Allison tranny problem??

steelman82 · April 2, 2006

I have an '04 Duramax w/Allison 4x4. When changing from D to R, there's a loud popping 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.

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.)

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.

noobie1 · April 2, 2006

I have an '04 Duramax w/Allison 4x4. When changing from D to R, there's a loud popping 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.

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.)

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.

<{POST_SNAPBACK}>

steelman; I'm not sure what you mean by "popping". Mine, 2002, has had harsh shifting ("Clunking") after warmup since new when shifting with the lever while stopped. I took it in under warranty and they reprogrammed the TCM which did no good at all. You can go onto the Allison site and get info about the 1000. And if I remember correctly they do mention harsh shifting being "normal". Imagine that.

Also, mine makes a very loud, metalic "Clank" when shifting from D to P. I've found a way around it though. Just pause in R and let it backup an inch bfore going into P. Works every time. What's got me worried is the noise described below, "Allison Knock". It sounds like this: $$$$$$$$!

HA!

-David

steelman82 · April 3, 2006

OK, I guess the D to R and R to D problem would be classified more as a clunk than a pop.

As for going from D to P, hit the tranny pan with a brass mallet (pretty hard), and that's exactly what it sounds like. I have noticed that if I go from D to R (pause) to P, that it doesn't do it, but I wasn't sure if that was any better for it considering the clunk from D to R!

Good to know somebody else is having the same problem & was told not to worry about it, but GM-Tech here seems to really know his stuff, so I hope to get a reply from him.

Thanks!

steelman82 · April 7, 2006

OK, I guess the D to R and R to D problem would be classified more as a clunk than a pop.

As for going from D to P, hit the tranny pan with a brass mallet (pretty hard), and that's exactly what it sounds like. I have noticed that if I go from D to R (pause) to P, that it doesn't do it, but I wasn't sure if that was any better for it considering the clunk from D to R!

Good to know somebody else is having the same problem & was told not to worry about it, but GM-Tech here seems to really know his stuff, so I hope to get a reply from him.

Thanks!

<{POST_SNAPBACK}>

Any techs out there that can offer any advice? Maybe one of the shift solenoids? Do you think a trans flush or fluid change would help?

ChevyTech007 · April 7, 2006

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)