Drum Brake System: Description and Operation

Important:
^ Install all new components included in the repair kit used to service drum brakes.
Lubricate parts as specified.
^ Do not use lubricated compressed air on brake parts as damage to rubber components will result.
^ If any hydraulic component is removed or disconnected, it will be necessary to bleed all or part of the brake system.
Replace shoe and linings in axle sets only.
^ The fastener tightening specifications are for dry, unlubricated fasteners.
^ Perform service operations on a clean bench, free from all mineral oil materials.

The drum brake assembly is a duo-servo design. In the duo-servo brake, the force which the wheel cylinder applies to the primary shoe is multiplied by the primary lining friction in order to provide a very large force applied to the secondary shoe. The brake shoes transfer torque to the anchor pin, through the backing plate and to the axle flange. Adjustment for both the primary and the secondary shoe and linings is automatic during the reverse brake applications.