oddly enough other than the atf leakage, which happened only while towing, I had no signs of damage or problems with the tcase. No growling, no whining, no vibration, nothing. I found all this totally by chance.

 

You'll get no chunks of RTV when draining the tcase. You'll only find them when you split it open. If your driveshaft yoke is at all scarred or scratched up, then you likely have some oil starvation issues like mine.

BTW my denali has just shy of 120k on it.

 

Mine is an 03 and at 80k, so time for a fluid change. I did the tranny fluid and filter at 60k. So transfer case and axles are next on the fluid change list. Dealer here charges $13 a quart for the axle fluid. No telling what they will charge me for the T-case fluid.

 

BTW, pretty sure that my truck originally came with a red t-case fluid in it, but the dealer flushed and replaced it with the AutoTrakII fluid under warranty in one of their attempts to get rid of my driveline clunk...

 

Here's the printout the dude at the dealership gave me. He says my denali's nvg np149 transfer case is RPO option code NP3, I've confirmed this elsewhere on the internet. You can see it listed here, calling for this red manual trans/transfer case fluid.




Then here in my 02 GM Factory Service Manual for my truck,



for the nvg np149 tcase it clearly specifies the autotrak II blue fluid. This is what I wound up using, mostly because I already purchased it.

 

UPDATE TIME:

After much parts ordering and some custom work, I've gone through the tcase and got it "rebuilt" and back in the truck working properly so far.

I took my driveshaft with the bad front yoke, to the driveshaft shop. I had them install a new yoke and also install my new u-joints. I could have done it myself but it was easier to let them do it for me for basically free. IT was nice because they had the yoke on the shelf ready to install. The dude said the vibration damper didn't matter, and that theirs usually balance better than the stock ones did to begin with anyway. Cost $100 plus the joints (about $30).




I cleaned up my front half case and taped it for powdercoating. Hey, I can do it in house, it's free, why the heck not, right? Also did the "adapter" between the trans and transfer case. There is still one shaft in the front case because there was not really any reason to take it out.






Here they are coated in gloss black.






While this was going on, I tried to hunt down a modified oil pump body to combat the pump rub. The only company I found that makes one was sold out for a while. I took pictures of that design along with my original pump body and rear tcase half to my welder. We decided to weld some aluminum tabs onto the pump body to mimic the upgraded design. This spreads the load on the case so the pump doesnt cut into it like a knife.

The welder wasn't able to do anything on the case itself...apparently the magnesium is hard to weld even for pros, and most people lack the experience or rods needed to do it, so they won't even try. I wound up using jb weld (the stick putty metallic type that is easy to work with and form) to fill in the holes in the inside of the case, and to patch over the hole and weak areas outside the case. Even though I only had one hole through the outside of the case (out of the 4 weak/cut points) I patched over all of them just in case.






Here's what we came up with on the oil pump body.

 

Since the welder had to have the oil pump body and the rear tcase half that it fits into in order to test fit it, I had to wait until later to clean and powdercoat the rear half.






Here's where I filled in the rubbed areas inside the rear tcase half, where the pump body cut into it.






Heres all the parts ready for assembly. There is a double lipped oil seal on the front input shaft of the tcase. ATF from the trans kind of sits in that "adapter" and could find it's way into the tcase, or the tcase fluid could find its way into the trans, if this seal went bad. I bought a new one, about 35 bucks. There's of course the rear output seal where the driveshaft comes in, and that one cost about $25. The new bushing for the driveshaft yoke in the tailshaft was about $7.50. I had to make a custom "tool" to help press the old one out and the new one in. I also got a new gasket and o-ring which go between the trans and adapter, and adapter and tcase, because atf does come out of the back of the trans and "sit" in this adapter...for reasons unknown to me.



Cleaned that damned oil pickup out.

 

Now this bad SOB right here is the front driveshaft output seal for the tcase. List on it is like 70 bucks at GM, I got it for about 55.




This thing is a NIGHTMARE to remove (if you are leaving that shaft/gear set in place). I spent a good 45 minutes with lots of various prying tools and screwdrivers, etc. trying to get it out without damaging the case and/or shaft. The reason its so bad is because it is a double seal...two metal seals together. One metal seal seats against the outer case hole, and the other seal press fits onto the shaft. The inner one is what causes the problem getting it off (and on).

By the time I got the old one off I KNEW there was a good chance I would f**k up the new $55 seal trying to install it like a regular single oil seal. The GM manual shows a special service tool for installing it, with two round surfaces meant to seat against each metal lip and force them into place without harming or bending the rest of the soft sealing surfaces.

When the new seal came in I took that half of the tcase to the dealer with me and asked the service guy if they could press it in for me. Well, they couldn't find that specific tool ANYWHERE in the service department for about 30 minutes. I went to the next closest dealer. They claimed not to have the tool either, they said that most GM dealerships don't have the tool and don't use it. The guy there said he always "just lubes it up with vaseline real good and taps it in with a hammer and never has a problem". Okay, cool. So I go home and try it, and almost immediately I can see its not going to work well because even with the rubber mallet, I bent a little of the softer metal area that has a sealing lip on it. I was lucky to be able to take the seal halves apart and bend the affected part back flat gently. While the halves were apart I test fit each half onto the case/shaft and realized that the outer seal would almost slide right into the case by hand...it was the inner seal that was being so hard to install. I then put the seal back together, found a pipe exactly the same diameter as the inner seal lip that seats onto the shaft, and put it into my press and gently pressed it down. I had to work the outer seal in by hand as the inner seal was pressed down, but eventually I got it in without tearing it all to hell. I forgot to take a pic of it installed, but here is where it goes.



Started assembling the oil pump, packed it with some vaseline for initial lube and to help prime it.





Here is the pump (and the reluctor wheel and bearing that have to be pulled off to get the pump off) installed on the output shaft.



Front tcase input shaft seal..




New rear bushing and seal




Front input shaft/bearing installed.



Coupling assembly and chain/sprocket installed.



Oilpump/output shaft assembly, pickup tube and pickup screen, and magnet installed.



Sealant...

 

Here it is finished and installed.









While I was there I connected an oil catch can to the existing trans/tcase vent tubes, to catch anything that may shoot out. The catch can still has an open air vent on it so that no unnatural pressure builds up in the trans/tcase. I mounted the catch can right on the hanger bracket for the gas tank with a hose clamp and routed the tube out of the way of the driveshaft.

 

Awesome write up. Thank you for taking the time to post up the pictures. They were very informative to me.