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Cab Vibration/Boom Noise at Highway Speeds (Replace Transfer Case Mounts/Shims/Spacers and Install New Rear Axle Spacer)

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


Object Number: 1829836  Size: SH

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

 


Object Number: 1829827  Size: SH
(1)3 New Washers
(2)2 Original Washers
  • Replace the rear and side transfer case mounts with new, stiffer mounts.

  • Install three new washers under the rear mount (totals approximately 12 mm). Also, use one of the new washers and a new bolt as the upper mount washer (save original washer to use for side mount spacer).

  • Replace the bolt with a new bolt and reuse the washer. Use the two previously removed washers from the vehicle as the new side transfer case mount spacers (total approximately 10 mm).

    Important: Assure that the mounts do not have gaps and the internal sleeve is not bound up in the hole in the mount bracket.

  • Rear Axle Spacer Installation

     


      Object Number: 1829842  Size: MH
    1. Install a new rear axle spacer. The height of the spacer depends on the suspension RPO code.
    2. Assure that the U-bolts have the proper amount of thread. Add a spacer under the U-bolt if necessary.

      • GR4 suspension -- Replace the 120 mm spacer with a 100 mm spacer.
      • GQ2 suspension -- Replace the 100 mm spacer with an 85 mm spacer.
    3. Verify if the new 6.1 degree shims are installed on the vehicle. Original equipment shim on the 152" wheelbase 4x4 vehicle was 8.1 degrees. If not, install 6.1 degree axle shims (1).
    4. Each shim has two part numbers on it. The first number is cast into the shim, which is the casting number. The second number, printed or stamped on the flat side of the shim, is the part number.

    Parts Information

    Part Number

    Description

    Qty

    14048990

    Bolt, Transfer Case

    2

    11519000

    Washer (Shim), Flat - Transfer Case

    5

    15892088

    Mount Asm-Transfer Case Side

    3

    15144874

    (Axle RPO GR4)

    Spacer, Axle (100 mm)

    2

    15862326

    (Axle RPO GQ2)

    Spacer, Axle (85 mm)

    2

    15640807

    Spring Seat (6.1 Degree Shim)

    2

    Warranty Information

    For vehicles repaired under warranty, use:

    Labor Operation

    Description

    Labor Time

    *F9705

    Replace Transfer Case Mounts and Install Rear Axle Spacers

    4.3 hrs

    *This labor operation number is for bulletin use only. This number will not be published in the Labor Time Guide.