Abstract: A vacuum-operated brake power booster is provided having a movable wall which is sealed off relative to the vacuum housing and a control valve body which is slidable jointly with the movable wall. A hollow cylinder-shaped expanded plastic ring is arranged in the annular clearance between the neck portion of the pedal side housing shell and the collar of the diaphragm, which collar sealingly surrounds the control valve body. The expanded plastic ring effects the air flow during brake operation such that the air flow, enters the annular clearance through the duct extending in a radial direction within the control valve body and is suitably deflected and cushioned so that no noises arise at this point. In the same manner and simultaneously, vibrations, especially those of the neck portion of the housing shell of the vacuum housing, are suppressed, since the expanded plastic ring adheres to the inside wall of the housing shell.

Abstract: In a known motorcycle brake system, the pedal-actuated master cylinder acts on the front-wheel brake and the rear-wheel brake and the hand-actuated master cylinder acts on the front-wheel brake. The brake force regulator's control behavior provided by a stepped control piston is influenced by the hand-actuated master cylinder. This known system has functional disadvantages since the rear-wheel brake is evacuated of fluid by movement of the control piston if the hand-actuated master cylinder is actuated alone. In addition, the regulator's change-over point is reached at a relatively high pressure. These disadvantages are eliminated in the present invention by the provision of a valve adapted to close independently of the position of the stepped piston which is prevented from moving when the hand-actuated master cylinder is actuated alone by a stop against which the stepped piston abuts.