Allison Transmission leaking between body and extension housing - Chevy and GMC Duramax Diesel Forum
01-04.5 LB7 Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

 
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post #1 of 9 (permalink) Old 05-17-2019, 09:42 PM Thread Starter
 
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Allison Transmission leaking between body and extension housing

Ive got an 03 2500HD with the 8.1/Allison. I believe the Allison should be more or less identical to the one that is in the Duramax trucks of the same year, so that is why i came here to ask my question.

So last weekend we drove 2.5hr towing a trailer with 2 ATVs and a Can Am SxS and when we got there the drivers side of the pickup had oil splashed all down the side and the trailer was starting to get some oil on it as well. The engine and trans oil were both at the full mark, so i assumed it was the transfer case. After i got back home and put the truck up on the lift most of the oil looks like it is coming from the gasket between the transmission and extension housing. the Transfer case is more or less completely dry. I have done some reading and found that to change this gasket it is best to pull the entire transmission and set it on its end to keep all the guts in. SO my question is, how likely is it that that gasket is leaking? Seems like an odd place to be leaking all of the sudden. I have read that is is more likely that the housing is cracked but i cannot see a crack anywhere on it. Up until now this truck has never leaked a drop, its only got about 110k miles.

What would you guys recommend doing? The oil is definitely coming from the back of the transmission, i just hate to go through all of this work to find out there is some simple common spot that they all leak from. My first thought was the dreaded transfer case pump rub, but like i said earlier its bone dry.

Thanks in advance.
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post #2 of 9 (permalink) Old 05-17-2019, 11:28 PM
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Sure it's not pump rub. Also the extension housing cracking is common with bad u-joints

2005 Silverado 2500, Crew Cab Short Bed. 122,000 miles
MODS: AFE intake, LBZ mouth piece, MBRP cat- less exhaust.
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post #3 of 9 (permalink) Old 05-18-2019, 07:16 AM Thread Starter
 
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Originally Posted by DailyDmax View Post
Sure it's not pump rub. Also the extension housing cracking is common with bad u-joints
im almost 100% certain it isnt the transfer case, its almost completely dry, the bottom part of the extension housing is what is wet. I checked all of my ujoints and they are all nice and tight.
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post #4 of 9 (permalink) Old 05-18-2019, 08:28 AM
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I'm not sure then. Hopefully someone else will chime in to assist

2005 Silverado 2500, Crew Cab Short Bed. 122,000 miles
MODS: AFE intake, LBZ mouth piece, MBRP cat- less exhaust.
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post #5 of 9 (permalink) Old 05-18-2019, 10:46 AM Thread Starter
 
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Is it possible for it to be leaking out of the electrical connectors on the pass side in that little valve body piece? I know it sounds weird but that is almost where it looks like most of the oil is coming from. And I cant for the life of me get the connectors unplugged.
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post #6 of 9 (permalink) Old 05-18-2019, 10:50 AM Thread Starter
 
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Originally Posted by nitrosport_5 View Post
Is it possible for it to be leaking out of the electrical connectors on the pass side in that little valve body piece? I know it sounds weird but that is almost where it looks like most of the oil is coming from. And I cant for the life of me get the connectors unplugged.

Sorry driver side electrical plugs. Not sure how to edit my last post on mobile.
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post #7 of 9 (permalink) Old 05-18-2019, 08:26 PM
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Are you saying your transfer case is not low on fluid, or is it still full and dry?
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post #8 of 9 (permalink) Old 05-18-2019, 08:31 PM Thread Starter
 
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Are you saying your transfer case is not low on fluid, or is it still full and dry?
I drained the transfer case and it had just under 2qt of oil. So it was full and more or less dry. It was a little wet around the front driveshaft, but most was under the extension housing.
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post #9 of 9 (permalink) Old 05-20-2019, 02:55 AM
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If its too difficult to detect the origin of the leak, try using dye, at one part at a time. If you think its the transmission, add the dye to it first. Run it for a day or two. If the dye does not show a leak point, then add the dye to the transfer case, and check it for leaks.

Transmission fluid is red in color; transfer case is a different color oil, unless you are using something different.

2003 2500HD 6.6 duramax (LB7) all stock (no mods)
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