Drum Brake System: Service and Repair
REAR DRUM BRAKES^ TOOLS REQUIRED
- J21177A Brake Shoe Setting Gage
DISASSEMBLY
1. Release park brake.
CAUTION: MAKE SURE VEHICLE IS PROPERLY SUPPORTED AND SQUARELY POSITIONED ON THE HOIST. TO HELP AVOID PERSONAL INJURY WHEN A VEHICLE IS ON A HOIST, PROVIDE ADDITIONAL SUPPORT FOR THE VEHICLE ON THE OPPOSITE END FROM WHICH COMPONENTS ARE BEING REMOVED.
2. Raise vehicle on hoist.
3. Remove rear wheel and tire assembly.
NOTICE: Do not pry against brake backing plate. This will bend plate.
IMPORTANT: If difficulty is encountered removing drum, use a small flat blade screwdriver to turn the star wheel adjuster assembly. Shortening the length of the adjuster will provide sufficient drum-to-shoe clearance for drum removal.
4. Remove rear brake drum.
5. Pull park brake shoe lever toward front of vehicle. Release park brake cable from park brake show lever.
NOTICE: Do not over extend spring. Over extending spring will weaken it.
6. Remove upper adjuster spring.
7. Remove lower return spring.
8. Remove trailing (rear) shoe hold down spring and hold down pin.
9. Remove trailing (rear) brake shoe and adjuster assembly.
10. Remove leading (front) brake show hold down spring and hold down pin.
11. Remove park brake lever retainer, wave washer, and park brake lever from trailing (rear) brake show.
12. Disassemble brake adjuster components: adjusting socket, screw, washer, and nut.
13. Using brake and choke cleaner (PIN 21007432 or equivalent), clean brake adjusting components: adjusting socket, screw, washer, and nut.
14. Inspect adjuster assembly, making sure that adjuster screw threads smoothly into brake adjusting nut over full threaded length of screw assembly.
IMPORTANT: Do not attempt to repair wheel cylinder. Replace wheel cylinder if any damage is present.
15. Inspect wheel cylinder for leakage or damaged boots. Ensure wheel cylinder is not seized.
ASSEMBLY
IMPORTANT: When replacing rear brake shoes, inspect backing plate for excessive wear at six raised shoe contact pads. Excessive wear at raised shoe contact pads, such as notches or deep grooves, could impede shoe travel.
IMPORTANT: Never replace brake shows/linings on one side of axle only. Brake shoes/linings must be replaced as axle sets.
1. Lubricate the following components:
^ Adjuster assembly. Apply to threads of screw and inner diameter face of socket.
^ Adjuster lever surfaces that rub on brake shoe web.
^ Backing plate at the six raised shoe contact pads.
^ Park brake lever pin and surfaces that contact brake shoe web.
2. Install leading (front) brake shoe, brake shoe hold down pin, and hold down spring onto brake backing plate.
IMPORTANT: Make sure to crimp ends of retainer securely to retain park brake lever to trailing (rear) brake show.
3. Install parking brake lever assembly onto trailing (rear) brake shoe and secure with wave washer and retainer clip.
4. Install trailing (rear) brake shoe assembly onto backing plate with hold-down spring and hold-down pin.
5. Install adjuster assembly and adjuster lever.
NOTICE: Check that both brake shoes are correctly engaged (shoe to wheel cylinder and adjuster on top and shoe to anchor on bottom of backing plate.)
NOTICE: Check that adjuster notches properly engage in brake shoe notches.
NOTICE: Check that both brake shoes are correctly engaged (shoe to wheel cylinder and adjuster on top and shoe to anchor on bottom of backing plate).
6. Install lower return spring.
7. Install upper adjuster spring.
NOTICE: Check that the adjuster lever is engaged with the teeth on the adjuster assembly.
8. Pull park brake shoe lever toward front of vehicle. Install park brake cable onto park brake lever assembly.
9. Check assembly location and installation of rear brake components:
^ Adjuster lever
^ Leading (front) brake shoe
^ Lower return spring
^ Park brake lever
^ Trailing (rear) brake shoe
^ Upper return spring
^ Adjuster assembly
10. Using Brake Shoe Setting Gage J21177A (or equivalent) measure inside diameter of brake drum.
IMPORTANT: Refer to "Inspecting and Refinishing Brake Drums". Brake Drums Inspecting and Refinishing
11. Measure outside diameter of brake shoes and adjust brake adjuster to obtain 0.50 mm (.020 inch) less than the reading obtained in previous step.
12. Install brake drum.
13. Bleed brakes if new wheel cylinder or backing plate was installed.
NOTICE: Before installing wheels, remove rust or corrosion from wheel mounting surfaces and brake drums. Failure to do so can cause wheel nuts to loosen in service.
14. Position wheel and tire assembly onto hub.
15. Install wheel nuts and tighten in a crisscross pattern. Repeat tightening pattern to be sure torque is correct.
Torque:
Wheel Nut: 125 Nm (92 ft. lbs.)
16. Lower vehicle from hoist.
CAUTION: IF THIS OPERATION IS NOT CARRIED OUT, BRAKES WILL NOT OPERATE PROPERLY DURING INITIAL BRAKE APPLICATIONS.
17. Apply and release brake pedal 20 times to allow adjuster to position brake shoes.
18. Adjust park brake cable.