Brake system comprising an electric brake booster

The system has an electric brake booster (200) with a rack drive (260) connected to an actuator piston to act on a tandem master cylinder (100). The piston has a flange ring forming a housing with a circular shoulder constituting a support surface for a reaction disk. The flange ring forms a plunger connected to a control rod (230) and housed in a sleeve of the piston to control the booster and to directly act on the disk in case of failure of the booster. The plunger is separated from the disk in a normal operation by a slip interval.