The present specification discloses a brake actuator incorporating a mechanically operated adjuster, the adjuster compensating for friction pad wear. Certain known adjusters are hydraulically operated and due to there being possible problems with hydraulic operation, e.g. seal failure, which are especially disadvantageous in certain applications, the use of a hydraulically operated adjuster is not fully approved.
The present invention provides a brake actuator comprising two adjuster members (1, 3) interconnected by a self-sustaining thread (5) and located between a friction pad (11) and an actuation member (17), the actuation member (17) being biassed by a main spring (19) to a brakes-on position with at least one hollow piston (23) being displaceable under hydraulic pressure to compress the main spring (19) and move the actuation member (17) to a brakes-off position, a second piston (27) being axially displaceable within said hollow piston (23) under said hydraulic pressure and against a further spring (29), to cause interengaging means (39, 41) to rotate one adjuster member (1) relative to the other adjuster member (3), stop means (43) being arranged to limit the available movement of said interengaging means (39, 41). The present invention thus provides a mechanically operated adjuster which avoids the inherent disadvantages of hydraulic operation.