Vacuum brake booster for motor vehicles comprising a booster housing whose interior is subdivided by a movable wall into a vacuum chamber and a working chamber, a control valve that controls a pressure difference acting upon the movable wall and is accommodated in a control housing that carries the movable wall, said control valve being composed of two concentrically arranged sealing seats and an elastically deformable valve member, wherein the control housing includes a cavity through which a cross member extends and delimits the axial movability of a valve piston relative to the control housing, and the cross member includes at least one projection made of an elastic material in the area where the cross member rests against the booster housing. At least one projection made of an elastic material is provided in the area of points of abutment between the control housing and the cross member.