A spring brake actuator, comprising: an actuator intermediate flange member; a spring housing configured to be affixed to a first side of the actuator intermediate flange member to form a parking brake actuator chamber; a service brake housing configured to be affixed to a second side of the actuator intermediate flange member opposite the first side; a parking brake release piston comprising a stamped piston plate and a flexible diaphragm, the parking brake release piston being configured to divide the parking brake actuator chamber into a parking brake release chamber on an intermediate flange side of the parking brake release piston and a power spring chamber on an opposite side of the parking brake release piston; a parking brake actuating power spring arranged in the power spring chamber to bias the parking brake release piston away from a rear wall portion of the spring housing; characterized in that the spring brake actuator further comprises a spring seat cap having at least a flange region arranged to transfer power spring biasing force between the power spring and the parking brake release piston plate in a region of an inner radius of the power spring, the spring seat cap having an axially-extending cap portion located within the inner radius of the power spring and extending from the flange region toward the spring housing rear wall portion; and a parking brake release operating rod affixed at a first rod end to the parking brake release piston and at a second rod end to a travel limiting member in the service brake actuator chamber, the operating rod having a rod length such that the travel limiting member abuts the second side of the intermediate flange before the spring cap contacts the spring housing when the parking brake release piston is located at a fully withdrawn position. an actuator intermediate flange member; a spring housing configured to be affixed to a first side of the actuator intermediate flange member to form a parking brake actuator chamber; a service brake housing configured to be affixed to a second side of the actuator intermediate flange member opposite the first side; a parking brake release piston comprising a stamped piston plate and a flexible diaphragm, the parking brake release piston being configured to divide the parking brake actuator chamber into a parking brake release chamber on an intermediate flange side of the parking brake release piston and a power spring chamber on an opposite side of the parking brake release piston; a parking brake actuating power spring arranged in the power spring chamber to bias the parking brake release piston away from a rear wall portion of the spring housing; characterized in that the spring brake actuator further comprises a spring seat cap having at least a flange region arranged to transfer power spring biasing force between the power spring and the parking brake release piston plate in a region of an inner radius of the power spring, the spring seat cap having an axially-extending cap portion located within the inner radius of the power spring and extending from the flange region toward the spring housing rear wall portion; and a parking brake release operating rod affixed at a first rod end to the parking brake release piston and at a second rod end to a travel limiting member in the service brake actuator chamber, the operating rod having a rod length such that the travel limiting member abuts the second side of the intermediate flange before the spring cap contacts the spring housing when the parking brake release piston is located at a fully withdrawn position.