Hydraulic master-cylinder with reduced lost motion

The braking system master cylinder has primary and secondary pistons (16, 44) that move axially inside working chambers (18, 52) linked by axial passages (22, 58) to fluid feed chambers (32, 60), and valves (26, 56) actuated by springs (28, 70) that close the passages once the pistons have covered their backlash in the working chambers from a rest position. The backlash is concealed by the use of additional valves (80) actuated by springs (84, 92) to close piston end ducts (30, 54). The additional valves are in the form of discs that can move on axial rods (82) linked to the main valves and have orifices that allow a reduced flow of hydraulic fluid in the ducts.