Document RjQ2RXY8Xbr1krqD0aQymOyBX

1961 FORD SERVICE FORUM NO. 9 BASIC AUTOMOTIVE BRAKES INTRODUCTION BRAKING PRINCIPLES........... Kinetic Energy.................... Coefficient of Friction.... Brake Linings and Drums HYDRAULIC SYSTEM VACUUM SYSTEM TROUBLE SHOOTING........ Trouble Shooting Chart Diagnosis Tips............... DUO-SERVO BRAKES................... Operation................................... Automatic Brake Adjustment TERMS AND DEFINITIONS 3 4 4 5 7 10 14 16 16 18 19 19 21 24 The descriptions and specifications contained in this booklet were in effect at the time the publication was approved for printing. The Ford Division of Ford Motor Company, whose policy is one of continuous improvement, reserves the right to discontinue models at any time, or change specifications or design without notice and without incurring obligation. COPYRIGHT, 1961, FORD MOTOR COMPANY, DEARBORN, MICHIGAN. ALL RIGHTS RESERVED. This Ford Service Forum Book let is published to assist the Serv ice Technician to more fully understand the braking system of present-day cars. The average person may think of automotive brakes as a simple, basic, wellunderstood component of the car; however, each model year in creases the need for better com prehension of the operational and design features in order to per form Quality Service. The Braking Principles section of this booklet explains the funda mentals involving kinetic energy and heat transfer as related to the braking system. Other sections cover the hydraulic and vacuum systems and the de sign and operation of the Ford Duo-Servo brakes. Diagnosis tips and a brake sys tem trouble shooting chart are also included to aid the Tech nician in locating possible trouble areas in the braking system. The use of the correct termin ology is as important in the brake repair field as in any other. This booklet fully explains the mean ing of all brake terms in common use today to assist in conveying reports and diagnosing trouble. I KINETIC ENERGY Among the principles of braking it is known that a moving vehicle is kept in motion not only by the power which started it moving, but also by the power of its own weight and velocity. This is called kinetic energy, or the energy of motion. Power Weight Velocity ssiisiii The heavier an object and the faster it is traveling, the more kinetic energy it possesses. Once energy is released, it can not be destroyed; it can only be changed into some other kind of energy. The heat energy pro duced by the engine in a car is changed into kinetic energy through the drive train. The brak ing system provides the means of converting the kinetic energy back into heat energy through the use of friction to slow or stop the car. I The friction created by the op posing force of the brake lining against the revolving brake drum causes heat. As the heat increases, it absorbs the kinetic energy and the heat passes from the brake assemblies to the atmosphere. COEFFICIENT OF FRICTION Friction is basically the resist ance to motion. The coefficient of friction is the effectiveness of one material to resist sliding over another. For example, it takes about 70 pounds of pulling effort to slide a 100-pound block of rubber over a concrete surface; but it takes only about two pounds of pulling effort to slide a 100-pound block of ice over the same surface. Thus, the pulling effort divided by the weight of the load equals the coefficient of friction. The friction of an object at rest is known as static coefficient of friction and is greater than the friction of motion, or kinetic coef ficient of friction. If the pulling effort required to keep a block of rubber moving is 70 pounds, the kinetic coeffi cient of friction is 0.70. However, the pulling effort required to start the block of rubber in mo tion would be considerably more and, therefore, the static coeffi cient of friction would be greater. rT 1 Coefficient of Friction (Cont.) In automobiles, static coefficient of friction exists between the brake linings and drums when the car is stopped and the brakes are applied. Kinetic coefficient of friction exists when the car is in motion and the linings contact the drum. The average 4,000 - pound car traveling at 60 mph represents a great amount of kinetic energy. Considering that it takes approxi mately ten seconds to accelerate from 0 to 60 mph, and only three or four seconds for the modern braking system to stop the car; the brakes must develop several times more horsepower than the engine. All of the kinetic energy built up in ten seconds must be cancelled-out in three or four seconds. <-3 TM SECONDS T Brake Linings and Drums CCont.) If the brake linings and drums get too hot, some of the binding agents in the lining may tend to soften or start to melt, thereby changing the coefficient of fric tion between the lining and drum, resulting in brake "fade." The area of contact between the lining and the drum is the great est determining factor in the amount of heat transferred and dissipated to the atmosphere. Therefore, heavier vehicles re quire increased braking area be cause more heat must be gen erated and dissipated. Assuming that 100 square inches of brake lining can absorb about 200 degrees of heat during a brake application; the same amount of heat distributed over 400 square inches, or four times the area, would amount to only 50 degrees of heat absorption per 100 square inches. This would result in greater heat dissipation for cooler - running brakes and longer lining life with a more stable coefficient of friction range. 8 I In an effort to keep brake tem peratures as low as possible, the material used in the linings and drums and the lining area of Ford brakes are carefully engi neered and machined to provide the most desirable frictional and heat conduction characteristics. In effect, the linings are "tailored" for each type of vehicle service. Non-standard brake linings may change the coefficient of friction in various undesirable ways and result in brake grabbing, fading, or short lining life. Always install genuine FoMoCo brake lining of the correct part number. TEMPERATURE tor 150 20Q 25tt 30U 35Q" 400Q 45U The hydraulic portion of the braking system consists of a mas ter cylinder that is controlled by brake pedal action, a hydraulic cylinder at each wheel, and the necessary connecting lines and fittings. The master cylinder assembly is a self-contained unit which has a fluid reservoir, a cylinder, a push rod, a piston, and a piston stop or snap ring. In the released position, both sides of the piston are open to the fluid reservoir through the compensating and breather ports of the cylinder. A stop light switch is installed in the pressure side of the master cylinder. The diaphragm of the switch is exposed to the hy draulic fluid; and when the brakes are applied, the diaphragm forces the movable contact of the switch toward the stationary con tacts to turn on the stop lights. As the brake pedal is depressed, the piston moves forward and the primary cup closes the compen sating port. As the piston continues to move forward, pressure is applied to the fluid in the cylinder and the fluid is forced out through the residual check valve into the brake lines and wheel cylinders. As the wheel cylinder pistons are pushe^d outward by the hydraulic pressure being applied from the master cylinder, the actuating pins move the brake shoes into contact with the drums. After the brake shoes have made contact with the drums, force on the master cylinder piston builds up pressure in the hydraulic system to apply increased force on the brake shoes. A boot at the ends of each wheel cylinder keeps dirt and moisture out of the cylinder. PISTONS When the brake pedal is released, the piston in the master cylinder moves rearward, and the fluid behind the primary cup, which has entered the master cylinder through the breather port, flows through the valve in the end of the piston and around the pri mary cup to reduce the pressure in the system. With reduced pressure in the sys tem, the brake shoe retracting springs push the wheel cylinder pistons INWARD to force fluid out of the cylinders. This over comes the residual pressure and the spring pressure in the master cylinder to allow the excess fluid to flow into the master cylinder reservoir. As the pistons in the wheel cyl inders move inward, the brake shoes move away from the drums. The residual check valve operates against a spring which offers enough resistance to maintain 8-15 pounds of residual pressure in the system at all times. This pressure keeps the wheel cylinder cup lips securely against the sides of the wheel cylinder and prevents air from entering the system. T The brake vacuum booster power unit is optional equipment on Ford cars and standard equip ment on Thunderbirds. The power unit consists of the vacuum reservoir and the booster. The reservoir receives vacuum from the engine intake manifold. When the engine is stopped, a check valve in the reservoir re tains the vacuum and prevents the accumulation of raw fuel vapor in the reservoir and in other parts of the vacuum system. The reservoir retains enough vacuum for several power-assisted brake applications after the engine has been stopped. In the event of vacuum power failure, the brakes will remain effective, although AIR CLEANER VACUUM PORT (CLOSED)^ ATMOSPHERIC PORT (OPEN)-. greater pedal effort will be re quired. Filtered air at atmospheric pres sure is admitted to the rear cham ber of the vacuum booster at all times through an air cleaner When the brake pedal is in the released position, the valve re turn spring holds the valve op erating rod and valve plunger against the piston rear plate, leav ing the valve atmospheric port open and the vacuum port closed. Atmospheric pressure passes through the port in the valve and through porting in the the booster piston to the front chamber of the booster. The piston is then balanced by the atmospheric pres sure on both sides and will remain in the released position. COMPENSATING PORT I I ATMOSPHERIC PRESSURE HH VACUUM E53 HYDRAULIC FLUID 14 T VACUUM FROM INTAKE MANIFOLD> VACUUM PORT (OPEN) ATMOSPHERIC PORT (CLOSED) AIR CLEANER COMPENSATING PORT r I I ATMOSPHERIC PRESSURE 5 VACUUM B HYDRAULIC FLUID HYDRAULIC FLUID PRESSURE As the brake pedal is depressed, the valve operating rod and plunger move forward against the poppet valve to close the atmos pheric port. Further travel of the rod and plunger moves the poppet valve and reaction disc to open the vacuum port and admit vacuum through the porting in the valve and piston to the for ward chamber of the booster. As the vacuum removes air from the forward chamber, atmospheric pressure behind the booster pis ton exerts force against the master cylinder push rod and piston to provide the power assist. As pressure is developed within the master cylinder, fluid is forced through the residual check valve and brake lines to the wheel cylinders. The hydraulic pressure acting against the piston in the master cylinder transmits a por tion of the force back through the piston and push rod which seats the reaction disc against the valve plunger to close the vacuum port and bring the booster piston to rest. The amount of assist supplied by the power unit is a direct multiple of the amount of pressure being applied to the brake pedal; thus, gradual application of the brakes is possible. 15 I SYMPTOMS ^ Brakes do not apply Pedal gradually goes to floor Excessive pedal travel Low pedal reserve Spongy pedal Hard pedal Pinch-out squeal Bonded brake squeal "" Wire brush noise POSSIBLE CAUSES Incorrect tire pressures Low fluid level Parking brake applied Damaged linkage Bent or improperly adjusted brake shoes Faulty or incorrect retracting springs Glazed linings Dirt on drum-to-lining surface Worn lining Faulty brake cylinder Air in hydraulic system Hydraulic lines restricted Improperly adjusted or worn wheel bearings Drum out of round Oil or grease on lining Loose carrier plate Self-adjusters not operating Threaded drum Incorrect undergrind _ Faulty holddown springs Loose linings Incorrect chamfer Drum finish too smooth Carrier plate ledges not lubricated iI__ Damp brakes High-speed stops with non-burnished linings Dirty brake fluid Faulty master cylinder Incorrect lining material 1 * Refer to "Terms and Definitions" section for explanation of brake terms. I I. T I DIAGNOSIS TIPS Before making brake system checks on cars equipped with a vacuum power booster unit, stop the engine and depress the brake pedal several times to relieve the vacuum in the system. If one or more of the brakes are locked, opeh the wheel cylinder bleeder screw to release a few drops of fluid. This will free the brake to allow the car to be moved to a service area for re pair. Push the brake pedal down as far as it' will go while the car is standing still. If the pedal can be pushed down more than half way between the released position and the floor, the brake fluid, brake adjustment, or the auto matic brake adjusters may re quire attention. 18 If the pedal feels "spongy" as a steady pressure is applied, it is an indication of air in the hy draulic system. The use of inferior brands of hydraulic brake fluid can cause air in the system; as the alcohol in the fluid will boil and evap orate to create air pockets in an otherwise tightly sealed and filled system. Use only FoMoCo Super Heavy Duty brake fluid B7A-19542-A. If it is necessary to add brake fluid to the system, inspect the master cylinder, brake lines, and wheel cylinders for leaks. If there is evidence of dirt in the brake fluid, flush the system with clean denatured alcohol, then install new fluid and bleed the system. T A PARKING BRAKE LEVER RETAINING CUP \ PARKING AWASHER BRAKE LINK SECONDARY SHOE / T OPERATION --ANCHOR PIN PLATE ------- ANCHOR PIN-------: CABLE ANCHOR FITTING SECONDARY SHOE-TO-ANCHORv SPRING V CABLE p l^GUIPEN^^ PRIMARY SHOE-TO-ANCHOR SPRING / /WHEEL CYLINDER \ (PRIMARY SHOE wAL SH0E HOLD-DOWN SPRINGS V M/UHK \b/ jjml SPRING Ml Ml W aBlE /$>. adjusting SECONDARY SHOE / BRAKE PARKING' Rear PRIMARY SHOE/ LEVER I PARKING BRAKE PIVOT HOOK/ CABLE HOOK1 / CABLE HOUSING RETAINER 7 LEVER /Front\ \AUTOMATIC \ ADJUSTER / \ SPRING PARKING BRAKE CABLE AND HOUSING SOCKET ' ADJUSTING SCREW ' PIVOT NUT Ford car and Thunderbird brakes of the Duo-Servo design are self energizing, single-anchor, internal expanding, self-adjusting type brakes. The parking brake is part of the rear wheel brake assmblies and is operated by mechanical linkage and cables. The duo-type wheel cylinders are double-acting to apply both the primary and secondary brake shoes. The initial hydraulic pres sure generated at the master cyl inder expands both pistons of each wheel cylinder equally, how ever the design of the brake shoe anchor pin incorporates a cham fer on the pin so that the primary brake shoe has less retracting spring resistance to overcome than the secondary shoe. This allows the primary shoe to move toward the brake drum an instant before the secondary shoe moves. PRIMARY SHOE RETRACTING SPRING SECONDARY SHOE RETRACTING SPRING r 19 As the toe, or top, of the primary lining contacts the brake drum, the frictional force between the brake drum and lining attempts to turn the primary shoe into the secondary shoe. This forces the secondary shoe into the drum and onto the anchor pin due to the connection between the two shoes at the adjuster. The rotation of the drum con tinues this wrap-around, or self energizing of the brake shoes, to utilize the frictional force to help the applying force on both shoes. r M The primary shoe is energized only by its own friction, and the secondary shoe is energized by its own friction and by the pri mary shoe. As a result, the sec I ondary shoe exerts about twice as much braking effort as the primary. Thus the secondary shoe has a longer and thicker lining than the primary. AUTOMATIC BRAKE ADJUSTMENT Automatic brake adjusters are standard equipment on Ford cars and Thunderbirds. Brakes will remain in adjustment for the service life of the linings. The design of the Duo-Servo brakes is such that proper liningto-drum clearance will be main tained without over-adjustment. When the car is moving in re verse, and the brakes are applied, the wrap-around action of the brake shoes following the drum forces the toe of the primary shoe against the anchor pin. T Automatic Brake Adjustment (Cont.) As the primary shoe moves against the anchor pin, the action of the wheel cylinder moves the toe of the secondary shoe away from the anchor pin. Movement of the secondary shoe causes the cable to pull the adjusting lever upward and against the end of a tooth on the adjusting screw star-wheel. As lining wear increases, upward travel of the adjusting lever in creases. This is because the secondary shoe travels further to reach the drum. When the lever can move upward far enough, it passes over the end of the tooth and engages it. When the brake is released, the adjuster spring pulls the lever downward, caus ing the star wheel to turn and expand the brake shoes. The starwheel is turned one tooth at a time as the linings wear. i V* / 22 I i i T I Satisfactory operation of the self adjusting mechanism depends upon the adjusting lever engaging the star-wheel notch when adjust ment is required. If proper en gagement is not made, the self adjusters will not function. If it is necessary to back-off the adjustment to facilitate the re moval of a brake drum, hold the adjusting lever away from the star-wheel while using the adjust ing tool. Different brake adjusting screw assemblies and adjusting levers are designed and manufactured for installation in the right and left side brakes. The adjusting screws and levers must not be interchanged. Interchanging the adjusting screw and levers from one side of the car to the other would cause the brake shoes to retract rather than expand each time the self-adjusters operated. The adjusting screw and lever are identified by an "R" or "L" stamped on the face of the lever and in the socket end of the screw. The adjusting pivot nuts can be identified by the number of lines machined around the body of the nut. Two lines in dicate a right-hand nut for the right side of the car; one line indicates a left-hand nut for the left side of the car. Use care not to burr, chip, or otherwise damage the notches iti the adjusting screw star-wheel. The adjusting screw must be free to turn with finger pressure, or the retracting spring will not be able to force the adjusting lever to turn the star-wheel. The use of high-temperature Lubriplate COAZ 19548-A is recom mended during brake repair. ADJUSTING NUT SCREW 23 I The correct interpretation of brake terminology is necessary when diagnosing brake troubles. This section explains the major terms in common use and gives the basic causes of the complaint. DRIFT--6-15 inches off a straight-ahead course Drift--Usually caused by a rear brake malfunction or by nonburnished linings. Drift may occur on level pavement during a light to moderate stop as the car slows from 45 to 25 mph. The car may drift off a straight ahead course from 6 to 15 inches. Pull--Front brakes that have been overheated or improperly installed or adjusted will cause the car to "pull" under the same road conditions as "drift." How ever, the car may pull off a straight-ahead course in excess of two feet. I Dive--Usually caused by a mal function of one of the front brakes. Dive is a severe pull to one side which is not controllable with the steering wheel. Often the brakes must be released be fore the car can be brought to a straight-ahead course. Over-Sensitive--A severe pull or dive usually occurring on the first several stops in the morn ing. Over-sensitiveness may be caused by the absorption of moisture from the atmosphere by the brake lining or by dust in the brake assembly. Occasionally, if there is a trace of a petroleum product on the lining, it will cause a pull or dive until the brakes reach oper ating temperature. Lock-Up--A locking or skid ding of only one wheel during a brake application. Lock-up is usually caused by overheating from a "dragging" brake, or from the parking brake being partially applied while the car is in motion. T T Fade--High pedal effort--hard pedal--without apparent wheel brake action is the result of brake "fade." Fading is usually caused by making several high-speed stops during a short period of time, or after many brake applica tions in heavy traffic. Severe braking service may require the use of police interceptor-type, fade-resistant linings. Fade of one brake will cause pull, dive, or lock-up. One or both of the rear brakes may fade due to partial application of the parking brake. Drag--If the brake linings continuously contact the brake drums, the brakes will "drag." Dragging brakes may be caused by "riding" the brake pedal, par tial application of the parking brake, improper installation or the use of incorrect parts, incorrect lining-to-drum clearance, or the lack of lubrication on the carrier plate ledges. On cars equiped with a vacuum 26 power booster unit, incorrect set ting of the master cylinder push rod may result in partial applica tion of the brakes and cause them to drag. Brake drag will result in com plaints of fade, pull, dive, and lock-up; and the braking system may be impaired by glazed or burnt linings, burnt drums, over heated brake fluid, or burnt wheel cylinder seals.  Glazed Linings--Usually the result of overheating of the lining induced by brake drag. This changes the coefficient of friction of the lining due to the "boilingout" of the resins. Glazing can be identified by small bubbles on the lining surface or small holes, or "pock" marks, into the lining. Also, the edges of the lining will usual ly lift away from the shoe. A shiny lining surface does not indicate a glazed lining. A com pletely shiny lining surface is an indication of successful burnish ing, or seating-in of the lining to the drum. I Undergrind and Fall-Off--An undergrind is usually used on service linings to produce proper clearance between the lining and the drum. A clearance of 0.005 0.015-inch is required to eliminate the possibility of heel and toe contact which would cause pull and dive. Production linings are cam ground so that initially only the center of the lining contacts the drum to produce a fall-off, or sufficient clearance, at the heel and toe when the center of the lining is in contact with the drum. Out of Round Drums--Erratic braking action may result if the brake drum runout is in excess of 0.008-inch. Out of roundness within 0.008-inch is satisfactory unless the entire specification tolerance is within a 30-degree radius. This is described as a bump or a hole in the drum. Front brake drums that are out of round can be detected by a pul sation felt through the brake pedal during a moderate-to-hard stop from approximately 50 mph. Out of round rear drums may produce a grab or slip feeling known as rear wheel hop, and may also cause a severe body vibration during brake application. Pedal Vibration or Light Pul sation--Usually occurs on very light brake applications or when "riding" the brake pedal. This possible malfunction may be mis taken for out of round drums. However, it is often caused by an unequal lining-to-drum clearance adjustment.  Threaded Drums--An imper fectly-turned brake drum with heavy tool marks resembling a a screw thread pattern will cause shoe slap, which is a "pop" or a "bang" in the brake assemblies during a slow-speed stop. This condition is usually found in left side brake assemblies as the lining "screws" into the drum, breaks free, and hits the carrier plate. Refacing the brake drum will us ually correct the trouble. Hard or Hot Spots on DrumFast, hard stops with incomplete ly burnished linings will create excessive heat and cause a series I of small blue spots running the full diameter of the drum and on the center of the lining. This con dition requires the replacement of the damaged parts. Hard Brake Pedal--If high pedal effort is required under normal operating and temperature condi tions, inspect the brake drums for a smooth finish which would allow the lining to slip due to low fric tional resistance. Be sure the lin ing is of the correct material, and not glazed or burnt. A restriction in the master cylinder check valve, or vacuum power booster failure will also cause hard brake pedal complaints. v - *- I Spongy Pedal--Air or dirt in the hydraulic system is indicated if the pedal feels spongy but can be "pumped-up" to apply the brakes. Flushing the system with denatured alcohol and bleeding the system should correct the trouble. Pinch-Out Squeal--If a highpitched noise is produced during the last three wheel revolutions before the car stops, inspect the brake lining to be sure it is of the correct material, and is tight on the shoes. Wire Brush Noise--A noise that sounds like a wire brush being rubbed against the drum, and is most audible during the last ten wheel revolutions of a normal stop. Wire brush noise is caused by the installation of non-specified brake lining material. Use only genuine FoMoCo brake lining of the correct part number. Brake Honk--A honk or a groan occurring the last few wheel rev olutions of a normal stop and is usually caused by the brake shoe assemblies vibrating against the carrier plate. Be sure the correct brake shoe hold-down springs are used. * Wrap-Up Clunk--The first re verse stop after forward stops, or the first forward stop after a re verse application, will produce a clunk noise. Some clunk noise is normal and is due to wrap-around effect of the brake shoe assem blies. If the noise is excessive, check the brake lining-to-drum clearance and tighten the carrier plate bolts. * Grating Brakes--A grating or grinding noise present during any stop is an indication of foreign objects in the brake assembly or lining rivets rubbing the drum be cause of excessive wear. Oiled Linings--Oil on the brake linings will cause drift, pull, dive, and over-sensitiveness. Do not at tempt to clean oiled linings; they must be replaced. Be sure to repair any leaking wheel cylinders and replace dam aged oil seals before installing new brake lining. Burnish--New brake linings must go through a break-in period known as burnishing. The micro finish of the brake drums is in tended to burnish-in new linings more rapidly, however, it is often 1000 miles before the linings are completely burnished, or seated to the drum. A fully-burnished lining has a uniformly shiny sur face which indicates that it has been making full contact with the drum. Non-burnished linings may have a tendency to cause drift or pull, therefore, attempts at repairs or adjustments should not be made before the car has been driven 1000 miles unless obvious mechanical trouble occurs. T mm* r