Allison tranny problem??

[steelman82]

I have an '04 Duramax w/Allison 4x4. When changing from D to R, there's a pretty significant clunk noise, seems to come from where the driveshaft meets the tranny. Almost like the driveshaft is super-torqued. It also does it going back to D from R, even if I pause in N between gears.

 

Also, when tranny is up to optimum temp (140+), it seems to shift hard from 3rd to 4th. It's smooth as ever when it's "cool" though. It gets pretty bad when I have the boat behind me.

 

Last concern is, when putting the truck in park, there's a loud popping sound that comes from the trans pan (I can feel it if I put my hand on the pan while I'm underneath). The sound is just like smacking the pan with a brass mallet, but when I took the pan off to change fluid, I could tell where any linkage would've been hitting the pan.

 

I have talked to service tech about all 3 problems. The first problem was supposed to have been taken care of with the installation of a "nickel plated yoke". Didn't have any effect. Dealer says not to worry about any of these because they are normal, but I don't think so. I have two friends who have the same eng/trans & neither have any of these three issues (one has '01, one has '05). Could these issues be related?

 

Any info would help.

[ChevyTech007]

I would say your dealer is correct. They should have given you a copy of this bulletin to ease you mind. I can understand you concern but just let it ride.

 

Subject: Allison LCT1000 Clunk Noise on Start in Park - kw automatic clutch GMT800 hard intermittent internal knock PQC #PIP3161 - (09/27/2004)

 

 

 

Models: .

 

 

 

 

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The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

 

Condition/Concern:

Some 01-05 GMT800 trucks equipped with the Allison LCT1000 transmission may experience a clunk type noise on start up with the vehicle in park. 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 diagnosis 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. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

 

Models:

(01-05 Chevrolet Silverado) and (01-05 GMC Sierra)

 

.

[steelman82]

I would say your dealer is correct. They should have given you a copy of this bulletin to ease you mind. I can understand you concern but just let it ride. 

 

Subject: Allison LCT1000 Clunk Noise on Start in Park - kw automatic clutch GMT800 hard intermittent internal knock PQC #PIP3161 - (09/27/2004)

 

 

 

Models: .

 

 

 

 

--------------------------------------------------------------------------------

 

The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

 

Condition/Concern:

Some 01-05 GMT800 trucks equipped with the Allison LCT1000 transmission may experience a clunk type noise on start up with the vehicle in park. 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 diagnosis 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. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

 

Models:

(01-05 Chevrolet Silverado) and (01-05 GMC Sierra)

 

.

 

<{POST_SNAPBACK}>

 

 

 

I REALLY appreciate the quick response, and I guess that will put my mind at ease hearing it from a THIRD tech, but what about the hard shift from 3-4?

[ChevyTech007]

Did they check for update programs for TCM? I know there are several.

[steelman82]

Did they check for update programs for TCM? I know there are several.

 

<{POST_SNAPBACK}>

 

 

 

Nope. The only thing that ever happened was after they told me nothing was wrong, I insisted that the tech that checked it come for a ride with me. Both told me "all clear, dude". I even mentioned a reprogram or flash of the TCM, but they said since nothing was wrong, it wouldn't help.

 

Should I ask specifically for an update of the TCM program?

 

By the way, I really appreciate your quick responses.