A hydraulic actuator including an actuator cylinder and a ram slidable therein from a retracted position to an extended position. This ram has an axially extending chamber positioned in an end section and a number of ball passageways extend between this chamber and the outer surface of the ram. A locking ball is positioned in each passageway. A ring is slidably mounted on the ram and is positioned at its forwardmost point of travel to hold the balls so that they do not project from the passageways. A spring biases the ring towards its forwardmost position. A ball moving spool is slidably mounted in the chamber and has an annular ball receiving recess. A stop is located in an end section of the cylinder for preventing further forward movement of the ring and this stop causes the ring to slide rearwardly relative to the ram upon further extension of the latter.