Patent ID: 8109088

Claim:
Brake master cylinder ( 1 ) comprising a piston ( 4 ) sliding in a bore ( 3 ) of a master cylinder body ( 2 ), the master cylinder body ( 2 ) comprises an inlet ( 17 ) allowing hydraulic fluid to enter a chamber ( 13 ), and a smooth seal ( 21 ) of circular shape with a U-shaped profile, the U-shaped profile being formed by an inner lip ( 28 ) and an outer lip ( 27 ) of the seal, the seal ( 21 ) being in contact via the inner lip ( 28 ) with the periphery of the piston ( 4 ), and via the outer lip ( 27 ) with the body ( 2 ) of the master cylinder ( 1 ), characterized in that it comprises reliefs ( 42 ) which are localized and produced on one inner lip facing outer lip and positioned in pairs and in that said reliefs ( 42 ) are spaced apart by a spacing ( 47 ) equal to about half the height ( 48 ) of the inner lip ( 28 ) as measured parallel to an axis ( 7 ) of movement of the piston ( 4 ).