Subject: | Cab Vibration/Boom Noise at Highway Speeds (Replace Transfer Case Mounts/Shims/Spacers and Install New Rear Axle Spacer) |
Models: | 2005 Chevrolet Kodiak C4500/C5500 Series |
| 2005 GMC TopKick C4500/C5500 Series |
| with Four-Wheel Drive (4WD) ONLY and 152" Wheelbase (RPO EG9) |
This bulletin is being revised to change the mount assembly part number. Please discard Corporate Bulletin Number 06-04-21-003A (Section 04 - Driveline/Axle).
Condition
Some of the above listed vehicles may exhibit a driveline boom/vibration between 80-96 km/h (50-60 mph). The condition is most noticeable on bare chassis (incomplete) vehicles or vehicles with light curb weight.
Cause
The working angles of the rear driveline may be causing this condition.
Correction
A new driveline design has been developed that decreases the working angles of the rear driveline.
The following procedures should be performed to achieve the desired results and correct the condition. Refer to the service procedures and the parts information below. Refer to the applicable SI procedures removal/installation of transfer case/rear axle
components.
• | Install shims under the transfer case mounts in order to lower and rotate the transfer case. |
• | Install axle shims in order to reduce the rear pinion angle. If not installed at the plant, replace the 8.1 degree axle shim with a 6.1 degree shim. |
• | Install the appropriate new rear spring spacers (depending on the rear suspension RPO) in order to slightly lower the rear of the chassis. |
• | Replace the transfer case rubber mounts with revised parts. |
Transfer Case Front Mount Replacement
Replace the front transfer case mount with a new, stiffer mount. Reuse the original bolt and replace the upper washer with a new washer. Retain the original washer for use later in this procedure. No spacer needs to be added at this position.
Transfer Case Rear and Side Mount Replacement