Centering device for pneumatic brake booster comprising a ball

The device has a round shape component (20) situated between a hydraulic piston (14) of a master brake cylinder (2) and a push rod (13). A front end (13a) of the rod or a rear end (14b) of the piston presents a plane surface perpendicular to one of two axial directions and being in contact with the component. The component is fixed in the end (14b) or at the end (13a) and is drowned in or coated with a lubricating product.