Abstract: A brake actuator is provided, in which a diaphragm, used in conjunction with a piston which compresses a parking brake-actuating spring, is arranged such that its outer peripheral region is captured between opposing housing flange portions such that a seal between the interior and exterior of the brake actuator housing is provided in a radially-oriented region of the diaphragm and the housing flange portions away from housing portion jointing components such as a clamp ring or individual fasteners. The diaphragm may also be provided with a wedge-shaped portion at its outer periphery which is axially oriented and configured to reside in a corresponding annular gap between the opposing housing flange portions.