Pneumatic servo with reduced equilibrium time

The pneumatic servo motor for a motor vehicle brake has a control shaft (38) which controls the opening and closing of an axial inlet valve (52) between a pressure source and a rear chamber (18) of the servo motor. The shaft also controls a rebalance valve (50) between a front chamber (16) and a rear chamber (18) to acuate a diaphragm between the chambers. The valve has an axially offset tube (76) with obturators (82,84) to seal the valves.