The invention utilizes a wheel speed proportional pressure generated by a transmission governor or equivalent means and a vehicle ground speed pressure provided by a vehicle ground speed computer and provides a hydraulic anti-lock brake system including a fluid pressure operated wheel brake, an operator actuated master cylinder, a hydraulic actuator which determines the level of brake pressure at the wheel brake, a control valve which modulates the wheel speed pressure to provide a regulated pressure proportional to the amount by which the master cylinder pressure exceeds the brake pressure, and a servo valve which amplifies the regulated pressure to provide a control pressure which operates the hydraulic actuator. The servo valve also compares the regulated pressure with the vehicle ground speed pressure and varies the control pressure in response to the wheel slip condition so as to provide a nearly constant wheel slip.