Drum Brake System: Testing and Inspection

This drum brake has an advanced leading/trailing design. The drum has fewer parts, is equivalent to other drum brakes in performance, and has improved reliability. A single universal spring holds both shoe and lining assemblies to the backing plate, and also acts as a retractor spring for them. When the brakes are applied, the wheel cylinder moves both shoes out to contact the drum. With forward wheel rotation, the forward (leading) brake shoe wraps into the drum and self-energizes. Force from the shoes is transferred through the fixed anchor and backing plate to the axle flange. The drum brakes self-adjust during any brake application, with no vehicle motion required. Once the shoes are installed, do not switch the positions, even though the forward shoe normally wears faster than the rear shoe. Switching positions may render the self-adjustment inoperative and result in increased pedal travel. For diagnosis of this system, refer to Testing and Inspection.