JPS643701B

The brake booster comprises a working piston for activation of a master cylinder piston and a transmitting piston having a greater diameter than the working piston in a tandem relationship with the working piston. A transmission pressure chamber is disposed between adjacent ends of the working piston and the transmission piston and a first valve arrangement is provided to load the transmission pressure chamber with pressure fluid or to relieve this chamber of pressure. A drive or actuating pressure chamber is disposed adjacent the other end of the transmission piston and a second valve arrangement is provided to load the drive pressure chamber with pressure fluid or to relieve this chamber of pressure. The first and second valve arrangements are controlled by the brake pedal and constructed in such a way that when the brake pedal is initially operated the brake pedal and the pistons come to a stop until all idle paths have been travelled.