Drum Brake Service Procedures
Safety Note: Asbestos has been used in brake linings for many years. Asbestos dust is a health hazard if inhaled. Do not clean brake parts with compressed air. Avoid breathing the dust off of brake parts.
Disassemble and Inspect
Remove the rear wheels.
Note: Before beginning this procedure, ensure that the vehicle is properly supported on axle stands.
Remove the brake drums. Do not step on the brake pedal while the brake drums are removed. This will cause the pistons to pop out of the wheel cylinders.
Inspect the brake drums for "hot spots" or excessive wear. The drums may be measured to determine if they can be reused.
Inspect the brake linings for wear, cracks, or oil-soaking. If the brake linings are oil-soaked, the source of the oil leak must be repaired at this time.
Check that both pistons in each wheel cylinder are moving freely by prying the brake shoes forward and backward against the wheel cylinder. Inspect the wheel cylinders for leaks by gently peeling back the boots and checking for brake fluid. Check that the bleed screw can be loosened. Use a six-point wrench or socket to avoid damaging the screw.
Operate the park brake lever inside the car and observe that the park brake cables are releasing fully at the rear brakes.
Remove brake linings from one side of the vehicle only. This will allow you to check the other side for correct reassembly.
Clean the backing plates. Use a solvent and a parts brush. Do not create dust. Inspect the backing plates for damage or wear.
Based on your inspection this far, create a parts list. Your work must be inspected by your teacher before proceeding to the next procedure.
Service and Reassemble
Repair or replace parts, as discussed with teacher.
Lubricate the contact points on the backing plates with an anti-seize compound.
Install the brake shoes on the backing plate. Install the primary shoe (long lining) on the rear of the backing plate. Clean and lubricate the self-adjustor screw. An anti-seize compound may be used on the threads.
If the drums require machining, mount the drums on the brake drum lathe and wrap the anti-vibration strap around the drum. Set up the cutter. Have the teacher inspect your machine set-up before starting the machine. Remove only enough material to true the drums.
Note: Safety glasses are required for this procedure.
Install the drums and adjust the shoes to fit. The drums should turn but have a slight drag. Be sure the park brake cables are loose when fitting the drums.
Fill the master cylinder brake fluid reservoir.
Note: Avoid contacting skin with the brake fluid.
Check the brake lines for air. Have an assistant hold firm pressure on the brake pedal. Open the bleed screw and check for air bubbles. Close the bleed screw before the assistant releases the brake pedal. Check the brake fluid level in the master cylinder.
Install the wheel and hubcap.