Vehicle wheel brake actuators

A vehicle wheel brake actuator comprising a first cylinder, a first fluid pressure operable member working in said first cylinder for service braking, a second cylinder, second fluid pressure operable member working in said second cylinder for parking or emergency braking, spring biassing means urging said second member towards a brake-applying position, said second member being normally held-off in an inoperative position by an opposing fluid pressure, force transferring means having axially inner and outer ends, said force-transferring means being supported at said inner end and extending axially outwardly and being movable with said second fluid pressure operable member upon release of said opposing fluid pressure whereby the force of said spring biassing means is transferred through said second member and said force transferring means to said first member, said force transferring means extending freely and with clearance through said second member and being disengaged from said second member when in its inoperative position and being engageable therewith upon release of said opposing fluid pressure, and manually operable quick release means movable to disengage said force transferring means from said second member in its brake-applying position, whereby to permit axial movement of said force transferring means relative to said second member to release said brake the clearance between and disengagement of said force transferring means and said second member in its inoperative position being such that there is unobstructed spacing between said second member and all of the force transferring means so as to prevent said force transferring means from being corroded in said second member due to non-use.