Find School Bus Exhaust Systems & truck exhaust systems | United Muffler Corporation, United Muffler Corp. manufactures and stocks and extensive line of heavy duty Bus and Truck exhaust systems that match OEM part numbers for Bluebird, International/Navistar, Thompson, Chevrolet/GM, Freightliner, Ford, Volvo Mack. Design onsite custom pipes and Mufflers. Variety of gas tanks, stainless steel pipes, stacks, clamps, hangers, radiators, available. Mandrel bent tubes from 1" to 6 inch.