The present invention provides a brake actuator assembly including a housing (30) having a generally radial annular flange portion (41) and a cover (32) having a generally radial annular flange portion generally co-axially aligned with the generally radial annular flange portion of the housing (30). A cup-shaped flexible diaphragm (40) having an outer radial rim portion is disposed between the generally radial annular flange portions of the housing (30) and the cover (32). A retaining element generally surrounds and compresses the generally annular flange portions of the housing (30) and the cover (32) against the rim portion (41) of the flexible diaphragm (40). The rim portion of the diaphragm includes a wedge-shaped edge portion (42) and co-axially aligned flats on opposite sides of the rim portion (41) adjacent to the wedge-shaped edge portion (42) aligning the flange portions of the housing (30) and the cover (32). In another embodiment, a flexible brake diaphragm includes a cup-shaped flexible diaphragm having an outer radial annular rim portion. The rim portion of the diaphragm includes a wedge-shaped edge portion and co-axially aligned flats (43) on opposite sides of the rim portion adjacent to the wedge-shaped edge portion (42).
