Abstract: A hydraulic brake booster includes a housing 12 with a first chamber 40 and a second chamber 42. An input member 54 extends into the first chamber 40 and is exposed to the second chamber 42. The input member is movable within the first chamber 40 to increase fluid pressure within the second chamber 42 and this fluid pressure operates a control valve 90 to communicate fluid pressure to the first chamber 40. The fluid pressure in the first chamber 40 acts against the input to bias the same toward the second chamber 42. An output member 70 is movable in response to the fluid pressure within the second pressure chamber 42 to actuate braking.