This caliper is operated by an automotive brake actuator. The brake actuator, which is used on medium and heavy duty trucks, has two functions. The upper housing has a spring which is forcing the actuator rod downward, pushing the wedge against the rollers and applying the brake. Air pressure is required to overcome the spring to put the brake into a released position. If there is no air pressure going to the actuator, the upper brake portion applies the brake providing emergency braking.

The lower portion of the actuator is a diaphragm that also pushes the rod downward and applies the brake proportionately. A very light return spring pushes the wedge upward to release the brake. This allows for the brake to be used in two different versions. The upper spring can only provide up to 60% of brake force. In order to modulate the brake, the air pressure can be varied in the diaphragm portion. Since there is no piston in this actuator assembly, there is practically no hysteresis, as far as the actuator is concerned. This makes it extremely sensitive to varying air pressures.

The wedge mechanism consists of a wedge and rollers that force the levers apart to apply pressure to the brake disc and give a very accurate control over the brake torque.