Drum brake

Front-wheel-drive Audi 80 models built before October 1992 (not equipped with ABS) have drum brakes on the rear axle. In this version of the brake, two brake shoes are pressed against the inner surface of the drum by the brake cylinder piston (located between the upper ends of the brake shoes). Due to the arrangement of the brake shoes in the drum brake used on the Audi 80 (Simplex brake – one wheel cylinder with two pistons), one of the two brake shoes works in a self-energizing manner. This means that this shoe is pressed against the brake drum within certain limits automatically by the rotation of the wheel, which reduces pedal effort. On the Audi 80 (when moving forward), the front brake shoe works in a self-energizing manner. In specialist terminology it is called the primary shoe or leading shoe. The rear one is correspondingly called the secondary shoe or trailing shoe.

Self-Adjusting Drum Brake
Drum brakes do not require adjustment. Unlike disc brakes, this task is handled by the self-adjusting mechanism. As the friction lining wears, the wheel cylinder pushrods extend between the brake shoes so that the shoes can again press against the drum. This is achieved by a spring-loaded adjusting wedge that extends the pushrods as the shoes wear.