Vibration

[kyle3]

I have a 2004 C1500 4.3 at 1200 rpms there is a vibration that sounds as if it is coming from under the front of the truck. The Chevy dealer said it was normal, but it doesn't sound normal to me. I have heard that the 2001-2002 had similar problem that was caused by the exhaust pipes. Any ideas warranty is about to run out.

[GM-Tech]

Tell your dealer to take a look at this TSB. This noise usually occurs around 900-1500 rpms, under light load, like when you're accelerating normally away from a light. It can make the whole dash rattle. VERY common on the 4.3.

 

 

Exhaust Moan/Vibration (Install Exhaust System Flex Pipe Kit) #02-06-05-003D - (Jan 31, 2005)

 

1999-2005 Chevrolet Silverado 1500 Series Extended Cab or Regular Cab/Long Box Pickups (New Style)

 

1999-2005 GMC Sierra 1500 Series Extended Cab or Regular Cab/Long Box Pickups (New Style)

 

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

 

This bulletin is being revised to add the 2005 Model year. Please discard Corporate Bulletin Number 02-06-05-003C (Section 06 -- Engine/Propulsion System).

 

Condition

Some customers may comment on a moan or vibration at low vehicle speeds between 900-1200 RPM under load.

 

Cause

Exhaust system resonance that is transmitted through the powertrain mounts into the body may cause this condition.

 

Correction

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 crossmember 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 2000-2005 2WD and 4WD Models Built After 1/00

These models only 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.

 

Raise the vehicle.

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

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

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

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

 

 

 

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.

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).

 

Lower the vehicle.

 

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.

 

Install the flex coupler using steps 1-7 of the above procedure.

Support the transmission with a suitable adjustable jack stand.

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

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

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

 

 

 

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.

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

 

Tighten

 

• Tighten the new transmission mount nuts to 25 N·m (18 lb ft).

 

• Tighten the two U-bolt clamps to 30 N·m (22 lb ft).

 

Lower the vehicle.

Parts Information

Part Number

Description

Usage

 

15076982

Exhaust System Parts Package

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

 

15076990

Exhaust System Parts Package

• 1999-2000 4WD Models Built Prior to 1/20/00

 

• All 2000-2005 2WD and 4WD Models Built After 1/00

 

 

• Kit P/N 15076982 includes a flex coupler, two support brace rods w/integral U-bolt pipe clamps, two U-bolt pipe clamps (for use with flex coupler) and two new transmission mount studs w/fasteners.

 

• Kit P/N 15076990 includes a flex coupler and two U-bolt pipe clamps.

 

Parts are currently available from GMSPO.

 

Warranty Information

For vehicles repaired under warranty, use:

 

Labor Operation

Description

Labor Time

 

*L3505

Exhaust Flex Pipe - Install

0.4 hr

 

Add:

To install transmission support brace rods (vehicles built prior to 1/00)

0.3 hr

 

 

*This is a unique labor operation number for use only with this bulletin. This number will not be published in the Labor Time Guide.

 

 

 

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

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[lch0]

My 06 GMC with the 4.3 and automatic does the vibration thing when it shifts into overdrive at low rpms. Is it possible this could be the same tsb. My truck is the 2wd short wheelbase regular cab. I know you stated earlier it was for long beds or short bed extra cabs but the same problem seems to exist.