Figure 5.2 Wedge Brakes. In this type of brake, the brake chamber push rod pushes a wedge directly between the ends of two brake shoes. This shoves them apart and against the inside of the brake drum. Wedge brakes may have a single brake chamber, or two brake chambers, pushing wedges in at both ends of the brake shoes. Wedge type brakes maybe self-adjusting or may require manual adjustment. Disc Brakes. In air-operated disc brakes, air pressure acts on a brake chamber and slack adjuster, like scam brakes. But instead of the scam, a "power screw" is used. The pressure of the brake chamber on the slack adjuster turns the power screw. The power screw clamps the disc or rotor between the brake lining pads of a caliper, similar to a large c-clamp. Wedge brakes and disc brakes are less common than scam brakes.