Fluid pressure operable brake actuators with fluid operable brake sock and release

A fluid pressure operable brake actuator including a housing having a first fluid pressure responsive member for exerting a brake applying force to an output member, said first member forming a movable wall of a first chamber having a brake-applying pressure input port, a second chamber sealed from said first chamber and having movable therein second and third pressure responsive members spaced from each other and movable relative to each other, a second fluid pressure input port in communication with the space between said second and third members, said third member forming a movable wall of a third chamber having a third input port, means engageable with said second pressure responsive member and sealingly slidable in the housing to cooperate with the first pressure responsive member such that force can be applied from said second pressure responsive member to said first pressure responsive member through said engageable means, a one-way clutching device coupled to the second pressure responsive member to retain it in engagement with said engageable means after application of a fluid pressure to the second input port such that said second pressure responsive member acts through said engageable means on said first pressure responsive member to lock-in a force applied to the output member due to a fluid pressure at the first input port, and means for releasing and clutching device upon selective movement of the third pressure responsive member in response to a fluid pressure at the third fluid pressure input port so as to permit release of said locked-in force.