Drum Brake System: Description and Operation

WARNING:
- BRAKES CONTAIN ASBESTOS FIBERS. AVOID BREATHING DUST. BREATHING ASBESTOS DUST MAY CAUSE ASBESTOSIS AND CANCER.
- BREATHING ASBESTOS DUST IS HAZARDOUS TO YOUR HEALTH.
- DUST AND DIRT PRESENT ON WHEEL BRAKE AND CLUTCH ASSEMBLIES MAY CONTAIN ASBESTOS FIBERS THAT ARE HAZARDOUS TO HEALTH WHEN MADE AIRBORNE BY CLEANING WITH COMPRESSED AIR OR BY DRY BRUSHING.
- WHEEL BRAKE ASSEMBLIES AND CLUTCH FACINGS SHOULD BE CLEANED USING A VACUUM CLEANER RECOMMENDED FOR USE WITH ASBESTOS FIBERS SUCH AS ROTUNDA ASBESTOS BRAKE DRUM SYSTEM WITH VACUUM 091-00025. DUST AND DIRT FROM VACUUM SHOULD BE DISPOSED OF IN A MANNER THAT PREVENTS DUST EXPOSURE SUCH AS SEALED BAGS. THE BAG MUST BE LABELED AS PER OSHA INSTRUCTIONS AND THE TRASH HAULER NOTIFIED AS TO THE BAG'S CONTENTS
- IF A VACUUM SUITABLE FOR ASBESTOS IS NOT AVAILABLE, CLEANING SHOULD E3E DONE WET. IF DUST GENERATION IS STILL POSSIBLE, TECHNICIANS SHOULD WEAR GOVERNMENT-APPROVED TOXIC DUST PURIFYING RESPIRATORS.
- GRINDING OR SANDING ON BRAKE LININGS, PADS, ROTORS, DRUMS OR CLUTCH FACINGS SHOULD BE DONE ONLY WHILE USING PROPERLY EXHAUST-VENTILATED EQUIPMENT.
- OSHA REQUIRES AREAS WHERE ASBESTOS DUST GENERATION IS POSSIBLE To BE ISOLATED AND POSTED WITH WARNING SIGNS. ONLY TECHNICIANS CONCERNED WITH PERFORMING BRAKE OR CLUTCH SERVICE SHOULD BE PRESENT IN THE AREA.

The rear drum brake system includes:
- Brake drums
- Rear wheel cylinders
- Brake adjuster screw
- Upper retracting springs
- Lower retracting springs
- Brake shoe hold-down springs
- Brake shoe hold-down pins
- Primary brake shoes and linings
- Secondary brake shoes and linings
- Parking brake rear cable and conduits
- Parking brake anchor plates
- Rear brake backing plates
- Parking brake control

The rear drum brakes use internal hydraulic rear wheel cylinder with expanding brake shoes and linings that are applied against a rotating brake drum. An incremental brake adjuster screw is actuated whenever sufficient wear occurs. Brake adjustment takes place in forward or reverse braking, but not with parking brake application.