Intermittent Boom, Rumbling Noise and/or Disturbance Heard in Passenger Compartment While Driving at Highway Speeds (Replace Rear Coil Springs)

This bulletin is being revised to add the breakpoint of 8/23/2004 for 2005 model year production with an updated spring material. Please discard Corporate Bulletin Number 02-03-09-002B (Section 03 -- Suspension).

Some customers may comment on an intermittent booming, rumbling noise and/or disturbance heard in the passenger compartment while driving the vehicle at highway speeds. This condition occurs while driving at steady speeds between 1550-1700 engine RPM in 4th gear (NOT during acceleration). This equates to 64-80 km/h (48-50 mph) for vehicles with a 4.10 axle ratio (RPO GT5), 83-86 km/h (52-54 mph) with a 3.73 axle ratio (RPO GT4) and 93-96 km/h (58-60 mph) with a 3.42 axle ratio (RPO GU6).

The noise/disturbance occurs when the torque converter momentarily goes to a full lock-up state, resulting in zero slip of the torque converter. When the torque converter returns to normal ECCC mode with 30 RPM of slip, the noise will go away. The disturbance generated by the zero slip condition is amplified and transferred into the passenger compartment by the rear coil springs.

Replace the rear coil springs using the following service procedure.

Notice: Use care when handling the coil springs in order to avoid chipping or scratching the coating. Damage to the coating will result in premature failure of the coil springs.

1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information in the Service Manual (SI Document ID #744862).
2. Support the front frame rail of the vehicle with a suitable adjustable jack stand.
3. Support the rear axle with a suitable adjustable jackstand.
4. Remove the two shock absorber lower mounting bolts.
5. Lower the rear axle enough to remove the tension on the rear coil springs.
6. Remove the rear coil springs.

Important: 

•	It is critical that the correct coil springs are installed in the correct location.

•	The LH and RH springs are not necessarily the same part numbers.

•	Each vehicle may have a different build combination.

•	Use the RPO label located in the glove box to determine what part number springs to replace.

•	Only small quantity of parts are available. Please DO NOT order for stock only.

7. Select the correct new rear coil spring part numbers. Refer to the Parts Information below.
8. Install the upper bushing seats on the new rear coil springs and install the springs into the vehicle.
9. Raise the rear axle with the adjustable jack stand.
10. Install the two shock absorber lower mounting bolts.

Tighten
Tighten the two shock absorber lower mounting bolts to 80 N·m (59 lb ft).

11. Remove both of the adjustable jack stands from under the vehicle.
12. Lower the vehicle.

Important: Only small quantity of parts are available. Please DO NOT order for stock only.

Parts are currently available from GMSPO.

For vehicles repaired under warranty, use: