Ford Mustang/Capri 1979-1988 Repair Guide

Basic Operating Principles


Drum brakes on all Ford and Mercury cars employ hydraulically actuated, internally expanding brake shoes. Correct operating clearance between the shoe linings and drums is maintained by a self-adjusting assembly, which moves in small increments, in direct proportion to lining wear. When applying the brakes while backing up, the linings tend to follow the rotating drum counterclockwise, thus forcing the upper end of the primary shoe against the anchor pin. Simultaneously, the wheel cylinder pushes the upper end of the secondary shoe and cable guide outward, away from the anchor pin. This movement of the secondary shoe causes the cable to pull the adjusting lever upward and against the end of the tooth on the adjusting screw star wheel. As lining wear increases, the upward travel of the adjusting lever also increases. When the linings have worn sufficiently to allow the lever to move upward far enough, it passes over the end of the tooth and engages it. Upon release of the brakes, the adjusting spring pulls the adjuster lever downward, turning the star wheel and expanding the brakes.