C H A P T E R 1 4 Disc Brake System Principles Chapter Objectives At the conclusion of this chapter you should be able to: KEY TERMS brake pads brake rotors caliper pistons composite rotor dust boot fade fixed calipers floating calipers shims square seal squealer Copyright 201 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the ebook and/or echapter(s).
346 Chapter 14 Disc Brake System Principles Disc Brake Systems and Components Even though disc brakes are not a new design, they were not widely adopted for use in passenger vehicles until the 1960s. Drum brakes were used on the front and rear of many vehicles, and disc brakes did not become standard equipment on many domestic vehicles until the 1970s. Since then, disc brakes have become standard on the front and rear of most passenger cars and light trucks sold today. Disc Brake Systems Front disc brakes are standard on all modern cars and light trucks, and disc brakes are often utilized for the rear brakes as well. The main advantages of disc brakes compared to drum brakes are: Increased resistance to brake fade Quicker shedding of water from the friction surfaces Self-cleaning of dust and debris Self-adjusting Brake pads Disc or rotor Hydraulic pressure FIGURE 14-1 Basic operation of the disc brake system; hydraulic pressure pushes the pistons against the pads, which rub against the rotor to slow its rotation speed. A disadvantage of disc brakes is that they require significant force to clamp the pads against the brake rotor. This increases the effort by the driver to slow and stop the vehicle. Because of this, disc brake-equipped cars require the use of a power assist system to decrease driver effort and fatigue. Disc Brake Types and Operation All disc brakes are similar in operation: pressurized brake fluid forces the caliper piston outward from the caliper bore, which applies pressure against the brake pads. This squeezes the two brake pads against the rotor or disc, as illustrated in Figure 14-1. The pads pressing against the rotor create friction and heat. The friction slows the disc, which in turn slows the wheel and tire. The heat is dissipated into the air. Disc Brake s The caliper is the hydraulic output for the disc brake system. Each caliper contains one or more pistons. The number of pistons depends on caliper design and its application on the vehicle. The caliper houses the piston(s) and pads and attaches to the steering knuckle, partially covering the rotor. An example is shown in Figure 14-2. There are two major types of disc brake calipers, the fixed and floating caliper designs. Fixed calipers tend to be larger and are mostly used on high-performance applications. Floating calipers are smaller, lighter, and FIGURE 14-2 An example of a common type of front disc brake assembly. are widely used on most passenger cars and light trucks in service today. Fixed s. Fixed calipers, like the caliper shown in Figure 14-3, have at least two pistons. Hydraulic pressure forces each piston out with equal force so that both brake pads apply equally against the rotor. Fixed calipers are bolted directly to the steering knuckle. The brake pads are often held in place within the caliper by a set of pins or covers, as shown in Figure 14-4. By removing the pins, the pads can be replaced without removing the entire caliper assembly.
Chapter 14 Disc Brake System Principles 347 FIGURE 14-3 An example of a fixed brake caliper. This design has pistons on both sides of the rotor. Since hydraulic pressure is transmitted without loss, the pressure applied to the inner and outer caliper pis tons is the same. This means that each piston will be applied with equal force against the brake pad and rotor, as shown in Figure 14-5. A brake hose supplies FIGURE 14-4 Fixed calipers use pins or bolt-on covers to retain the pads. Boot Seal Hydraulic pressure Hydraulic pressure Piston Rotor FIGURE 14-5 This illustration shows the operation of a fixed caliper. Hydraulic pressure is equal in the caliper, so each piston moves with the same amount of force against each pad. Copyright 201 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the ebook and/or echapter(s).
348 Chapter 14 Disc Brake System Principles Fluid passage FIGURE 14-6 Inside of a fixed caliper. Internal passages allow fluid to pass from one side to the other. brake fluid to the caliper, and internal passages in the caliper supply fluid to the outer pistons, as shown in Figure 14-6. The piston seal, sometimes called a square seal, seals each piston in the bore. A dust boot protects the outside of the piston and the piston bore from debris. The dust boot is an accordion-type seal, meaning it will expand and contract to cover the piston as the piston moves outward in the bore. Fixed calipers have at least one bleeder screw, and some designs have more than one to provide complete bleeding of air from the system. When the brakes are applied, hydraulic pressure pushes on the back of each piston. As the piston moves outward in its bore, the piston seal deforms slightly, twisting to follow the piston. When the brakes are released, the caliper seal returns to its original shape, pulling the piston back into the bore. By doing this, the piston seal acts as a return spring for the disc brakes. As the brake pads wear, the pistons will move further out of their bores to compensate for the space left by the worn pads. When the brakes are applied, the high pressure in the hydraulic system forces the pistons out and takes up the void in the caliper piston bore. When the brakes are released, the piston seal returning to its normal shape cannot force the piston back more than a very slight amount. So each time the brakes are applied and the pads wear slightly, the piston also moves a very slight amount further out of the bore. This is how the disc brakes self-adjust for wear. Floating s. The most widely used type of caliper is the floating caliper. This is because floating calipers are less susceptible to pulsation from rotor runout and because they are smaller and lighter than fixed calipers. Floating calipers are mounted so that they can move laterally on bolts or pins, as shown in Figure 14-7. FIGURE 14-7 An example of mounting bolts on a floating caliper. Floating calipers generally use only one or two pistons mounted on the inboard side. A cross section of a floating caliper is shown in Figure 14-8. As hydraulic pressure forces the piston out of its bore, the caliper body is forced in the opposite direction on the mounting hardware. This is a result of Newton s Third Law of Motion: for every action there is an equal and opposite reaction, as shown in Figure 14-9 in the case of caliper action. For the floating caliper to operate correctly and for both the inner and outer pads to wear equally, the caliper must be able to move freely on the mounting hardware. As the brakes are exposed to normal operating conditions, rust and corrosion can limit the caliper s ability to float. This will lead to uneven pad wear. A variation of the floating caliper is the sliding caliper. Sliding calipers do not use mounting bolts or pins; instead they are mounted so that they can slide on the steering knuckle. An example is presented in Figure 14-10. An example of a common sliding caliper used for many years on Ford vehicles is shown in Figure 14-11. The operation of the sliding caliper is the same as that of the floating caliper, in that it must be able to move in response to piston movement. Both floating and sliding calipers operate hydraulically, the same as fixed calipers. When the piston is forced outward by hydraulic pressure, the piston seal deforms
Chapter 14 Disc Brake System Principles 349 Bleeder screw Pads Pad spring Brake line connection Hollow piston body Piston seal FIGURE 14-8 This illustration shows the inside view of a floating caliper. Rotor Reaction support (anchor plate) Piston Action housing ways Hydraulic pressure FIGURE 14-9 Floating calipers use Newton s Third Law for every action there is a reaction. If the caliper is floating properly, the hydraulic force on the piston also pushes the caliper backward to apply force against the outboard pad. slightly, as shown in Figure 14-12. When the brakes are released, the piston seal retracts the piston. Floating and sliding calipers self-adjust in the same fashion as do fixed calipers. A dust boot protects the outside of the piston and the bore just as in fixed caliper designs. support spring Antirattle spring support Retaining screw FIGURE 14-10 An illustration of a type of sliding caliper.
350 Chapter 14 Disc Brake System Principles FIGURE 14-11 An example of a sliding caliper used on a Ford vehicle. FIGURE 14-13 Examples of steel and phenolic plastic caliper pistons. Before application During application After application Seal deflection FIGURE 14-12 During operation, the square seal deforms slightly. When pressure drops, the seal returns to its original shape, which pulls the piston back into its bore. Construction. s can be made from cast iron or aluminum. Many older vehicles use cast iron calipers since they are strong, have adequate heat dissipation abilities, and are inexpensive. Most modern vehicles have aluminum calipers to reduce weight. pistons are made of steel, phenolic plastic, or aluminum. Examples of steel and phenolic pistons are shown in Figure 14-13. Steel pistons have been in service for many years and continue to be widely used. Steel pistons are strong and can be fitted very close in the caliper bore, usually within 0.005 inches. Phenolic plastic pistons have also been in use for many years and are used to reduce weight. Plastic pistons, while lighter, have much thicker walls than comparable steel pistons to increase strength. Plastic pistons tend to expand more than steel pistons and require a larger clearance to the piston bore, typically 0.008 to 0.010 inches. Many calipers use aluminum pistons. Aluminum pistons are lightweight and strong, having the advantages of both steel and plastic pistons. As discussed above, the caliper piston seal is a square seal, housed in a recess in the piston bore, as shown in Figure 14-14. The inner surface of the seal encircles the piston, prevents fluid loss, and acts as a piston return spring. The dust boot is attached to the outside edge of the piston bore, and its inner surface attaches to the outer lip of the piston. This is shown in Figure 14-15 with the seal removed from the caliper for clarity. As the piston moves outward, the dust boot expands to protect the outside surface of the piston. Dust boots may be secured to the caliper with a snap ring, by a press-fit between the seal and the caliper, or with the lip of seal placed into a groove cut into the caliper body. Floating calipers have mounting bolts, pins, or bushing bores, as shown in Figure 14-16. Many calipers bolt directly to the steering knuckle, as shown in Figure 14-17, while other vehicles use a caliper support
Chapter 14 Disc Brake System Principles 351 Piston seal FIGURE 14-14 The square seal keeps fluid in the caliper and acts as the return spring for the piston. Dust boot FIGURE 14-17 Some vehicles have the caliper mount directly to the steering knuckle, as in this example. piston FIGURE 14-15 The piston dust boot protects the surface of the piston as it extends further out of the bore as the pads and rotor wear. bracket to hold the pads and caliper to the knuckle, as shown in Figure 14-18. s that are bolted to the knuckle often use a combination mounting bolt and sleeve that rides in the caliper body, as shown in Figure 14-19. The bolt/sleeve allows the caliper to move backward as the piston is pushed against the inner pad. Vehicles that use a mounting bracket often use a type of floating pin that connects the caliper to the bracket, like that shown in Figure 14-20. The caliper bolts to the housing Bushing Mounting bolt Flexible seal boot Lube exterior of bushing and bolt with brake lubricant FIGURE 14-16 The bolts and sleeves allow the caliper to float in operation, meaning the caliper can move side-to-side as the piston moves out and back into the bore.
352 Chapter 14 Disc Brake System Principles bracket This bushing and bolt secure the caliper to the bracket. These bolts hold the bracket to the steering knuckle. FIGURE 14-18 Many cars and trucks use a support bracket that mounts to the knuckle, and the caliper then bolts to the bracket. FIGURE 14-20 An example of a caliper and support bracket. FIGURE 14-19 An example of a caliper that bolts to the knuckle without a bracket. pins, which float in the bracket. When the brakes are applied, the caliper piston moves against the inner pad, and the caliper moves backward as the pins extend out of their bores in the bracket. FIGURE 14-21 Springs, clips, and retainers of various shapes and sizes are used to hold the pad and prevent vibration and noise. Most caliper arrangements use some type of hardware to reduce pad noise. Pad clips, like the type shown in Figure 14-21, are used to keep the pads secure in the bracket and to reduce vibration and noise. The pads must be able to move laterally in the clips, but they are held tight radially to prevent noise. Many pads also use shims attached to the pad backing, like those shown in Figure 14-22, to help reduce noise. Many replacement pads have the shims attached to the backing plate, while other pad sets have shims with adhesive backs that need Copyright 201 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the ebook and/or echapter(s).
Chapter 14 Disc Brake System Principles 353 FIGURE 14-22 Shims are used to alter the frequency of pad vibrations so that they are inaudible to humans. Airflow to be applied to the pads when they are installed. Regardless of the type of shims and hardware, it is important that these pieces be installed and that they are installed correctly. Disc Brake Rotors. The brake rotors are half of the friction components in disc brake systems; the pads are the other half. Rotors, also called brake discs, are mounted to the hub and rotate with the wheel and tire. As the caliper clamps the brake pads against the rotor, a substantial amount of friction is created between the pads and rotor. This friction is what slows the wheel and also causes the intense heat generated by the brakes. Because of the stresses of braking and the heat that is generated, brake rotors have to be strong and able to withstand high operating temperatures. The most common brake rotors are made of cast iron and have two friction surfaces separated by vents. The center of the rotor, called the hat, provides the mounting point for the rotor on the hub. The center hub hole is designed to fit precisely to the hub. Replacement rotors should always be checked against the original rotors to ensure that the hat areas match and that the rotors will correctly fit the vehicle. The type of rotor pictured in Figure 14-23, is called a vented rotor. The vents are located between the two friction surfaces. The overall friction surface area is large, but the contact area of the pads is small. As the pads are pressed against the rotor, Dirt and water FIGURE 14-24 An illustration of how airflow through the rotor draws heat away from the brakes. heat is generated all around the rotor s surfaces. As the rotor spins, air is pulled through the vents to remove heat from the friction surfaces and cool the rotor, as shown in Figure 14-24. The front brake rotors on all modern cars and trucks are vented. Nonvented or solid rotors, like the rotor in Figure 14-25, are used on the rear of some vehicles, and they can be found on the front of some older, smaller vehicles. Nonvented rotors can be used in the rear since the rear brakes are doing less work than the front brakes, and the additional cooling is not necessary. For many vehicles, the vents in the rotors are simply straight passages from the outside to the inside of the hub or hat section of the rotor. Some vehicles use rotors that have curved or directional vents. Rotors with directional vents have improved airflow for better heat dissipation, but they must be installed on the correct side of the vehicle to work correctly. Swept area two surfaces 100 Square Inches FIGURE 14-23 An illustration of a brake rotor and the amount of surface area of the friction surfaces.
354 Chapter 14 Disc Brake System Principles Ventilated rotor Braking surfaces Solid rotor FIGURE 14-25 Examples of vented and solid rotors. Cast iron friction surfaces Steel web FIGURE 14-26 Composite rotors use a steel hat to reduce weight. Some rotors, instead of being made completely of cast iron, are a composite of a steel hub and iron friction surface, like the composite rotor in Figure 14-26. This type of rotor offers a slight weight reduction over a cast iron rotor. Brake rotors on some high-performance vehicles may be drilled and/or slotted. Drilled and/or slotted rotors are common on motorcycles but are not generally found on passenger cars or trucks. Drilled rotors, like that shown in Figure 14-27, have a series of holes drilled through the friction surface. Slotted rotors are similar except that the slots do not go through the entire depth of the friction FIGURE 14-27 An example of a high-performance rotor, cross-drilled to vent gases and dust. surface, as shown in Figure 14-28. When the brakes are applied, the point of application between the pads and rotors can create a gas barrier that reduces braking ability. The holes and slots in these rotors allow this gas to escape, which improves braking. Some high-performance vehicles offer ceramiccomposite brake rotors. These rotors and pads offer extreme heat dissipation, reduced weight, and the ability to withstand high-speed braking with reduced fade or distortion. Fade is the term used to describe the loss
Chapter 14 Disc Brake System Principles 355 FIGURE 14-30 Examples of brake pads. Pads come in many sizes and shapes depending on how they are mounted. FIGURE 14-28 An example of a high-performance rotor that is slotted. The slot improves pad cleaning and also helps reduce gas and dust. of braking power or performance, usually as a result of heat. Ceramic-composite brakes are optional equipment on cars such as the Corvette Z06 and on many other vehicles, but they can add several thousand dollars to the price of the car. Disc Brake Pads. Brake pads, which are comprised of the friction material or pad lining and the backing or support plate for the lining, clamp down on the brake rotor to slow the wheel. The parts of a brake pad are shown in Figure 14-29. The materials that make up the Lining Tab Antirattle spring Backing plate Tab Wear indicator FIGURE 14-29 The parts of a brake pad. Not all pads have antirattle clips mounted on them; many use shims and springloaded clips between the pad and caliper bracket to reduce noise. pad friction material determine its coefficient of friction and ultimately, how well the vehicle stops. As with brake shoe linings, brake pad friction materials vary depending on the manufacturer and the application. Common ingredients include iron, steel, copper, synthetic fibers, and ceramics. Brake pads, as shown in Figure 14-30, are shaped to follow the curve of the brake rotor. When the caliper piston(s) move outward, the pads are pressed against the rotor with great force, which result in friction and generate heat. The pads must be made from materials that can not only withstand the friction and heat of braking, but also be able to operate effectively when the brakes are cold. Brake pad linings are a compromise between several factors, such as pad life, noise generation, and cold and hot coefficients of friction. Brake pads that use soft friction compounds offer quiet operation and will not wear the brake rotors very fast, but will themselves wear quickly and may not have the stopping power of semi-metallic or metallic pads that contain metal shavings and other materials that increase stopping performance. Semi-metallic pads, however, will cause more rapid wear of the rotor and also tend to generate more noise and rust-colored brake dust. Pads are often categorized as asbestos, organic, semimetallic, or ceramic. Asbestos pads were made with asbestos fibers, which tolerated the high temperatures generated by the brake system but also produced dust that if inhaled, could cause lung damage and cancer. Asbestos has been phased out of brake linings since the 1990s. Organic pads are made of natural compounds such as glass and Kevlar. These pads are softer and create less noise but also wear faster and make a lot of brake dust due to the softer compounds. Semi-metallic pads contain iron, steel, copper, and graphite, which are mixed together into the friction compound. Semimetallic pads offer longer service life but also wear the brake rotors faster and can generate more brake noise and dust. Many newer brake pads use ceramic fibers and other materials, such as copper, and are often considered
356 Chapter 14 Disc Brake System Principles FIGURE 14-31 An example of pads with grooves for dust dispersion and chamfered edges to reduce noise. The groove also provides an indication of wear. When the pad is worn to the point where the groove disappears, the pad needs to be replaced. superior to other pads due to their ability to dissipate heat, long service life, provide quiet operation, and generate low dust. Brake pads often have grooves and chamfers cut into the lining, as shown in Figure 14-31. Grooves are used to help remove the dust generated between the pad and FIGURE 14-33 A close up of a wear indicator. the rotor during braking. Chamfering the leading edges of the pads helps decrease noise. Many pads have a built-in wear indicating device, sometimes called a squealer due to the noise it makes when it comes into contact with the rotor, as shown in Figure 14-32. Figure 14-33 shows an example of a wear indicator tab. Some pads use an electrical pad wear indicator that is embedded into the pad s friction material. Pad Rotor Pad Rotor Wear indicator New pad Wear indicator Worn pad FIGURE 14-32 The wear indicator makes a high-pitched noise when it contacts the spinning rotor.
Chapter 14 Disc Brake System Principles 357 The pad shown in Figure 14-34 has the electrical con nector and sensor used to alert the driver when the pads are worn out. An example of how this looks installed on the vehicle is shown in Figure 14-35. This sensor acti vates a warning light on the dash, an example of which is shown in Figure 14-36, to alert the driver that the brake pads need to be inspected and/or replaced. FIGURE 14-34 An example of a pad with an electronic wear indicator. REAR DISC BRAKE SYSTEMS Rear disc brakes are replacing rear drum brakes on more and more cars and trucks. Rear disc brakes oper ate exactly like those on the front, but they are smaller in both rotor and pad size. Rear Disc Brake Designs. Rear disc brakes can be either fixed caliper or floating caliper designs. Fixed compared to floating calipers. Rear brake rotors can be either vented or solid, depending on the requirements of the vehicle. Figure 14-37 and Figure 14-38 show a front and rear disc brake assembly for comparison. The front rotor is vented, and the pads are larger than those used on the rear brake. The rear rotor is also a solid rotor. Rear Disc Brakes and Parking Brakes. All vehicles sold in the United States are required to have a parking or emergency brake. The parking brake is a FIGURE 14-35 This brake system uses electronic pad wear sensors. The wire leading into the center of the caliper is attached to the brake pad sensor. FIGURE 14-37 An example of a front rotor for comparison to a rear rotor, shown in Figure 14-38. FIGURE 14-36 When the pad wears to the point when the sensor touches the rotor, the warning light on the dash is illuminated. FIGURE 14-38 An example of a rear rotor for comparison. Rear rotors have smaller pads and typically, a narrower friction surface area. Copyright 201 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the ebook and/or echapter(s).
358 Chapter 14 Disc Brake System Principles Piston seal Cone Piston Screw Outboard brake pad Rotor Inboard brake pad Parking brake lever Internal thread nut FIGURE 14-39 An illustration of an integral parking brake caliper. The piston is threaded to the parking brake lever to provide a mechanical connection, not dependent upon the hydraulic system. mechanical brake that often uses components of the hydraulic service brakes but does not rely on the hydraulic system to operate. This is so that in the event of a loss of hydraulic pressure, the parking brake can be used to slow and stop the vehicle, albeit with a much longer stopping distance. When the parking brake is part of the rear disc brake caliper, it is called an integral parking brake caliper. Figure 14-39 shows an illustration of this type of caliper. The piston, under normal braking, is applied by hydraulic pressure, but when the parking brake is applied, a lever pushes the caliper piston out slightly, which locks the pads against the rotor. There are two methods for applying the caliper piston with the parking brake, a threaded piston and a ball-and-ramp design. A threaded caliper, as shown in Figure 14-39, uses a threaded piston and a screw that passes through the caliper body. When the parking brake is set, the brake cable pulls on the lever at the back of the caliper. An example is shown in Figure 14-40. The lever is attached to the rear of the screw, and the front of the screw is seated against the rear of the caliper piston. When the lever rotates the screw, the screw turns in the caliper and pushes against the piston. The piston moves out slightly, setting the pads against the rotor. A spring, often located at the rear of the caliper at the lever, retracts the lever and screw when the parking brake is released. The ball-and-ramp design uses an actuator with reliefs that are cut into its surface. The reliefs are tear drop shaped and are deeper at the large end and shallow at the point. Ball bearings are placed between the piston and the actuator and sit in the reliefs. When the parking brake is applied, the actuator turns and the ball bearings move from the deep to the shallow part of the relief. This action pushes the bearings against the piston to set the brake. When it is released, the actuator rotates back and the bearings recess back into the reliefs. FIGURE 14-40 An example of an integral rear brake caliper.
Chapter 14 Disc Brake System Principles 359 FIGURE 14-41 An example of a drum in hat rear brake system. Drum in Hat Designs. Another type of rear parking brake system is called the drum in hat design, shown in Figure 14-41. In this arrangement, the rear disc brakes operate exactly as the front disc brakes. The only difference is that the inside of the hat of the rear rotors contains a machined surface. This surface is the brake drum for a set of small brake shoes, which are used only as the parking brake. Servicing this type of brake is covered in detail in Chapter 13. Electrically Operated Parking Brake. A new development in rear disc brakes is the use of an electrically operated parking brake system. Two types of systems are in use: one system uses an electric motor to pull the parking brake cables, and the other uses a motor housed in each of the rear calipers. An example of a caliper with a motor is shown in Figure 14-42. In both designs, the motors are not designed to be used to stop the vehicle in the event the service brakes fail; instead, the system is used only for holding the vehicle in place when it is parked. Servicing these systems will require the use of a scan tool. Refer to the vehicle s service information for specific service procedures. Hybrid Vehicle Disc Brakes. As discussed in Chapter 10, hybrid vehicles can recover braking energy to recharge the high-voltage (HV) batteries. Because of this, the service brakes tend to last much longer on these vehicles than on nonhybrids. On vehicles such as the Toyota Prius, the driver can select the B mode while driving, which allows even more brake energy to be recaptured. The B mode is designed to utilize more regenerative braking than the mode for normal driving conditions. The disc brakes on hybrids operate exactly like those on nonhybrid vehicles. The disc brakes on the Toyota FIGURE 14-42 A rear brake caliper containing an electrically operated parking brake motor. Prius, Honda Insight and Civic hybrids, and others are single-piston floating caliper designs. What is different about how the brakes operate on hybrid vehicles is that the on-board computer system monitors brake pedal input and then controls braking through the regenerative process and the service brakes. This means that even though the driver is pressing the brake pedal, the computer system is determining how much braking will be done by the hydraulic brake system. The split between hydraulic braking and regenerative braking depends on many factors but is mostly dependent upon the HV battery state of charge. The idea is to recapture as much energy as possible to recharge the HV battery. However, when the battery is charged, the system will greatly reduce or stop the amount of energy recaptured by the brakes. In the event of a malfunction in the braking circuits, the regenerative system is disabled, and normal brake operation remains. One special brake service note for Ford Escape Hybrid vehicles: these vehicles perform periodic brake system integrity tests when the vehicle is parked and off. During this test, the brake system is pressurized for short periods of time. To perform brake services on these vehicles, it is necessary to place the vehicle into Pad Service Mode. This will prevent the self-test from operating. To perform brake service and place the vehicle into service mode, refer to the manufacturer s service procedures.
360 Chapter 14 Disc Brake System Principles SUMMARY Disc brakes are less prone to fade than drum brakes. There are two major types of disc brake calipers, the fixed and floating caliper designs. Fixed calipers are bolted directly to the steering knuckle. Floating calipers move laterally on bolts or pins. Pad clips and shims are used to keep the pads secure in the bracket and reduce vibration and noise. Some pads use an electrical pad wear indicator that is embedded into the pad s friction material. When the parking brake is part of the rear disc brake caliper, it is called an integral parking brake caliper design. REVIEW QUESTIONS 1. A caliper that is mounted directly to the steering knuckle and has a piston on each side of the rotor is called a caliper. 2. The seal in the caliper seals the brake fluid around the piston and allows for selfadjustment. 3. A rotor with a cast iron friction surface and a thin stamped steel hat is called a rotor. 4. Clips and are commonly used to limit the noise generated by disc brakes. 5. The seal around the caliper piston prevents fluid loss and acts as the piston return spring. 6. s can be which of the following types? a. Floating c. Fixed b. Sliding d. All of the above 7. Technician A says all fixed-caliper designs have at least two pistons. Technician B says some floating calipers use two pistons. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 8. Which of the following is not a common type of disc brake rotor? a. Composite steel hat and iron friction surface b. Drilled or slotted friction surface c. Composite aluminum friction surface and steel hat d. Solid friction surface and cast iron hat 9. All of the following statements about disc brakes are true except: a. Disc brakes resist fade better than drum brakes b. Disc brakes are self-adjusting c. Disc brakes require less application force than drum brakes d. Disc brakes are commonly used on the rear wheels 10. Technician A says that pad wear indicators may turn on a warning light on the dash. Technician B says pad wear indicators may make a loud squealing noise when the pad is worn too thin. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B