Abstract: A vehicle brake actuator has actuator components in the form of a cylinder body and a piston operatively associated respectively with a non-rotatable adjuster shaft and a rotatable nut member threadedly interengaged by way of a reversible screw thread connection, the nut member being arranged to follow brake-applying movement of the component being movable axially along the shaft by rotating therealong when adjustment is required and being otherwise prevented from rotation by a clutch. The piston includes an auxiliary piston part axially and rotationally movable relative thereto and arranged to be manually operable from the exterior of the actuator. The piston part is provided with axial projections, which upon axially inward movement of the piston part, may be brought into engagement with recesses in the nut member, whereby the nut member may be wound along the shaft to de-adjust the adjuster without the necessity to rotate the piston.