Operation

OPERATION

When the parking brake is applied, the parking brake cables pull on the operating levers of the parking brake calipers. This rotates the discs and worm shaft inside each caliper causing the piston to extend and apply the brakes. Since normal brake shoe operating clearance is quite small, only a modest amount of piston movement is needed for brake application. A stop bolt is used to limit the total amount of piston extension.

The worm shaft is attached to the piston with a spring washer and lock ring. The driven disc is threaded to the worm shaft and the drive disc is seated in the caliper. The operating lever is bolted to the drive disc. The operating lever is connected to and operated by the parking brake rear cable. The lever return spring is attached to the operating lever and a bracket on the caliper body.

The drive disc rotates the spring loaded driven disc by means of ball bearings. The bearings are secured to the drive disc and seat in cam ramps machined in the driven disc.

The parking brake mechanism is self-adjusting to compensate for lining wear. As wear occurs, drive-to-driven disc clearance increases. This causes the drive disc ball bearings to move farther up the cam ramps in the driven disc increasing the amount of rotation. The extra rotation produced is enough to extend the piston for adjustment.