Abstract: A master cylinder provides separate flow paths through its secondary piston to provide greater fluid flow capacity from the reservoir to both the primary and secondary pressure chambers in response to the removal of brake fluid from the brake lines fed by the primary and secondary pressure chambers by a pump providing brake pressure for activation of one or more wheel brakes independently of the master cylinder. The secondary piston is provided with an axial fluid flow passage having check valves at each axial end permitting fluid flow only out of the axial fluid flow passage into the primary and secondary pressure chambers. A cross flow passage intersects the axial fluid flow passage between the primary and secondary check valves to communicate the axial fluid flow passage with the intermediate chamber and thus with the reservoir through the secondary compensation opening. The additional flow capacity to both pressure chambers provides improved reaction time for a traction control system at any wheel brake.