Exhaust Moan/Vibration Noise (Install Exhaust System Flex Pipe Kit)

Models: 1999-2007 Chevrolet Silverado 1500 Series Extended Cab or Regular Cab/Long or Short Box Pickups (Classic)

2007-2010 Chevrolet Silverado 1500 Series Extended Cab or Regular Cab/Long or Short/Standard Box Pickups (New Body Style)

1999-2007 GMC Sierra 1500 Series Extended Cab or Regular Cab/Long or Short Box Pickups (Classic)

2007-2010 GMC Sierra 1500 Series Extended Cab or Regular Cab/Long or Short/Standard Box Pickups (New Body Style)

Equipped with 4.3L Engine (VINs W, X -- RPOs L35, LU3) and Automatic Transmission (RPO M30)

This bulletin is being revised to add additional steps for regular cab short bed vehicles. Please discard Corporate Bulletin Number 02-06-05-003H (Section 06 -- Engine/Propulsion System).

Condition: 

Some customers may comment on a moan or vibration noise at low vehicle speeds 40-64 km (25-40 mph) or between 900-1700 RPM under load.

Cause: 

Exhaust system resonance may be transmitted through the power train mounts into the body causing this condition.

Correction: 

Caution: Personal injury or burns may occur when working on a hot exhaust system, let the exhaust system cool off prior to performing the repair.

An exhaust system flex pipe kit is available to correct this condition. If diagnosis leads to this condition, install the applicable exhaust system flex pipe kit listed below using the following procedure. Refer to the Parts Information for kit applications and usage.

Important: This fix and the kit part numbers are specific to vehicle frame type. A Level 3 frame was introduced interim 2000 model year (approximately January 2000). With a Level 3 frame, the transmission cross member was moved forward of its previous location. Pre-Level 3 frames will require the installation of additional components to correct the condition.

1999-2000 4WD Models Built Prior to 1/20/00 and All 2000-2010 2WD and 4WD Models Built After 1/00 (Except Regular Cab Short Bed Vehicles)

Subject: Exhaust Moan/Vibration Noise (Install Exhaust System Flex Pipe Kit)

Models: 1999-2007 Chevrolet Silverado 1500 Series Extended Cab or Regular Cab/Long or Short Box Pickups (Classic)

2007-2010 Chevrolet Silverado 1500 Series Extended Cab or Regular Cab/Long or Short/Standard Box Pickups (New Body Style)

1999-2007 GMC Sierra 1500 Series Extended Cab or Regular Cab/Long or Short Box Pickups (Classic)

2007-2010 GMC Sierra 1500 Series Extended Cab or Regular Cab/Long or Short/Standard Box Pickups (New Body Style)

Equipped with 4.3L Engine (VINs W, X -- RPOs L35, LU3) and Automatic Transmission (RPO M30) these models require the installation of a flex coupling. The flex coupling has adapter sleevesfor the installation of U-bolt clamps. This procedure uses the U-bolt clamps, but the preferred installation method is to weld the flex coupler to the exhaust pipe.

1. Raise the vehicle.

2. Locate the first available straight section of pipe rearward of the mid-joint flange and forward of the muffler assembly.

3. Measure approximately 228 mm (9 in) on the straight pipe and mark.

4. Using a suitable cutting tool, cut out the marked section of the pipe and remove.

5. Remove any burrs, if necessary, before installing the flex coupler pipe.

6. Install the flex coupling (1). Expand the sleeves of the flex coupler, if necessary, to properly fit over each pipe end. The centerline of the installed flex coupling should run parallel to the straight section of pipe (no bends in the coupling) for optimum performance.

7. Install the U-bolt clamps (2) on each sleeve end of the flex coupling. Tighten Tighten the U-bolt clamps to 30 N·m (22 lb ft).

8. Lower the vehicle.

9. Verify that the condition has been fixed.

1999-2000 4WD Models Built Prior to 1/20/00 and All 2000-2010 2WD and 4WD Models Built After 1/00 (With Regular Cab Short Bed )

Note: This procedure uses a locally obtained 76 mm (3 in) flex coupling. Most larger exhaust shops will have these available. The kit listed below (P/N 15076990) is too long to use on regular cab short bed vehicles. Do not order the parts listed below.

These models require the installation of a flex coupling. The flex coupling has adapter sleeves for the installation of U-bolt clamps. This procedure uses the U-bolt clamps, but the preferred installation method is to weld the flex coupler to the exhaust pipe.

1. Raise the vehicle.

2. Locate the first available straight section of pipe rearward of the mid-joint flange and forward of the muffler assembly.

3. Measure approximately 76 mm (3 in) on the straight pipe and mark.

4. Using a suitable cutting tool, cut out the marked section of the pipe and remove.

5. Remove any burrs, if necessary, before installing the flex coupler pipe.

6. Install the flex coupling, follow the manufacturer's installation instructions (1). Expand the sleeves of the flex coupler, if necessary, to properly fit over each pipe end. The centerline of the installed flex coupling should run parallel to the straight section of pipe (no bends in the coupling) for optimum performance.

7. Lower the vehicle.

8. Verify that the condition has been fixed.

1999-2000 2WD Models Built Prior to 1/00

These models will require the installation of a flex coupler, two Y-pipe support brace rods w/integral U-bolt clamp assemblies on the LH and RH sides of the transmission rear mount and new transmission mount studs and nuts. The Y-pipe support braces are used in combination with the flex coupler to reduce exhaust moan.

1. Install the flex coupler using steps 1-7 in the first procedure(s).

2. Support the transmission with a suitable adjustable jack stand.

3. Remove the two bolts and nuts from the transmission rear mount.

4. Position the transmission rear mount and install two new studs to the mount.

5. Install the new studs supplied with the kit to the transmission mount. 

6. Loosely position the Y-pipe support braces w/integral U-bolt clamps (LH and RH) to the underside of the transmission rear mount and the crossover pipe as shown. The top ends of the braces attach to the underside of the transmission rear mount. The bottom ends of the braces attach to the crossover pipe using the integral U-bolt clamps. The braces support the LH leg of the Y-pipe where it crosses over the vehicle to meet the Y-pipe collector.

7. Install the two nuts to the transmission rear mount and the two nuts to the U-bolt clamps.

Tighten

8. Lower the vehicle.

9. Verify that the condition has been fixed.