The air activated heavy truck disc brake is similar in principle to the disc brake used on passenger vehicles. Air pressure acts on a brake chamber and slack adjuster, activating the brakes. For light truck and passenger car braking systems, hydraulic pressure is used. Instead of the cam or wedge used in conventional heavy truck drum brakes, a power screw is used. A ‘power screw’ works like a C-clamp, so that the lining pads exert equal force to both sides of the disc or rotor. Some types of disc brakes have a built-in automatic adjuster. Disc brakes that require manual adjustment have adjustment specifications different from conventional ‘S’ cam braking systems. ALWAYS CHECK MANUFACTURER’S SPECIFICATIONS BEFORE ADJUSTING.