Improvements relating to brake actuators

The present invention relates to a brake actuator for use in a disc brake, the brake actuator incorporating an automatic adjuster mechanism to take account of friction pad wear. In certain known brake actuators a clutch mechanism comprising one or more clutches is used to provide for the required control of the rotational movement of a threaded adjuster sleeve (19) in which a tappet (21) is located. These clutches are located around the outside surface of the adjuster sleeve (19) and thus, due to overall spatial requirements within the actuator (1), the outside diameter of the adjuster sleeve (19) and as a result, the diameter of the threaded bore in the adjuster sleeve (19), have to be limited in size. The threaded tappet (21) thus comprises an enlarged diameter head region and a reduced diameter threaded region. Due to the limited diameter of the tappet (21), the tappet (21) can tilt or be damaged, resulting in premature and/or even pad wear. The present invention provides a brake actuator comprising a drive shaft 93) rotatably supported in an actuator housing (1) and coupled to an internally threaded adjuster sleeve (19) by coupling means (7) which convert rotational movement of the drive shaft (3) into axial movement of the adjuster sleeve (19). The internally threaded adjuster sleeve (19) is retained against rotational movement and is screw threadedly engaged with a hollow tappet (21) within which a clutch mechanism (23, 35) for interconnecting the drive shaft (3) and tappet (21), is located. The clutch mechansim (23, 25) is thus located within the hollow tappet (21) so that the diameter of the threaded connection between the tappet (21) and adjuster sleeve (19) can be optimised to at least reduce the problems of premature and uneven pad wear inherent in previous constructions.