a master cylinder in a vehicle hydraulic braking installation uhydraulic - fluid supply device for actuating wheel brake cylinders . the master cylinder being isolated from the wheel brake cylinders by at least one shut - off valve . the master cylinder being associated with a simulator having a piston located in a simulator chamber . the piston being subjected to fluid pressure of brake fluid from the master cylinder and an elastic element . the master cylinder being of the having a primary piston and a secondary piston slidably located in a bore of a housing . bore has a peripheral groove which is associated with a land on the secondary piston to allow communication with the simulator chamber when the master cylinder is in a positon of rest . a sealing element carried by the secondary piston engages the housing when the secondary piston moves to interrupt communicaton between the bore and simulator chamber to thereafter simulate brake actuation travel .