Drum Brake System: Description and Operation

IMPORTANT:
- Install all new components included in the repair kit used in order to service the drum brakes.
- Lubricate the parts as specified.
- Do not use lubricated compresses air on the brake parts. Damage to the rubber components may result.
- If any hydraulic component is removed or disconnected, bleed all or part of the brake system.
- Replace the shoe and the linings in axle sets only.
- The torque values specified are for dry, non-lubricated fasteners.
- Perform service operations on a clean bench free from all mineral oil materials.

This drum brake has an advanced leading/trailing design. It 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 in order 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, their positions should not be switched, 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 in hydraulic System.