not not reduce reduce master-cylinder master-cylinder diameter. diameter. Instead, Instead, use use other other methods methods to to reduce reduce pedal pedal effort, effort, such such as as larger larger caliper-piston caliper-piston diameters. diameters. Changing Changing Dual Dual Master Master CylinCylinders - There are ders-There are two two reasons reasons for for changing changing master-cylinder master-cylinder diameter diameter on on aa car car equipped equipped with with dual dual cylinders: cylinders: to to change change pedal pedal effort effort or or brake brake balance. balance. Changing Changing one one master master cylinder cylinder affects affects both both simultaneously. simultaneously. Calculating Calculating new new pedal pedal effort effort reresulting sulting from from changing changing one one master master cylinder cylinder in in aa dual dual system system isis more more comcomplex plex than than with with aa single-cylinder single-cylinder system. system. You You must must also also consider consider the the brake-balance brake-balance change change that that occurs occurs when when only only one one cylinder cylinder isis changed. changed. If If your your brakes brakes were were balanced balanced before before the the change, change, you you must must change change the the brake brake balance balance afterward afterward to to obtain obtain maximum maximum braking. braking. Use Use the the formulas formulas in in Chapters Chapters 66 and and 99 to to calculate calculate the the new new pedal pedal effort. effort. If If
you are are changing changing one master cylinder to to reduce reduce pedal effort, effort, and and brake balbalance is is correct, correct, follow follow these steps: steps: the balance-bar setting. setting. Refer • Find the to the formulas formulas on on page page 75. 75. ratio. • Find approximate pedal ratio. each present • Find the diameter of each master master cylinder. cylinder. Estimate pedal effort effort before before changchang• Estimate ing ing the the master master cylinder. cylinder. Calculate Calculate new new pedal effort effort by by beginbeginning ning with the the following following steps: steps: Calculate present force force on on balance balance • Calculate bar: bar: MUltiply Multiply pedal pedal effort effort by by pedal ratio. ratio. Calculate force force on on each each master master • Calculate cylinder cylinder from from the the formulas formulas on on page page 75. 75. Calculate area area of of each each master master • Calculate cylinder. cylinder. Calculate pressure in in each each master master • Calculate cylinder: cylinder: Divide Divide force force on on each each master master cylinder cylinder by its its area. area. Choose a new new diameter diameter for for the the • Choose master master cylinder. cylinder. Calculate piston piston area area of of the the new new • Calculate master cylinder. cylinder. Pressure Pressure in in new new master master cylinder cylinder will will not not change change if brakes brakes were were properly balanced balanced before before modification. modification. Calculate force force on on the the new new master master • Calculate cylinder cylinder by by multiplying multiplying pressure pressure by by piston piston area. area. Because Because the the area area changed changed and and not not pressure, only only the the force force changes. changes. Add new new cylinder cylinder force force to to force force on on • Add the the other other master master cylinder. cylinder. Total Total force force isis the the new new force force on on the the balance balance bar. bar. Notice must be be adadNotice that that the the balance balance bar bar must justed justed to to give give the the correct correct forces. forces. Calculate new new pedal pedal effort: effort: Divide Divide • Calculate the the new new force force on on the the balance balance bar bar by by pedal pedal ratio. ratio. Calculate position position of of the the balance balance • Calculate bar bar for for new new forces forces using using the the formulas. formulas. To To illustrate, illustrate, let's let's run run through through aa typical typical problem. problem. Assume Assume the the brake brake system system isis as as shown shown in in the the accompanyaccompanying ing drawing. drawing. Original Original master master cylinders cylinders are are 1.00-in. 1.00-in.diameter. diameter. With With original original pedal pedal effort effort of of 100 100 lb, Ib, I'll I'll try try aa 0.875-in. 0.875-in. master master cylinder cylinder to to reduce reduce this this effort. effort. Assuming Assuming that that the the brakes brakes were were balanced balanced before before the the modification, adjustment adjustment to to the the balbalmodification, ance ance bar bar will will be be made made after after the the modification. modification. Pedal Pedal ratio ratio isis 5.0. 5.0. Using Using this information: information: this Force Forceon on balance balancebar bar == RpPE R,P, Rp Pedalratio ratio R, == Pedal PP,E == Pedal Pedaleffort effort in in pounds pounds Force on balance bar (5.0)(100Ib) Ib) Force on balance bar == (5.0)(100 Force Forceon on balance balancebar bar == 500lb 500 Ib
From formulas, the force on each master cylinder is:
From formulas, the force on each is: master cylinder (500Ib)
FL = (2 in.)
= 200 Ib
(5 in.) (500 I b) F, = (2 in.)= 200 Ib (5 in.) (500Ib)
FR = (3 in.) ( . ) = 300 Ib 5 In.
F,
=
(500 I b) (3in.) -= 300 1 b (5left in.)master cylinder in Force on
FL = pounds F, = FR = Force Force on on left rightmaster mastercylinder cylinderinir pounds pounds
F, Notice = Forceon right master cylinder ir that the sum of masterpounds cylinder forces must equal total force the sum of masteronNotice balancethat bar. That is a check on the cylinder forces must equal total force previous calculation. onUsing balance bar. That is a check on the piston diameter, old masterpreviousarea calculation. cylinder is: Using piston diameter, old masterArea = 0.78540 M 2 cylinder area is: OM = Master-cylinder diameter in Area = 0.7854DM2 inches D M = =Master-cylinder diameter in (0.7854)(1.00 in.)2 Area inches Area = 0.785 sq in. Area = (0.7854)(1.OO in.I2 Instead of calculating area, you Area = 0.785 sq in. could use the table on page 101 to find Instead of calculating area, you master-cylinder area. could use the table on page 101 to find Hydraulic pressure master-cylinder area. in each master cylinder is : Hydraulic pressure in each master Pressure = Force/Area in pou nds per cylinder is: square inch Pressure = Force/Area in pounds per 200lb square inch P = = 255 psi L 0 .785sqin 200 1 b . = 255 psi P, = 0.785 sq in. 300lb P = = 382 psi R 0.785 1 b in . 300 sq
P,
=
P,
=
=
382 psi
sq in. PL = 0.785 Pressure in left master cylinder PR = Pressure in right master cylinder Pressure in left master cylinder
, change the right cylinder to P, Now = Pressure in right master cylinder 0.87S-in. diameter. I selected the Now, the right cylinder to right onechange to change because the bal0.875-in. I selected the already adjusted for more ance bar isdiameter. right to change becauseWith the balforce one on the right cylinder. the ance bar is already adjusted for new sm aller cylinder, less forcemore will force on thetoright the be required give cylinder. the same With pressure. new smaller cylinder, lessbeforce will Thus, the balance bar will adjusted be required to new give cylinder. the same pressure. away from the Thus, the balance bar willnew be adjusted Find the area of the master away from thethe newtable cylinder. cylinder from or as follows:
Find the area of the new master Area = 0.78540 M 2 in square inches cylinder from the table or as follows: Area = (0.7854)(0.875 in.)2 Area = 0.7854DM2in square inches Area = 0.601 sq in. Area = (0.7854)(0.875in.I2 Remember that pressure in the new Area = 0.601 sq in. master cylinder remains the same. Remember the new However, the that forcepressure changes.inThe new master cylinder remains the is: force on the right master cylindersame. However, the force changes. The new Force = (Pressure)(Area) in pounds force on the right master cylinder is: FR = (382 psi)(0.601 sq in .) Force = (~ressure)(Area) in pounds FR = 230 Ib F, = (382 psi)(0.601 sq in.) F, = 230 Ib
6 .
*ib
Conventional power booster will not fit this Triumph Spitfire. There is not enough room around the master cylinder. For this application, ATE makes a booster that can be mounted in any location. It uses hydraulic pressure from the existing master cylinder to operate the booster rather thancylinder. using force directly pedal remote booster is called around Conventional the master power booster For will this not application, fit from this Triumph ATE linkage. makes Spitfire. aThis booster There that is not can enough be mounted room the ATE T -50 series. Bendix makes as similar unit called the Hydroin any location. I t uses hydraulic pressure from the existing masterVac. cylinder to operate the
booster rather than using force directly from pedal linkage. This remote booster is called the ATE T-50 series. Bendix makes as similar unit called the Hydro-Vac.
New force on balance bar is found by adding left-cylinder force to rightNew force balance bar isforce found is cylinder force.onLeft-cylinder by adding left-cylinder force to rightthe same as before-we didn't change cylinder force. Left-cylinder force is it.
the same as before- we didn't change Force on balance bar = F L + FRin it. pounds where: Force on balance bar = F, + F, in FL = Force on left master cylinder in pounds where: pounds F, = = Force Force on on right left master FR mastercylinder cylinderinin pounds pounds F, = Force on right master cylinder in Force on balance bar = 200 Ib + 230 pounds Ib 200 Ib + 230 Force on on balance balance bar bar == 430 Force Ib New onpedal effort 430 Ibnow be Force balance bar = can calculated : New pedal effort can now be calculated: F Pedal effort
=
_B
Rp
F6 -
Pedal effort on = balance bar in pounds FB = Force RP Rp = Pedal ratio F,
Force on balance bar in pounds = ~~O Ib New pedal effort = 430 1b =
New R, = pedal Pedaleffort ratio New pedal effort
=
86 Ib
With an effort original pedal New pedal = 86 Ib effort of 100 Ib, pedal effort is reduced by 14 lb. Withbalance an original effort of 100 must pedal now be readjusted Brake Ib, pedal effort is reduced by Ib. using the new force on the 14 right Brake must now be masterbalance cylinder. Because thereadjusted right and using the are new force on equal, the right the left forces close to being master cylinder. Because the righttoand balance bar can be adjusted close its left forces are close the to being the Changing rightequal, cylinder center.
balance bar can be adjusted close to its center. Changing the right cylinder
made the balance change in the desired direction. If we had changed made balancebalance-bar change in the the leftthe cylinder, adjustdesired direction. If weinhad changed ment would have gone the opposite the left cylinder, balance-bar adjustdirection - way off center. ment would have gone in cylinder the opposite had Also , if the left master direction-way off center. been changed instead of the right one, Also,effort if thewouldn't left master cylinder pedal have been had rebeen changed instead themore righteffecone, duced as much. Why? of It's pedal wouldn't have been rechange the master cylinder tive toeffort duced as much. Why? It's more effecwith the highest force when doing it tive to change the master cylinder pedal effort. to reduce with the highest force when doing On a dual master-cylinder system,it to reduce pedal effort. it's relatively easy to find master cylinOn with a dualdifferent master-cylinder system, ders diameters that it's easybolt to find master cylinhaverelatively the same pattern . Racingders with different catalogs diameters that brake-manufacturer usually have the same bolt pattern. Racingsupply all the necessary information. brake-manufacturer catalogs that usually piston Finally, remember supply all theincreases necessary when information. movement masterFinally,diameter remember that piston is reduced. Make cylinder movement increases when mastersure the new master cylinder provides cylinder diameterfluid is reduced. Make the required displacement sure thebottoming. new master cylinder provides before theAlso,required fluid not displacement if you could lock the before bottoming. wheels before the modification, the Also, formulas if you could the previous won't not worklock because wheels before that the operating modification, the it was assumed pressure previous formulas won't work because is maintained with the new master it was assumed that operating pressure cylinder. Instead, go through the is maintained calculations with the new master brake-system in Chapter cylinder. Instead, through the 9. Most cars are not go at the force limit, brake-system calculations in Chapter so the previous formulas should 9. MostBut cars are not forget at the force apply. don't the limit, usual
so the previous formulas should apply. But don't forget the usual
153
T50 / 14 Boosier
1600
T50/14 Booster
1600 -1400
T50/12 Booster
1400 -1200 T50 Booster
1200 --
-?! 5 V)
1000
a 3
1000
--
ul V)
o::J
Bi L
800
No Boost
::J
3
P
zb Qj
-;;; o
600
o
pressures at a given pedal effort is effect of booster.
rnul
&
0 0
m
You may be able to measure pedal effort directly with a small fish scale. If there is a way may to measure fluid pressure at effort same You be able to measure pedal time, you cana small determine effectIf there of power directly with fish scale. is a booster. Measure pedal effort and at hydrauway to measure fluid pressure same lic pressure boostereffect working. Then, time, you canwith determine of power try it again with vacuum line to and the hydraubooster booster. Measure pedal effort disconnected. The booster difference between two lic pressure with working. Then, pressures a given pedal effect try it againat with vacuum lineeffort to theisbooster of booster. disconnected. The difference between two
400
200
600 200 400 800 Booster I nput Pressure (psil
200
400
600
800
ATE T -50 series remote boosters have performance curves Booster Input Pressure (psi) as shown here. There are three
different models offered, each with a different boost. For most racing applications, only the T -50T-50 unit series would remote be used. More-powerful boosters curves would as be shown useful here. on heavy cars boosters have performance Thereroad are three ATE where more boostoffered, is required. different models each with a different boost. For most racing applications, only the
1-50 unit would be used. More-powerful boosters would be useful on heavy road cars
1000 maximum safe where-1500-psi more boost is required. operating pressure. If operating pres1000-gets 1500-psi maximum safe sure too high , you cannot reduce operating pressure. If operating presmaster-cylinder diameter.
sure gets too cannot reduce Adding a high, PoweryouBooster-Conmaster-cylinder diameter. verting to power brakes is a good way Adding a Power Booster-Coneffort. This method is to reduce pedal verting powercarbrakes is a good way used bytomost manufacturers for to reduce is road cars.pedal Eveneffort. light This cars method with disc used by most car manufacturers for brakes now come equipped with a road Even With light power cars with disc, brakes powercars. booster. brakes now come equipped with a don't have to fight the problems you power booster.pedal Witheffort poweror brakes, of excessive travel. you don't have to fight problems Instead, you can have thethe best of both of excessive pedal assist: effort low or travel. worlds with power pedal Instead, have the best of both travel andyou lowcan pedal effort. worlds with power pedal The easiest car to assist: convertlow to power travel and low pedal effort. brakes is a road car that could be The easiest carpower to convert to power purchased with brakes as an brakes is road becarable thatto could be option. Youa may purchase purchased with power an all the necessary partsbrakes from asyour option. Youa may be able purchase dealer, or salvage yard.toAsk your all the necessary parts from your dealership parts man what's necessary dealer, or to a salvage yard. Ask power brakes. This your may to convert dealership partsvacuum man what's necessary extra lines and a require to convertpedal to power brakes. This may different , master cylinder and require extra vacuum lines pedal-support bracket. Get the and entirea different pedal, master cylinder and pedal-support bracket. Get the entire 154
picture before buying parts. If power brakes weren't offered, picturemay before buying parts. fitting a you have trouble If power weren't offered, If brakes the master cylinder is booster. you may have trouble fitting mounted under the floor or close toa booster. If itthe cylinderto fit is the engine, maymaster be impossible mounted under the floor or close to a conventional vacuum brake booster. the engine, it may to fit might be able be to impossible install a smaller You ahydraulic conventional brakevacuum booster,brake but abooster. powerYou might be able install a smaller steering pump musttobe plumbed into hydraulic brake booster, but or installed . This requires aa powerlot of steering pump must be plumbed into work. or Some installed. requires a lot of brakeThis boosters are designed work. as an accessory for existing brake Some brake are designed One boosters such booster is the systems. as-50, an accessory existing T made by forATE in brake West systems. is the Germany. One This such unit booster is designed to T-50, ATE thein master West mount made remotelyby from Germany. rather This unit cylinder, than isin designed tandem. to It mount remotely master uses input pressurefrom from the the existing cylinder,cylinder rather and thanraises in tandem. It master this presuses input pressure from the existing sure with a vacuum-operated piston master and extra raisesforce. this presor supply ATE to boost,cylinder sure withdata a vacuum-operated on this unit. Inputpiston presprovides to boost, or output supply pressure extra force. ATE sure versus is shown provides data on this unit. Input presby the nearby curve. This booster may sure versus output is shown if youpressure have difficulty be desirable
by the nearby curve. This booster may be desirable if you have difficulty
mounting a booster in the conventional location. Bendix makes a similar mounting booster inVac. the conventionunit called athe Hy droal Most location. makesuse a similar race Bendix cars don't power unit called the Hydro- Vac. brakes because: Most race useonpower is notdon't required light • Power assist cars brakes because: race cars . If pedal effort is too high on Power assist isunder not required light a car weighing 2500 Ib, on there 's race cars.aIfbrake-design pedal effort problem is too high probably . on a• car weighing under 2500 Ib, there's equipment adds Power-brake probably a brake-design weight and complexity. problem. Driver feel is notequipment as precise as adds with • Power-brake weight and brakes. complexity. unboosted Driver feelrace is not precise with A heavy car as with disc as brakes unboosted brakes. may require power brakes. For A heavyonrace car car, withthere disc may brakes example, a stock be may require power solution if hardbrakes. linings For are no other example, on a stock car, maycars be mostthere stock used . Fortunately, no other solution if hard linings are have enough room under the hood to used. mostbooster. stock This cars mount Fortunately, a power.. brake havebeenough room under the hood to can a simple change if stock pedals mount a p o w e ~ b r a k e booster. This and master cylinder are used . canWhen be a simple pedals adding change a powerif stock booster, try and master are used. that goes the cylinder master cylinder to use When booster, with the adding booster.a Ifpower you don't , youtry ' ll to use the master cylinder that goes have to check the stroke of the booster with master the booster. If you don't, and cylinder to be sureyou'll they have compatible. to check the stroke of the booster If master-cylinder are and master cylinder to bebooster, sure they stroke is more than the the are compatible. If master-cylinder booster will not bottom the cylinder. stroke is more than the booster, However, if master-cylinder strokethe is booster will no notproblem. bottom the cylinder. less, there's However, if master-cylinder stroke is investigate the inner You must less, there's no problem. workings of both the master cylinder Youbooster must investigate the inner and to determine their workingsSee of the bothfactory the master cylinder strokes. shop manuals and booster to determine their for this. strokes. Seeother the factory manuals mastershop cylinder, one Like any for this. from a power-brake system must have Like anydisplacement. other master So, cylinder, one sufficient if you're from a power-brake system must have using the brakes from one car and a sufficient displacement. So, if you're master cylinder from another, check
using the brakes from one car and a master cylinder from another, check
Part No. 3188 3/8-24 3149 3/8-24 *3555 3/8-24 3353 3/8-24
Bore Bore Size. Size. (in.) (in.) 3/4 13/16
7/8 15/16
* Part Illustrated
Drawing was taken from Bendix Bendix Brake Brake Drawing Reference and and Identification Catalog. It Reference shows a wheel cylinder which which comes in in shows four different diameters. Many wheel cylinders are illustrated. This will show you what other size wheel cylinders may be be car. Go to an an auto-parts available for your car. Bendix parts. parts. Drawing store that sells Bendix courtesy Bendix Bendix Corp. Corp.
master-cylinder displacement. displacement. If it bottoms, the brakes won't won't work. Displacement of the new master cylinder should be equal to or greater than the one designed for the brake system. system. The big problem in adapting a brake booster to a special special car is getting the correct pedal effort. effort. If the booster supsupplies excessive boost, the brakes will be too sensitive. Too much boost can be dangerous. dangerous. It's too easy to lock the wheels wheels ifpedal if pedal effort is low. low. Pedal effort with power brakes is determined by the design of the brakes and booster, pedal ratio, and vacuum or power-steering-fluid power-steering-fluid pressure supplied to the booster. Calculating pedal force is complex. And, it is difficult to get all the required information. To get this information, start by testing to determine brake-fluid pressure. Find a car with the power booster you plan to use. Install a fluidfluidpressure gage gage in the line to the front brakes. With the engine running, apply the brakes and record pedal effort and fluid fluid pressure. You can use a small small scale scale to measure pedal force. force. Try various forces and plot a graph of pedal effort versus hydraulic pressure. If you know the hydraulic pressure for for a given pedal effort, you can use formulas in Chapter 9 to design the formulas your brake system. system. Correct for any difdifference in pedal ratio between your
car and the one the power booster came from. from. If your car's pedal ratio is higher, fluid pressure on your car will be higher and vice versa. versa. Let's run through a sample calculacalculation to correct for pedal ratio. ratio. Assume the pedal ratio is 8.0 8.0 on your car and 5.0 on the car the brake booster came from. from. Let's also also assume that you tested the car with the brake booster and got 500-psi 500-psi fluid pressure for 20-lb pedal effort. effort. With the pedal ratio of 5.0, 5.0, the force on the booster-input rod is: is: on booster == R,P , E Force on pP R, == Pedal Pedal ratio ratio Rp P,E == Pedal Pedal effort in in pounds pounds Force Force on on booster
= = = =
(5.0)(20 (5.0)(20Ib) Ib) 100 Ib 1001b
Fluid pressure from the boosted 100-lb force cylinder is 500 psi with a 100-lb on the booster. If you put this booster and cylinder on your car with its pedal 8.0, pedal effort will be lower ratio of 8.0, for the same hydraulic pressure, providing vacuum or hydraulic same. pressure to the booster is the same. Your car's pedal effort at 500-psi 500-psi hydraulic pressure will be: be: FB F, Pedal Pedal effort == -Rp RP
F, FB R, Rp
= Force on on booster = = Pedal Pedal ratio ratio =
in pounds pounds in
100lb Ib = Ib. Pedal = loo - 12.5 lb. Pedal effort =
s:o--
This compares to the 20-lb effort on the car with a pedal ratio of 5.0. 5.0. Larger Wheel Cylinders - If you Cylinders-If have drum brakes on all four wheels, pedal effort can be reduced by replacing the wheel cylinders with larger ones. ones. The effect of increa8ing increasing wheelcylinder diameter is the same as reducing master-cylinder size. size. Wheelcylinder changes changes typically are more difficult than changing mastercylinder diameter because wheel cylinders are more trouble to adapt. And, you're you're working with more of them. However, the advantage of changing wheel cylinders is that fluid pressure is not affected. affected. Input pressure from the master cylinder is unchanged for a given pedal force. force. If the hydraulic system operates at high pressure, changing wheel cylinders is better than going going to a smaller master cylinder. cylinder. Regardless of pressure, larger wheel cylinders have the same effect as a smaller
master cylinder. cylinder. Both situations rerequire more fluid displacement, so check for adequate master-cylinder displacement as already discussed. discussed. The trouble with changing wheel cylinders is finding ones that will fit. fit. Often, Often, the mounting is different, the bleeder is in the wrong place, or other physical differences make the job impractical. impractical. If you decide to try changing wheel cylinders, first check wheel cylinders from from a car by the same manufacturer as yours. yours. For example, example, if you have a Chevrolet, Chevrolet, first consider Chevrolet cylinders. If that fails, fails, look at cylinders from other GM divisions. divisions. If you can't find a suitable cylinder, cylinder, try other American cars using a similar drum-brake design. Calculate the effect on pedal effort of changing wheel-cylinder diameters as as follows. follows. This assumes the car has drum brakes all around, all use the same-size wheel cylinders, and all cylinders are changed. changed. pedal effort New pedal
= =
2 0D2wo ,, EO D , P
---f!2--
o WN WN
PEO P ,, == Old Old pedal pedal effort in in pounds = ,0wo D , = Old Old wheel-cylinder wheel-cylinder diameter in in inches inches OWN DwN== New wheel-cylinder wheel-cylinder diameter in in inches inches
Notice that the cylinder diameter is squared, so a small change in diameter has a major effect on pedal effort. The previous formula only works if if all the brakes use the same size wheel cylinders and all brakes are modified the same way. way. On most cars, this will not be true. Instead, a wheel-cylinder modification would usually fall into one of two categories: • Disc brakes are used on the front and drums on the rear. Only the wheel cylinders on the rear brakes are modified. • Four-wheel drum brakes are used, but only one pair of brakes has the wheel cylinders modified. In either case, the wheel-cylinder modification affects affects both pedal effort and brake balance. Make sure you can deal with two changes changes at once before modifying the wheel cylinders on only one end of the car. car. To see what a wheel-cylinder change does, it's easiest to determine the effect changing wheel-cylinder size has on brake torque at a given hydraulic pressure. Then, by using the formulas in Chapter 9, calculate the effect on pedal effort. effort. This formula asas155
-
~"""--~17""-.....,---
This double-piston caliper is manufactured by JFZ Engineered Products. If you want to double brake torque or is cutmanufactured pedal effort This double-piston caliper in half, install double-piston in by JFZ Engineered Products. Ifcalipers you want place of single-piston Of course, to double brake torquecalipers. or cut pedal effort this alsoinstall doubles pedal travel. Photo in half, double-piston calipers in courtesy JFZ. place of single-piston calipers. Of course,
this also doubles pedal travel.
Photo
courtesybrake JFZ. balance is not changed sumes after the modification. Readjusting sumes brake balance changed brake balance usuallyis not reduces the after the modification. Readjusting effect of a wheel-cylinder change.
brake balance usually reduces the D2change. effect of a wheel-cylinder WN Newbraketorque=T o in inch-pounds New brake torque
2
D wo D2WN = To
D wo in inch-pounds To = Old brake torque in inch-pounds DWN = New wheel-cylinder diameter in To = Old brake torque in inch-pounds inches DwN= wheel-cylinder diameter diameterinin Dwo = New Old wheel-cylinder inches inches Dwo = Old wheel-cylinder diameter in
Changing only the rear-wheel cylininches ders only has less effect on pedal Changing rear-wheel cylinthan ifonly onlythe the front ones are effort ders only has less effect on changed . This is because the pedal front effort if only thework. front ones are brakesthan do most of the changed. This is because front With disc brakes only on the the front, brakes do most of the work.cylinders to changing the rear-wheel With pedal disc brakes on worth the front, reduce effort only is not the changing the rear-wheel cylinders to trouble. If the brakes were balanced reduce effort is not, worth the the modification the new before pedal trouble. If cylinders the brakeswould were cause balanced rear-wheel the before the modification, the also rear wheels to lock up first. There new rear-wheel would cause the would be acylinders small reduction in pedal rear wheels up first. also effort. If to youlockuse an There adjustable would be a small reduction in pedal the proportioning valve to balance effort. If you use an adjustable brakes, rear-brake torque is reduced. proportioning valve to balance the Consequently, reducing rear-brake brakes, reduced. tends to torque cancel is Ollt the torque rear-brake Consequently, reducing reduction in pedal effort rear-brake gailled by torque tends cancel Alloiit the changing wheel to cylinders. you've reduction in time pedalandeffort gaii~ed by done is spent money without changing wheel cylinders. you've significantly reducing pedal All effort. done spent time moneytowithout Youis should onlyand change larger significantly reducing pedal rear-brake wheel cylinderseffort. if someYouisshould change to larger thing done toonly increase front-brake rear-brake wheel cylinders if sometorque at the same time. thing is done to increase front-brake Larger Piston-Area Calipers-If you torque at the same time. have disc brakes, pedal effort can be Larger Calipers-If you reducedPiston-Area by installing calipers with have disc brakes, pedal effort can in bigger pistons or with more pistons be
reduced by installing calipers with bigger pistons or with more pistons in
156
Installing two calipers per rotor and a slightly larger-diameter master cylinder can cut pedal effort and Significantly improve lining life. This Formula 1 Grand Prix car uses two AP Racing calipers on each a track that requires little braking, one caliper can Installing two calipers perfront rotorrotor. and aOn slightly larger-diameter master cylinder can cut pedal be removed to save weight. Notice temperature-indicating paint on rotor nearest effort and significantly improve lining life. This Formula 1 Grand Prix car under uses two AP caliper. Photo courtesy Racing. Racing calipers on eachAP front rotor. On a track that requires little braking, one caliper can
be removed to save weight. Notice temperature-indicating paint on rotor under nearest caliper. Photo courtesy AP as Racing. each caliper. As long total piston one piston set. Depending on the
area is increased, this has the same
each as drum-brake total piston effect caliper. as goingAstolong bigger area iscylinders. increased, this has the same wheel effect as goingcaliper-piston to bigger drum-brake Increasing area is a wheel cylinders. good modification on a system with Increasing area is isa pressure. Pressure high operatingcaliper-piston good modification onisathe system with reduced afterwards as deflection highbrake operating Pressure is of hosespressure. and other parts. reduced afterwards as is the deflection However, increased piston area also of brake brake-pedal hoses and travel. other Thereparts. increases However, increased pistontoarea alsoa fore, you may also have go to increases brake-pedal travel. Therelonger-stroke master cylinder. fore, may with also installing have to go to a Theyou problem calipers longer-stroke master cylinder.pistons is that have larger-diameter The problem with installing that calipers usually have the calipers largest that have larger-diameter is a caliper pistons possible. If you findpistons that calipers usually have the largest with larger pistons, it probably has pistons possible. If you find a caliper larger pads. The problem here is that with pistons, a itlarger-diameter probably has larger larger pads require larger pads. The problem is that rotor. Therefore, findinghere a caliper larger pads require a larger-diameter with larger pistons not requmng a rotor. rotor Therefore, finding caliper generally is nota usually larger with larger pistons not requiring a possible. larger rotor generally is not usually Multiple-Piston Calipers-The usupossible. al modification for disc brakes is inMultiple-Piston Calipers-The usuof stalling calipers with multiple sets al modification disc have brakesa single is inpistons. If your for calipers stalling withofmultiple setsyou of piston oncalipers each side the rotors, pistons. If your calipers have a single may be able to replace them with twopiston on each side the rotors, you or three-piston sets.of Racing calipers may be able to replace them with twoare sometimes made with more than or three-piston sets. Racing calipers are sometimes made with more than
number of pistons used, calipers are one piston set. Depending ontriplethe single-piston, dual-piston or called
number of pistons used, calipers are piston calipers. called or iripleYou single-piston, may have dual-piston trouble mounting piston ca Iipers. new multiple-piston calipers even if Youfindmay mounting onehave that trouble fits your rotors. you new multiple-piston Check with one orcalipers more even of theif you find onemanufacturers that fits yourlisted rotors. brake-caliper in Check with one or more of the the Suppliers Index for calipers and brake-caliper listed in mounting kitsmanufacturers to fit particular cars. the Suppliers Index for tocalipers and You may also have purchase mounting kits tohardware. fit particular cars. caliper-mounting You may also have to purchase If you change to multiple -piston caliper-mounting an added benefit calipers , there's hardware. If youreduced changepedal to effort. multiple-piston besides The calicalipers, there's an added benefit pers must be larger and heavier to besides reduced pedal effort. The calicontain multiple pistons. As a result, pers must bewilllarger and heavier to run cooler than the the calipers contain As a result, smaller multiple calipers pistons. they replaced. Fade the run with coolerthethanlarger the will calipers be less will likely smaller calipers they replaced. Fade calipers. In addition, larger pads will will longer. be lessEven likely with bigger the larger last though calicalipers. In addition,you larger pads will get value for pers are expensive, last additional longer. Even the cost. though bigger calipers expensive, you get for Thearenew pedal effort forvalue calipers the additional cost. with larger-diameter pistons can be The new pedal calipers calculated using effort the forfollowing with larger-diameter pistons can all be formula. Note: This assumes that calculated using the following four brakes have the same-size califormula. assumes all pers andNote: are This changed the that same four brakes have the same-size caliamount: pers and are changed the same amount:
Using low-profile tires will lower pedal effort slightly. If you put wider wheels and tires on a car, use lowest profile tire possible to end up with minimum pedal effort. This Fiat owner was able to lower the CG put pedal a lot ofeffort rubber on the Ifroad low-profile tires. Using low-profile.tires willand lower slightly. youwith put wider wheels and tires on a car, use lowest profile tire possible to end up with minimum pedal effort. This Fiat owner was able to lower the CG and put a lot of rubber on the road with low-profile tires.
New pedal effort
=
02 P EO /0 in pounds oD CN
New pedal effort = pE0+in
pounds
D pounds CN Old pedal effort in DEO = Old caliper-piston diameter in P, , = Old pedal effort in pounds inches DEo DCN = = Old Newcaliper-piston caliper-pistondiameter diameterinin inches inches PEO =
= New caliper-piston diameter in When changing to multiple-piston inches calipers with the same diameter as the changing multiple-piston oldWhen pistons, use the to following formula calipers with the same diameter as the to find the new pedal effort. Again, it old pistons, use formula is assumed thatthe allfollowing four brakes are to findchanged the newidentically. pedal effort. Again, it being is assumed that all four brakes are being changed identically. NpO
D ,,
New pedal effort
=
PEO - - in pounds NpN
New pedal effort = P,,-
NpO
in pounds
Old pedal effort inNPN pounds Npo = Number of pistons in old caliper PEo pedalofeffort in pounds NpN = = Old Number pistons in new caliper PEO =
N,, = Number of pistons in old caliper For floating calipers, multiply the NpN = Number of pistons in new caliper number of pistons by two . Each piston floating calipers, multiply the in For a floating caliper does the job of two number of pistons by two. Each piston pistons in a fixed caliper. in When a floating caliper both does piston the jobdiameof two changing pistons in a fixed caliper. ter and the number of pistons , use When changing both piston both formulas . First, correctdiamepedal ter and for the the number of pistons, use change in piston effort both formulas. First, correct pedal diameter. Then, put that pedal effort effort the forchange piston into the for formula numberin of pistons diameter. Then, that pedal effort and calculate finalput pedal effort. into formula number pistons Twinthe Calipers - for If you have of a race car and calculate final pedal effort. with one caliper on each r'o tor it may Twin Calipers-If you two havecalipers a race car be possible to mount on with one caliper eachreduce rbtor itpedal may each rotor. Thisonwill be possible to if mount two calipers on effort by half you change all four
each rotor. This will reduce pedal effort by half if you change all four
twin calipers. This brakes to modification has the same effect as brakes to twin calipers. changing the brakes from singleThis to modification has the as It mayeffect actually double-piston calipers. same changing theaddition, brakes from single to you can always cost less. In double-piston calipers. It may actually remove one set of calipers if you run cost In addition, you on can brakes. always on aless. track that is easy remove one set of calipers if you run Remember that doubling caliperon a track is easy on brakes. piston areathatwill double fluid Remember thatso doubling caliperdisplacement, master-cylinder piston area will double stroke or area may have tofluid be displacement, so master-cylinder increased to compensate. stroke area master-cylinder may have to area be If you or increase increased to compensate. by a lesser percentage than caliperIf youarea, increase master-cylinder area piston you'II get a pedal-effort by a lesser percentage than caliperreduction. Also, the doubled lining pistonwill area, you'll getincrease a pedal-effort area significantly lining reduction. Also,you themay doubled lining life. Therefore, run soft linarea will significantly increase lining ings with twin calipers and hard linings life. youlinings may run linwith Therefore, singles. Softer willsoft further ings with twineffort. calipers and hard linings reduce pedal with singles. linings willtoofurther If you are Softer thinking this is good reduce pedal effort. to be true, you're right. Adding a If you caliper are thinking is too good second on a this rotor restricts to be true, you're right. Adding cooling. Because more of the rotor isa second caliper a rotor covered, airflow on through the restricts rotor is cooling. Because more of is restricted. Consequently, the therotor rotor covered, airflow through the rotor is doesn't cool as well. restricted. Consequently, The previous formulas inthe thisrotor secdoesn't coolonly as well. tion apply to a car that has the The previous in this secsame-size brakesformulas on all four wheels tion apply only to a car that has and to the same modification to the all same-size all four four brakesbrakes at theonsame time.wheels This and to the the formulas same modification all makes simple, buttothey four brakes at the same time. This may not apply in your situation. Most makes formulas simple, front but they cars arethe modified differently and may not your situation. Most or apply don'tin have the same-size rear, cars arefront modified differently front and brakes and rear.
rear, or don't have the same-size brakes front and rear.
Unfortunately, there are no simple formulas to predict exactly what hapUnfortunately, there areyou no modify simple pens to pedal effort when formulas to predict exactly what only one pair of brakes. However, hapyou pens make to pedal effort whenestimates. you modify can some rough If only one pair of brakes. you you modify only the However, front brakes, can make some rough estimates. If you'll realize about two-thirds of the you modify only the front brakes, change in pedal effort that the formuyou'll about two-thirds of the las forrealize changing all four brakes change pedal effort let's that the predict. in For example, use formuone of las for changing brakes the simple formulasallto four predict the predict. For example, let's use one of new pedal effort for a modification to the simple only the frontformulas brakes. to predict the new pedalsayeffort a modification Let's the for formula predicts toa only thefrom front abrakes. change 90-lb pedal effort to a Let's sayeffort the offormula predicts new pedal 30 lb. The changea change from a 90-lb pedal effort in pedal effort is 60 lb. Because to thea new pedal effort of 30 lb. The change rear brakes were not modified, the in pedalchange effort isis about 60 lb. two-thirds Because the actual of rear brakes not the modified, the this change.were Thus estimated actual change aboutis two-thirds (2/3) X 60 of lb change in pedaliseffort this change. Thus the estimated = 40 lb. The estimated new pedal changeafter in pedal effort is (213) X 60 the modification is 90 Ib -lb effort = 40 lb. The estimated new pedal 40 lb = 50 Ib: effort afterfront the modification is 90 If both and rear brakes arelbthe 40 lb = 50 Ib: same size, but are not modified If both front rear brakes are can the theand simple formulas identically, same size, are not new modified again be usedbut to estimate pedal identically, can effort. Use the the simple formulaformulas twice-once again be used to estimate new pedal for the front-brake modification and effort. Use formula modification. twice-once rear-brake again for thethe for modification and Addthe thefront-brake two answers and average again for the rear-brake modification. them to get a rough estimate of the Add the effort. two answers and average new pedal them to get rough estimate To get an a accurate answer offorthea new pedal effort. modification, you must use the To get inan Chapter accurate9.answer for a formulas This means modification, you must use the performing a number of calculations formulas 9. This for both intheChapter old and new means brake performing a number of 'calculations systems. for both Tire the .Diameter-If old and newyou brake Reducing insystems. stall tires with a smaller outside Reducing Tire,Diameter If you will indiameter or roll-out, pedal effort stall tires with a smaller outside be reduced. This is an easy change to diameter roll-out, pedal effort will make, butoronly a small reduction in be reduced. This is an to pedal effort results. Youeasy willchange not want make, butmoney only aforsmall in new reduction tires only to to spend pedal effort results. You will not want change brake-pedal effort. The to spendofmoney new be tires onlythe to amount changefor won't worth change brake-pedal However, changingeffort. tires canThe be cost. amount offor change be worth desirable otherwon't reasons , such the as cost. However, changing tires can be lowering the car for improved desirable for other reasons, such as handling. lowering car smaller-diameter for improved Usually, the putting handling.on a car won't work. The wheels Usually, putting designed smaller-diameter brakes are usually to be as wheels on a car won't big as possible and still fitwork. inside The the brakes are usually designed to betire as wheels. Therefore, if you change big as possible and still inside the diameter, you should do itfitwith lowerwheels. Therefore, if you change Tire designations refertire to profile tires. diameter, you should do it with the ratio of height to width.lowerFor profile tires. Tire designations to example, a 50-series tire has a refer section the ratio height to width. width.A For height that of is 50% of its 50-
-
example, a 50-series tire has a section height that is 50% of its width. A 50157
Disc Brake
120
100
100
:c
~pedal
-
Bracket
80
:2
--b £i5
Li:i 4-
Cii
"0
m
u
Leading-and-TrailingShoe Brake
60
60
-
Ball of Foot
Leading-and-TrailingTwo Leading-
Foot
Shoe ShoeBrake Brake \
40
,
L'~\
Longer Pedal (Too Low)
20
20
\
\
Duo-Servo Brake
-
o~----~----~----~----~--~--o 0.1 0.2 0.3 0.4 0.5 0
0.1
Lining Coefficient of Friction
0.2
0.3
0.4
0.5
of Friction Graph shows how pedalLining effortCoefficient would change if you change servo action of your brakes. Converting to drum brakes from disc brakes has the biggest effect, but I don't know why anyone would do such a thing.ofThis assumes that all are the same action yourgraph brakes. Converting tobrakes drum biakes from d i seffective i brakes radius haveeffect, typicalbut cylinder Purposewould of this has theand biggest Idon'tdiameters. know why anyone dograph such is thing. to compare various types that of drum brakes, disc-brake a This graph assumes all brakes arebecause the same effective pedal can typical be varied greatly with caliper design. curve radiuseffort and have cylinder diameters. Purpose of This this graph should be usedvarious only as types a rough becausebecause actual numbers will is to compare of guide, drum brakes, disc-brake vary onevaried car to greatly another.with caliper design. This curve pedalgreatly effort from can be
Most race-car brake pedals are designed to fit the driver's foot. If you changed pedal ratio by making the pedal arm longer, the pad would be in the wrong place. Changingtothe pedal bracket Most race-car brake pedals are designed fit the driver's foot. or If master-cylinder location is making nearly impossible on most beyou changed pedal ratio by the pedal arm longer,cars, the pad cause mounting areplace. an integral part of thepedal framebracket structure. would be in thepoints wrong Changing the or Don't try changing pedal ratio unlessimpossible your car ison well suited to this master-cylinder location is nearly most cars, bemodification. cause mounting points are an integral part of the frame structure.
Don't try changing pedal ratio unless your car is well suited to this modification.
should be used only as a rough guide, because actual numbers will rolling radius of the tire is used. As vary greatly from one car to another.
discussed on page 94, it's the distance rolling of the oftire used. and As betweenradius the center theiswheel 94, it's the distance discussed on page the ground. between the centertires, of the wheel both and. When changing measure the tires.ground. Measuring rolling radius is When on changing covered page 94.tires, measure both tires. Measuring rolling is Once you have the rollingradius radius of covered on page 94. both tires, calculate the new pedal Once you have the rolling radius of effort:
both tires, calculate rthe new pedal effort: New pedal effort = P EO"::: in pounds
This slalom racer uses VW drum brakes in a 15-in. wheel. On this car, it is possible to increase effective radius of drum brake.brakes Usually, VW in This slalom racer uses the brake on a On race fits close to the a 15411, wheel. thiscar car, i t is possible to wheel rim.effective If larger-diameter Porsche drum increase radius of brake. Usually, brakes were effort the brake on ainstalled, race car the fits pedal close to the would be by a noticeable amount. wheel rim.reduced If larger-diameter Porsche drum
brakes were installed, the pedal effort would be reduced by a noticeable amount.
series tire is lower than a 60-series tire of the same section width. Because series tire isare lower than a 60-series tire tire sizes confusing and tread of the same section width. Because widths vary, the best way to choose tire sizes isare confusing andor comtread new tires to measure them widths vary, the best way to choose pare their published specifications. new tiresdiameter is to measure themused or comTire is not in pare their published specifications. brake-system calculation . Instead,
Tire diameter is not used in brake-system calculation. Instead,
158
ro New pedal effort: = , ,P in pounds PEQ = Old pedal effort in0pounds rN = New-tire rolling radius in inches P ,, = =Old-tire Old pedal effort in pounds ro rolling radius in inches = New-tire radius in inches r, As you can rolling see, smaller tire rolling rolling radius in inches rradius , = Old-tire reduces pedal effort. By install-
you can see, tirecar, rolling on your you ingAslow-profile tiressmaller radius improve reduces pedal By installcan botheffort. braking and ing low-profile tires on your car, you handling. Larger-Diameter Drumsbraking or RotorsCan improve both and handling. If there is room in the wheels, changLarger-Diameter Drums or Rotorsing to brakes with larger-diameter If there or is room the wheels, drums rotorsin will reduce changpedal ing to This brakes with larger-diameter modification will result in effort. drumsimprovements, or rotors willtoo:reduce pedal other The brakes effort. modification will result in runThis cooler and pads or shoes may will other atimprovements, too: Tbrakes h e brakes wear a lower rate. Bigger are will runmodification cooler and pads or shoes may a good if possible.
wear at a lower rate. Bigger brakes are a good modification if possible.
The critical dimension of a brake is its effective radius, as described in T h e critical of aradius brake of is Chapter 9. Thisdimension is the inside its eflective radius, as described in a drum, or the rotor radius measured Chapter 9. This is the radiusefof to the center of the pad.inside Increasing a drum,radius or thewill rotor radius measured fective reduce pedal effort. to The the center of the pad.isIncreasing new pedal effort calculatedefas fective radius will reduce pedal effort. follows:
The new pedal effort is calculated as rEO follows: New pedal effort = P EO in pounds
r EN 'EO New pedal effort = -P ,, in pounds P EO = Old pedal effort inTENpounds rEO = Old brake effective radius in ,P , = Old pedal effort in pounds inches rE0 = New Old brake r EN = brakeeffective effectiveradius radiusin in inches ,,r = New brake effective radius in Because effective radius is limited inches
by existing wheel diameter, it can't be Because much. effectiveTherefore, radius is limited it will increased by existing wheel diameter, give only small benefitsit can't and be is increased much. Therefore, it will will expensive. However, the benefits give onlyif small benefits is be great you can make and a large expensive. However, the benefits will change in effective radius. beTogreat if you can make a large brakes for a find larger-diameter change in effective radius. check the brakes used on road ca~ To similar find larger-diameter brakesbrakes for a cars to yours. Locate road car, check the brakes used on that will mount easily on your car. cars similar to yours. Locate brakes Often, larger-diameter brakes from
that mount on your car. one will model will easily fit another. Check Often, larger-diameter brakes from brakes from a station wagon or truck. one model will fit another. Check brakes from a station wagon or truck.
They may fit a sedan suspension and be larger. Some manufacturers They fit asizes sedan suspension and changemay brake during a redesign, be larger. the Some manufacturers but retain original mounting change a redesign, points. brake See sizes your during car dealer for but retain the original mounting information. points. See Servo your car dealer Increasing Action - D rufor m information. brakes are designed with varying Increasing Servo Action-Drum amounts of servo action . As you may brakes from are Chapter designed 2, with varying recall the amount amounts of servo action. As you may depends on the geometry of the interrecall from Chapter 2, the amount nal parts of the brake. Leading-shoe depends the geometry of theaction; interbrakes on have high servo nal parts of the brake. Leading-shoe trailing-shoe drum brakes do not. If brakes high servo brake action; you put ahave dual-leading-shoe in trailing-shoe drum brakes do If brake, place of a single-leading-shoe not. you put a dual-leading-shoe brakeand in this usually increases servo action place of apedal single-leading-shoe brake, reduces effort. A duo-servo this usually increases servo action and brake has the most servo action. reduces pedal effort. A duo-servo Replacing single-leading-shoe brakes brake has the brakes most servo with duo-servo would action. cause Replacing single-leading-shoe brakes the greatest reduction in pedal effort. with duo-servo brakes cause Changing servo actionwould is difficult the greatest reduction in pedal effort. and expensive. Also, it is difficult to Changing servo action is difficult predict the resulting pedal effort. You and it is difficult to mustexpensive. know the Also, coefficient of friction predict the resulting pedal effort. You and the exact geometry of the brake must know thecalculate coefficient of friction to accurately servo action. and the exact geometry of the brake The graph at left gives you a rough to accurately calculate idea of what will happen.servo The action. curves The graph at left you a of rough in this graph applygives to brakes the idea of what will happen. The curves same diameter, but with different in this graph applyaction. to brakes of the amounts of servo These are same diameter, but 1101with different rough estimates-do use them for amounts of servo action. These are exact calculations. rough estimates-do use them for If you want a big not change in pedal exact effort calculations. and are willing to change the If you want big changetryintopedal complete brake aassembly, find effort and are willing to change brakes with a differen t servo action.the It complete brake asseibly, ro find may be difficult to find a try brake that brakes a different action. It will boltwith onto your car. servo As with many may be difficult to find a brake that other modifications discussed, start will bolt onto car. atAsbrakes with many the search by your looking used other discussed, start on cars modifications by the same manufacturer. theThe search by looking at brakes servo used problem with increasing on cars by the same manufacturer. action is that the tendency to fade The problem withifincreasing servo increases . However, your car has no action is that the increasing tendency to servo fade fade problems, increases. if your car already has no action mayHowever, work. But, if you fade problems, increasing experience fade, stay away servo from action But, action. if you Anothalready brakes may with work. high servo experience fade, ofstay away servo from er disadvantage increased brakes on withfront highdrum servobrakes action.isAnothaction that it er servo cause the brakeofto increased pull. can disadvantage action on front drum brakes is that it To summarize, modifying servo can cause brake to pull. action is the expensive, somewha t unTo summarize, predictable , and maymodifying cause fadeservo and action is expensive, unpull problems. It is notsomewhat a good choice predictable, and may cause fade and for lowering ped al effort. I t isRatio-An not a goodobvious choice pull problems. Increasing Pedal for lowering pedal effort. way to reduce pedal effort is to inIncreasing Pedal ratio RatioAn means obviousa crease the pedal . This way to reduce pedal effort is indifferent brake pedal with more to lever-
crease the pedal ratio. This means a different brake pedal with more lever-
This Mercury requires adjustable brake balance for two reasons. Switching from street driving to racing increases weight transfer and requires more braking effort on the front wheels. RaCingrequires in the rain reducesbrake weightbalance transfer requires less braking on thestreet front This Mercury adjustable forand two reasons. Switching from wheels to compared to racing inweight the dry. Photo by Steven Schnabel. driving racing increases transfer and requires more braking effort on the front
wheels. Racing in the rain reduces weight transfer and requires less braking on the front wheels compared to racing in the dry. Photo by Steven Schnabel.
age on the master cylinder. The pedal ratio is determined from the methods age on theinmaster cylinder. The pedal discussed Chapter 6. ratio is determined Pedal ratio is from hard the to methods change. discussed Chapter 6. Normally, insimply extending the pedal Pedalwork ratio is hard to change. won't because the pedals are deNormally, simply extending pedal signed to fit the driver's foot the while the won't work because the pedalsposition. are dedriver is in his normal signed to fit athelonger driver'spedal foot arm whilemay the Therefore, driver is in his normal position. make the pedal pad too high or low for Therefore, a longer aim may comfort. And, there'spedal a danger that make the pedal pad too high low for the extended pedal will or bottom comfort. And, there'shanging a dangerpedals that against the floor-if the extended pedal will bottom are used-and not match the position against the floor-if hanging pedals. pedals of the clutch and accelerator are used-and not match the position The only solution is to remove the of the mechanism clutch and accelerator pedals. pedal and redesign the The solution is torelocating remove the wholeonly thing, including the pedal mechanism and redesign the master cylinder. Because the master whole including relocatingonthea cylinderthing, generally is mounted master cylinder. Because theormaster reinforced part of the chassis body, cylinder generally is mounted on a it is difficult to move. reinforced chassis or body, The bestpart timeoftothe modify pedal ratio itis iswhen difficult the to carmove. is being designed. As timecar to with modify pedalinratio forThe an best existing pedals the is when the car is being designed. As correct position, don't try to modify for an ratio. existing pedalsInstead, in the pedal It's car toowith difficult. correct position, don't trymaster to modify try a smaller-diameter cylpedal ratio. It's too difficult. Instead, inder. The effect on the brakes is the try a assmaller-diameter master cylsame a higher pedal ratio - more inder. The effect and on lower the brakes pedal movement effort.is the same as adohigher pedal If you manage to ratio-more change the pedal movement and lower pedal ratio, calculate the effort. effect on If you do manage to change the pedal effort:
pedal ratio, calculate the effect on pedal effort:
New pedal effort
=
R PEO~ in pounds RpN
New pedal effort = PE0-RPOin pounds PEO =
Old pedal effort inRPN pounds
Rpo = Old pedal ratio P ,, = RpN = Old Newpedal pedaleffort ratio in pounds
Rpo =
oldpedal ratio
You can see that a larger pedal ratio R~~ = New pedal ratio results in a lower pedal effort.
You can see that a larger pedal ratio REDUCING LINING WEAR results in a lower pedal effort. Reducing lining wear is important REDUCING LINING WEAR for both street driving and rac ing. Reducing lining wear important Unfortunately, . making ischanges to for both street driving and racing. reduce lining wear often has undesiraUnfortunately, changes to ble effects on making brake performance. reduce wear these often has undesiraBefore lining I discuss effects, let's ble effects on brake performance. look at common ways of increasing Before I discuss brake-lining life: these effects, let's look at common of increasing cooling ways airflow. • Increase brake-lining • Use harderlife: lining material. Increase lining coolingarea. airflow. • Increase
-
Use harder lining material. Followinglining is a area. brief review of these Increase modifications that are covered in this Following is a brief review of these chapter. modifications that are covered in this Cooling modifications are imporchapter. tant to all phases of brake perCooling so modifications are imporformance, they are top priority. On phasesimprovements of brake peratant roadtocar,allcooling can formance, so they lining are topwear priority. On cause increased if not adone roadcorrectly. car, cooling improvements can For example, removcause increased if not ing splash shieldslining from wear disc brakes done correctly. For example, removcan cause increased lining wear from ing splash dirt shieldscontamination from disc brakes increased and can cause increased lining wear from corrosion. increased dirt contamination and corrosion. 159
Racing a road car on racing tires requires adjustable brake balance. Street tires on this car are being changed to racing slicks for a slalom. Car will decelerate faster with slicks, and brake will on have to be adjusted more towards brake the front. proportioning Racingbalance a road car racing tires requires adjustable b a l An a nadjustable a t r e e t tires on this car valve couldchanged make balancing easy. Car will decelerate faster with slicks, and are being t o racingbrakes slicks fast for aand slalom. -
brake balance will have to be adjusted more towards the front. An adjustable proportioning valve could make balancing brakes fast and easy.
Typical balance bar used in a race car. If your car does not have a brake-balancing feature, balance balance bar bar used couldinbe adapted. Typical a race car. It If means and conyour carchanging does notpedals, have alinkage, brake-balancing verting tobalance dual master cylinders. Fitting an feature, bar could be adapted. It adjustable proportioning valve and is much means changing pedals, linkage, coneasier and cheaper. verting to dual master cylinders. Fitting an
adjustable proportioning valve is much easier and cheaper.
If you change CG height of a car, you need to change brake balance. A tall car has a greater weight transfer than one with a low CG. I hope the owner of this truck never has to stor; fast from high CG speed-or hasa to doyou anything else at high speed. If you change height of car, need to change brake balance. A tall car has a greater
weight transfer than one with a low CG. I hope the owner of this truck never has t o stop fast from high speed-or has to do anything else at high speed.
Harder lining material is a good way to reduce wear. Unfortunately, Harder lining material is aharder good pedal effort increases with way to reduce wear. Unfortunately, linings . Be sure you can operate the pedal effort increases with harder brakes at maximum deceleration after linings. Beto sure youlinings. can operate the harder Hard linchanging brakes at maximum deceleration after ings combined with other modificachanging to harder linings. tions to reduce pedal effortHard may linbe ings with compromise other modificathe combined best overall for tions to lining reducewear. pedal effort may be reducing theIncrease best overall compromise for lining area by installing reducing lining wear. wider drums or multiple-piston caliIncrease lining arealife. by Temperainstalling pers to increase lining wider drums oralso multiple-piston caliture reduction results . The compers to increase lining life. Temperabination of larger lining area and reture reduction also will results. comduced temperature haveThe a major binationonof larger area and reeffect wear. lining On disc brakes, duced temperature will have major multiple-piston calipers also areduce effect on wear. On disc brakes, pedal effort.
multiple-piston calipers also reduce pedal effort. 160
BRAKE-BALANCE MODIFICATIONS
BRAKE-BALANCE On most road cars, there's no way MODIFICATIONS to adjust brake balance. Balance adOn mostisroad cars, there's no way justment usually a reasonable to adjust brake adcompromise, as balance. designed.Balance However, justment is reasons usuallywhy a modifying reasonablea there may be compromise, designed. However, car to allow as balance adjustment is there may be reasons why modifying a desirable. carIf to is youallow drive balance your caradjustment on the street desirable. and occasionally race it, a balance adIf you drive car on theRacing street justment may your be necessary. and occasionally race it, a balance adtires have much higher grip than justment be necessary.theRacing street tiresmay . Consequently, additires have higher tional weightmuch transfer with grip race than tires street tires. Consequently, requires more braking at the the frontaddiand tionalat weight transfer with raceis tires less the rear. The opposite true requires more Ifbraking at the frontvalve and on the street. a proportioning less at the rear. The opposite is true is used, it partially compensates for on the street. If a proportioning valve is used, it partially compensates for
Tilton adjustable proportioning valve is used on this stock car instead of a balance bar. A tandem master cylinder is valve used for Tilton adjustable proportioning is safety. valveofisamounted used onThe thisproportioning stock car instead balance on drive-shaft tunnel cylinder where is driver bar. A tandem master usedcan for easily reach lever. Valvevalve is installed in safety. The proportioning is mounted brake line to reartunnel brakes.where driver can on drive-shaft
easily reach lever. Valve is installed in
tire-grip But a more precise brake linechanges. to rear brakes. baljmce adjustment may be needed tire-grip for racing.changes. But a more precise balance needed If you adjustment drive on icemay and be snow, you for racing. may wish to change brake balance for If you drive on ice same and snow, this condition. The goes you for may wish to change balance for driving off-road or onbrake unpaved roads. this condition. The same goes for With reduced grip, the rear brakes do off-road roads. adriving greater share or of on theunpaved work. If you With the, rear do changereduced brake grip, balance yourbrakes car may ahave greater of the bettershare braking on work. snow , Ificeyou or change brake balance, your car may dirt.
have better braking on snow, ice or dirt.
This handy adjustable proportioning valve is manufactured by Kelsey-Hayes. Adjustment handy is made by turning knob. Valve is This adjustable proportioning valve available from aftermarket-parts is manufactured by Kelsey -Hayes.suppliers Adjustsuch Worldknob. in San Diego, ment as is Performance made by turning Valve is CA and from fromaftermarket-parts many U.S.-car suppliers dealers available through their high-performance-parts such as Performarice World in San Diego, catalogs. CA and from many US.-car dealers
through their high-performance-parts catalogs. There are several ways to modify a
car to allow brake-balance adjustThereHere are are several ways toways modify a ments. the easiest : car to allow brake-balance adjustproportioning • Install an adjustable ments. Here are the easiest ways: valve. adjustable proportioning • Install Install an a dual master-cylinder and valve. balance-bar system. Install a dualValve-On master-cylinder Proportioning a road and car, balance-bar system. the adjustable proportioning valve is Proportioning a road car, best. It' s muchValve-On easier and cheaper the is thanadjustable changing proportioning the pedals, valve master best. It'sand much easier and cheaper cylinder linkage. A proportioning than the pedals, master valve changing is virtually a bolt-on cylinder and linkage. A proportioning component. For a race car, use a balvalve virtually bolt-on ance bar -isit gi ves a firmer apedal. component. race car, use a balThere are For twoa types of adjustable ance bar-it gives a firmer pedal. valves-one can be adproportioning There are two types and of adjustable justed from the cockpit the other proportioning valves-one canthat be can adcan't. A proportioning valve justed from the cockpit and is, thebyother cockpit far, be adjusted in the can't. A proportioning can the most convenient. It valve has thethat advanbe adjusted in the cockpit is, by far, tage of allowing the driver to know the mostwhere convenient. It has the advanexactly the adjustment is. On tagetype of allowing thewith driver to know the that adjusts a screw, you exactly where the adjustment is. On can't judge easily where the valve is the type that adjusts withthe a screw, set without counting turns you or can't easily where the valve is measurement. takingjudge a precise setThe without counting the turns or in-cockpit adjustable proportaking a precise measurement. tioning valve that I like is the Tilton The in-cockpit adjustable Engineering CP 2611-3. Thisproporlevertioning likesettings is the Tilton and is operatedvalve valvethat has Ifive Engineering 261 1-3. designed for CP racing. The This driverlevercan operated valve has five settings is make changes from the cockpit and while designed for street racing.use, The can at speed. For youdriver may wish make changes cockpit the from valve the where the while lever to mount at speed. For street use, you may wish This can' t be moved accidentally. to mount where the lever valve and the thevalve Alston Performance can't moved accidentally. Brakes ,be Direct Connection This and valve and the screw-type Alston Performance Kelsey-Hayes adjustable Brakes, Direct Connection in valve are discussed in more detailand Kelsey-Hayes screw-type adjustable Chapter 5. valve are discussed in more detailare in Screw-type adjustable valves Chapter available5. from several car makers. Screw-type adjustable valves are Ford and Chevrolet installed Porsche, available from several car makers. adjustable proportioning valves on Porsche, Ford and installed some models. TheyChevrolet are also available
adjustable proportioning valves on some models. They are also available
Triumph Spitfire was modified to add balance bar and dual master cylinders. Pedal was modified to was install balance bar, baland Triumph Spitfire modified to add master-cylinder was changed. ance bar and dualbracket master cylinders. Pedal This an easy to road car tobalance modify, because was is modified install bar, and master cylinders bracket are easilywas accessible in master-cylinder changed. engine compartment. that because flexible This is an easy road carNotice to modify, hoses used on master cylinder, master are cylinders areeach easily accessible in resultingcompartment. in extra pedal Notice motion.that Avoid using engine flexible flexible where isn't hoses arehoses used on each movement master cylinder, required. resulting in extra pedal motion. Avoid using
flexible hoses where movement isn't required. from Alston Performance Brakes and
Direct Connection. See your dealer or
from Alston Brakes and one Performance of the brake-equipment contact Direct Connection. See your dealer or suppliers listed in the Suppliers Index contact one of the brake-equipment for this type of valve. suppliers listedreview in the Suppliers what wasIndex disTo briefly for this type of valve.5, adjustable procussed in Chapter To briefly review what was dischange the pressureportioning valves cussed in Chapter 5, adjustable prorise-reduction rate to the rear brakes portioning change the pressureafter fluid valves pressure reaches a certain rise-reduction ratethe to the value. Changing pointrear at brakes which aft& fluid pressure reaches the valve starts to operatea certain is the value. Changing the point at which adjustment. Above the actuating the valvethere starts operate is the pressure, is atosmaller increase in adjustment. Above the actuating pressure to the rear brakes than there pressure, is athe smaller in would be there without valve.increase This efpressure to the rear brakes than there fectively distributes more braking to would be brakes withoutand theless valve. Thisrear. efthe front to the fectively distributes more to doesbraking not affect However, its operation the front brakes and less to the rear. pressure to the front brakes. However, its operation not affect is installed in A proportioning valvedoes Dressure to the front the line between thebrakes. master cylinder A rear proportioning installed in and brakes . Its valve use is isindependent the line between the master cylinder of the type of master cylinder. One and rear brakes. Its use is independent can be used in brake systems using of the single, type oftandem masterorcylinder. One either dual master can be used in brake systems using cylinders. either single, or dual If you wish tandem to race your car, master a procylinders. portioning valve will work well. If you wish race your rear-wheel car, a proif youtowa nt more However, portioning valve will work well. braking, you ' ll first have to modify However, if you want more rear-wheel the brake system, then reduce it with you'll first haveThis to modify proportioning valve. should abraking, the brake system, then reduce it with not be done by installing harder linaings proportioning valve. This should on the front brakes only, which not be done by installing harder with linresults in balance changes ings on the front brakes only, which temperature. Instead, install larger results . in balance changes with wheel cylinders or calipers with more temperature. Instead, install larger piston area at the rear, or change to a wheel cylinders or calipers withformore smaller-bore master cylinder the piston area at the rear, or change to a rear brakes only. smaller-bore master cylinder for the rear brakes only.
Adjusting balance bar in hanging pedal. This mechanic highly recommends remote adjusters! Adjusting balance bar in hanging pedal.
This mechanic highly recommends remote If your car has a proportioning adjusters!
valve and you have excessive rear If yourunder car all hasconditions, a proportioning install braking valve and youvalve haveinexcessive rear an adjustable line between braking install the stockunder valve all andconditions, the rear brakes. an adjustable valve's intooline between Afterward, if there much front · the stock valve and the rear brakes. and braking under some conditions Afterward, if there's muchothers, front brakingtoo under too much rear braking the under remove stocksome valve conditions or gut it. and
too much rear braking under others, remove the stock valve or gut it. DIAGONALLY SPLIT BRAKE SYSTEMS
DIAGONALLY SPLIT Brake-balance-adjustment devices BRAKE can be SYSTEMS added only if the front Brake-balance-adjustment devices brakes are actuated by one hydraucan be and added if the by fronta lic line the only rear brakes brakes areline. actuated by onesplit hydrauseparate Diagonally sysa lic line andwork the with rear abrakes tems won't balancebybar separate line. Diagonally splitvalve. sysora single proportioning tems workis with a balance bara Such won't a system designed to have or a single valve. diagonal pair proportioning of brakes operate a system designed to have a Such separately fromisthe opposite diagodiagonal pair means of brakes operate nal pair. This the left-front separately from diagobrake is tied to the theopposite right-rear, and nal pair. vice versa.This means the left-front is tieda to the right-rear, and brake To modify diagonally split brake vice versa.for balance adjustment, system To modify diagonally split brake either install afwo adjustableproporsystem valves for .balance tioning or change adjustment, the hydraueither installplumbing tho adjustable proporlic system in a major way. tioning valves or change the hydrauThe major change may require a diflic system plumbing in a major ferent master-cylinder size way. and The change may requireSuch a dif-a othermajor changes to the system. ferent master-cylinder and modification is too complexsize for most other changes to the Such a road-car owners. If system. two adjustable too complex for most modification isvalves proportioning are 'Used, they road-car owners. If twosoadjustable must be synchronized they give proportioning valves are used, they the same olJtput pressure at each must pressure. be synchronized s o they give input
the same output pressure at each input pressure.
Balance Bar-For an all-out race car, a balance bar is the best way to adjust Balance Bar-For Asan aall-out race car, brake balance. modification, aadding balance bar is the best way to You a balance bar is difficult.adjust brakehave balance. As and a modification, to design fabricate the may adding a balance is difficult. pedal and linkage.barOr, you mayYou be may have to design and the new pedal, able to adapt a completefabricate pedal linkage. Or, you assembly may be bracketandand balance-bar able to Neal adapt aProducts complete new pedal, or Tilton from
bracket and balance-bar assembly from Neal Products or Tilton 161
Steel-braided, high-pressure hoses are used to reduce deflections in brake system. They are stiffer than reinforced original-equipment rubber hoses, and are less likely to be damaged. Usually, adapter fittings available from companies sell system. hoses. Photo Steel-braided, high-pressure hoses are are used to reduce deflections that in brake They courtesy D Engineering Ltd. are stifferC & than reinforced Supply original-equipment rubber hoses, and are less likely to be
damaged. Usually, adapter fittings are available from companies that sell hoses. Photo courtesy C & D Engineering Supply Ltd.
AP Racing caliper offers a stiff bridge to minimize deflection. This caliper is made for 12-in.caliper -diameter rotor, from bridge 1.10- to AP aRacing offers a stiff 1.375-in. If you This can fit that size rotor minimize thick. deflection. caliper is made to your racer, you probably won't1 . find a I 0 - to for a 12-in.-diameter rotor, from stiffer caliper. courtesy AP Racing. 1.375-in. thick.Photo If you can fit that size rotor to your racer, you probably won't find a stiffer caliper. Photo courtesy AP Racing.
Engineering. For a road car, an adjustable proportioning valve gives good Engineering. a road an adjustresults. On aFor road car car, modified for able proportioning gives good to a balance bar racing , converting valve results. On a roaddue cartomodified for the cost and may be impractical racing, converting to a balance bar effort involved. An adjustable propormay be valve impractical duework to the and tioning will also forcost racing, effort involved. adjustable proporbut pedal travel isAn increased. tioning will also work for racing, Whenvalve changing from a tandem or but pedal travel is increased. single master cylinder to a dual arWhen changing from abar, tandem or rangement with a balance rememsingle master cylinder to a dual arber to recalculate pedal effort. Because rangement a balance rememthe balancewith bar divides thebar, pedal force ber to recalculate pedal effort. Because into approximately two equal halves, the divides the system pedal force the balance pressurebar in each brake will into approximately two equal halves, roughly in half. This will rebe cut the pressure each brake system quire double inthe pedal effort for will the be cutdeceleration roughly in half. This will resame if master-cylinder quire double pedalForeffort for the same. this reason, diameter is thethe same deceleration if master-cylinder dual master cylinders are about threediameterthe is the same.of For this reason, fourths di ameter a tandem or a dual master cylinders are about threesingle master cylinder.
fourths the diameter of a tandem or a single master cylinder.
162
Reverse-mounted, hanging-pedal setup is easy to service.
Reverse-mounted, hanging-pedal setup is easy to service. REDUCE DEFECTIONS
Many brake systems have excessive
REDUCE deflections.DEFECTIONS This causes increased Many brakeand systems havefeel excessive a spongy to the ' pedal travel deflections. increased pedal. If you This install causes a small-diameter pedal and(s), a spongy to the mastertravel cylinder considerfeel reducing pedal. If you install a small-diameter brake-system deflections at the same master cylinder (s) , consider time. The small master reducing cylinder brake-system deflections the same increases required pedal atmovement. time. The small master cylinder If deflections can be reduced, you can increases required pedal movement. regain some of this extra movement. If deflections reduced, you can Deflections can in be a brake system are regain some of this extra one ismovement. small. You cumulative. Each Deflections in a deflections brake system are couldn't see most if you cumulative. Each one is small. You were looking at them as they occur. couldn't see they most are deflections if you But, because cumulative and were looking at them theythey occur. by the pedal as ratio, can magnified But, because they cumulative Forareinstance, if and the be significant. magnified by the they can pedal ratio is pedal 8.0, ratio, a deflection be significant. instance, ifat the requiring 1/8 in.For of movement the pedal cylinder ratio iswill8.0, master give aan deflection additional requiring in,pad. of movement at the 1 in. at the 118 pedal master cylinder will give of an deflection additional Some of the causes 1 in. at the pedal pad. that can be corrected are : of the causes . of deflection • Some Brake-hose expansion that can be corrected are: • Caliper flexing . Brake-hose expansion. • Bending of master-cylinder mount@ Caliper flexing. ing structure. Bending of master-cylinder mounting structure.
• Bending of pedal or linkage . • Compression of gas in the brake Bending pedalfluid or linkage. fluid, or theofbrake itself. Compression of gas bein the Modifications can madebrake to fluid, or the brake fluid itself. reduce each of these deflections. They can be made to never be reduced to zero-only canModifications reduce smaller. each of these They made Everydeflections. object deflects can never be reduced to zero-only under load . It is only a matter of how made itsmaller. much deflects.Every object deflects under load. ItExpansionis only a matter how Brake-Hose The of rubber much deflects. hoses itused on most road cars where Brake-Hose Expansion -The orrubber flexing is necessary expand, swell, hoses used on most road under pressure. Additional cars fluidwhere is reflexing to is necessary expand,hose or .swell, quired fill an expanded This under pressure. Additional is reup to fluid noticeable swelling may add quired to fill an expanded hose. This pedal movement. swelling may toaddhose up deflection to noticeable The answer is to pedal movement. install stiffer hoses. Use steel-braided The answer ones. to hose deflection is to Teflon-lined They are stiffer install stiffer hoses. Use steel-braided than fabric-reinforced rubber hoses, Teflon-lined ones. stiffer underare pressure. so they deflect less They than , fabric-reinforced rubber hoses, Also steel-braided hoses are usually so they than deflect less hoses. under The pressure. smaller rubber smalAlso, steel-braided hoses are hose ler diameter further reducesusually smaller swelling.than rubber hoses. The smallerSteel-braided diameter further reduces hose hoses are available in swelling. kits from brake-product outlets such hoses are in Earlavailable ' s Performas Steel-braided C & D Engineering, kits from brake-product outlets such Products, or WREP Industries. ance as Longer C & D Engineering, Performbrake hosesEarl's deflect more ance Products, or WREP Industries. than shorter ones; one that's twice as Longer brake hoses deflectand more long deflects twice as much, so thanOn shorter one hoses that's are twice as on. some ones; cars, flex used long deflects as much, and so where flexingtwice is not required-say on. OnaT-fitting some cars,to flex from eachhoses brakeare onused the where flexing is not required-say rear axle . In some cases, a complete from T-fitting eachbeen brakeplumbed on the brake asystem maytohave rear In some cases, unnecessary a complete with axle. flex hoses. Replace brakehoses system may have been toplumbed flex with steel tubing reduce with flex hoses. Replace unnecessary . Don't deflection in a brake system flex steel tubing to reduce cheathoses by with excessively reducing the deflection in hoses a brake system. Don't length of the to the wheels. If a cheat by excessively reducing hose doesn't have sufficient slack,the it length of the hoses to the wheels. If a will likely fail with extreme wheel hose doesn't have sufficient slack, it movement. will likelyFlexing fail with wheel Caliper - A extreme disc- brake-calimovement. per body will deflect away from the Caliper of Flexing disc-brake-calisurfaces a rotor Awhen the fluid is per body willThis deflect away from the pressurized. deflection is from surfaces of a rotor when the fluid is bending of the bridge between the inpressurized. This deflection is from board and outboard sections of the bending of the bridge between the incaliper. board anddeflection outboard can sections of the Caliper be measured caliper. with a dial indicator. If it deflects, Caliper deflection can be measured and fluid additional piston movement with isa dial indicator. If it deflects, necessary to maintain brake flow additional piston movement andasfluid pressure. The driver senses this inflow is pedal necessary maintain stroketoand a spongybrake feel. creased pressure. The senses thisflex as inThe best waydriver to cure caliper is creased pedal stroke andcalipers a spongy feel. to install more-rigid . They way to cureorcaliper flex is canThe be best bigger, wider of another to install more-rigid calipers. They material. Cast-iron calipers are about can be bigger, wider or of another twice the stiffness of aluminum cali-
-
material. Cast-iron calipers are about twice the stiffness of aluminum cali-
pers of the same size and design. Iron calipers aren't used on race cars due pers of the weight, same size design. Iron to higher butand they certainly calipers aren't used on race cars due are stiffer. On a road car, iron calipers to higher weight, but they certainly are better. areRacing-caliper stiffer. On a road car, ironsuch calipers as suppliers are better. Hurst, JFZ or Tilton can help you Racing-caliper suppliers as select a stiffer caliper for a such race car. JFZexpensive, or Tilton can you Hurst, Although betterhelp brakes selectresult. a stiffer caliper for car. will Remember thata arace caliper Although may expensive, brakesa change also better require will result. Remember that a caliper mounting-bracket change. change may also Master-Cylinder-Mount require Deflec-a mounting-bracket change. tions- The master cylinder may Master-Cylinder-Mount Deflec"see" a force exceeding 1000 lb tions-The master Ifcylinder may the mount is during hard braking. "see" a additional force exceeding 1000 lb flexible, pedal movement during hard braking. If the mount is will be noticeable. flexible, pedal movement Check additional for master-cylinder deflecwill be bynoticeable. remotely mounting a dial intion Check master-cylinder andfor setting the indicator deflecplungdicator tion by remotely mounting dial iner against the master cylindera near its dicator andindicator setting the indicator plungbase shouldn't be end. The er against the cylinder near its mounted on master or near the masterend. The indicator base shouldn't be cylinder mount. Have someone step mounted on or near the masteron the pedal while you observe the incylinder mount. Have Check for someone deflectionsstep in dicator dial. on the pedal while youOften observe inan the entire different directions. dicator Check for deflections in fire wall dial. will flex. different directions. an entire The answer is Often to stiffen the fire wall will flex.best method is a strut structure. The answer to stiffen the or The several struts is attached to or near structure. The best method is a strut the master-cylinder mount. Airheart or attached to or have near andseveral Alstonstruts master cylinders
the master-cylinder mount. Airheart and Alston master cylinders have
If master cylinders are mounted to a sheet-metal fire wall, they may flex too much when driver pushes hard on pedal. To prevent front end of master cylinders from flexing upward, designer this stock added atotab to each frame tube. With a bolt both If master of cylinders arecar mounted a sheet-metal fire wall, they maypassing flex toothrough much when masterpushes cylinders, flexing is greatly reduced. The driver feels this as a firmer driver hard on pedal. To prevent front end of master cylinders from pedal. flexing upward,
designer of this stock car added a tab to each frame tube. With a bolt passing through both master cylinders, flexing is greatly reduced. The driver feels this as a firmer pedal.
additional mounting holes at both ends of the fluid reservoir for mountadditional both ing struts.mounting Thicker holes sheet at metal ends of the fluid reservoir for mountdoesn't do much. Beware of thin ing struts. Thickerin bending. sheet metal sheet metal loaded The doesn't do much. Beware thin brake-pedal pivot and the ofmaster sheet metal loaded in bending. The cylinder should be attached to a brake-pedal pivot and the master common bracket if possible.
cylinder should be attached to a common bracket if possible.
Pedal or Linkage Bending-Brake pedals are usually quite stiff because Pedalareordesigned Linkagewith Bending-Brake a large safety they pedals are usually quite factor. However, a pedal stiff armbecause that is they areordesigned withside a large curved bent to the maysafety twist factor. However, a pedal arm that is excessive deflection at the and cause curved or bent to the side may twist pad. If you have such a pedal arm, add and at into the metalcause to theexcessive pedal armdeflection to make it
pad. If you have such a pedal arm, add metal to the pedal arm to make it into
Master-cylinder bracket on this car needs some modifications to stiffen the pedal. An angle bracket will deflect in bending-this can be eliminated with two 45° gussets. Bracket is mounted in center of thin sheet-metal panel. Tubular cross member is needed to minimize bending of floor panel.bracket Cross member be firmly to each side Master-cylinder on this should car needs someattached modifications t oframe stiffen themember. pedal. An angle bracket will deflect in bending-this can be eliminated with two 45" gussets. Bracket is mounted in center of thin sheet-metal panel. Tubular cross member is needed t o minimize bend-
ing of floor panel. Cross member should be firmly attached to each frame side member.
163
Original Pedal Arm
I
Original Pedal Arm
I
Side Plates
Drawing shows section cut through pedal arm. Original pedal arm is shaped like an I-beam To through keep it pedal from Drawingcross showssection. section cut twisting, a side plate each arm. Original pedal armis iswelded shapedonlike an side of the I-beam to make box-section. I-beam cross section. Toit akeep it from Resistence to twisting much on greater twisting, a side plate is is welded each with of this modification. side the I-beam to make it a box-section.
Resistence t o twisting is much greater with this modification.
Pads normally wear on a taper because trailing edge of pad runs hotter than leading edge. Becausewear wear with Pads normally on aincreases taper because temperature, edge wears faster. trailing edge oftrailing pad runs hotter than leading Tapered Because pads makewear pedal increases feel spongy with beedge. cause caliper trailing or bracket to flex to temperature, edgehas wears faster. bring pads in make contact with Some Tapered pads pedal feelrotor. spongy bepads wear leading faster to calicause caliper or edges bracket has due t o flex to per design. bring pads in contact with rotor. Some
pads wear leading edges faster due to caliper design.
Bleeder on this race-car rear brake is below brake hose! Backing plates were mounted on axle. By unbolting Bleeder upside on thisdown race-car rear brake is and repositioning plates, below brake hose!backing Backing platesspongy were pedal wasupside cureddown forever. Bleeders must be mounted on axle. By unbolting at highest spot in cylinder be effective and repositioning backing to plates, spongy in removing all air.forever. Bleeders must be pedal was cured
at highest spot in cylinder to be effective in removing all air.
Checking brake-fluid level periodically is an important maintenance job on every car. If fluid reservoirs are hard to reach, consider a modification. These race-car reservoir caps are fitted withbrake-fluid plastic breather whichiscould feed lines from a remote-mounted .. ..-.-I Checking level tubes, periodically ar. be used -..- as ...-....-..-..-,---.. -.-. , reservoir. Be reservoir-breather tubes breath from These a clean, dry place such ascaps inside a reservoirs aresure hard t o reach, consider a modification. race-car reservoir are roll cage. fitted with plastic breather tubes, which could be used as feed lines from a remote-mounted
reservoir. Be sure reservoir-breather tubes breath from a clean, dry place such as inside a
aroll cage. tube. A closed- boxed-tubular structure, round or square, has much a tube.torsional A closed-boxed-tubular greater strength than a flat structure, round square, hasaccommuch or or I-beam. The plate, channel greater torsional strength than a flat panying drawing shows one method plate, channel or I-beam. The accomof how to do this. panying drawing showsdon't one method Linkages usually deflect of how to do However, this. noticeably. if the system usually don't subjected deflect hasLinkages a bell crank or anything noticeably. However, if the system to bending or twisting, it may be a has a bell Acrank or anything must be subjected as stiff as problem. linkage to bendingCurved or twisting, it may be a possible. or bent pushrods problem. A linkage must be as stiff as should be strengthened or replaced possible. Curved or bent pushrods with straight ones. ~his applies even if should strengthened or replaced a major design change . it meansbe
with straight ones. This applies even if it means a major design change.
164
Compression
of
Air
in
Brake
Fluid-If a brake system always acts Compression of bled, Airmaybe i n itBrake if it needs to be does. as Fluid-If a brake systeminalways acts Ai r tends to get trapped high spots as if i t needs to be bled, maybe it does. and corners of a hydraulic system. Air tends that to get trapped in high spots Check the bleeders are and corners of the a hydraulic positioned so all air can getsystem. out. A Check that be theat high bleeders spots inare a bleeder should positioned s o all the air can get out. A hydraulic system. Some special cars bleeder should be at high spotsatinana have the calipers mounted may hydraulic Some specialofcars angle that system. trap a small amount air. may havehave the calipers at an If you such a mounted car, remount angle thator trap a small amount air. calipers remove them from oftheir If you have such a car, remount mounts and position the bleeder high calipers or remove them from their for bleeding. Then remount calipers.
mounts and position the bleeder high for bleeding. Then remount calipers.
If a master cylinder is not mounted level, it can trap air. With this If a master condition, trycylinder tilting is thenotcarmounted with a level,when it can trap the air.brakes With sothis bleeding no jack try tilting theclosed car with a condition, air can be trapped at the end of jack when bleeding the brakes so no the master cylinder. Check the air can beoftrapped at the closed of position the cylinder with aend level the master cylinder. the car sits on a levelCheck surface. the while position of the lines cylinder a level If the brake havewith a fitting at while the car sits on a level surface. any high spot, there may be bubbles If the inside brake lines have a Examine fitting at the fitting. trapped any high spot, there may to be be bubbles the details of the fitting sure. trapped inside the fitting. Examine Perhaps you can reroute the line to the detailsthe of the sure., eliminate highfitting spot to or, be maybe Perhaps reroute to you can you use can another typethe of line fitting eliminate thetrap. high that will not air. spot But, or, firstmaybe, , avoid you can use another typesystem. of fitting high spots in the hydraulic that will not trap,air. But, first, avoid A spongy pedal can be caused by high spots in the hydraulic system. compression of the brake fluid . Brake A spongy can be caused by compression, fluid normallypedal has little compression of the brake fluid. Brake but some fluids are better than others fluid normally has little compression, in this respect. For instance, at high but some fluidssilicone are better thanhave othersa temperatures, fluids in this respect. For instance, compression stiffnessat high than lower temperatures, fluids silicone fluids athavelowa glycol-based . But, lower compression stiffness comthan temperatures, silicone-fluid glycol-based fluids.notBut, at low pressibility is usually a problem . temperatures, silicone-fluid comIf you have a race car with a spongy pressibility is usually a problem. thenotfluid is the pedal, perhaps If you have a race car with spongy problem . If you are using asilicone pedal, tryperhaps the fluid is the as fluid, a glycol-based fluid such problem. If you using silicone AP Lockheed racingare fluid.
fluid, try a glycol-based fluidPads such- as Deflections Due to Tapered A AP Lockheed racing fluid. worn disc- brake pad usually is Deflections to Tapered Padstapered. TheDue lining thickness of Aa worn pad usually is used paddisc-brake is usually thicker at the leadtapered. The lining thickness of ing edge than at the trailing edge. Thisa used padfrom is usually thickeredge at theofleadresults the trailing the ing edge than at the trailing edge. This results from the trailing edge of the
o
Trailing~ .
Edge
...........
Friction Material
Friction Material
Rotor Motion
Leading Edge
Rotor Motion
Leading Edge
Lining Cut Away From This Area
Lining Cut Away From This Area By removing some friction material on slow-wearing, leading edge of pad, taper wear can be reduced. If pad wears evenly, pedal travel will not increase as much as pad wear. Make sure both sides of the car are modified same so braking will edge be even. By removing some friction material onthe slow-wearing, leading of pad, taper wear can
be reduced. If pad wears evenly, pedal travel will not increase as much as pad wear. Make sure both sides of the car are modified the same so braking will be even.
pad running hotter than the leading edge, thus wearing more. Some caliper pad running hotterthethan the edge leading designs also cause leading to edge, thus wearing more. Some caliper wear more. designs edgethe to Once also padscause are the wornleading tapered, wear more. caliper assembly must deflect for the pads are worn fully. tapered, padOnce to contact the rotor This the incaliper assembly must deflect the creases pedal travel and effort. for It can pad to contactthethe rotor by fully. This the incaliper cocking also damage creases andAlthough effort. It this can pistons pedal in thetravel bores. also damage the caliper cocking the by by changing the can be minimized pistons in the bores. Although this pads before they are worn much, can be modification minimized by another canchanging help, too. the pads beforematerial they are much, Remove fromworn the sides of another modification can help, too. the pad at its leading end to reduce from the sidesrate of padRemove area material and increase wear the pad at its leading end to reduce locally. See the accompanying pad area This and increase wear rate helps balance the drawing. locally. See the accompanying unequal wear rates . The amount of drawing. helps balance the material toThis remove is found by trial unequal wear rates. The amount of and error. Start by removing about material to width remove is found by trial 25% of the at the slow-wearing and error. Startwhat by removing about edge and see happens. Make 25% of the width at the slow-wearing sure all pads and both sides of the car edgemodified and seeequally what to happens. preventMake pullare sure bothbraking. sides of the car ing toall thepads sideand during areTapered modified equally to prevent pullpads can also be caused by ing to the side during braking. flimsy caliper-mounting brackets. If canthis alsococks be caused by theTapered bracketpads twists, the califlimsy If taper. This per andcaliper-mounting makes the pads brackets. the cocks the taperbracket wear twists, due tothis twisting willcalibe per and on makes the padsandtaper. This unequal the inboard outboard taper wear due to twisting will be pads. One will show more wear on the unequal on thethan inboard and outboard trailing edge the other one on pads. One will show weartapers on thea If more one pad the leading edge. trailing edge than the other one on lot compared to the other, caliper the leading edge. If one pad tapers twist and higher trailing-edge tem-a lot compared to the other, caliper perature are involved. twist and caliper higher twist trailing-edge Reduce by using atemstifperature are involved. fer caliper-mounting bracket. I suggest Reduce caliper by using asteel stifusing at least a flattwist 1I2-in.-thick fer caliper-mounting bracket. I suggest plate for a caliper bracket. If that thick-
using at least a flat 112-in.-thick steel plate for a caliper bracket. If that thick-
This caliper bracket is cut from a flat plate. It adapts a disc brake to a spindle from a car with drum brakes.isThis flat plate This caliper bracket cut from a flatbrackplate. et should abe 1/2in. thick, if possible, I t adapts disc brake to a spindle fromto a resist twisting. car with drum brakes. This flat plate brack-
et should be 1/2-in. thick, if possible, to resist twisting.
ness is impossible, use the thickest possible steel plate. ness is impossible, use the unequal thickest With sliding calipers, possible steel plate. inner-to-outer lining wear can be With bysliding calipers, caused high slide friction.unequal Clean inner-to-outer lining wear canwith be the slides and lubricate them caused by high slide friction. Clean high-temperature grease between the the slides and caliper lubricate them with inner and outer sections.
high-temperature grease between the inner and outer STABILITY caliper sections. IMPROVING DURING BRAKING
IMPROVING STABILITY Stability refers to how straight the DURING BRAKING car travels during braking. When the Stability how an straight the brakes are refers appliedtohard, unstable car travels during pull braking. When car may swerve, to the side, the or brakes areout. applied an unstable even spin Therehard, are many things car pullbuttothe thefollowing side, or that may affectswerve, stability, even out. There are many things items spin are the most likely. that affectbraking stability, but the Stable depends on following balanced items areattheboth mostsides likely.of the car. If braking Stableisbraking depends on balanced braking different from right to left, braking at both sides of car. by If the car will be unstable.the Start braking is different from right tolining left, checking brake diameters, the car will unstable. condition Start by andbemechanical condition, checking brake diameters, of the brakes to be sure they are lining equal condition, and Also mechanical condition on both sides. check tire rolling of the brakes to bethis sure radius to be sure is they equalare onequal each on both sides. Also check tire rolling side. Measure with a tape wrapped radius to the be sure this is equal of on each around circumference each side. with a tape tire-itMeasure is more accurate than wrapped measuraround ing radius.the circumference of each tire-it is more accurate than measurThe car's suspension must work ing radius. well for stability. It's essential that the The car's must toe-in work wheels don't suspension steer or change well that tips the whenfor thestability. brakes It's are essential applied. For wheels don't steer or change toe-in on setting up a chassis, read my HP when areYour applied. For tips Book, the Howbrakes to Make Car Hand/e. onExcessive setting up front a chassis, my can HP scrubread radius Book, to Make Your Car Handle. cause How instability during braking. Excessive front scrub radius Scrub radius is the distance from can the cause instability during braking. point the kingpin axis intersects the Scrub radius the distance from the ground to the iscenter of the tire patch. point the kingpin axis intersects the ground to the center of the tire patch.
Bolted pad retaining plate increases caliper-bridge strength. Studs with quickrelease used inplate placeincreases of bolts pad are retaining Bolted clips when quick padstrength. changes are required. caliper-bridge Studs with quick-
release clips are used in place of bolts when quick pad changes are required.
Widening the track by installing wheels with increased offset increases Widening by installing scrub radiustheby track the same amount. wheels with increased increases Cars should not have offset a scrub radius scrub radius by the 2 same amount. greater than about in., although Cars have scrub radius many should road andnot race carsahave been degreater thanmore. about 2 in., although signed with many road andproblems race cars are havecaused been deIf stability by signed with more. rear-wheel lockup, that can be elimIf stability problemsthearebrakes. causedSee by by balancing inated rear-wheel lockup, thatchapter can bedealing elimthe earlier part of this inated modifications by balancing the See with for brakes. balancing the earlier part of this chapter dealing brakes. Adding an adjustable proporwith balancing tioning modifications valve can be for the answer to brakes. Adding an adjustable proporrear-wheel lockup. tioning can with be thehigh answer to Drum valve brakes servo rear-wheel lockup. action, such as duo-servo brakes, are Drum brakes with high notorious for causing pulls servo and action, suchIf as brakes, are is a problem, be sure instability. thisduo-servo notorious for causing pulls and the drums, linings and wheel instability.are If this is a problem, cylinders in good condition.beIfsure this the drums, and or wheel doesn't help, trylinings harder linings disc cylinders are in good condition. If this brakes. Instability with duo-servo doesn't help, try harder linings or disc drum brakes is a major reason why brakes. Instability with duo-servo modern American cars use front disc drum is a major reason why brakes brakes exclusively.
modern American cars use front disc brakes exclusively. 165
.......uble·Shooling Guide Rouble-Shooting Trouble-shooting brakes brakes is too big of a subject for for complete complete coverage coverage in this subject of maintenance and testing would wou Id not be complete complete withbook. However, the subject out aa trouble-shooting trouble-shooting guide. guide. Briefly listed below are are some some possible possible causes of of out trouble. Cures Cures are covered covered in this book, the factory manual, manual, and and in in other pubbrake trouble. lications on on brake brake repair and maintenance. maintenance. lications trouble-shooting may help you with a quick quick solution at This reference guide to trouble-shooting the test track:
Problems pedal-will pump up Low pedal-will
Possible Possible Cause Rotor Runout Loose wheel bearings Air in hydraulic system Drum brakes out of adjustment
pedal-won't pump up Low pedal-won't
Bad seals in caliper Badly worn pads Rotor runout Leak in in hydraulic system Loose wheel bearings Excessive free-play in brake Iin kage linkage Balance bar too far off-center
Changing brake-pedal travel
Slop in in wheel bearing or suspension Balance-bar failure Balance bar too far off center
Spongy pedal pedal
in hydraulic system Air in Deflection of caliper or mount Deflection hoses Deflection of hoses Brake fluid fluid too hot Badly worn linings or pads Concave or convex lining wear Deflection of master-cylinder mount Deflection small Master cylinder too small Pedal ratio ratio too high high Pedal Drum-brake-shoe arc incorrect brake shoes or backing backing plate plate Distorted brake Old brake brake fluid fluid Old Cracked brake brake drum drum Cracked
Brake Brake pedal pedal not returning returning
reservoir not not vented vented Master-cylinder reservoir No clearance in in brake brake pushrod pushrod No Binding in in pedal pedal pivots pivots or or pushrod pushrod Binding
Front Front or or rear rear brakes brakes locking locking
Too much much front- or rear-brake rear-brake balance balance Too Failure in in opposite brake brake system system Failure
One One brake brake locking locking
Caliper piston piston seizing seizing in in cylinder cylinder Caliper Wheel cylinder cylinder seizing seizing Wheel Bad brake-shoe brake-shoe return return spring spring Bad Loose or or distorted distorted backing backing plate plate Loose Oil or or fluid fluid leak leak into into brake brake Oil Loose caliper caliper mount mount Loose Excessive weight weight on on other other wheel wheel Excessive Twist in in car car chassis chassis or or suspension suspension Twist Mismatched rotors, rotors, linings linings or or drums drums Mismatched Master cylinder cylinder too too small small Master Pedal ratio ratio too too high high Pedal Too much much servo servo action action on on drum drum brakes brakes Too Liningstoo too soft soft Linings Too much much power power assist assist Too Defective booster booster Defective
Pedal Pedaleffort effort too too low low
Pedal Pedaleffort effort too too high high
166
Master cylinder cylinder too too large large Master Pedalratio ratiotoo too low low Pedal Linings too too hard hard Linings Racing linings linings too too cold cold Racing Power-assist failure failure Power-assist
Vibrating Vibrating pedal pedal
Brakes Brakes wet wet Glazed Glazed linings linings Oil Oil or or fluid fluid on on linings linings Drum-brake-shoe Drum-brake-shoe arc arc incorrect incorrect Brakes Brakes too too hot hot Excessive ickness variation Excessive rotor rotor runout runout or or th thickness variation Damaged Damaged wheel wheel bearings bearings Cracked Cracked drum drum or or rotor rotor Bent Bent axle axle Drum Drum warped warped or or eccentric eccentric Brakes Brakes not not releasing releasing Vented-rotor Vented-rotor fins fins rusted rusted out out so so side side plates plates deflect deflect under under pressure pressure
Swerving Swerving under under hard hard braking braking
Front Front suspension suspension bottoming bottoming Toe-in Toe-in adjustment adjustment wrong wrong Bump-steer Bump-steer problems problems Shock-absorber Shock-absorber failure failure Shock-absorber Shock-absorber adjustment adjustment dissimilar dissimilar Brake Brake balance balance way way off off Caster Caster or or camber camber uneven uneven Chassis Chassis or or suspension suspension twisted twisted Worn Worn steering steeringor or suspension suspension pivots pivots Tire Tiresizes sizes dissimilar dissimilar Excess Excess front-wheel front-wheel scrub scrub radius radius
Pedal Pedalgoes goes to to floor floor
Air Air in in hydraulic hydraulic system system Leaking Leakingseal seal in in master master cylinder cylinder Leak Leak in in hose hoseor or tube tube Leak Leak in in caliper caliper or or wheel wheel cylinder cylinder Tapered Tapered pad pad wear wear Drum Drum brake brake not not adjusting adjusting Electric Electric current current passing passing through through fluid fluid
Brakes Brakes grab grab or or lock lock
Drum-brake-shoe Drum-brake-shoe arc arc incorrect incorrect Loose Looseor or distorted distorted backing backingplate plate Contaminated Contaminated linings linings Brakes Brakeswet wet Racing Racinglinings liningstoo too cold cold Failed Failed brake-shoe brake-shoereturn returnspring spring Drum-brake Drum-brake linings linings burned burned up up
Brakes Brakes not notreleasing releasing
Blocked Blockedmaster-cylinder master-cylinder port port Binding Bindingpedal pedalpivots pivots No Nofree free play play in inpushrod pushrod Seized Seizedcaliper caliper or or wheel wheel cylinder cylinder Aged Aged or or overheated overheated caliper caliper seals seals Swollen Swollenseals-incorrect seals-incorrect fluid fluid Caliper Caliper slides slides corroded corrodedand andstuck stuck Heel Heeldrag dragon oncup-type cup-type seals seals Parking Parkingbrake brakeon onor or maladjusted maladjusted Power Power booster booster faulty faulty Distorted Distortedshoes shoesor or backing backingplate plate
Brakes Brakessqueal squeal
Wear Wear ininbrake brakeshoes shoesor or attachments attachments Worn Worn pads pads Cold Cold linings linings Need Neednew newbrake-pad brake-padanti-squeal anti-squeal shims shims Need Needanti-squeal anti-squeal compound compoundbehind behindpads pads Need Needto tochamfer chamferends endsof of linings linings Brakes Brakeswet wet
Rapid Rapidlining liningwear wear
Wrong Wrongsurface surfacefinish finishon onrotor rotoror ordrum drum Lining Liningtoo toosoft soft Cracks Cracksinindrum drumor orrotor rotor Adjustment Adjustment too tootight tight Brakes Brakesnot notreleasing releasing Inadequate Inadequatebrake brakecooling cooling
167
Trouble-Shooting ooting This road-car hydraulic-brake-system hydraulic-brake-system diagnostic procedure may help you solve some perplexing brake-system problems:
PRELIMINARY ACTION 1. 1. Clean master-cylinder cap. 2. Fill Fill master-cylinder reservoir. reservoir. 3. 3. Turn ignition switch to start to prove out instrument-panel brake light. light. PEDAL· FEEL CONDITIONS & APPROPRIATE PEDAL-FEEL APPROPRIATE ACTIONS 1. 1. Pedal to the floor quickly-light quickly-light on: on: Perform Perform action action A. A. If pedal holds, holds, perform perform Action B. B. If pedal does not hold, hold, perform perform Action C. 2. Pedal to the floor slowly (creeps)-light (creeps)-light on: Perform Perform Action C. C. 3. 3. Pedal Pedal firm-long firm-long stroke-no stroke-no light: light: Perform Perform Action A. A. If pedal pumps up-perform up-perform Action B. B. If pedal does not pump up-perform up-perform Action D. D. 4. Pedal spongy-no spongy-no light: Perform Perform Action A. If pedal pumps up-perform up-perform Action B. B. If pedal pedal does not pump up-perform up-perform Action G. G. 5. 5. Pedal Normal-Goes Normal-Goes to floor at times: If disc brakes-perform E. brakes-perform Action E. Perform Perform Action F. F.
ACTIONS A. Pump pedal as fast as possible possible 30 30 times and hold hold pedal pedal down on last stroke. stroke. B. B. Have Have an assistant remove master-cylinder cap and observe reservoir-fluid levels as the pedal pedal is released released as quickly as possible. possible. A spout in in either chamber indicates indicates the possibility of air in the system. system. Bleed Bleed the brakes. brakes. If problems remain, adjust the brakes. brakes. remain, C. Have an assistant observe master-cylinder-fluid master-cylinder-fluid levels as the brake pedal is slowly depressed. A level that rises 1/16 1/16 in. in. on pedal application and drops to original level on release-not indicates an internal release-not including the spout on applyapply-indicates internal bypass leak in in a tandem-type master cylinder. cylinder. A reservoir that overflows after long use while the other reservoir drops also indicates an internal bypass. bypass. Rebuild Rebuild or replace master cylinder. A reservoir that drops progressively with each pedal stroke indicates an external pressure pressure leak. Check all lines and fittings of the affected system-front system-front or rear-and rear-and repair as required. D. D. Adjust brakes. brakes. Check for loose wheel bearings and adjust to specifications if required. required. E. E. Check for loose wheel bearings and adjust to specification if required. required. F. F. If condition condition occurs only after long periods of idleness, replace the hydraulic stoplight switch and flush front-system front-system brake fluid. A shorted shorted switch can pass current through the brake fluid. fluid. Fluid subjected subjected to electric current for a long period of time will bubble. bubble. G. Check caliper slides, slides, pins and pistons for sticking. Check disc-brake linings for tapered wear. Check drum brakes for bent shoes or backing plates. plates.
168
Suppliers List Suppliers Suppliers are are listed listed two two different different ways. ways. First, First, they they are are listed listed by by company company name name in in alphabetical alphabetical order-then order-then the the products products are are listed listed alphabetically. alphabetically. IfIf you you are are looking looking for for aa particular particular product, product, look look first first in in the the product product list. list. The The number number behind behind each each item item refers refers to to the the number number of of the the company(ies) company(ies) shown shown in inthe the alphabetical alphabetical supplier supplier list. list. Every Every year year new new companies companies are are formed formed and and some some go go out out of of business. business. Thus, Thus, you you should should not not consider consider this this list list to to be bethe the last last word. word. IfIf you you want want aa complete and corr~plete and current current list list of of companies companies supplying supplying aa particular particular brake-related brake-related product, product, refer refer to to ads ads in in the the latest latest trade trade and and racing racing publications. publications. The The following following supplier supplier list list is is merely merely aa guide guide to to get get you you started started on on your your shopping shopping task. task.
ALPHABETICAL ALPHABETICALLIST LIST OF OFSUPPLIERS SUPPLIERS Aeroquip 11. . Aeroquip Corp. Corp. 300 300 S. S. East EastAve. Ave. Jackson, MI49203 49203 Jackson, MI Alfred 2. Alfred Teves TevesTechnologies, Technologies,Inc. Inc. 2. (ATE (ATEBrakes) Brakes) 2718 271 8 Industrial Industrial Row Row Troy, Troy, MI48084 MI 48084 2A. 2A. Alston Alston Industries Industries 6291 6291 Warehouse Warehouse Way Way Sacramento, Sacramento,CA CA95826 95826 3. AMMCO 3. AMMCO Tools, Tools,Inc. Inc. Wacker Wacker Park Park North NorthChicago, Chicago, IL IL60064 60064 4. AP AP Racing Racing 4. Leamington LeamingtonSpa Spa Warwickshire, Warwickshire, England EnglandCV31 CV31 3ER 3E R Automotive 5. 5. AutomotiveProducts ProductsUSA, USA,Inc. Inc. 1864 1864Northwood NorthwoodDr. Dr. Northwood NorthwoodIndustrial IndustrialPark Park Troy, Troy,MI48084 MI 48084 Bendix 6. BendixAutomotive AutomotiveAftermarket Aftermarket 6. 1904 1904Bendix BendixDr. Dr. Jackson, Jackson,TN TN38301 38301 CC&81DDEngineering 7.7. EngineeringSupply SupplyLtd. Ltd. Rt. Rt.2, 2, Box BOX47-1 47-1 Fort FortValley, Valley,CA CA 31030 31030 7A. 7A. Chrysler ChryslerCorporation Corporation Direct DirectConnection Connection P.O. P.O.Box Box1718 1718 Detroit, MI48288 48288 Detroit,MI Columbia 8. ColumbiaMotor MotorCorp. Corp. 8. 140 140West West 21 21st stSt. St. New NewYork, York,NY NY10011 1001 1 Contemporary 9. 9. ContemporaryChassis ChassisDesign Design 15506 15506Vermont VermontSt. St. Paramount, Paramount,CA CA90723 90723 10. CRCChemicals Chemicals 10. CRC 885 885Louis LouisDr. Dr. Warminster, Warminster,PA PA18974 18974
Deist Deist Safety, Safety, Ltd. Ltd. 641 641 Sonora Sonora Ave. Ave. Glendale, Glendale, CA CA 91201 91 201 12. 12. Delco Delco Moraine MoraineDiv. Div. General General Motors Motors Corp. Corp. 1420 1420Wisconsin Wisconsin Blvd. Blvd. Dayton, Dayton, OH OH 45401 45401 13. Dick Guldstrand GuldstrandEnterprises Enterprises 13. Dick 11924 11924 W. W. Jefferson Jefferson Blvd. Blvd. Culver Culver City, City, CA CA 90230 90230 13A. 13A. Dillon DillonEnterprises Enterprises 66820SR 66820 SR 23 23 North North Liberty, Liberty, IN IN 46554 46554 14. 14. Dow Dow Corning CorningCorp. Corp. Box Box 0994 0994 Midland, Midland, M148640-0994 MI 48640-0994 15. Dwyer Instruments, Instruments,Inc. Inc. 15. Dwyer P. P.O. 0 . Box Box 373 373 Michigan Michigan City, City, IN IN 46360 46360 15A. EISAutomotive AutomotiveCorp. Corp. 15A. EIS 129 129Worthington Worthington Ridge Ridge P.O. P.O. Box Box 1315 1315 Berlin, Berlin, CT CT06037 06037 16. 16. Earl's Earl'sPerformance PerformanceProducts Products 825 825 E. E.Sepulveda Sepulveda Carson, Carson, CA CA 90745 90745 17. 17. Edco EdcoSpecialty Specialty Products Products 3411 341 1W. W. MacArthur MacArthur Blvd. Blvd. Santa Santa Ana, Ana, CA CA 92703 92703 117A. 7 A. Ford FordMotorsport Motorsport Ford FordMotor Motor Co.-SVO Co.-SVO 17000 17000Southfield Southfield Rd. Rd. Allen Allen Park, Park,MI MI48101 48101 18. Friction FrictionProducts ProductsCo. Co. 18. 920 920Lake LakeRoad Road Medina, Medina, OH OH44256 44256 19. ELSCO Inc. 19. ELSCOlnc. 1843 1843E. E.Adams AdamsSt. St. Jacksonville, Jacksonville, FL FL 20. FranklandRacing RacingEquipment Equipment 20. Frankland P.O. P.O. Box Box278 278 Ruskin, Ruskin, FL FL33570 33570 21. 21. Girling GirlingLtd. Ltd. 200 200Manchester ManchesterAve. Ave. Detroit, Detroit,MI MI Girlock 22. Girlock 22. c/o C/OTilton Tilton Engineering Engineering McMurray McMurrayRd. Rd.&& Easy EasySt. St. Buellton, Buellton,CA CA93427 93427 23. Girlock GirlockLtd. Ltd. 23. 36-40 36-40 Harp. Harp.St. St. Belmore, Belmore,N.S.w. N.S.W.2192 21 92 Sydney, Sydney, Australia Australia 24. 24. Grey GreyRock RockDiv. Div. Raybestos RaybestosManhattan ManhattanCorp. Corp. P.O. P.O.Box Box9140 9140 Bridgeport, Bridgeport,CT CT06603 06603 25. 25. Harwood Harwood Performance Performance Sales, Sales, Inc. Inc. 11501 1 1501Hillguard HillguardRd. Rd. Dallas, Dallas,TX TX 75243 75243
11 11..
26. 27.
28.
29. 29A.
30. 31.
32.
33. 34. 35.
37.
38.
39.
40. 41. 42. 43.
Henry's Henry'sEngineering EngineeringCo. Co. P.O. P.O. Box Box 629 629 Prince Frederick, Frederick, MD MD 20678 20678 Prince Huffaker Huffaker Engineering, Engineering, Inc. Inc. 22 Mark Mark Dr. Dr. 22 San San Rafael, Rafael, CA CA 94903 94903 Hurst Hurst Performance, Performance,Inc. Inc. Airheart Brakes Brakes Airheart 50 50West West Street Street Road Road Warminster, Warminster, PA PA 18974 18974 JFZ JFZ Engineered EngineeredProducts Products 9761 Variel Variel Ave. Ave. 9761 Chatsworth, Chatsworth, CA CA 91311 91 31 1 Ja-Mar Off-Road Off-Road Products Products Ja-Mar 29300 3rd 3rd St. St. 29300 San Rafael, Rafael, CA CA 94903 94903 San Kano Laboratories Laboratories Kano 1000S. S. Thompson Thompson Ln. Ln. 1000 Nashville, TN TN 37211 3721 1 Nashville, Kelsey-Hayes Kelsey-Hayes Co., Co., Inc. Inc. Kelsey Kelsey Axle Axle && Brake Brake Division Division 5800 5800W. W. Donges Donges Bay Bay Road Road Mequon,WI WI 53092 53092 Mequon, Kelsey-Hayes Kelsey-HayesCo., Co., Inc. Inc. Kelsey Products Products Division Division Kelsey 38481 Huron HuronRiver River Dr. Dr. 38481 Romulus, Romulus, MI48174 MI 481 74 LakewoodEnterprises Enterprises Lakewood 4566 Spring Spring Rd. Rd. 4566 Cleveland, Cleveland,OH OH 44131 441 31 LambComponents Components Lamb 150 150W. W.College College Way Way LaVerne, Verne,CA CA91750 91 750 La Lee LeeManufacturing ManufacturingCo. Co. Divisionof of Rolero Rolero Division P.O.Box Box7187 7187 P.O. Cleveland, Cleveland,OH OH 44128 441 28 LucasIndustries, Industries,Inc. Inc. Lucas Girlock Girlock Girling Girling Brake Brake && Hydraulic Hydraulic SysSystems Group Group tems 5500 New NewKing KingSt. St. 5500 Troy, MI48098 MI 48098 Troy, MarshInstrument InstrumentCo. Co. Marsh 3501W. W.Howard HowardSt. St. 3501 IL60076 60076 Skokie,IL Skokie, McLeodIndustries Industries McLeod 1125 N. N.Armando Armando 1125 Anaheim,CA CA92806 92806 Anaheim, MidwestRace RaceEngineering Engineering Midwest 503S. S.7th 7thSt. St. 503 Boonville,IN IN47601 47601 Boonville, MICO,Inc. Inc. MICO, 191 1Lee LeeBlvd. Blvd. 1911 NorthMankato, Mankato,MI MI56001 56001 North MorakBrakes, Brakes,Inc. Inc. Morak 9902Ave. Ave.DD 9902 Brooklyn,NY NY 11236 11236 Brooklyn, MuellerFabricators Fabricators Mueller 10872Stanford StanfordAve. Ave. 10872 Lynwood,CA CA90262 90262 Lynwood,
169
Suppliers List 44. 44.
45. 45. 46. 46. 47. 47.
48. 49.
50. 51.
Nationwide Electronic Electronic Systems, Systems, Nationwide Inc. Inc. 1536 Brandy Parkway 03 Streamwood, IL 601 601 03 Streamwood, Neal Products, Inc. 7170 Rd. 71 70 Ronson Rd. San Diego, CA 921 92111 San 11 Engineering, Inc. Omega Engineering, 4047, Springdale Station Box 4047, 06907 Stamford, CT 06907 Performance World 3550 University Ave. San Diego, CA Technology Inc. Plasma Technology 1754 Crenshaw Blvd. 90501 Torrance, CA 90501 Professional Racers Emporium E. 223rd St. 1463 E. Carson, CA 90745 R.A.C.E. Pads R.A.C.E. 8 S. 582 John St. 605111 Big Rock, IL 6051 Ron Minor's Racing Specialties Ron 65111 N. Ave. 651 N. 27th Ave. Phoenix, 85017 Phoenix, AZ 8501 7
52. 52.
Servex Servex 1520 10th 10th Ave. Ave. 1520 98122 Seattle, Washington Washington 981 Seattle, 22 53. Simpson Simpson Safety Safety Equipment, Equipment, Inc. Inc. 53. 22630 S. S. Normandie Normandie Ave. Ave. 22630 90502 Torrance, CA CA 90502 Torrance, 54. Speedway Engineering 54. Bradley Ave. Ave. 13040 Bradley 91342 Sylmar, CA 91 342 54A. Speedway Motors 54A. P.O. Box Box81906 P.O. 81 906 68501 Lincoln, NE 68501 55. Stainless Steel Brakes Corp. 11470 Rd. 11 470 Main Rd. 14031 Clarence, NY 14031 55A. Stop & Go Products 1835 Whittier, Suite A5 Costa Mesa, CA 62627 55B. Tempil Division 558. Big Three Industries, Inc. 2901 Hamilton Boulevard 2901 South Plainfield, NJ 07080 56. Tilton Engineering, Inc. McMurray Rd. & Easy St. Rd. 8 P.O. Box 1787 P.O. Buellton, CA 93427
Troutman, Troutman, Ltd. Ltd. 31 98 'L' 3198 'L' Airport Airport Loop Loop Dr. Dr. Costa Costa Mesa, Mesa, CA CA 92626 92626 58. Velvetouch Velvetouch Div. Div. S.K. S.K. Wellman Wellman Corp. Corp. 200 200 Egbert Rd. Rd. Bedford, 46 Bedford, OH 441 44146 59. Weevil Ltd. Ltd. 206 206 Queens Queens Court Court Ramsey, Ramsey, Isle of of Man Man British British Isles 60. White Post Restorations White Post, A 22663 Post, V VA 22663 61. Wilwood Engineering 4580 Calle Alto Camarillo, CA 91 360 91360 61 A. Winters Performance Products 281 9 Carlisle Rd. 2819 York, PA 17404 62. WREP Industries, Ltd. 140-C Shepard Wheeling, 1 11. 60090 III. 63. Yankee Silicones, Silicones, Inc. P.O. Box 1089 Schenectady, NY 12301 12301
Hand-Operated 29A, 45 Hand-Operated Brake 29A, Hats 2A, 2A, 4, 28,29,56, 28, 29,56,61 61 A Hoses 1,4,5,6,7, 1, 4, 5, 6, 7, 16,62 16, 62
2A, 4, 13A, 13A, 28, 51, Racing Brakes 2A, 28, 29, 29,51, Racing 54A, 55A, 56,61 A 54A,55A,56,61A 15A, 28, 29,45, Rebuilding Kits 4,5,6, 15A, 55,56,62 Remote Balance-Bar Adjuster 13A, 13A, 45, Remote 54A, 56,61 A 54A,56,61A Reservoirs 5,45,51, 5, 45,51, 55A, 56 Reservoirs 45,51,55A, Reservoir Extensions 45, 51, 55A, 56 28,45 Residual-Pressure Valves 28, 45 Return Springs 5, 5 ,6 Return Rotors 2A, 2A, 4, 4, 5, 5,6, 12, 13A, 13A, 15A, 15A, 28, 28, 29, 29, Rotors 6,12, 29A, 32,51,52,54A, 55A, 61A 29A,32,51,52,54A,55A,61A
57.
PRODUCT INDEX Numbers Numbers refer to those shown in in alphabetical suppliers list. list. Adjustable Proportioning Valve A, 2A, 7 7A, Valve 2A, 17A, 17A, 32, 32, 47, 47, 56, 56, 61 61 Adjusters 5, 5 ,6 Anti-Noise Compound 10 10 Balance 56, 61 A 29A, 45, 45,56,61 Balance Bars Bars 29A, Bleeder Screws Screws 5, 5 , 66 6, 7, 15A, Brake 5,6,7, 15A, 45, 45, 47, 47, 51, 51, Brake Fluid Fluid 4, 4, 5, 54A,55A,56,61,62 54A, 55A, 56,61,62 Brake-Locking Brake-Locking Valves 29A, 29A, 37 37 Brake Brake Tubing 6, 6, 45 45 Calipers 5, 6, 13A, 28, 2A, 4, 4,5, 6, 12, 12,13A, 28, 29, 29, Calipers 2, 2, 2A, 29A,32,51,54A,55,56,60,61,61A 29A, 32, 51,54A, 55,56,60,61,61 A Caliper Brackets 56 Brackets 28, 28,56 Cleaning Cleaning Fluids Fluids 10,51 10, 51 Cutting 29A, 45 45 Cutting Brakes Brakes 29A, Cylinder Restoring Restoring 55, 55, 60 60 Decelerometers Decelerometers 33 29, 31,61 Dragster Dragster Brakes Brakes 2A, 2A, 28, 28,29,31,61 Drums 15A, 29 5,15A, 29 Drums 5, Fast-Fill Fast-Fill Master Master Cylinders Cylinders 41 41 Finned Finned Drums Drums 55 Fittings Fittings 1,4,5,6,7, 1,4,5, 6, 7, 16,45,51,52,56, 16,45,51, 52, 56, 62 62 Flaring Flaring Tools Tools 66 Gage Gage Protectors Protectors 41 41
170
Lining 5, 6, 24, 50, Lining Material 4, 4,5, 6, 8, 8, 13A, 13A, 24,50, 51, 54A, 55A 51,54A, Master Cylinders 2A, 4, 4, 5, 5, 6, 6, 12, 12, 13A, 13A, 28,29A,37,45,51,54A,55A,56,61, 28,29A, 37,45,51,54A, 55A, 56,61, 61A,62 61A, 62 Metric Adapter Fittings 45, 62 7,45, 62 Fittings 6, 6, 7, Moisture Moisture Barriers Barriers 45, 45, 56 56 Pads 2A, 4, 5, 6, 7, 12, Pads2A,4,5,6,7, 12, 13A, 13A, 15A, 15A, 18, 18, 28,29,29A,32,50,51,54A,55A, 28,29, 29A, 32,50,51,54A, 55A, 61A 61 A Parachutes 11,53 11,53 Pedals 51,51, 54A, Pedals 2A, 2A, 13A, 13A, 29A, 29A, 45, 45,51,51,54A, 56,61,61 A 56,61,61A Pedal 54A, Pedal Brackets Brackets 2A, 2A, 13A, 13A, 29A, 29A, 45, 45,54A, 56,61 56.61A A Penetrating penetrating Oil30 Oil 30 Power Power Boosters Boosters 2, 2, 5, 5, 66 Pressure 15A Pressure Bleeders Bleeders 6, 6,15A Pressure Pressure Gages, Gages, Air Air 15 15 Pressure 38, 41 Pressure Gages, Gages, Hydraulic Hydraulic 28, 28,38,41 Pressure PressureSwitches Switches 41 41 Proportioning 2A, 7A, 7A, 17A, 17A, 31, 31, Proportioning Valves Valves 2A, 47,56 47,56 Pushrods Pushrods 56 56 Pyrometers/Thermometers 4, 4,44,46, Pyrometers/Thermometers 44, 46, 51,56 51,56
5,6, 15A, 18, 18,32,52,55 Shoes 5, 6, 15A, 32, 52, 55 Fluid 15A, 15A, 47, 47, 51,55,62,63 51, 55,62, 63 Silicone Fluid 29,54A, 55A, Brakes 28, 28, 29, Sprint-Car Brakes 54A, 55A, 56,61 56,61 Hoses 1,4,7, 1,4, 7, 16,52,62 16,52, 62 Steel-Braided Hoses Brakes 13A, l3A, 28, 28,29, 54A, Stock-Car Brakes 29, 54A, 55A, 56, 56,61,61 61,61 A 55A, Switches Switches 6 Indicators 4,46,51, 4, 46, 51,558, Temperature Indicators 55B, 56,59 56,59 Tools 3, 3, 66 Tools Water-Cooling System System 56 56 Water-Cooling Wheel Cylinders Cylinders 5,6 5, 6 Wheel
METRIC. CUSTOMARY-UNIT EQUIVALENTS by: I Multiply: EQUIVALENTS by: to get: to get: I METRIC CUSTOMARY-UNIT .
Multiply:
LINEAR Multiply: inches LINEAR feet inches yards feet miles yards inches miles microinches inches AREA rnicroinches 2 inches AREA 2 inches inches2 feee 2 inches2 yards feet2 acres 2 yards2 miles acres VOLUME miles2 3 inches VOLUME 3 inches 3 inches3 inches inches3 quarts inches3 gallons 3 quarts feet 3 gallons feet feet3 fluid oz 3 feet3 yards fluid oz teaspoons yards3 cups teaspoons MASS cups ounces MASS (av) pounds (av) ounces (av)Ib) tons (2000 pounds (av)Ib) tons (2000 tons (2000 Ib) FORCE tons (2000 Ib) ounces-t(av) FORCE pounds-t(av) ounces-f(av) kilograms-f pounds-f(av) TEMPERATURE kilograms-f
-40 -40
X X
X X X X
X X X X X X X X X X X X X X X X X X X X X X X X X
X X X X X X X
I
I 0
I
-20
Multiply:
millimeters(mm) meters (m) = meters millimeters(mm) (m) = kilometers meters (m) (km) = meters (m) centimeters (cm) = kilometers (km) micrometers (M m)
X X
centimeters (cm) micrometers(Mrn) 2 millimeters (mm2j centi meters 2(cm 2j millirneters2(mrn2) meters2(m2j centimeters2(crn2) meters 2(m2j rneters2(m2) 4 m2j (ha) hectacres(10 meters2(m2) kilometers 2(km 2j hectacres(104m2)(ha) kilometers2(km2)
= =
= = =
= = =
millimeters 3(mm~ 3 centimeters (cm 3) = liters millimeters3(mm3) (I) = centimeters3(crn3) liters (I) = liters liters (I) (1) = Iliters (1) iters (I) = liters (1) meters 3 (m 3) = liters (1) milliliters (mil 3(m 3) = meters meters3(m3) = milliliters(ml) milliliters (mil = meters3(m3) liters (I)
milliliters (ml) liters (1) grams (g) kilograms (kg) grams (g) (kg) kilograms kilograms metric tons(kg) (t) kilograms (kg) metric tons (t) newtons (N) newtons (N) newtons newtons (N) (N) newtons (N) newtons (N)
=
=
= = = =
= = =
I I
"C -40Celsius -20 (C) Degrees
'
32 40 I l l
o =
II I I 98.6 80
I
by: X X
X X X X X X X X
X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X
0 .03937 3.281 0.03937 1.0936 03.281 .6214 01.0936 .3937 0.6214 39.37
120 I
I
I 80I I 120I
0 0.556 (F20 - 32)
= = = =
0.3937 39.37 0.00155 0.155 0.00155 10.764 0.155 1.196 10.764 2.471 1.196 0.3861 2.471 0.3861 0.000061 0.06102 61 .024 1.0567 0.2642 0.03531 35.315 0.03381 1.3080 0.2029 4.227
inches rnicroinches 2 inches 2 inches 2 = feet inches2 2 = inches2 yards = feet2 acres = yards2 miles 2 - acres = miles2 3 inches 3 inches 3 inches3 inches inches3 quarts inches3 gallons 3 quarts feet 3 gallons feet feet3oz fluid 3 feet3 yards fluid oz teaspoons yards3 cups teaspoons cups ounces (av) 0.03527 pounds (av) 2.2046 0.03527 = ounces (av)Ib) '0.001102 tons (2000 2.2046 = pounds (av)Ib) 1.1023 tons (2000 '0.001 102 = tons (2000 1b) 1.I 023 = tons (2000 Ib) 3.597 ounces-f(av) 0.2248 pound's-f(av) 3.597 = ounces-f(av) 0.10197 kilograms-f 0.2248 = pound's-f(av) 0.10197 = kilograms-f
I
i 160
I
240
I I 00
21 I, 00 I 2I
40
60
80
40
60
80
Degrees Celsius (C) = 0.556 (F - 32)
100
I
I
= =
120
280
I
I l I I
240
I I I I I l I I l , l I I I I I I I
20
to get: inches feet inches yards feet miles yards inches miles microinches
212
98.6
o
I
I
2.54 0.0254 645.16 6.452 645.16 0.0929 6.452 0.8361 0.0929 0.4047 0.8361 2.590 0.4047 2.590 16387 16.387 16387 0.01639 016.387 .94635 0.01639 3.7854 0.94635 28.317 3.7854 0.02832 28.31 7 29.57 0.02832 0.7646 29.57 4 .929 0.7646 0.2366 4.929 0.2366 28.35 0.4536 28.35 907.18 0.4536 0.90718 907.1 8 0.9071 8 0.278 4.448 0.278 9 .807 4.448 9.807
X X X X X X X X X X
TEMPERATURE -40 O F
25.4 0.3048 25.4 0.9144 0.3048 1.6093 0.9144 2.54 1.6093 0.0254
X X
1
to get:
by: X X X X X X X X X X
I
I
I
280 I
I
I I l I I
140
"F
320 160
°C
100 Farenheit 120 140 (F) = (1160 .8C) Degree
+OC 32
Degree Farenheit (F) = (1.8C)
+ 32
ACCELERATION 2 feetlsec X ACCELERATION 2 inches/sec X
0.3048 0.0254
2 meters/sec (m/s2j metersl sec 2(ml s 2j
X X
3.281 39.37
feetlsec 2 2 inches/sec
171 171
I Multiply:
by:
to get:
Multiply: Multiply: by: to get: ENERGY OR WORK (Watt-second=joule=newton-meter)
by:
to get:
foot- pounds X (Watt-second=joule= 1.3558 joules (J) ENERGY OR WORK newton-meter) calories X 4.187 joules (J) foot-pounds X = joules Btu X 1.3558 1055 joules (J) (J) calories X = joules watt-hours X 4.187 3600 joules (J) (J) Btu X = joules (J) (MJ) kilowatt-hrs X 1055 3.600 megajoules watt-hours X 3600 = joules (J) FUEL ECONOMY X & FUEL CONSUMPTION kilowatt-hrs 3.600 = megajoules (MJ) = kilometers/ liter(km / I) miles/ ECONOMY gal X FUEL 0.42514 FUEL & CONSUMPTION Note : X 0.4251 rniles/gal 235.2/ (mi / gal) = liters/ 1 OOkm 4 = kilorneters/liter(km/I) Note: 235.2/ (liters/ 1OOkm) = mi / gal 235.2/(rni/gal) =liters/l OOkm PRESSURE OROOkm) STRESS = rni/gal 235.2/(liters/l inches Hg (60F) X 3.377 kilopascals (kPa) PRESSURE OR STRESS pounds/sq in. X 6.895 kilopascals (kPa) inches Hg (60F) X = kilopascals inchesHzO(60F) X 3.377 0.2488 kilopascals (kPa) (kPa) pounds/sq in. X = kilopascals bars X 6.895 100 kilopascals (kPa) (kPa) inchesH20(60F) X = kilopascals pounds/ sq ft X 0.2488 47.88 pascals (Pa)(kPa) bars X 100 = kilopascals (kPa) POWER pounds/sq ft X 47.88 = pascals (Pa) horsepower X 0.746 kilowatts (kW) POWER ft-Ibflmin X 0 .0226 watts (W) X 0.746 = kilowatts (kW) horsepower TORQUE X 0.0226 = watts (W) ft-lbf/min pound-inches X 0.11298 newton-meters (N-m) TORQUE pound-feet X 1.3558 newton-meters (N-m) X 1298 = newton-meters pound-inches pound-inches X 0.1 0.0115 kilogram-meters(N-m) (Kg-M) X 1.3558 = kilogram-meters newton-meters (N-m) pound-feet pound-feet X 0.138 (Kg-M) X 0.01 15 = kilogram-meters (Kg-M) pound-inches VELOCITY pound-feet X 0.138 = kilogram-meters (Kg-M) miles/ hour X 1.6093 kilometers/ hour(km / h) VELOCITY feet/sec X 0 .3048 meters/ sec (m/ s) miles/hour X 1.6093 = kilometers/hour(km/h) kilometers/ hr X 0.27778 meters/ sec (m/ s) feet/sec X = rneters/sec miles/ hour X 0.3048 0.4470 meters/ sec (m/s) (m/ s) kilorneterdhr X 0.27778 = rneters/sec (m/s) COMMON METRIC PREFIXES miles/hour X 0.4470 = meters/sec (rn/s) (M) mega 1,000,000 10 6 centi (c) COMMON METRIC PREFIXES or (k) kilo (m) 1,000 or 10 3 milli (M) = 100 1,000,000 or l o 26 centi (c) = mega (h) hecto or 10 micro (ttl milli (m) = or 1 (k) = 1,000 kilo or 10' micro = hecto (h) = 100
X X X X X X X X X X X
0.7376 0 .2388 0.7376 0.000948 = 0.2388 0.0002778 = = 0.000948 = 0 .2778
foot-pounds calories foot-pounds Btu calories watt-hours Btu kilowatt-hrs
X X X X XX XX X X X X X X X X X X X X X X X X X X X X X X
0.2961 0.145 0.2961 4.0193 0.145 0.01 4.0193 0.02088
inches Hg pounds/sq in inches inches Hg H2O pounds/sq in bars inches 2 0ft pounds/Hsq
Multiply:
by:
to get:
o3
I
0.0002778 = watt-hours 0.2778 = kilowatt-hrs 2.3522 miles/ gal
= = =
0.01 0.02088 1.34 44.25 1.34 44.25 8.851 0 .7376 8.851 87 0.7376 7.25 87 7.25 0 .6214 3 .281 0.6214 3.600 3.281 2.237 3.600 2.237
0.01 0.001 0.01 0 .000,001
0.001 0.000,001
= =
= =
= = = =
= = = =
or or or or
or or
bars pounds/sq ft horsepower ft-Ibflmin horsepower ft-lbf/min pound-inches pound-feet pound-inches pound-feet pound-feet pound-feet pound-feet pound-feet miles/ hour feet/sec miledhour kilometers/h r feet/sec miles/hour kilorneters/hr miledhour . 10- 2 10-3 10-6
'
Convers ion chart courtesy Ford Motor Company.
Conversion chart courtesy Ford Motor Company.
172
BOLT TORQUE BY GRADE SAE Grade Number
1 or 2
Manufacturer's marks may SAE Grade Number
1 or2
vary. Bolt grades up through Manufacturer's marks may grade 8 are shown at right. vary. Bolt grades up through grade 8 are shown at right. Capscrew Diameter (inch) and Minimum Tensile Capscrew(psi) Diameter (inch) Strength and Minimum Tensile Bolt size (psi) & thread pitch Strength
5 BOLT TORQUE BY GRADE 8 5 8
~
~ I I
Special Alloy*
~ 9 /, I
~
Special Alloy*
e
To 1/2-69,000 To 3/4-120,000 To 1 -150,000 To 1 -185,000 To 3/4-64,000 3/4 to 1-115,000 To 1/2-69,000 To 3/4- 120,000 To 1 - 150,000 To 1 - 185,000 To 1-60,000 To 3/4-64,000 3/4 to 1 - 1 15,000 Torque (foot-pounds) for plated bolts with clean, dry threads. To 1-60,000
1/4-20 6 12 Bolt size & thread pitch Torque (foot-pounds)10 for plated bolts with clean, dry threads. 14 -28 7 12 17 15 1/4-20 6 12 10 14 5/16-18 13 20 24 29 -28 7 12 15 17 -24 14 22 27 35 5/16-18 13 24 20 29 3/8-16 23 36 44 58 -24 14 22 27 35 -24 26 40 48 69 3/8-16 23 36 44 58 7/16-14 37 52 63 98 -24 2 6 40 48 69 -20 41 57 70 110 7/16-14 37 52 63 98 1/2-13 57 80 98 145 -20 41 57 70 110 -20 64 90 110 160 1/2-13 57 80 98 145 9/16-12 82 120 145 200 -20 64 90 110 160 -18 91 135 220 165 9/16-12 82 120 145 200 5/8-11 111 165 210 280 -1 8 91 135 1 65 220 -18 128 200 245 310 5/8-11 111 165 21 0 280 3/4-10 200 285 335 490 -1 8 200 128 245 31 0 223 -16 315 370 530 3/4-10 200 285 490 335 7/8-9 315 430 500 760 223 -1 6 31 5 530 370 -14 340 470 550 800 7/8-9 430 31 5 7 60 500 1-8 400 650 760 1130 -1 4 340 470 800 550 -14 460 710 835 1210 400 1-8 650 1130 760 For lubricated-1 threads, reduce torque amount: 45% when compound; 40% 4 71 0 460 values by the following 835 using anti-seize1210 with grease or heavy oil; 30% with graphite; or 25% with white lead. "Torque Values shown are for high nicklechrome alloy Bowmalloy cap screws. Other high-alloy cap screws maY .not have the same values. Always use with grease or heavy oil; 30% ifwith or 25% white lead. *Torque manufacturer's specifications theygraphite; do not agree withwith values listed in this chart.Values shown are for high nicklechrome alloy Bowmalloy cap screws. Other high-alloy cap screws m a y n o t have the same values. Always use manufacturer's specifications if they do not agree with values listed in this chart.
DECIMAL EQUIVALENTS 0.0156-1/64 0.2656-17/64 0.5156~33/64 0.7656-49/64 DECIMAL EQUIVALENTS 0.0312 1/32 0.2812 9/32 0.5312 ' , 17/32 0 .7812 25/32 56- 1 /64 0.265617/64 0.5156-33/64 0.7656-49/64 00.01 .0469-3/64 0.2969-19/64 0.5469-35/64 0.7969-51/64 1 /32 5/16- 0.281 0.0312 9/32 9/16- 0.531 2 2' 17/32 13/16- 0.781 2 25/32 1/16-0.0625 0 .3125 0.5625 0.8125 0.29691 9/64 0.5469-35/64 0.7969-51 /64 00.0469-3/64 .0781-5/64 0.3281-21/64 0.5781-37/64 0 .8281 -53/64 1 /I 6- 0.0937 0.0625 0.5625 8125 3/32 5/16-0.3125 0 .3437 11/32 9/16-0.5937 19/32 13/16- 00. .8437 27/32 0.0781 -5/64 0.3281 -21 /64 0.5781 -37/64 0.8281 -53/64 0.1094-7/54 0.3594-23/64 0.6094-39/64 0.8594-55/64 .09373/32 6/16- 0.3437 1 1 /32 1'0/16- 0.6250 0.593719/32 14/16- 0.8750 0.843727/32 2/16- 0 0.1250 0.3750 0 .1094-7/54 0.3594-23/64 0.6094-39/64 0.8594-55/64 0.1406-9/64 0.3906~25/64 0.6406-41/64 0.8906-57/64 2/16-0.1250 0.3750 0.6250 0.1562 5/32 6/16-0.4062 13/32 ?0/16-0.6562 21/32 14/16- 00.8750 .9062 29/32 -57/64 0.1406-9/64 0.390625/64 0.6406-41/64 0.1719-11/64 0.4219-27/64 0.6719-43/64 00.8906 .9219-59/64 21 /32 15/16- 00. 906229/32 0.15625/327/16-0.4375 0.406213/32 11/16- 0.6876 0.6562 3/16-0.1875 .9375 0.1719-1 1/64 0.421 9-27/64 0.671 9-43/64 0.921 9-59/64 0.2031-13/64 0.4531 -29/64 0.7031-45/64 0.9531-61/64 ' 3/16-0.1875 0.2187 7/32 7/16-0.4375 0.4687 15/32 1 1 /16- 0.6875 0 .7187 23/32 15/16-0.9375 0.9687 31/32 0.2031-1 3/64 0.4531-29/64 0.7031-45/64 0.9531-61 /64 0.2344-15/64 0.4844~31 /64 0.7344-47/64 0.9844-63/64 0.21877/328/16-0.5000 0.468715/32 12/16- 0 .718723/32 16/16-10. 968731 /32 4/16-0.2500 0.7500 .000
-
-
-
-
0.2344- 1 5/64 4/16-0.2500
0.4844-31 /64 811 6-0.5000
0.7344-47/64 12/16- 0.7500
0.9844-63/64 16/16- 1 .OOO
Chart courtesy Acme Rivet & Machine Corp.
Chart courtesy Acme Rivet & Machine Corp.
173
Index A A AP AP Racing Racing 26, 26, 28, 28, 30 30 actuating actuating system system 5, 5, 85 85 adjusters, adjusters, automatic automatic 22, 22, 121 121 aerodynamic aerodynamic braking 82 82 aerodynamic aerodynamic drag drag 9, 9, 82 82 aerodynamic 147 aerodynamic modifications modifications 147 air air brake, see see pneumatic brakes brakes air air ducts ducts 139 139 air-pressure 1 13, 142 142 air-pressure gage gage 113, Airheart, Frank 31 31 Alfa Romeo Romeo 20, 20, 22 22 Alston Alston Industries 31 31 anti-skid control 59 control 58 58 -- 59 ATE ATE 58,59 58, 59 Bosch 58,59 58,59 Chrysler Chrysler 58 58 Delco 1)elco 58 58 Ford Ford 58 58 GM G M 58 58 Honda Honda 58 58 Kelsey-Hayes Kelsey-Hayes 58 58 Mercedes Mercedes 58 58 Mitsubishi Mitsubishi 58 58 Porsche Porsche 58 58 Auto Auto Union 20 20 arcing21,41,134 arcing 21,41, 134 asbestos 36,41, 134, 134, 150 150 asbestos 36,41,
B backing backing plate plate 15,20 15, 20 backing-plate backing-plate modifications modifications 147 147 balance I 62 balance bar bar 6, 6, 50, 50, 74, 74, 100, 100, I114, 14, 160160-162 adjustable adjustable 74,100,161 74, 100, 16 1 Neal Neal Products Products 75 75 Tilton Tilton Engineering Engineering 75 75 Winter Winter Performance Performance 75 75 bedding bedding in in 40 40 bellmouthing 19 bellmouthing 19 Bendix Bendix 15, 15, 79 79 Bignotti, Bignotti, George George 104 104 bleeder bleeder screw screw 49, 49, 52,123,127,164 52, 123, 127, 164 bleeding bleeding 123 123 bonded bonded lining lining 37 37 booster booster 77, 77, 135, 135, 154 154 ATE ATE T-50 T-50 153,154 153, 154 air-suspended air-suspended 79 79 Bendix Bendix Hydro-Boost Hydro-Boost 81 81 Girlock Girlock LSC LSC 5077 50 77 hydraulic hydraulic 80 80 Master-Vac Master-Vac 79 79 tandem tandem 79 79 Brabham Brabham 28 28 brake 121 brake adjustment adjustment 22, 22, 121 brake brake balance balance 14, 14, 54, 54, 74, 74, 114, 114, 152, 152, 160 160 brake brake components, components, AP AP Racing Racing 137 137 brake brake design design 88-103 88- 103 brake brake drum drum 4, 4, 18, 18, 146 146 AI-Fin Al-Fin 19, 19, 146 146 bi-metallic 18 bi-metallic 18 Buick Buick 146 146 brake brake effectiveness effectiveness 118 1 18 brake brake fade fade 14, 14. 25 25
174
brake fluid fluid 42, 63 63 brake history 6 -- 77 brake brake hose, hose, Aeroquip Aeroquip 61 61 brake line, line, Bendix 61 61 brake 34 brake lining lining 5, 5, 15, 15, 21, 2 1, 34 brake brake pads 5,22,32 5, 22, 32 brake pedal pedal 5,66-76 5, 66-76 brake brake shoe, shoe, aluminum aluminum 20 20 brake shoes shoes 4, 4, 15,21 15, 21 brake brake testing testing 104 104 brake brake torque torque 55, 55, 93 93 brake brake warning-light warning-light switch switch 59 59 brakes brakes diagonally diagonally split split system system 45, 45, 48, 48, 56, 56, 161 161 hydraulic hydraulic 66 inboard inboard 98 98 mechanical mechanical 6, 6, 87 87 British (BTU) 88 British Thermal Thermal Units Units (BTU) r7 C L C C && D D Engineering Supply Supply Ltd. Ltd. 63 63 CR C Disc CRC Disc Brake Brake Quiet 136 136 caliper 156 caliper 5,28,52,97, 5, 28, 52, 97, 156 AP AP Racing Racing 161 161 Bendix Bendix 52 52 bridge bridge 30, 30, 162 162 Corvette 95 Corvette 95 fixed fixed 28 28 flexing flexing 30, 30, 106, 106, 162 162 floating floating 28 28 hinged hinged 29 29 Hurst/ Airheart 100, I4urstlAirheart 100, 145 145 JFZ JFZ Engineered Engineered Products Products 156 156 mounting mounting 32 32 piston piston 30, 30, 52 52 Lockheed Lockheed 53 53 Camaro Camaro 83 83 Can-Am McLaren 140 140 Can-Am McLaren Can-Am Can-Am Porsche Porsche 139 139 center (CG) 8,13,92 8, 13, 92 center of of gravity gravity (CG) center center of of pressure pressure 93 93 changeover 74 54,74 changeover pressure pressure 54, Chaparral Chaparral 84, 84, 85 85 charts charts Brake Brake Test Test Data Data Sheet Sheet 109 109 CG CG location location 93 93 Chrysler Chrysler Imperial Imperial 24 24 Chrysler hemi 19 19 Chrysler hemi combination combination valve valve 60 60 compensating compensating port port 46 46 composite composite drum drum 19 19 composite composite rotor rotor 27 27 -- 28 28 control control valve valve 79 79 cooling 139-147 cooling improvements improvements 139-147 Corvair Corvair 145 145 Corvette Corvette 29, 29, 33, 33, 36, 36, 146, 146, 148 148 Corvette Corvette GTP G T P 44 Crosley Crosley 77 cup cup expander expander 47,51 47, 51 cup-type cup-type seal seal 46 46 cutting cutting brake brake 87 87 cutting cutting brake, brake, Ja-Mar Ja-Mar 87 87
D D deceleration 11 11 deceleration deceleration test test 112, 112, 116 116 decelerometer, deceleronieter, AMMCO AMMCO Tools Tools Inc. Inc. 112 1 12 deflection deflection reduction reduclion 162-165 162-165 Department Department of of Transportation Transportation (DOT) (DOT) 64 64 design 90 design criteria criteria 88 88 -- 90 disc disc brake brake 4, 4, 5, 5, 23-33 23-33 mechanical mechanical 66 disc-brake disc-brake rotor rotor 5, 5, 23, 23, 25, 25, 96,132 96, 132 discard diameter 134 134 discard diameter discard discard thickness thickness 132 132 displacement displacement fluid fluid 44 44 dog dog drive drive 25 25 drag drag 9, 9, 82 82 drag drag coefficient coefficient 83 83 drilling drilling drums drums 149 149 drilling drilling rotors rotors 26, 26, 148 148 drum 40 15 -- 22, 22,40 drum brake brake 4, 4, 15 duo-servo duo-servo 16 16 -17 -17 external external 55 shoe shoe 4, 4, 15,21 15,21 Duesenberg 6, 6, 77 dust dust shield, shield, modifying modifying 146 146 Dwyer Instruments 113 Instruments 113 dynamometer dynamometer 104 104 -- 105 105 E E Eagle Eagle Indy lndy Car Car 73 73 Edwards, Edwards, Wally Wally 146 146 effective effective piston piston area area 99 99 effective 99 effective piston piston diameter diameter 99 effective effective radius radius 99,158 99, 158 energy energy 77 -- 11 11 kinetic kinetic 8, 8, 96, 96, 105 105 potential potential 99
FF factor Sactor of of safety safety 68,91 68, 91 fade fade 14, 14, 25,148 25, 148 fatique fatique 27 27 fittings tittings 62-63 62-63 flare flare 62 62 fluid fluid 42, 42, 63-65 63-65 boiling boiling 63 63 glycol-based glycol-based 63, 63, 129 129 silicone silicone 63, 63, 65, 65, 129 129 fluid-inlet 46 porl46 fluid-inlet port fluid-level fluid-level indicator indicator 60 60 Ford Ford Motorsport Motorsport 56 56 Formula car 156 156 Formula II car Formula Formula Ford Ford 138 138 friction friction 4, 4, 77 -- 8, 8, 34 34 friction 35 35 friction friction 1 1, 34 34 friction coefficient coefficient 8,8, II, friction friction force force 34 34 friction friction material material 4, 4, 34-41 34-41 Bendix Bendix EDF E D F 40 40 Ferodo 39,40,41 Ferodo DSll DS l l 39,40,41 Hardie-Ferodo Hardie-Ferodo 110339 1103 39 Hardie-Ferodo I4ardie-Ferodo Premium Premium 40 40 Hardie-Ferodo DP11 DPI I Hardie-Ferodo bestos M Ray Raybestos M19 1939, j 9 , 4400
I
Raybestos 5191 5 191 40 4.0 Raybestos 5262 40 frontal frontal area 83 83 G Girling 51 51 Girlock 21 21 glaze 41 41 Goodyear 53 53 graphs Aerodynamic Drag vs. Speed 84 Deceleration vs. vs. Aerodynamic Downforce 116 116 Drum Brake Servo Action 158 158 Fluid Pressure vs. Proportioning Valve Settings 57 Fluid Pressure vs. vs. Pedal Effort 81 with Booster 81 Fluid Pressure with AP Racing Proportioning Valve 55 Fluid Pressure with Kelsey-Hayes proportioning valve 56 Fluid Pressure with AP Racing proportioning valve 55 vs. Rear Pressure with Pressure Front vs. Limiting Valve 57 Glycol Brake Fluid Boiling Point 63 63 Ideal Front vs. Rear Fluid Pressure 56 Pedal Effort vs. vs. Lining Friction Coefficient 17 Pedal Effort vs. Master-Cylinder Diameter 151 151 Pedal Effort/ATE EffortIATE Boosters 154 154 Rear Fluid Pressure for Maximum Deceleration 54 Rear Fluid Pressure with Proportioning Valve 54 gravity force (g's) 11,91 11, 91 green fade 40 grip 35, 92 grooving rotors 148 148 groving linings 150 150
H H HPBooks 86 hand-operated brakes 87 hard lining 37 hat25,97 hat 25, 97 heat 8 heel drag, 129 129 I31 Honda 131 Honda Civic 57 hone 129 129 hoses 60, 60, 122, 122, 162 162 How 10 to Make Your Yolir Car Cbr tlat~dle Handle 165 165 Howe 50 hydraulic brake 6 hydraulic system 42-65 hydraulic tubing 61-62,123 61-62, 123 hydroscopic 64 Hurst 163 163 HurstIAirheart Hurst/ Airheart 32
I IMSA road racer 95 95 Indy Car 39,50,95,144 39,50,95, 144 inertia 12 12 inertia force 12, 12, 91 91 input piston 45
JJ JFZ 7,25,2.9,33, 7, 25, 2.9, 33, 163 163 Jaguar 7 K kinetic energy 8, 96
L Lancia Monte Carlo GP G P 5 Turbo 28 leading shoe 16, 16, 52 Lee, Geoff 116 116 LeMans 7 Lincoln Mark VII 58, 58, 59 lining 5, 15,21,34 15, 2 1, 34 metallic 35 molded 36 organic 35 replacement 131 13 1 semimetallic 37 Long Beach 37 M M MG5 MG 5 March Indy Car 23,141 23, 141 master cylinder 6, I, 128, 6, 46, 10 101, 128, 151 151 Airheart 50 fast fill 49, 50 Girling 46 Howe 65 65 Hurst! Airheart 47 HurstIAirheart tandem 48 master-cy linder bail 48 master-cylinder master-cylinder ports 46 mechanical advantage 69 mechanical brake 6 Mercedes 300SLR 82, 84 Mercury 159 159 metering valve 53-54 minimum-wear thickness 132 132 Monroe, Tom 86 Monza 86 multi-disc brake 22, 86
N NACA duct 115,140,141,142 115, 140, 141, 142 noncircular piston 31, 3 1, 99 normal force 34
o0 O-ring seal 53 53 Omega Engineering, Inc. 11 1 Inc. 106, 106, 110, 110, III Omega Label 110 1 10 operating pressure, 99 output piston, 45 p P pad backing plate 32 pad, brake 5, 22, 32 parking brake 30, 30, 122, 122, 135 135
pedal 66, 99,135,163 66,99, 135, 163 arm 66 bracket 72, 102, 102, 163 163 design66,91,99,163 design 66, 91, 99, 163 effort 17,68,101,150 17, 68, 101, 150 floor-mounted 73 73 hanging 66, 73 73 linkage 5, 66, 99, 99, 102,135 102, 135 pad 67 pivot 69 ratio 68,101,159 68, 101, 159 stop 76 pedal-and-bracket assembly Tilton Engineering 72 Neal Products 72 pedal bracket, Neal 102 102 perpendicular force 34 Peugeot 6 Phoenix International Raceway 23, 96 pneumatic brakes 6, 6, 85 85 potential energy 9 power assist 77 -- 81 81 power booster 77 power chamber 78 pressure 42, 78, 99 pressure bleeding 124 124 pressure-limiting valve 57 primary piston 48 primary shoe 16 16 proportioning valve 54, 161 54, 100, 100, 161 AP Racing 55 55 adjustable 55, 74,100,161 74, 100, 161 Alston Performance Brakes 161 161 Chevrolet 161 161 Chrysler 56 Corvette 56 Direct Connection 161 161 Ford 56,161 56, 161 Kelsey-Hayes 161 161 Porsche 56, 161 161 Tilton Engineering 160 160 puck 5 push rod, adjustable 81 pushrod, 81 pyrometer 105, 105, 110 110 AP Racing 106 106 Nationwide Electronic Systems III 1 11 Omega Engineering 106, 106, 110 110 Tilton Engineering 106, 106, 110 110
R regenerative braking 9 reservoir 50 residual-pressure valve 47 return spring 21, 2 1, 76 Riverside Raceway 34 riveted lining 37 Road Road & Track magazine 28 rollback 50 rolling drag 82 158 rolling radius 94, 158 rotor surfacing 132 132 rotor composite 27 -- 28
175
discard thickness thickness 132, 132, 133 133 discard 96 IIHurst urst 96 graphite 27 27 graphite JFZ96 96 JFZ Sphericone 26 26 Sphericone Tilton 96 96 Tilton Wilwood 96 96 Wilwood runout point point 81 81 runout
SS Safety Braker Braker 59 59 Safety safety factor factor 68, 68, 91 91 safety San Angelo, Angelo, Texas Texas 53 53 San scoops 39 39 scoops secondary piston piston 48 48 secondary 16 secondary shoe shoe 16 secondary servo action action 16, 16, 159 159 servo shear 27 27 shear Simpson Safety Safety Equipment Equipment Co. Co. 85 85 Simpson sintering 37 37 sintering sliding caliper caliper 29 29 sliding sliding friction friction 35,54 35, 54 sliding Sneva, Tom Tom 104 104 Sneva, (SAE) Society of Automotive Engineers (SAE) Society 63, 64 64 63, soft lining lining 37, 37, ISO 150 soft Iieat 88 specific heat specific splash shield shield 32 32 splash spot brake brake 24 24 spot squeal 136 136 squeal stability 165 165 stability static friction 35, 54 static friction 35,54
176
stock-car brake brake 40 40 stock-car stoplightswitch switch59 59 stoplight stress, thermal thermal 27 27 stress, 26,96 swept area area 18, 18,26, swept 96 StainlessBrakes BrakesCorporation Corporation 131 13 1 Stainless Super Vee Vee 39 39 Super 170 supplierslist list 169 169-- 170 suppliers TT tables tables Bolt Torque Torque Bolt Brake-Fluid Boiling Boiling Point Point 64 64 Brake-Fluid Decimal Equivalents Equivalents 173 173 Decimal Master-Cylinder Size Size vs. vs. Piston Piston Area Area Master-Cylinder 10 1 101 Melting Temperature Temperature 99 Melting Metric Equivalents Equivalents 171 171 -- 172 172 Metric Pedal Pedal Effort Effort vs. vs. Brake Brake Type Type and and Friction Friction 17 Coefficient 17 Coefficient Performance Specifications Specifications 90 90 Performance Power to to Brakes Brakes 105 105 Power 99 Total Caliper Piston Area 99 Typical Typical Swept Swept Areas Areas per per Ton of of Vehicle Vehicle 28 Weight 28 Talbot 18 18 Talbot 1 19, 164 164 taper wear 119, temperature indicator Indicator temperature 111 AP Racing III 110 Omega Engineering 110 Tempil 1 10 TempilllO 10, 95 95 temperature rise 10, 105, 110 110 temperature tests 105,
Tempilabel Ternpilabel 110 110 test test track track 106, 106, 113 1 13 thermal thermal stress stress27 27 thermocouple 111 thermocouple lOS, 105, III Tilton Tilton Engineering Engineering 55, 55, 56, 56, 163 163 tire tire friction friction 35,54,92 35, 54, 92 toppling 1 13, 117 1 17 toppling blocks blocks 113, trailing tralling shoe shoe 16 16 trouble-shooting trouble-shooting 135, 135, 166 166 Trouble-Shooting Trouble-Shooting Guide Guide 166 166-- 168 168
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U unbalanced unbalanced force force II I1
V v VW VW Rabbit Rabbit 90 90 vacuum vacuum bleeding bleeding 125 125 vacuum vacuum suspended suspended booster booster 79 79 vented rotor rotor 26, 26, 97, 97, 144 144 vented vented wheel wheel 144 144
W water-cooling water-cooling 147 147 wear reduction reduction 159 I59 wear test 119 l I9 weight transfer 13 I3 wheel 144 144 wheel cylinder 15,22,51,129 15, 22, 5 I, 129 wool-tuft testing 140 testing 140 WREP Industries 63 63 White Whlte Post Restorations 129 129
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Mark Selix bleeds brakes on Protofab-constructed Trans-Am Capri, page 123. Photo by Tom Monroe.
Mark SeCix bleeds brakes on Protofab-constructed Trans-Am Capri, page 123.Photo by Tom Monroe.
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Corvette disc-brake pads being tested to destruction on Girlock dynamometer, page 105. Photo courtesy Girlock Ltd.
Paul Miller braking hard for kink in 944 Turbo Porsche at Firebird Lake Trans-Am race. Photo by Tom Monroe.
Corvette disc-brake pads being tested to destruction on Gir courtesy Girlock Ltd.
Paul Miller braking hardfor kink in 944 Turbo Porsche at Firebird Lake Trans-Am race. Photo bv Tom Monroe.
105. Photo
BRAKE HANDBOOK
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BRAKE HANDBOOK
How to bleed your street-car brakes or design a complete race-car brake system. Drum and disc brakes are covered in detail. Why the designers did what How to bleed your street-car brakes or design a complete race-car brake they did. system. andmaterial-organic, disc brakes are covered in detail. the designers DetailsDrum friction semimetaliic andWhy metallic, and harddid andwhat they soft. did. How each affects pedal effort, stopping force and wear. How to test to Details friction material-organic, and metallic, and hard and determine which is best for street or semimetallic track. soft. How each affects pedal effort, stopping force wear. How test to to modify yourto existing Covers pedal and hydraulic-system design. Howand determine which is best for street or track. brakes or design the latest racing-brake system . Covers pedal and hydraulic-system to modify youranywhere existing at The most comprehensive and usefuldesign. book onHow brakes available brakes or design thebra' latest racing-brake system.' and suppliers. any price! Includes k e-hardware manufacturers ailbbie anywher a The most comprehensive and useful book on bra^ any price! Includes brake-hardware manufacture s
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TAG McLaren twin-caliper setup gets maximum workout on city streets such as Detroit GP circuit. Photo by TomMcLaren Monroe. twin-caliper setup gets maximum TAG
workout on city streets such as Detroit GP circuit. Photo by Tom Monroe.
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B I P A D 0-89586-232-8 68272 ISBN
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