With the drum removed, you can see how a drum brake works. A hydraulic actuator (wheel cylinder or brake cylinder) exerts pressure outward enabling the linings to contact the rotating drums to bring your Mustang to a stop. There are two shoes-primary (front) and secondary (back). The primary shoe has less lining than the secondary. Drum brakes lose performance through wear and tear. Linings glaze from wear and drums get a mirror finish from wear. Backing plates wear at shoe contact points, causing uneven drum contact. Wheel cylinders develop leaks, which reduces hydraulic pressure and contaminates linings. All of these elements adversely affect braking effectiveness.