Abstract: A disc brake, particularly suitable for use in tractors and like vehicles, is disclosed. Balls are located in complementary inclined recesses in a pressure plate and in an adjacent end wall of the brake housing. The brake is actuated by radial movement of the pressure plate, which produces a camming effect as the balls tend to ride out of the recesses, so that the pressure plate moves axially to urge a rotatable friction disc into engagement with a surface of the housing. Pilot pins engage with lugs on the pressure plate, constraining it against angular movement, so that when on application of the brake the pressure plate engages the friction disc, the pressure plate is prevented from being carried round with the friction disc, ensuring that no servo effect takes place.

Abstract: A pair of tandem master cylinders have primary pressure spaces connected to the brakes on one pair of wheels on opposite sides of the vehicle, and an actuator for the brakes on a trailer is supplied with fluid under pressure from pipe-lines connected to each of the four pressure spaces and under the control of first and second disabler valves. Each disabler valve has a pair of inlet ports, each connected either to respective primary pressure spaces or respective secondary pressure spaces, and an outlet port connected to the actuator. When one master cylinder is operated on its own both disabler valves are closed to prevent the actuator from being operated. Failure of one pressure space, when both master cylinders are operated simultaneously, causes the corresponding disabler valve to close but the actuator can still be operated from the operative pressure spaces, through the other disabler valve.

Abstract: A master cylinder assembly comprising two separate master cylinders is disclosed. Pressure spaces of the master cylinders are interconnected through outlet passages and a transfer passage, and a transfer valve is housed within each outlet passage. When the master cylinders are inoperative both transfer valves are retained by yieldable spacers in intermediate positions in which a limited flow can take place through both valves in both directions. This prevents hydraulic fluid from being trapped in the transfer passage which otherwise might cause a fracture to occur upon expansion with temperature of the fluid. Each transfer valve comprises a valve member which is engageable with a seating. The yieldable spacers by which the valve members may be held away from the seatings may be the thickness of a film of hydraulic fluid therebetween.

Abstract: In a spreading disc brake recesses for co-operation with balls located between pressure plates comprise straight grooves of progressively varying depth in inserts mounted in the pressure plates for angular movement about axes normal to the planes of the plates.