Allison Transmission Slipping

07sierra8.1 · January 27, 2013

Hello,

I got a 2007 Sierra 2500HD "Classic" with an 8.1/Allison in it. Truck has 110K on it.... When the temps outside are around 20 degrees or below and the truck has sat over night, when I first start it and put it in drive, it wont move...it will sit and slip the transmission(or at least thats what it feels like) till about 3500 RPM then the truck will start to move. However if I let the truck sit and idle and warm up..its fine. Its not throwing any codes, Fluid is filled, does not smell or look burnt.

I know the allisons used to have trouble with the torque converter leaking down and GM had a service bulletin out about it. My dealer ensures me though that they had the problem corrected by 2007 and that there is no way that could be whats wrong in my situation, yet it was a $150-$200 diagnostic fee to look at it.

I wanted to get some other opinions first before I dumped hundreds of dollars into a dealer to find out it might be a simple fix.

oldscsc · January 27, 2013

How long does it have to idle before it drives fine?

Carder09 · January 27, 2013

Have you tried putting it in third or second gear to see if it would go?

07sierra8.1 · January 27, 2013

@oldscsc- Idles for about 10-15 minutes before its fine......

@carder- I dont have an option to put it in third, all i have it P-R-N-D-M-1 But I have pulled it down to "M" & "1" with no difference

gmtech4 · January 28, 2013

a scanner will see the input speed data to show the the TC fail

take it in ,...no guessing

yukon25008.1 · January 28, 2013

my ally is at 110,000 also and even at 9 degrees the other morning after 2-3 mins of idling/warmup It worked and shifted flawlessly..

The cold will cause the tranny to do funny things but youve got something else going on, Like govtech said have it really looked into to see whats going on inside..

@oldscsc- Idles for about 10-15 minutes before its fine......

@carder- I dont have an option to put it in third, all i have it P-R-N-D-M-1 But I have pulled it down to "M" & "1" with no difference

Where in strdsbrg are you?

07sierra8.1 · January 28, 2013

I live off of Chipperfield Dr.

Doug_Scott · January 29, 2013

Generally when a trans is slow to engage when cold it is a clutch pack or servo seal leaking. Torque convertor does not use a seal or mechanical connection from a stop, so it is very unlikely that. Once fluid warms up, seal softens, and starts to seal again. Does not take much in the way of warming up either. Does reverse work? Not sure about Allisons, but, old Chrysler Torqueflites ran double line pressure in reverse, and that would work when a seal was on its way out, yet that same seal would fail in drive, causing a flare-up on the shift into high gear when seal was bad.

gmtech4 · January 29, 2013

if it honestly slipped ,there would be a gear ratio code in about,,,,2 seconds

07sierra8.1 · February 15, 2013

Like I said the truck is at 110K...Not sure when or IF the fluid was ever changed...in about a month I have to haul my Father's race car down to Maryland on a trailer towed by said Truck...and will be hauling back on the trailer my 86 K20....Lately the transmission Has not done any of its slipping fits, but I have noticed that when cold..it seems to shift real hard..kinda feels like it slams into gear....or sometimes it waits to shift till I slightly let off the gas

I was thinking of changing the fluid, External spin on Filter and even the internal filter...replacing fluid with Allison's Transynd fluid.

Do you think it would be worth doing this to see if it corrects problem or is it just a waste of time and money?