A heavy truck's brake air cylinders do not directly apply the brake pads through pistons as in a hydraulically operated system. Heavy truck air applied brakes use a mechanical operating system to apply force to the disc brake pads. Also, it is important that disc brakes on a given axle operate in unison to avoid undue lateral forces. Courtesy of the Government of the Province of British Columbia. Figure 1 illustrates a typical medium and heavy truck air operated disc brake.
Adjustment is automatic.
Several malfunctions are possible. The floating caliper, single piston design may have dirt built up on the guides and ways or these may have become corroded due to the protective lubricant loss. Lack of lubrication prevents the caliper from fully retracting when the brake pedal is released. Figure 2 illustrates a typical floating caliper disc brake. The brake pad drags the rotor as a result.