A/T/Suspension - Intermittent Rumbling/Booming Noise
TSB SB05-06-S001Intermittent Boom, Rumbling Noise
and/or Disturbance Heard in Passenger
Compartment While Driving at Highway
Speeds
Light Duty ASCENDER 2003 Bulletin SUSPENSION 02/01/05
Light Duty ASCENDER 2004 Bulletin SUSPENSION 02/01/05
Light Duty ASCENDER 2005 Bulletin SUSPENSION 02/01/05
ISSUE DATE: FEBRUARY 2005
Affected Vehicles
2003-2005 Isuzu Ascender (UT)
Do not perform this bulletin for vehicles built after 8/23/04.
Service Information
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 52-54 mph (83-86 km/h) with a 3.73 axle ratio (RPO GT4) or 58-60 mph (93-96 km/h) with a 3.42 axle ratio (RPO GU6).
Possible 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 Electronically Controlled Capacity Clutch (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.
Service Procedure
Note:
Use care when handling coil springs to avoid chipping or scratching the coating Damage to the coating will result in premature failure of the coil springs.
1. Raise and support vehicle. Refer to Lifting and Jacking the Vehicle in General Information in the Service Manual.
2. Support front frame rail of the vehicle with a suitable adjustable jack stand.
3. Support rear axle with a suitable adjustable jack stand.
4. Remove the two shock absorber lower mounting bolts.
5. Lower rear axle enough to remove tension on the rear coil springs.
6. Remove 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 a small quantity of parts is 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 rear axle with the adjustable jack stand.
10. Install the two shock absorber lower mounting bolts. Tighten the two shock absorber lower mounting bolts to 80 N~m (59 lb ft).
11. Remove both adjustable jack stands from under the vehicle.
12. Lower vehicle.
Parts Information
Important:
Only a small quantity of parts is available. Please DO NOT order for stock only.
Warranty Claim Information
Use the labor operation shown.
Disclaimer