A hydraulic brake booster system. The hydraulic brake booster system includes a primary piston axially moveable within a bore of a cylinder, a booster chamber located rearwardly of the primary piston within the bore, an input rod extending within the booster chamber, a booster vent path in selective fluid communication with the booster chamber, and a seal member located between the forward face and the primary piston, the seal member in a fixed relationship with the input rod and configured to (i) seal the booster vent path from the booster chamber when the input rod is in a first position, and (ii) not seal the booster vent path from the booster chamber when the input rod is moved rearwardly within the booster chamber to a second position.