oil leak

[Woody1]

Any of you guys that work on the Allison tranny may be able to help me here I hope. I have an 01 GMC HD crew cab with 8.1/Ally trans 4 x 4. 78,000 miles. I took it into dealer a few days ago to have the tranny fluid/filter changed. Mechanic came out- (is only one mechanic at dealer I let work on it) , said my tranny fluid was high to begin with, and he had to add a little over 1 quart to the transfer case. Says I probably have a leak in the "shared" seal between the two. Said it would cost 4-600.00 to fix it. I didnt have that sort of $$$ right then, so have driven it around a bit. I have oil leak under truck on cross members and under the truck now. ( I had the same thing last february, took it in to them to find out where leak was from and they couldnt find one then.) At that time-last feb., me and a friend had just changed all fluids in D.train, so everything was full again at that time. Anyway, he says it is a shared seal between the two.

Question is, how/why does/did this seal go out, and is this a common thing to happen? This is the 2nd trans in the truck.....1st replaced by previous owner due to shimmy in truck at take-off that come to find out, had nothing to do with the tranny----- changed driveshaft to fix it under my possession. Could the dealer have screwed up the seal at 16k miles when it was replaced? Not that it makes any difference at this point, cause it still needs to be replaced. Is this an easy job? I took it to the Detroit/Allison dealer in town to see if they had a better idea. I have an appointment with them on Friday for them to fix it. Will it cost more for Detroit dealer to fix? or the dealer to fix? D/A dealer says if its the transfer case seal, its the dealers, if its the Allison seal, its theirs to fix. Either way, I pay. Just wondering which is best way to go.

[bigdogs]

I have heard of that seal going out before. On a Blazer I had the seal in the TH400 went out and would leak tranny fluid into the NP20transfer case and would cause that to overfill...

[chevroletmb]

the seal your referring to is on the input shaft of the t-case

i doubt the allison place would have the proper seal driver to

install the new one. i'd recommend the dealer doing it.