Automotive vehicle brake system

An automotive vehicle brake system having a vacuum brake power booster which is interposed between a brake pedal and a master brake cylinder which comprises at least two working chambers subdivided by a first movable wall, a first one of said chambers communicating with a vacuum source, a second one of said chambers being ventilated by means of a control valve actuatable by the brake pedal, said working chambers generating a boosting force that is proportional to a brake pedal force, wheel brake cylinders connected via brake lines to a primary and a secondary pressure chamber of the master brake cylinder, a central electronic control, and sensors allocated to the wheels to be braked which sense and provide output signals corresponding to the rotational behavior of the wheels in order to determine wheel-lock, said output signals being delivered to said central electronic control, said central electronic control providing control signals which control electromagnetically actuatable pressure-fluid inlet and outlet valves inserted into the brake lines for slip control, and said system further comprising a second movable wall provided in the vacuum power booster to which a controllable pressure differential is applied, first and second pneumatic working chambers isolated from each other by said second movable wall, and two compensating cylinders which, when slip control is activated, move said second movable wall in a direction opposite to the actuating direction of the master brake cylinder, said compensating cylinders being connected to said primary and secondary pressure chambers of said master cylinder, and further comprising a hydraulic chamber, a push-rod of the vacuum brake power booster operatively connected to said hydraulic chamber, an unpressurized pressure-fluid supply reservoir, and a retention valve selectively closing a connection between said supply reservoir and said hydraulic chamber.