A vehicle braking system comprising an air pressure operated brake motor and a spring-applied fluid pressure released motor combined as a unit, said unit including in the spring motor a central sleeve movable with the piston thereof and in screwthreaded connection with a hollow release screw, said screw having operative connection with a push rod by which the thrust of the unit is transmitted to the brake linkage, and means for rotating the release screw to effect further movement of the piston beyond the ''''brakes-on'''' position to decompress the piston loading spring and release the brakes.