Exaust - Noisy or Low Hanging Mufflers
89chevy09
Number: 88-393-6F
Section: 6F
Date: FEB., 1989
Subject: NOISY OR LOW HANGING MUFFLERS
Model and Year: 1987-88 R/V MODELS WITH 5.7L OR 7.4L
(VIN CODE K OR N) ENGINE
TO: ALL CHEVROLET DEALERS
Customer comments may be received on 1987 and 1988 R/V models built prior to VIN breakpoint (JF165082) equipped with 5.7L or 7.4L engine, of low hanging or throaty sounding (rumbling on acceleration) mufflers. Mufflers designed for usage on TBI equipped engines are of a high flow/low restriction design for increased engine performance and are somewhat louder than mufflers used in previous years. If either of these conditions are experienced, they can be repaired by installing a revised muffler and tailpipe assembly.
Parts Information
Parts Quantity
Number Description Application Required
15616421 Muffler R1,2 5.7L Federal 1
(NA5/NA6)
R2 7.4L Export (NM8)
15616422 T/Pipe R1,2 5.7L Federal 1
(NA5/NA6)
R2 7.4L Export (NM8)
15616423 Muffler R2 5.7L Calif. (NB2) 1
R2 7.4L Federal
(NA5/NA6)
15616424 T/Pipe R2 5.7L Calif. (NB2) 1
R2 7.4L Federal
(NA5/NA6)
15616425 Muffler V1,2 5.7L Federal 1
(NA5/NA6)
Parts Quantity
Number Description Application Required
15616426 T/Pipe V1,2 5.7L Federal 1
(NA5/NA6)
379360 Clamp R/V 1, 2 5.7L only 2
15624612 Hanger Muffler V1,2 only 1
15624613 Shield Muffler All 1
14029140 Bracket, Shield All 2
15549331 Hanger T/Pipe R1, 2 1
15549332 Hanger T/Pipe V1, 2 1
435611 Bolt 3/8"- All 2
16 X 1.00
103321 Washer 3/8"flat All 2
9414034 Nut 3/8"-16 All 2
180083 Bolt (T/Pipe Hgr) R1, 2
5/16 X 18 X 1.5" V1, 2 1
2
9439511 Washer (T/Pipe Hgr) R1, 2
5/16 lock V1, 2 1
2
9439493 Nut (T/Pipe Hgr) R1, 2
5/16 X 18 X 1/4 V1, 2 6
9
9418918 Bolt (Conv Shld/
T/Pipe Hgr)
5/16 X 18 X 1" All (R Model) 5
(V Model) 8
11514363 Bolt (Conv Shld)
M6 X 1 Self Tapping All 1
456846 J-Nut (Conv Brkt)
5/16 x 18 All 2
2436162 Washer (conv Shld)
5/16 Flat All 2
Parts are currently available from GMSPO.
When making the above changes to the exhaust System, it is necessary to replace the muffler heat shield to maintain proper passenger Compartment temperature. It is also necessary on V models to add a secondary T/Pipe hanger to maintain proper alignment. On all models it will also be necessary to replace the tailpipe hanger.
Figure No. 1:
Service Procedure
1. Raise vehicle on hoist
2. Remove muffler and tailpipe following procedures in section 6F - Engine Exhaust, of the appropriate year service manual.
3. using an air chisel or a high speed cut off wheel, remove the original muffler heat shield flush with the floor pan, see Figure 1.
Figure No. 2:
4. Assemble the new muffler heat shield, see Figure 2.
5. Slip the new muffler assembly onto the catalytic converter and align muffler. Do not install clamps.
6. Slide assembled muffler heat shield over muffler and position shield onto frame. Shield must be centered over muffler. Mark bracket bolt hole locations on frame, see Figure 2. Remove heat shield and muffler assembly. Using a 5/16" drill, drill the four (4) holes in the frame side rail. Using a 3/16" drill, drill the one (1) hole in top of the frame rail. Install the heat shield on the frame and torgue side rail bolts to 20-28 N-m (15-20 ft/lbs), and top rail bolt to 14-20 N-m (12-20 ft/lbs).
Figure No. 3:
Figure No. 4:
7. Using an air chisel, grinding wheel, etc., remove the
(2) rivets from the existing tailpipe hanger. Install the new hanger for the appropriate model with 3/8" - 16 x l.00" bolts, nuts, arid washers and torque nuts to 27-40 Nm (25-35 Ft/lbs) , see Figure 3 .
8. Install muffler and tailpipe using procedures in section 6F of the appropriate service manual.
IMPORTANT: On V models (4WD) it will be necessary to add a new rear tailpipe hanger, see Figure 3. Measuring from the center of the forward muffler bracket, measure back 48" on the frame. Center the rear hanger on the mark and using the hanger as a guide, mark the bolt holes. Using a 5/16" drill, drill the holes in the frame side rail and install the hanger as shown in Figure 4. Torgue all bolts to 20-28 N-m (15-20 lb/ft) .
9. Lower vehicle and road test.
Use: Labor Operation: T7700
Labor Time: 1.2 hr