1,025,851. Braking systems. BENDIX CORPORATION. Jan. 9, 1963, No. 1067/63. Heading F2F. A vehicle braking system comprises front and rear brakes, an hydraulic pump for actuating the front and rear brakes, and a pressure modifying unit for modifying the actuating pressure for at least the rear brakes. In one embodiment, Fig. 1, an atmosphere suspended vacuum powered servomotor A, when actuated by brake pedal 64, displaces hydraulic fluid from a master cylinder B to fluid pressure motors C and D for actuating the front and rear brakes respectively. The units C, D comprise hydraulic input pistons 10, 10<SP>1</SP> that are directly connected to output pistons 12, 12<SP>1</SP> which displace fluid from master cylinders 14, 14<SP>1</SP>. The hydraulic pressure received from the master cylinder B at the two motors C and D is respectively increased and decreased by the atmosphere suspended air motors 20<SP>1</SP>, 20. One side of the pistons 22, 22<SP>1</SP> is subjected to atmosphere via ports 60, 58<SP>1</SP> and the other side of the pistons is subjected to the pressure present in chamber 68 of the servomotor A. On actuation of the latter by the pedal 64, vacuum from a reservoir 66 is communicated to the chamber 68 to provide the servo effect and is communicated to one side of the pistons 22, 22<SP>1</SP> to increase and decrease the pressure supplied respectively to the front and rear brakes. In a modification, a pedal-operated master cylinder actuates a vacuum suspended servomotor, the hydraulic output of which is modified by motors C and D. In another embodiment, Fig. 3 (not shown), the motors C, D are actuated by a master cylinder which may be servo operated and is connected to conduit 72. A deceleration responsive device G is inserted between the vacuum reservoir 66 and the port 60 of the motor D to provide an opposing force to the actuating force on piston 10 proportional to the vehicle deceleration. The motor C is only used when the master cylinder is servo operated. The device G comprises a weight 112 which on deceleration moves forwardly with diaphragm 102 to allow a spring-loaded poppet valve 104 to close the apertures in the diaphragm and open valve 108 to communicate atmosphere to the vacuum suspended motor D to oppose the applying force. In a modification, the deceleration responsive device is replaced by a similar unit which is attached to the vehicle front axle and is actuated by downward movement of the front portion of the vehicle frame. In another modification wherein the master cylinder is servo operated, the deceleration responsive device is inserted in the vacuum line from the servomotor to the motor D. In a further embodiment, Fig. 7 (not shown), the deceleration responsive device J is a variable ratio valve. On actuation of the vacuum suspended servomotor E an increasing control pressure is communicated to inlet chamber 138 which passes through open valve seat 152 to the control chamber 144 and thence to the rear side of the air piston 22. The increase in pressure in the chamber 144 moves the diaphragm 134 and the partition 150 forwardly to abut poppet 154 and thereby close off the valve seat 152 to prevent further build-up in pressure in control chamber 144. The piston 136 is inclined forwardly and outwardly so that the diaphragm 134 will normally be abutted by the tapered surface. The face 176 of the housing section 130 is inclined forwardly and inwardly. On forward movement of the piston 136 therefore the diaphragm rolls out of engagement with the inclined surface 174 and into engagement with the inclined surface 176 to reduce the effective area of the diaphragm 134. The surfaces 174, 176 are tapered to produce the required rear wheel braking pressure. On deceleration of the vehicle the weight 112 overcomes the effect of spring 168 to bias poppet member 154 out of engagement with the valve seat 152. This permits a flow in pressure to the motor D to further oppose the applying pressure. In a modification wherein the servomotor is of the atmosphere suspended type, an atmosphere suspended valve similar to valve J is used.