Drum Brake System: Description and Operation

IMPORTANT:
1. Replace all of the components included in the repair kits that are used to service this drum brake.
2. Lubricate the parts as specified.
3. Do not use lubricated shop air on brake parts. Damage to rubber components may result.
4. If any hydraulic component is removed or disconnected, bleed all or part of the brake system.
5. Replace the brake shoe (11 & 5) and the brake linings in the axle sets only. (Rear together and front together).
6. The torque values specified are for dry, non-lubricated fasteners.
7. Perform service operations on a clean bench free from all mineral oil materials.

This drum brake is an advanced leading/trailing shoe design. The advanced design operates with less total parts. The drum brake performance is equivalent to other drum brakes while providing improved reliability. The operation and servicing of the advanced design brake is much simpler than traditional drum brakes.
This brake system employs a single universal spring (4). The single universal spring holds both the shoe and the lining assemblies (11 & 5) to the backing plate (10). The spring also acts as the return spring for both the shoe and the lining assemblies. Force from the brake shoes transfers through the fixed anchor and backing plate to the axle flange.
Adjustment is automatic and occurs on any service brake application. Also, with leading/trailing brakes, it is normal for the leading (front) shoe to wear at a faster rate than the trailing (rear) shoe. Do not switch the position of shoes that have been in service. Switching shoes may render the self adjustment feature inoperative and result in increased pedal travel.


INSPECTING AND REFINISHING BRAKE DRUMS
Servicing the front brakes will usually correct pulsation in the brake pedal. Service the rear brakes only if the problem persists.
Thoroughly clean and inspect the brake drums for the following condition when the drums are removed for service:
1. Cracks
2. Scores
3. Deep grooves out-of-round
4. Taper

Normal, light scoring of the brake drum surfaces not exceeding 0.51 mm (0.020 inch) in depth will not affect brake operation.