Abstract: The dual braking unit includes a cylinder with a diaphragm 4, 11-17) for controlling the service braking and a cylinder with a drive spring (3, 6-10) for controlling the parking and emergency braking. The cylinder with the spring includes a piston (6, 10) with an operating tube or tubular push rod (10) which extends sealingly through a hole (5) in a wall (2) separating the operating chambers (8; 12) of the cylinders. There is a pair of holes (35, 36; 35, 34) in the tube (10) for enabling communication between the chamber (7) with the spring (9) and the operating chamber (12) of the cylinder with the diaphragm when only the parking and emergency brake is applied. A cut-off valve device (40-43) is associated with the holes (35, 36; 34. 35) for preventing air from flowing from the operating chamber (12) of the cylinder with the diaphragm to the chamber (7) with the spring (9) when the service brakes are applied while the parking and emergency brake is applied.

Abstract: Each rear wheel has a respective associated hydraulic brake actuator. A brake corrector device of the variable operating pressure type is connected in the operating circuit for the brake actuator associated with the rear wheels and includes, in known manner, a movable control member for regulating the operating pressure of the corrector in dependence on the force acting thereon. A control device is coupled to the brake corrector and applies to the control member of this corrector a force which is variable in a predetermined manner in dependence on the air pressure in the air springs of the rear suspensions of the motor vehicle.