The hydraulic brake system has a brake pressure control valve (24) between the master brake cylinder (10) and the rear brakes, to ensure that the rear brake pressure is always less than that for the front wheel brakes. An anti-slip valve is fitted between the brake pressure control valve and a separate pumped unit (33) in the return line of the rear brakes, to isolate the rear brakes during anti-slip control. The brake pressure available from the separate pumped units is applied to the rear brakes via the brake control valves for the rear brakes, independent to the control brake system. No enhancement of the rear brake pressure is required.
