| Subject: | Allison LCT1000 Clunk Noise Shifting into Park or On Start Up In Park |
| Models: | 2003-2007 Chevrolet Kodiak C4500, C5500 |
| 2001-2007 Chevrolet Silverado Classic |
| 2001-2007 GMC Sierra Classic |
| 2003-2007 GMC TopKick C4500, C5500 |
| Equipped with a Allison Lct1000 Transmission |
This PI is being superseded to update model list. Please discard PIP3161A.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:
Some trucks equipped with the Allison LCT1000 transmission may experience a clunk type noise on start up with the vehicle in park. Some trucks may also experience a clunk noise when shifting into park from reverse or a drive range. The condition may be
intermittent.
The noise is a result of internal transmission clutch drag which is sufficient enough to load the output planetary carrier. The resultant load on the output planetary carrier can result in park pawl gear tooth impact against the park pawl and cause the
clunk noise. The magnitude of the noise is dependent on the position of the park pawl gear relative to the park pawl
Recommendation/Instructions:
This condition is considered to be an operating characteristic of the Allison LCT1000 transmission. Repairs or replacement of the transmission will not correct this condition.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
