Drum Brake System: Description and Operation

The drum brake assembly is a leading/trailing shoe design. When the brakes are applied, the wheel cylinder moves both shoes out to contact the drum. With forward wheel rotation, the leading brake shoe provides the majority of the braking force, since it is self-energized (meaning that drum rotation draws the brake shoe into the drum). With reverse wheel rotation, the trailing brake shoe is self energized. Force from the brake shoes is transferred through the shoe anchor, the backing plate, the axle flange, and finally to the wheels. Brake adjustment is automatic, on any brake application. With leading/trailing brakes, it is normal for the leading (front) shoe to wear at a faster rate than the trailing (rear) shoe.