Pneumatic brake booster having a crimped diaphragm

The servomotor has a sealing diaphragm (30) made of an elastomer material and whose periphery is fixed to a casing. A peripheral skirt (28) is provided, in the vicinity of its periphery, with a stamped annular recess (42) defining an internal groove that serves to receive snugly a peripheral bead (46) projecting from a surface of the sealing diaphragm to fix the diaphragm to the skirt.