Master cylinder for electro-hydraulic brake system

The master cylinder for a motor vehicle electro-hydraulic brake has a reaction cartridge (28) with a piston (42) having one face (44) acted upon by brake fluid pressure from the master cylinder and a second face (46) engaged by a return spring assembly. The return spring assembly has first (434) and second (60) helicoidal springs which are coaxial and intercalated so that the coils of the second spring form movable contact surfaces for the coils of the second spring.