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Allison Leaking at shift linkage/nsbu

45956 Views 31 Replies 17 Participants Last post by  LBZ-MAX
Went on a long drive today, up a mountain pass over and back. On the way back my trans temp got up to 200*F. Which I thought was odd.
When I finally got home I noticed that there was oil under the drivers side. Upon further inspection it was coming from the tranny. I've noticed a sound coming from it upon start up.(sounds like a light metal sound) But goes away after warm up. Not sure if its related or not.
Inspecting the tranny it looks like its coming from around the shift linkage/NSBU switch. I thought it was coming out of the breather on top but when I looked it doesn't have that clean look,Like when oil is leaking out some where and cleans all the dirt off. But the Shift linkage/NSBU area does have that clean look.
I will attach some pictures.
I've circled the breather in one picture and the NSBU switch in another. Notice how much oil and how clean that area is.
Any help would be Appreciated.
Also I checked my tranny level and it seemes fine. I just checked it a couple days ago and it was good then too. I have't changed it or filled it in along time. So I don't think it was because it was overfull.
Sorry so long. Thanks again.


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I know, I haven't either. Usually if the tranny is overfilled it will come out the breather.
And any other tranny leaks that are common are from the tailshaft or I've read some threads where it is coming from the front seal of the tranny.
I thought I'd ask around here first and see if anyone has any ideas.
I'm probably just gonna have to take it to a shop.
I have had that exact thing happen, there is a seal between the trans. and the tranfer case that goes bad..(there is a bulletn from GM about it) what happens is the fluid from the tranny overfills the transfercase and it will come out of the breather for the transfer case. I did not want to do the job so i had ammco do it and it cost about 400.00 for everything... hasent leaked since :)
I know, I haven't either. Usually if the tranny is overfilled it will come out the breather.
That also can happen if the vent is plugged..
Thanks for the replies guys.

daddysLBZ-You have a good point.

When I was looking under the truck and taking pictures. It looked to me like the oil came from the pan gasket. At the area I circled in red in one of the pictures. And not the breather. Just because it is so clean in that area. All that fluid coming out cleaned it. When I look up at the breather, indeed there is fluid all around it doesn't look as though a large amount came streaming down and cleaned all the dirt away. (Hope this makes sense).

D2ka4-I did have a leak between the transfer case and tranny before. Had a machanic fix it.

Anyone know how or if I can remove the breather and check it.(It looks like a PITA to get to.)
Thanks again fellas
have you found the problem aaronslb7? Mine just did the same thing this weekend pulling vantage grade
Where exactly is your fluid level. From the pictures it looks like it's coming down from the top. There is a linkage seal behind the NSBU switch which will leak if it gets old or if it's over full. It will only leak after truck is shut off and it sits for a while. Your fluid level must not be over half way up the hot grid on the dipstick, otherwise it will blow out the vent. If the vent on top of case is plugged, fluid will blow out the filler tube on passenger side.
when i noticed it leaking Ichecked the level and found it in the middle of the hot grid. My trans temp had gotten up to about 230(it usaualy runs 190-210 on my 8.1l). I had my dad tow my trailer home and drove the last 100 miles empty with no problems and the temp only reached 175.
Keith2001, No I haven't found the problem yet. It only happened that one time. I was going over White Pass between Colville and Republic. I didn't have a load on either.
You said you were going up vantage pass. Same vantage pass in washington?
I had checked my fluid before it happened and after and the level was in the right range. I still check it occationally and still checks out fine.
I thought that it did come from the breather but when I look it over really good there really wasn't any oil that had come from there. I looked more like it came from between the pan gasket and transmission.
I just looked at my pictures again and there is some oil from the breather. But I would have thought there would be alot more from the breather area. Considering how much was around the bottom by the nsbu switch. I also thought maybe the oil shot out between the pan and transmission and the front drive line slung the oil making it look like it may have come from the breather. But I can't remember if the front drive line turns constantly.
thanks for the response and yes the same vantage grade I am from western wa. I will be looking in to this more tomorrow when I can get the truck on the lift
Fluid cannot shoot out from the pan area as there is no pressure there. In hot climates the fluid in the pan should even be lower than half way up the hot grid. I would have it at the bottom of the hot grid. If you have a deep pan, all bets are off as you will not get an accurate fluid reading. In this case keep letting fluid out till it stops.
Thanks Mike, probly the breather or that leakage area then. When I get home from Alaska this weekend I'm going to clean everything really good. Then I'll just keep watching to see where it comes from.
Kieth let us know what you find out.
after an hour of looking and an entire can of brake clean to get the fluid off the underside of the truck we found no smoking gun. My mechanic says to keep driving and checking he thinks that it came from the breather and may have been overfull before. But after pulling a 8000 pound trailer up a 10 mile long hill at 3000 rpm with 30-40 mile an hour head wind the entire way I think that it just got hot and built pressure, then released through the vent
What was the fix?

I am leaking in the same place?

Incase of overfill where would it come out on tcase?
no fix yet put another 350 miles on with the trailer climbed the same pass and this time didn't push so hard and had no problems temp never got over 200 on a 90 degree day. I have been checking the fluid levels everything is staying clean and dry. Not sure where the vent is on the t-case but the tranny and t-case have seperate fluids
Well I have a 02 GMC that leaking in the same area. It looks to be at the electric connection into the trans to me. It started as a drip at about 190K and has gotten worse from there.
Well I have a 02 GMC that leaking in the same area. It looks to be at the electric connection into the trans to me. It started as a drip at about 190K and has gotten worse from there.
You will need an internal wiring harness to fix this.
after my initial problem I have had no more leaks, everything is staying clean annd dry. However I have noticed that my tranny temp seems to stay at 190 towing my trailer and has climbed to 210 with the a/c on towing.
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