Main cylinder with enhanced security

The master cylinder comprises body(2) with bore(3) containing piston(s)(8,10), and passage(36) with valve(18) linking feed chamber to working chamber connected to brakes. In valve's rest state the distance between first end(44) of slot furthest from valve and first side(46) of thrust element further from base(5) of cylinder body is less than distance between first end(34) of piston and base(5). The master cylinder consists of a body (2) with a bore (3) containing at least one piston (8, 10) having a lengthwise slot (30) acting as a hydraulic fluid feed chamber, and a passage (36) with a valve (18) linking the feed chamber to a working chamber connected to the brakes. In the valve's rest state its shutter (22) presses against a thrust element (42) fixed across the body of the cylinder in the lengthwise slot, and the distance between a first end (44) of the slot furthest from the valve and the first side (46) of the thrust element further from the base (5) of the cylinder body is smaller than the distance between the first end (34) of the piston and the base (5). The thrust element is in the form of a transverse pin, and the slot ends in a curved section of similar diameter to the pin to ensure an event distribution of stresses applied by the pin to the piston.