Chap78

[object Object],[object Object],[object Object],OBJECTIVES: After studying Chapter 78, the reader should be able to: Continued

[object Object],[object Object],OBJECTIVES: After studying Chapter 78, the reader should be able to:

PARKING BRAKE ,[object Object],Continued

Figure 78–1 Typical parking brake cable system showing the foot-operated parking brake lever and cable routing. Continued

PEDALS, LEVERS AND HANDLES ,[object Object],Continued Foot pedals and floor-mounted levers are the common means of applying parking brakes. See Figure 78–3.

Figure 78–3 Typical hand-operated parking brake. Note that the adjustment for the cable is underneath the vehicle at the equalizer. ,[object Object],Continued

Figure 78–4 A ratchet mechanism is used to lock parking brakes in the applied position. ,[object Object],Continued Some vehicles were equipped with a system that required the driver to depress the parking brake pedal to release the parking brake once it was set. The rubber pad on the parking brake pedal usually states “push to release.”

Figure 78–5 A remote-mounted parking brake release lever. Continued

Figure 78–6 Automatic parking brake release mechanisms usually use a vacuum servo to operate the release lever. ,[object Object],Continued

[object Object],Pump To Release A metal rod connects the vacuum servo to the upper end of the parking brake release lever. When the engine is running (to provide vacuum) and the shifter is placed in gear, an electrical contact closes to energize the solenoid and route vacuum to the servo. The servo diaphragm then retracts the rod, which releases the parking brake. See Figure 78–7. Continued

Figure 78–7 The two plastic vacuum tubes on the steering column are used to release the parking brake when the gear selector is moved from park into a drive gear.

PARKING BRAKE WARNING LAMP ,[object Object],Continued

PARKING BRAKE LINKAGES ,[object Object],Continued Linkage Rods Parking brake linkage rods made from solid steel are commonly used with floor-mounted actuating levers to span the short distance to an intermediate lever or an equalizer. Linkage Cables Parking brake cable is made of woven-steel wire encased in a reinforced rubber or plastic housing. The housing is fixed in position at both ends, and is routed under the vehicle through mounting brackets that hold the cable in position, yet allow a small amount of movement. The cable slides back and forth inside the housing to transmit application force.

Figure 78–8 The cable from the activating lever to the equalizer is commonly called the control cable. From the equalizer, the individual brake cables are often called application cables. These individual cables can usually be purchased separately. Continued

[object Object],Look for Swollen Parking Brake Cables Figure 78–9 Notice how rust inside the covering of this parking brake cable has caused the cable to swell.

Figure 78–10 Intermediate levers in the parking brake linkage increase the application force. ,[object Object],Straight-pull parking brake handles are not levers; they are commonly connected to other levers in the linkage. A lever in the parking brake linkage under the vehicle is called an intermediate lever , and provides leverage in addition to that supplied by the parking brake control. Continued

[object Object],Continued To prevent unequal application, most parking brake linkages use an equalizer to balance the force from the parking brake control, and transmit an equal amount to each friction assembly. See Figure 78–11.

Figure 78–11 A cable guide is a common type of parking brake linkage equalizer. Equalizers come in many shapes and sizes, but the simplest is the cable guide attached to a threaded rod. This type of equalizer pivots or allows the inner cable to slide back and forth to even out the application force. Continued

Figure 78–12 Some parking brake equalizers are installed in the brake cable. ,[object Object],Continued

Figure 78–13 Many parking brake linkages use both an intermediate lever and an equalizer. ,[object Object],Most combine intermediate levers and equalizers in various ways and use from one to four cables to actuate the friction assemblies. Continued

[object Object],FRONT AND REAR ENTRY PARKING BRAKE CABLES Continued

DRUM PARKING BRAKES ,[object Object],Continued Figure 78–14 Notice the spring at the end of the parking brake strut. This antirattle spring keeps tension on the strut. The parking brake lever is usually attached with a pin and spring (wavy) washer and retained by a horseshoe clip. Excellent parking brakes because of high static coefficient of friction and self-energizing action. Integral Drum Parking Brakes Mechanically apply the rear drum service brakes to serve as parking brakes. Shown at right.

Figure 78–15 The parking brake cable pulls on the parking brake lever, which in turn forces the brake shoe against the drum. Continued

Figure 78–16 The inside “hat” of the disc brake rotor is the friction surface for the parking brake shoes. ,[object Object],Continued Inside the drum is a small dual-servo drum brake friction assembly that serves as the parking brake. The rotor splash shield, or a special mounting bracket, provides the backing plate for the friction assembly.

[object Object],Continued NOTE: T o reassemble a drum brake is to remember the parking brake lever is usually attached to the secondary (rearward) brake shoe. The parking brake strut attaches between the shoes with the spring toward the front of the vehicle (remember, “ spring forward ”).

Figure 78–17 A typical rear disc brake auxiliary drum brake friction assembly. Continued

CALIPER-ACTUATED DISC PARKING BRAKES ,[object Object],Continued

Figure 78–18 A Ford rear brake caliper ball and ramp-type apply mechanism. ,[object Object],Continued

Figure 78–19 Operation of a ball and ramp-type rear disc brake caliper parking brake. Continued

Figure 78–20 Automatic adjustment of a ball and ramp-type rear disc brake parking brake occurs when the service brakes are applied. ,[object Object],Continued A drive ring on the nut prevents it from rotating in the opposite direction when the parking brake is applied.

[object Object],Figure 78–21 A typical GM rear disc brake with an integral parking brake. This type uses a screw, nut, and cone mechanism to apply the caliper piston. Continued

Figure 78–22 Parking brake application of a General Motors rear drive brake caliper. ,[object Object],Continued The caliper piston has a specially shaped nut that threads onto the actuator screw, butts against the backside of the cone, and is splined so it can’t rotate unless the cone does. The cable moves the lever and rotates the actuator screw. The cone is a slip fit in the piston, free to rotate unless held against a clutch surface located near the outer end of the piston bore.

Figure 78–23 Automatic adjustment of a General Motors rear disc brake caliper. ,[object Object],This prevents the cone from rotating as the caliper piston is keyed to the brake pad, which is fixed in the caliper. Movement of the nut along the actuator thread forces the cone and piston out against the inboard pad to apply the brake. Adjustment of the screw, nut, and cone occurs automatically during normal operation as the service brakes are released. Continued

[object Object],Figure 78–24 Removing the piston from a typical General Motors rear disc brake caliper. Continued See Figures 78–25 through 78–31.

Figure 78–25 Installing the piston into a General Motors rear disc brake caliper. Continued

Figure 78–26 A piston installation tool is required to fully install the piston into a General Motors rear disc brake caliper. Continued

Figure 78–27 A spanner wrench (or needle-nose pliers) can be used to rotate the caliper piston prior to installing the disc brake pads. A notch on the piston must line up with a tab on the back of the brake pad to keep the piston from rotating when the parking brake is applied. Continued Figure 78–28 After removing parking brake lever and thrust bearing, remove the antirotation pin.

Figure 78–30 To test the piston adjuster, thread the thrust screw into the piston. Hold the piston and pull the thrust screw outward 1/4 in. (6 mm). The adjuster nut should not turn when the thrust screw retracts. Replace the piston assembly if not functioning correctly. Figure 78–29 Unscrew the thrust screw from the piston with an Allen (hex) wrench. After removing the thrust screw, push the piston out of the caliper bore. Continued

Figure 78–31 To adjust the parking brake cable on a Ford vehicle equipped with rear disc brakes, start by loosening the cable adjustment until the cables to the calipers are slack Tighten until the caliper lever moves. Position a 1/4-in. drill bit or dowel into the caliper alignment hole. Adjustment is correct if the parking brake lever does not hit the 1/4-in. dowel. Continued

[object Object],The Parking Brake Click Test If the rear brake lining is usable, check for the proper operation of the self-adjustment mechanism. If the rear brakes are out of adjustment, the service brake pedal will also be low. This 10-click test is a fast and easy way to determine if the problem is due to rear brakes. CAUTION: Do not adjust the parking brake cable until the rear brakes have been thoroughly inspected and adjusted.

PARKING BRAKE CABLE ADJUSTMENT ,[object Object],Continued General procedure for parking brake adjustment: ,[object Object],[object Object]

[object Object],Figure 78–32 After checking that rear brakes are OK and properly adjusted, parking brake cable can be adjusted. Always follow manufacturer’s recommended procedure. Continued See Figure 78–33.

Figure 78–33 Many hand-operated parking brakes are adjusted inside the vehicle. ,[object Object],Continued NOTE: Some vehicles are equipped with an automatic adjusting parking brake lever/cable. Simply cycling the parking brake on/off/on three times is often all that is required to adjust the parking brake cable.

NOTE: The rear parking brake adjustment should always be checked whenever replacing the rear brake linings. It may be necessary to loosen the parking brake cable adjustment to allow clearance to get the drum over the new linings. This could happen because someone may have adjusted the parking brake cable during the life of the rear linings. Figure 78–34 Always check that the brake shoes contact the anchor pin.

[object Object],Continued ,[object Object],[object Object],[object Object]

[object Object],Figure 78–35 A 1/8-in. (3-mm) drill bit is placed through an access hole in the backing plate to adjust this General Motors leading-trailing rear parking brake. Adjust the parking brake cable until the drill can just fit between the shoe web and the parking brake lever. Continued

[object Object],The Hose Clamp or Wrench Trick Figure 78–36 Many parking brake cables can be removed easily from the backing plate using a 1/2-in. (13-mm) box-end wrench. The wrench fits over the retainer finger on the end of the parking brake cable.

[object Object],How Does An Electric Parking Brake Work? Some vehicles use an electric parking brake (EPB) that can be activated when the vehicles stops and then goes off as soon as the gas pedal is pressed, preventing the car from moving while stopped. ,[object Object],[object Object],Figure 78–37 An electric parking brake button on the center console of a Jaguar.

SUMMARY ,[object Object],[object Object],[object Object],[object Object]

Chap78

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Chap78