Drum Brake System: Description and Operation

GENERAL DESCRIPTION
The drum brake assembly has a self shoe clearance adjusting system so that drum-to-shoe clearance is maintained appropriately at all times. For details, refer to Compensation of rear brake clearance.

NOTE: Replace all components included in repair kits to service this drum brake. Lubricate parts as specified.

WARNING: If any hydraulic component is removed or brake line disconnected, bleed the brake system. The torque values specified are for dry, Unlubricated fasteners.





Compensation of rear brake clearance.
The brake is equipped with an auto-adjust mechanism which consists of an adjuster, pawl lever, etc. When the brake pedal is depressed, shoe clearance is adjusted automatically.





The pawl lever supported by pin "A" is subject to the turning force caused by the spring but prevented from turning by the end of the adjuster. In this state, when the brake pedal is depressed, the gap between shoes increases while the length of the adjuster remains unchanged. As a result, the pawl lever moves in the direction as shown in the figure. At this time, with the tip "B" of the pawl lever engaged with the gear of the adjuster, the gear turns in the direction as indicated in the figure and the overall length of the adjuster increases. This is because the external thread of the adjuster gear is in mesh with the internal thread of the adjuster body and the gear turns in the unscrewing direction.

When the shoe clearance is large, every time the brake pedal is depressed, the gear turns by one notch. Once the clearance has reached the appropriate level, even when the brake pedal is depressed, the shoe stroke is not enough to cause the gear to turn by 1 notch (i.e., pawl lever does not move) and thus the clearance remains unchanged.