Vibration or Rattle Type Noise in Exhaust System at Idle (Install Exhaust System Dampener Assembly)

This bulletin is being revised to add 2003-2004 RPO LU3 information. Please discard Corporate Bulletin Number 01-06-05-003 (Section 06 -- Engine/Propulsion System).

Some customers may comment on a vibration or rattle-type noise coming from the exhaust system at idle with engine RPMs between 613 and 712.

An exhaust system dampener assembly, tuned to 40.25 Hz, P/N 15762298, or 42 Hz, P/N 15047524, is available for service to correct this condition. Install the applicable exhaust system dampener assembly on the affected vehicles. Use the following procedure and the applicable part number listed below.

1. Raise the vehicle. Suitably support the vehicle. Refer to the General Information subsection of the applicable Service Manual for information on lifting and jacking the vehicle.
2. Remove the two nuts from the dampener assembly. Remove the dampener, the heat shield and the clamp plate from the U-bolt.
3. Position the U-bolt around the tailpipe (open end facing downward) approximately 25 mm (1.0 in) forward of the tailpipe kick-up and 190 mm (7.5 in) rearward of the muffler hanger.
4. Install the clamp and a nut on the short end of the U-bolt.

Exhaust Dampener (4.3L - RPO L35)




5. Install the heat shield and then the dampener (with the cast part number visible) on the long end of the U-bolt. Install the nut. Orient the assembly with the dampener below the pipe as shown.

Tighten
Tighten the clamp nuts to 30 N·m (22 lb ft).

6. Lower the vehicle.

The RPO LU3 vehicles will require the use of exhaust dampener kit, P/N 15047524.

This dampener assembly is installed essentially in the same manner as the L35 procedure above. Use the above procedure sequence to install the dampener assembly over the exhaust pipe. Position the dampener assembly approximately 101 mm (4 in) from the weld bead of the Y intersection of the pipe. Refer to the above illustration.

In order to prevent the mass dampener from grounding out at the flanged nut, a 3/8" inside diameter lock washer, P/N 11500046 or equivalent, should be added as a spacer (1) between the nut and the mass dampener as shown above.

Three 3/8" inside diameter and 1/16" thickness flat washers, P/N 11509161 or equivalent, should also be added between the top of the dampener and the heat shield plate. These washers are not included in the dampener kit.

Also, a large pair of channel locks may be needed to help secure the clamp.

Parts are currently available from GMSPO.

For vehicles repaired under warranty, use: