Leak started about a month ago. A few weeks ago, I pulled it out and resealed the two halfs with RTV. It was still leaking, so I pulled it again thinking it was one of the seals. Just got it out and I don't see ANY fluid on the seals. Hard to tell if it is leaking between the two cases or out the top vent.

I lost about 1.2 qts in 8-9 days. It was sprayed all over the bottom of the truck towards the back, so it is mainly leaking while moving. 4wd works fine. No noises. Drained the rest of the fluid and no metal shavings. When I pulled it apart last time, it all looked good.

The center drive shaft support bearing is toast, so I was thinking the vibration caused a leak on the rear seal, but it is dry. I plan on replacing the bearing anyway.

I bought all new seals, but I doubt that fixes it.

My guess is that it is blowing out the top vent, but why??

ideas? I did a search and didn't find anything like this.

edit:
Looks like most of the fluid is coming from here (on top of the case). Could that just need replacing?

 

Two questions.
1> How much fluid are you putting in it? Approximately.

2> Is this a hole?

 

Could be that plug... but fairly common for the pump clip to fail and rub a hole in the case.

 

^^^^^what he said^^^^^
Also if the driveshaft was moving all over the place it could have worn the output shaft bushing enough that even with a new seal the drive line yoke wont seal... how many miles on it?

 

Looks like pump rub to me. Just put the Kennedy Diesel pump rub fix plate in the transfer case on my dads 02 duramax. It wasn't leaking but had some pretty hard rubbing going on and the clip was broken. Shouldn't ever be an issue now. I need to get one put in my 99 Z71 sometime. Stupid crap like this really makes me appreciate my 2wd 95.

 

pumped fluid till it was level with the fill hole.

that is not a hole, just dirt.

200k miles on it.

The shaft vibration wasn't all that bad, but who knows.

I'll search for the Kennedy fix plate

 

Thats a problem with a few of the NP/NV transfer cases. It takes one good bump and the clip holding the pump in slips. This allows the pump to rub on the case, and it eventually rubs a hole through the case. From what I remember it usually happens on the top of the case, you can't see the hole, and it only leaks when fluid is moving through the T-case. You will need a new case half, or you can weld it up, and look for those new clips.

A bunch of diesel guys figured this out a few years ago and where trying to get it covered under warranty/defective part. But GM wouldn't do anything so one of them made the new clips to fix the problem.

 

Well, ya'll are pretty good. You nailed it. After more cleaning, I found the hole. I'm going to search more to see if there are any others. I'm sure TIG is preferred, but will a MIG work on magnesium? I just need a temporary fix until I can order the Kennedy piece and new half case. (edit: never mind, every corner is worn thin. I'm just going to find a new half case.)

Here is another write up on the issue.
http://www.thedieselpage.com/reviews/tcase.htm

And here is the Kennedy fix (transfer case tab)
http://www.kennedydiesel.com/

hole