Patent ID: 8209978

Claim:
Master cylinder for a motor vehicle and comprising a body ( 2 ) in which a bore ( 3 ) is formed longitudinally with respect to an axis ( 6 ) of the master cylinder, a hydraulic fluid reservoir ( 9 , 10 ) opening into the bore of the master cylinder, a piston ( 4 , 5 ) sliding in the bore and defining a chamber ( 7 , 8 ) of the master cylinder, the piston comprising a port ( 13 , 14 ) opening, at one end, to face a wall ( 17 ) delimited by the bore, and, at the other end, opening into the chamber, the port receiving hydraulic fluid from the reservoir, and a sealing means ( 18 , 19 ) housed in a groove formed in the wall, the sealing means controlling the passage of hydraulic fluid through the port through collaboration between the sealing means and the piston, characterized in that a first indentation ( 24 ) and a second indentation ( 27 ) are created upstream of the port of the piston in the direction of forward travel of the piston during the braking phase, a reduction in a diameter ( 35 ) of the piston being obtained from the second indentation to the first indentation, characterized in that the piston ( 4 , 5 ) has a first connecting surface ( 28 ) and a second connecting surface ( 29 ), the first connecting surface ( 28 ) connecting the first indentation ( 24 ) to the second indentation ( 27 ), the second connecting surface ( 29 ) connecting the second indentation ( 27 ) to a remainder of the surface of the piston, the first and second connecting surfaces being chamfered.