A hydraulic booster brake mechanism for use with an open center power steering system of a motor vehicle in which a booster brake mechanism employs a mechanism permitting operation of the booster brake mechanism utilizing the pressures already made available due to operation of the power steering system. In the event the available pressure from the power steering system is not sufficient to accomplish the degree of braking desired, the control mechanism is actuated to increase and maintain the pressure produced by the power steering system at predetermined minimum pressure levels slightly above the pressure level necessary to accommodate the requirements of the booster brake mechanism.