replying to SteveBrady, Rick Nock, ASE Master Tech, retired Auto Tech
Instructor wrote:
Self adjusters have been around on drum brakes for decades. Some are cable,
some are linkage and a few odd ones out there. Bendix self energizing brakes
use vehicle direction to multiply the stopping force. These type of brakes
have the shoes installed against a top large anchor pin, with the adjuster on
the bottom. When installed, the lower end of the shoes will move freely with
the top against the anchor pin. When driving forward applying brakes, the
shoes expand against the rotating drum. The rotational force tries to turn the
brake shoe assembly which can't move because the anchor pin stops them. The
front shoe pushes the rear shoe against the brake drum which pushes against
the anchor pin at the top. When operating in forward direction, the rear shoe
does most of the work as the front shoe does not even touch the anchor pin.
The front (primary) shoe usually has a shorter friction pad than the rear
(secondary shoe). The adjuster star wheel generally is closer to the rear shoe
so it can engage in the self adjuster lever. The movement of the shoes
reverses when you back up. It is this motion that allows the adjuster to catch
the next notch on the star wheel. When you release the brake, the return
springs pull the brake shoes back to the anchor pin. If the brakes have worn
enough to require adjusting, this is when the lever will move the star wheel.
Hope this explanation wasn't too complicated.

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