Abstract: In a dual master cylinder assembly comprising two independently and simultaneously operable master cylinders, primary pressure spaces between primary and secondary pistons are interconnected by a pipe-line, and secondary spaces between the secondary piston and adjacent ends of the master cylinders are connected to a common auxiliary braking system through a pipe-line. Each secondary piston is provided with an arrangement of passages in communication at all times with a reservoir for fluid, and normally open primary and secondary recuperation valves provide communication between the passages and the respective pressure spaces when the pistons are in their retracted positions. Simultaneous operation of both master cylinders causes both pairs of primary and secondary recuperation valves to close followed by pressurization of the fluid in both pairs of primary and secondary pressure spaces, whereby to apply simultaneously the brakes on opposite sides of the vehicle and to operate the auxiliary braking system.