Hydraulic master cylinder

A master cylinder for use in a motor vehicle split hydraulic braking system having disc brakes for acting on one set of wheels and drum brakes for acting on another set of wheels, the master cylinder comprising:

• a body having first and second bore portions therein;
• a first piston slidable in the first bore portion;
• a second piston slidable in the second bore portion;
• a first chamber defined by the housing and the first piston, and which in use is pressurised by movement of the first piston in a brake-applying direction;
• a second chamber defined by the housing and the second piston and which in use is pressurised by movement of the second piston in a brake-applying direction;
• a first outlet port communicating with the first chamber for connection to the drum brakes;
• a second outlet port communicating with the second chamber for connection to the disc brakes;
• delay valve means to control flow from the second chamber to the second outlet port, said delay valve means comprising a valve member mechanically connected to one of said first and second pistons and being movable to close communication from the second chamber to the second outlet port in direct response to initial movement of said one piston away from a brake released position, a plunger movable by fluid pressure in the second chamber to re-open communication from the second chamber to the second outlet port and a control spring biassing the plunger in the opposite direction to delay such movement of the plunger until pressure in the second chamber reaches a predetermined magnitude;
• and non-return valve means allowing return flow from the second port to the second chamber.