Drum Brake System: Description and Operation

The rear drum brake is a duo-servo design. In the duo-servo brake, the force which the rear wheel cylinder applies to the primary shoe is multiplied by the primary lining friction to provide a very large force which is applied to the secondary shoe. Torque from the brake shoes is transferred to the anchor pin, through the rear brake backing plate and to the axle flange. The adjustment for the brake shoe to brake drum clearance is automatic during reverse brake applications. Brake shoe to drum clearance can also be adjusted manually after rear brake service. The rear brake drum has a honed friction surface that reduces shoe slap, increases shoe life, and reduces the break-in time.