Envoy 2WD V8-5.3L VIN P (2004)
Suspension Spring ( Coil / Leaf ): Customer Interest
Suspension - Boom/Rumble Heard at Highway Speeds
Bulletin No.: 02-03-09-002C
Date: December 06, 2004
TECHNICAL
Subject:
Intermittent Boom, Rumbling Noise and/or Disturbance Heard in Passenger Compartment While Driving at Highway Speeds (Replace Rear Coil
Springs)
Models:
2002-2005 Chevrolet TrailBlazer
2002-2005 GMC Envoy with Rear Coil Springs
2003-2004 Oldsmobile Bravada with Rear Coil Springs
Built Prior to August 23, 2004
(Refer to Parts Information table below for applicable RPO Code usage)
Attention:
Do not perform this bulletin for vehicles built after 8/23/04.
Supercede:
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).
Condition
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).
Cause
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.
Correction
Replace the rear coil springs using the following service procedure.
Note:
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.
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.
