Patent ID: 7024854

Claim:
A master cylinder comprising a body ( 2 ) in which is made a bore ( 3 ) blocked off at one end by an end wall ( 5 ), at least one piston ( 8 , 10 ) slideably mounted in a sealed manner in the bore, a hydraulic fluid supply chamber formed in a longitudinal slot ( 30 ) in the piston, a working chamber connected to brakes, said working chamber being connected to the supply chamber through a passage ( 36 ) made in the piston ( 8 , 10 ), a valve for blocking off said passage ( 36 ) during a braking phase, said valve ( 18 ) comprising a shutter ( 22 ) and a valve seat ( 20 ) borne by the piston ( 8 , 10 ), said shutter ( 22 ) bearing at rest against a bearing element ( 42 ) fixedly mounted in the body ( 3 ) of the master cylinder, said bearing element being mounted to pass through the longitudinal slot ( 30 ), a distance (L) separating a first end ( 44 ) of the slot remote from the valve ( 20 ) and a first end ( 46 ) of the bearing element remote from the end wall ( 5 ) being less than a distance (D) separating a first end ( 34 ) of the piston close to the end wall ( 5 ) and the end wall ( 5 ), the bearing element being a pin, characterized in that the first end ( 44 ) of the slot ( 30 ) is in the form of a circular arc and in that the circular arc has a diameter which is substantially equal to the diameter of the pin so as to achieve uniform distribution of the stresses applied by the pin to the piston ( 8 , 10 ).