Abstract: A modified AB test rack for testing freight car brake equipment valves in which excessive noise produced during standard tests by air exiting the quick action exhaust port of the emergency portion and the duplex release valve of the service portion is eliminated by connecting, by a quick action valve operating by an air cylinder, the respective port and release valve, to a manifold which is in turn connected to a muffler having an inlet at one end, a number of baffles and apertured plates forming a tortuous path to an outlet formed by a number of holes through the opposite end and adjacent sides.