Abstract: The invention relates to a tandem master-cylinder for a split braking system of an automotive vehicle. The master-cylinder comprises two pressure chambers, the first one between the control piston and the floating piston and the second or front chamber before the floating piston. The first chamber communicates with a first outlet port which is connected to a second outlet port through a by-pass valve. The by-pass valve is secured to a tappet-rod projecting into the second chamber to be engaged by the floating piston, upon pressure failure in the second chamber and so that the by-pass valve is opened. The first outlet port is adapted to be connected to a set of brake actuators through a braking correcting valve while the second outlet port is adapted to be directly connected to said set of brake actuators.