NP246 Transfer Case

[WVtrucker]

I have been hunting for a mysterious vibration in my truck. After much trouble and little success, I am starting to get the driveline of my 99 sierra straightened out. I had the front end rebuilt because the pinion bearings went out and caused a lot of trouble. I replaced the rear driveshaft and most recently set my sights on the Tcase. It makes a lot of noise in 4wd and I was wondering if that is normal. I have never had one of these new automatic jobs so this is virgin territory for me. After doing some research it looks like to me that this tcase is nothing but an AWD unit that was modified for pu use. Upon changing fluids I discovered that there was ATF in the Tcase instead of the synthetic gear lube called for. So just thought I'd throw a line out there to see if anyone else has had major problems with these trucks (aside from the cold start-up rattle and horrific spark nock) or did I get a lemon here. The truck had 20K on it when I bought it and now has 65K (last 40 have been all highway).

If anyone else has had any peculiar experiences with the new GM series I would love to hear about it because I would hope I'm not alone in this one.


:banghead:

Mike

[WES]

Well first off welcome to our boards. We hope you enjoy them. It sounds like to me that you may have a problem with the adapter sleeve between your transmission and transfer case. I lean toward that because of the automatic transmission fluid that you found in your transfer case. That indicates that the seal that keeps the 2 fluids seperate from each other has gone bad allowing tranny fluid to flow to your transfer case. The adapter sleeve goes strait through the center of it. That would indicate a problem there to me and is where I would look next. It may not vibrate in 2 wheel drive, but when under the extra load of 4 wheel drive it could then. At any case you should change out that seal because even though the automatic transmission fluid shouldn't hurt the transfer case, it will eat out the seals causing it to leak like a son of a gun. Good luck... Vibrations can be hell to track down. WES www.ClassicHeartbeat.com

[WVtrucker]

Wes,

First of all let me thank you for putting these boards up. I have picked up a lot of little suttle tips and tricks here just looking through the posts. Thanks for the insight on that sleve, however I think the plot has thickened a bit. Let me clarify on the ATF situation. It wasn't gear oil with ATF in it. As near as I can tell there was nothing but ATF in it. But let me back up a bit. At this point I have replaced the rear drafshaft because it was bent all to the devil, I have had the front diff rebuilt because the pinion bearings went out and just caused all kinds of trouble. As I crawled under the truck last night to check the fluid levels I noticed some numbers painted on the tcase. That raised all kinds of red flags to me because junkyards mark thier parts that way. The other thing that I found is that there is slop in the front side slip yoke. So I think I have found the final culprit. That would explain why there is more noise when the case is under a load in 4wd. So I have a couple of questions for anyone out there.

First If I have the VIN and the Serial for the Tcase can I find out if they match (i.e. have been swapped).

Second how big a deal is it to change out that front bearing in the case because best guess says that that is the least that is wrong.
The real aggravating factor here is that after I took it to the local GMC dealers body shop (I got rearended a while back but it was very minor) to check it out they diagnosed it for me as the front diff and front tcase bearings (which was all pretty noticeable when the thing was up on the lift running). I took it to the garage (same dealership) told them that and they didn't even check the tcase after I told them to. You'd think that any mechanic worth his salt would have noticed that (especially if they test drove it). If I were still living at home in WV this would not have been an issue. I'd have put it in the garage and tore it down myself. I am really loosing faith in the GM mechanics (at least around here). I think I have vented enough now. :D


Thanks,

Mike

[WES]

Well it does sound like the transfer case was swapped for anouther. It sounds like your truck has a pretty rough past. Road hard and put away wet so to speak. Another way to tell if the seal is bad between the transmission and transfer case is when you remove the oil fill plug and transmission fluid come poaring out of it, you have a bad seal. There would be no other way for the transfer case to fill past that point. I have seen many transfer cases that looked like all they had in them is tranny fluid, and the reason for it is because the problem had gone so long without being noticed, that it had actually washed the gear oil out. Another tell tale sighn would be if you are having to add fluid to your transmission once and a while.

It does sound like you found your problem though with the slip yoke being sloppy. WES www.ClassicHeartbeat.com

[WVtrucker]

Wes,

That is an excellent point about overfilling of the gear case. I still have the fluid. I should measure it and find out how much there actually is. I don't remember if I took the fill plug completely out before dropping the drain although I did break it loose. Any thoughts on how much fluid it should hold because I think that I only got about 2 qts. in it before it started running out of the fill hole. How hard is it to change that seal? Is it just a matter of splitting the tranny and case? I am going home for Christmas so it looks like I may have real busy vacation. :banghead:

Oh how I want to go back to when times were simpler and if you wanted you could crawl up under the hood and take a nap beside your engine. I'm still nosing around for a 67-69 swb chevy pu. Hopefully I'll find one eventually.

Thanks again,

Mike

[WES]

I haven't taken one apart to be able to tell you haw easy it would be. I do know however yours should be easier than the ones in the 70-72. Those are NP205s and weigh about 150 lbs. Yours will be lots lighter. Therefor easier to install. I also don't know how much fluid you t-case holds, but if you got 2 quarts in when it started to run out, then that is what it holds. The fill level for the t-cases is the bottom of the fill plug, just like the rear ends. WES www.ClassicHeartbeat.com

[WVtrucker]

Wes,
I measured the fluid that came out of the case and there was two quarts almost exactly. So that tells me that hopefully the seal between the tranny and tcase is okay. It also tells me that some genious put ATF in the tcase. I have had a 205 apart once a long time ago and yeah it is a beast. If you haven't tried putting a 4spd. tranny with one of those in a truck w/o a tranny jack you should try it some time. :D :D It's almost bullet proof but you make pay for it in sheer mass.

[WES]

Been there, done that!! Got the hernia to remember it by. LOL.... WES www.ClassicHeartbeat.com

[WVtrucker]

:D :D :D :D :D LOL!
Mike

[WVtrucker]

Just to follow up. I ordered a tcase for my truck today and will install it over the weekend. GM wants 1200 for the case and 500 to install it. That was for a reman case. I ordered a new one from an outfit in Spartanburg SC. (they also have a place on CA). It was brand new from the factory and shipping was free. All of that for $995. I don't think I will pay GM $500 to remove the two driveshafts and six nuts. For late model stuff if you can't find one I'd give these guys a call. Transfer case express I think is the name of the place.

Mike