Pneumatic brake booster for a vehicle with a guiding device and method for mounting said booster on a master cylinder

The pneumatic brake booster servomotor (1) for a motor vehicle has a front chamber (11,12) and a rear chamber (13,14) with a pneumatic piston (5) and a return spring (4). The return spring has guides (45) formed of two connectors (20,21) between the brake pedal and the master cylinder along the servomotor axis (7). The connectors can be formed as discs (24,25) connected by a tongue.