Abstract: A brake actuator for a railway vehicle brake system has a thrust sleeve configured to provide braking force to the brake system, and a slide axially moveable in the thrust sleeve between a release position and a locking position. The actuator further has a piston biased by spring means and linked to an anchoring member. A plurality of balls are disposed in respective openings of the sleeve between the slide and the anchoring member. In the locking position, the balls are configured to move under the action of a profiled surface of the slide to axially couple the anchoring member with the sleeve. In the release position, the balls are configured to axially uncouple the anchoring member from the sleeve. The profiled slide surface has a locking groove configured to engagingly receive the balls when the slide is in the locking position.