Abstract: A diaphragm (32) for a servomotor which separates the interior of first (12) and second (14) shells into first (18) and second (20) chambers. The diaphragm (32) has an external bead (30) with first rib (31) having first (40) and second (42) sealing surfaces and an annular projection (46) extending therefrom which engages the rear shell (14) or divider (15) to guide the first (40) and second (42) sealing surfaces into contact with corresponding surfaces on the first (12) and second (14) shells. When the first (12) shell is connected to the second (14) shell, the projection (46) is compressed into the first rib (31) while a portion (33, 35) of the first rib (31) expands into cavities (37, 39) on both sides of the annular projection (46) to develop internal resiliency that uniformly acts on the first (40) and second (42) sealing surfaces. The diaphragm (32) has an internal bead (34) with a second rib (56) that snaps into a groove (36) on the hub (38) located in the servomotor.