1. CHAPTER 33
Drum Brake Systems

2. Removing, Cleaning, Inspecting, and Measuring Brake Drums
33-1
To remove a hubless-style drum, first make matching marks on the drum and hub for reinstallation in the correct position.
If there are screws or speed nuts holding the drum to the hub, remove them following the specified procedure. The speed nuts can be discarded and are not needed upon reassembly. The screws will be reused.
Remove the drum from the hub.

3. Removing, Cleaning, Inspecting, and Measuring Brake Drums
33-1
To remove a hub-style drum, first remove the wheel bearing locking mechanism (cotter pin, lock nut, or peened washer).
Remove the wheel bearing adjusting nut, thrust washer, and outer bearing.
If the rear bearing needs to be removed for service, or replacement of the drum, remove the inner bearing and grease seal.

4. Removing, Cleaning, Inspecting, and Measuring Brake Drums
33-1
Reinstall the adjusting nut onto the spindle about five turns. Grasp the drum/hub assembly on the top and bottom and push it toward the center of the vehicle. Hold slight downward pressure as you firmly pull the drum/hub assembly toward yourself.
(continues)

5. Removing, Cleaning, Inspecting, and Measuring Brake Drums
33-1
... This should cause the adjusting nut to catch the wheel bearing and pull it and the seal out of the rear of the hub. The grease seal will need to be replaced with a new one. Once the drum is removed, clean, inspect, and measure it. Clean the drum with approved asbestos removal equipment. Inspect the drum for hard spots/hot spots, scoring, cracks, and damage.

6. Removing, Cleaning, Inspecting, and Measuring Brake Drums
33-1
Measure the drum diameter at the deepest groove or most worn part of the drum and compare to specifications. If it is over the size limit, it will need to be replaced. If it needs to be machined and is below the maximum diameter, check to see how badly it is scored.
(continues)

7. Removing, Cleaning, Inspecting, and Measuring Brake Drums
33-1
... Find the smallest diameter of the drum and write down the reading. Find the largest diameter of the drum and write down that reading. Calculate the difference between the two readings, which is the out-of-round measurement, and compare it to specifications. Determine any necessary actions.

8. Refinishing Brake Drums
33-2
Research the brake lathe manufacturer’s procedure for properly refinishing the drum. Clean any nicks, burrs, or debris from the mounting surfaces of the drum. Mount the drum on the brake lathe. Check to see that the drum is running true on the lathe.

9. Refinishing Brake Drums
33-2
Install the anti-chatter band on the drum.

10. Refinishing Brake Drums
33-2
Set the position of the cutting tool so that the brake drum is close to the brake lathe when the cutting bit is in the far corner of the drum. Make sure the cutting bits will not contact the face of the drum, and move the cutting head about 0.5″ (12.7 mm) in from the outside of the drum. Turn on the brake lathe and set the depth of the cutting tool so it just touches the surface of the drum. Slowly remove the ridge.

11. Refinishing Brake Drums
33-2
Run the drum all the way in so the cutting bit is in the inner corner of the drum.

12. Refinishing Brake Drums
33-2
Set the cutting bit to the proper depth and lock it in place. Engage the automatic spindle feed and set it to the proper speed (if equipped), lock it in place, and watch for proper machining action. Repeat this step until the worn surface areas have been removed all the way around the surface of the drum. If the brake lathe is not a single-cut machine, perform a finish cut on the drum.

13. Refinishing Brake Drums
33-2
Move the drum well away from the cutting bit and use sandpaper to give the drum surface a non-directional finish. Remeasure the drum diameter and discard if above specifications.

14. Removing, Cleaning, Inspecting, and Reassembling a Duo-Servo Brake
33-3
Research the procedure for disassembling the brake assembly. Clean brake shoes, hardware, and backing plates using equipment and procedures for dealing with asbestos/dust.

15. Removing, Cleaning, Inspecting, and Reassembling a Duo-Servo Brake
33-3
To disassemble a duo-servo brake, first remove the return springs, cable guide (if installed), and shoe guide. Remove the parking brake strut and spring. Remove the primary shoe hold-down spring, retainer, and pin. Remove the self-adjuster spring and star wheel assembly and primary shoe.

16. Removing, Cleaning, Inspecting, and Reassembling a Duo-Servo Brake
33-3
Remove the secondary hold-down spring, retainer, pin, and secondary shoe. Disassemble the parking brake lever from the brake shoe and hardware from the backing plate. Finally, clean and inspect all parts according to the manufacturer’s procedure.

17. Removing, Cleaning, Inspecting, and Reassembling a Duo-Servo Brake
33-3
To reassemble a duo-servo brake, first reassemble the parking brake lever on the brake shoe and parking brake cable. Reassemble the star wheel assembly, lubricate the floating end, and set aside. Also lubricate the pads on the backing plate. Install both shoes to the backing plate with the hold-down spring assemblies. Install the shoe guide and self-adjuster cable over the anchor pin.

18. Removing, Cleaning, Inspecting, and Reassembling a Duo-Servo Brake
33-3
Install the cable guide and return spring in the secondary shoe. Also align the wheel cylinder pushrod in the shoe. Position the secondary shoe in place and use brake spring pliers to install the return spring over the anchor pin.
(continues)

19. Removing, Cleaning, Inspecting, and Reassembling a Duo-Servo Brake
33-3
... Install the parking brake strut rod onto the secondary shoe, and pull the primary shoe engaged with the parking brake strut rod. Install the return spring in the primary shoe and use brake spring pliers to stretch the return spring over the anchor pin. Install the self-adjuster link, cable, and spring into position. Install the star wheel between the bottoms of the two shoes. Finally, check the fit of all springs, clips, and levers.

20. Disassembling, Cleaning, Inspecting, and Reassembling a Non-Servo Brake
33-4
Research the procedure for disassembling the brake assembly. Clean brake shoes, hardware, and backing plates using equipment and procedures for dealing with asbestos/dust. To disassemble a non-servo brake disassembly, first remove the hold-down springs, retainers, and pins. Spread the shoes apart and remove the parking brake strut and self- adjuster components.

21. Disassembling, Cleaning, Inspecting, and Reassembling a Non-Servo Brake
33-4
Remove the return springs. Disassemble the parking brake lever from the brake shoe and hardware from the backing plate. Finally, clean and inspect all parts.

22. Disassembling, Cleaning, Inspecting, and Reassembling a Non-Servo Brake
33-4
To reassemble a non-servo assembly, first assemble and lube the self-adjuster/parking brake strut assembly. Lube the backing plate pads. Place one shoe on the backing plate and install the hold-down spring and pin. Place the self-adjuster/parking brake strut on the installed brake shoe.

23. Disassembling, Cleaning, Inspecting, and Reassembling a Non-Servo Brake
33-4
Place the retracting springs on both shoes, and fit the loose shoe to the backing plate, being sure to line up the wheel cylinder pushrods, the self-adjuster, and the parking brake mechanism. Install the hold-down spring and pin. Check the fit of all springs, clips, and levers.

24. Removing, Inspecting, and Installing Wheel Cylinders
33-5
Use a flare nut or line wrench to unscrew the brake line from the wheel cylinder. Remove the wheel cylinder from the backing plate.

25. Removing, Inspecting, and Installing Wheel Cylinders
33-5
Peel back the dust boots and check for brake fluid behind them. Determine any necessary actions.

26. Removing, Inspecting, and Installing Wheel Cylinders
33-5
Disassemble the wheel cylinder and inspect each part. Determine any necessary actions.

27. Removing, Inspecting, and Installing Wheel Cylinders
33-5
If the cylinder can be reused, rebuild it, preferably with new seals and dust boots. If not, replace it with a new wheel cylinder. Reinstall the brake line by hand. Install and tighten any mounting screws. After that, tighten the brake line with a flare nut or line wrench.

28. Pre-Adjusting Brakes and Installing Drums and Wheel Bearings
33-6
Make sure the brake shoes are centered on the backing plate.

29. Pre-Adjusting Brakes and Installing Drums and Wheel Bearings
33-6
Set the pre-adjustment gauge to the drum diameter and lock it in place.

30. Pre-Adjusting Brakes and Installing Drums and Wheel Bearings
33-6
Place the pre-adjustment gauge over the center of the brake shoes.

31. Pre-Adjusting Brakes and Installing Drums and Wheel Bearings
33-6
Adjust the star wheel until the centers of the brake shoes just contact the pre-adjustment gauge.

32. Pre-Adjusting Brakes and Installing Drums and Wheel Bearings
33-6
Test install the brake drum to verify the drum fits. Adjust the shoes as necessary. Pre-adjust the parking brake according to the manufacturer’s procedure. If the drum has serviceable wheel bearings, repack, install, adjust, and secure them.

33. Installing Wheels, Torquing Lug Nuts, and Making Final Checks
33-7
Start the lug nuts on the wheel studs by hand. Carefully run all of the lug nuts down so they are seated in the wheel. Lower the vehicle so the tires are partially on the ground. Use a torque wrench to tighten each lug nut to the proper torque in the proper sequence. Once all of the lug nuts have been torqued, go around them again, this time in a circular pattern.

34. Installing Wheels, Torquing Lug Nuts, and Making Final Checks
33-7
Reinstall hubcaps and valve stem caps.

35. Installing Wheels, Torquing Lug Nuts, and Making Final Checks
33-7
Check the brake fluid level in the master cylinder reservoir. Start the vehicle and check the brake pedal for proper feel and height. Check the parking brake for proper operation. Inspect the system for any brake fluid leaks and loose or missing fasteners.