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Trans fluid low, T case overfilled


The dude abides
Jun 8, 2020
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I got an S10 with a 4L60E and NP231 Tcase. Trans fluid got low. Topped it up. Couple weeks later, fluid is low again. No external leaks on trans. Then noticed the transfer case appears to be seeping. Opened the fill plug and it was overfilled by 2 qts.

So the fluid is leaking from the trans into the tcase. I googled and read something about the rear output seal on the trans being the culprit. So I ordered up the seal at my local parts store, going to pull the t case this weekend and take a look.

besides removing the transfer case, is there any other disasembly reqd on the trans? Or can the seal be removed easily once the case is pulled? Are there any other seals that should be changed out during the repair?
Recent work on either ?

Bad seal at adapter is my guess.
I didnt think 4l60/65 had rear output seals in 4x versions.

They are open assholes and require a sealed gasket at the adapter. But then again s10 have different bolt patterns and adapters.

Tcase input seal or input pilot bearing worn through the shield.
We put a slip yoke eliminator in a few years back. It has been good until we discovered this leak. I pulled the transfer case this morning. I think you are right on the no output seal on trans, I looked in there and dont see anything resembling a seal on that shaft and that open cavity looks like it fills up full of fluid. There is some play on the shaft, I can wiggle it up and down a little... normal??

the input seal on the t case looks intact but the rubber is kind of stiff. Popped the seal off and went to local parts store. The timken part they had looks like it could work but only had a single lip. The seal I removed would double lipped and was twice as tall. Not sure if that seal I pulled came with the kit I got when we did the SYE or if the timken part is wong....


Do you think there is a seal between the adapter and trans? That extension has 4 bolts, looks like it comes off. I have never taken that part off....
So the only other thing sealing between the cases is the silicone on that flange on the front of the t case. I figured I would just pop that cover off and re seal it but 2 of the bolts will not budge and are going to round out. I would likely have to drill out the heads and extract them...

Eff it and leave it, or get that cover off and re silicone and find new bolts? Where can I get new bolts for that cover if I go that route?
Found this place that sells the seal, bearings, etc. Emailed a Q about the bolts for that cover, I may be SOL on the bolts so that plate is stayin in place. Needed a couple u joint straps anyway so ordered up the double lipped seal.

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