Abstract: A cup for a master cylinder coming into contact with its primary piston or its secondary piston and subjected to the pressure of the brake fluid of the primary chamber and of the secondary chamber. The cup has two large grooves bordered: by a rib between the heel and the first groove, by a rib between the first groove and the second groove, by a rib between the second groove and the small grooves, these ribs being in protrusion relative to the cylindrical surface of the heel in the mounted position of the cup in order to separate the heel from the surface of the piston and form, between the heel and the surface of the piston, a gap with a film of brake fluid. Master cylinder notably a tandem master cylinder fitted with such cups.

Abstract: “Cup for master cylinder, advantageously a tandem master cylinder, and a tandem master cylinder fitted with such cups” The cup for a master cylinder coming into contact with its primary piston or its secondary piston and subjected to the pressure of the brake fluid of the primary chamber and of the secondary chamber. The cup (60) has two large grooves (622, 624) bordered: by a rib (627) between the heel (621) and the first groove (622), by a rib (623) between the first groove (622) and the second groove (624), by a rib (625) between the second groove (624) and the small grooves (626), these ribs (627, 623, 625) being in protrusion (DS) relative to the cylindrical surface (D) of the heel (621) in the mounted position of the cup (50) in order to separate the heel (620) from the surface of the piston (30) and form, between the heel (620) and the surface of the piston (30), a gap (621) with a film of brake fluid (628). Master cylinder notably a tandem master cylinder fitted with such cups.