Allison LCT1000 Clunk Noise Shifting Into Park Or On Start Up In Park - keywords drive shift park

This PI was superseded to update model years. Please discard PIP3161B.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

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.

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.