1942 - 1947 Chevrolet Shop Manual



	*8-3*

	providing additional road clearance. Basically there are three perforated tubes: inlet, intermediate, and outlet. The inlet and outlet tubes are encased by separate perforated tubes. The primary purpose of these encasing tubes is to prevent short circuit of the gases, which try to flow through the perforation in the inlet tube directly to the outlet tube, carrying noises with them and causing noises at the end of the tail pipe at low speeds. Incorporated in the front end of the muffler is a resonance chamber, with a narrow annular opening around the inlet pipe. The volume of this chamber is such that "period" noises, which usually occur in exhaust on coasting, are tuned out. The gas flow from the engine, considerably straightened out by the small exhaust pipe, reaches the muffler through the inlet tube, reverses at the rear end and flows from tube to tube to the outlet as shown. The flow, however, is not restricted to the tubes, since the gases pour out in jets from each perforation, mingling with the gases from adjoining tubes. The resulting mixing and baffling, with velocity changes and reversals in direction of flow, aids in silencing. Every part of the muffler is attached to the assembly by electric arc welding, making failure or rattling practically impossible. TRUCKS The truck exhaust system includes such items as a unit muffler of integral construction, employing the reverse flow and diffusion principles used so successfully on the passenger cars to obtain quiet operation, Fig. 4, heavy tail pipe metal for durability, and a large diameter tail pipe to reduce back pressure. The tail pipe extends back of the rear axle to the end of the chassis, discharging exhaust gases at a point that prevents fumes entering the driver compartment.	PASSENGER CARS The center mounting directly back of the muffler is a vulcanized rubber cushion design. This holds to a minimum the transfer of any exhaust vibrations to the frame and body, Fig. 5.

		Fig. 5—Passenger Muffler Mounting The rubber cushion is mounted to the muffler outlet pipe, and the support is on a frame bracket. The tail pipe support consists of a rubber grommet located on a separate bracket riveted to the rear cross member. The rubber grommet is held in controlled suspension by a spacer, insuring proper tension on this mounting at all times. Locating lugs and slots on the exhaust pipe, muffler inlet and outlet pipes and tail pipe insure proper assembly and correct angular relation and lineup of all parts. There are three points to consider when installing a muffler and tail pipe. 1. The oval section of the muffler should lie in a horizontal plane. 2. There should be 5/8" clearance between the underside of the floor pan and the tail pipe at the kick-up. 3. The tail pipe support at the rear must be assembled in a vertical position. If it is at an angle the tail pipe is apt to strike the bumper. TRUCKS The muffler end of the exhaust pipe slides into the muffler inlet pipe and is held in place by a clamp. Small projections on the exhaust pipe properly locate the exhaust pipe depth in the muffler. A bracket extending from the frame, with the underside conforming to the curvature of the

	Fig. 4-Truck Muffler EXHAUST SYSTEM SUSPENSION When installing a muffler, exhaust pipe or tail pipe assembly, care should be taken to have the proper assembly and relationship of each part or assembly to the other. Incorrectly assembled parts of the exhaust system are frequently the cause of annoying rattles due to incorrect clearances, and unusual noises, difficult to locate, because of some change or obstruction to the normal flow of exhaust gases through improper mounting.