An air-operated diaphragm brake, more particularly a brake actuator assembly containing a diaphragm with a rib or ring design for centering and maintaining the location of a piston or push plate and for reducing debris build up in the brake actuator assembly. The diaphragm includes a projecting rim for engaging a housing containing a piston, a bottom wall having an interior surface for engaging the piston, a sidewall connecting the projecting rim with the bottom wall; and a plurality of ribs or a ring disposed on the interior surface of the bottom wall. The ribs or ring structure extends in a direction away from the intersection between the sidewall and the bottom wall, toward the center of the interior surface, and revolving around the center point of the interior surface.