Driveline grind/bucking->Shelled Transfer Case

[novamodeler3]

http://www.tahoeyukonforum.com/forum/showthread.php?t=57115

The above thread was my first try.. Now here's what happened.

Last week, while driving at appx 55 MPH, my wife heard a big bang, immediately followed by an engine stall, and rear tire lockup. When my father in law got to the scene, he observed the chain drive hanging out of the transfer case, and a lotta pieces...

So, he found a replacement part, and went to install it. As it turns out, IT DIDN'T FIT! After some research, come to find that my 99 2 Door came equipped with a special option in the 4WD system, specifically the "AUTO 4WD" setting on the switch in the cab. Making the transfer case a special part, not like a usual case. I learned that I have 2 slip-yokes, unlike any xfer case I've seen where the front driveshaft has the slipyoke on the diffential side of the shaft. Also, he told me that the overall length of the tail sections of the two were different, and the rear driveshaft was too long for the usual replacement.

Now, given my symptoms described in the above thread, I imagine that a short, or misread signal caused the actuator to actuate, and lockup the transfer case.

Needless to say, $350 later, I have a new case for the 'special option' Tahoe.

I've requested that he disconnect the connectors for the actuators (ensuring the vehicle is in 2WD first) to avoid this issue until i get back from my trip overseas. (Matter of weeks, thank goodness. Don't think the Tahoe can take much more of me being gone, lol)

All this being said, I called a trusted tech and he found 2 TSB's on Mitchell referring to a Transfer Case Shudder.... TSB 99-06-04-056

As well as one for the Front Output Shaft Seal TSB 00-04-21-001

I couldn't find any info specifically on these, as I don't have an alldata or mitchell account.

I was just curious if anybody had any input on what would be my next best move. Slave in my own toggle switches (if this is possible, given the "auto" setting), re wire the whole system, switches, grounds, connectors (the whole 9), or doing the work and installing a manually actuated xfer case, and installing a switch for the front diff actuator. This option leads to some driveshaft modifications, as the different cases utilize different length driveshaft, as well as slip-yoke configurations.

Any input is appreciated. And any good technical information on the system, and how 'unique' this option is, and what I might expect in the future.

Thanks for the help!

-Justin

 

[BirchyBoy]

Can't offer any advice but I'm sorry that it grenaded. I know mine is the the Autotrac as well. I think they're common in the '99s.

 

[SunlitComet]

Honestly your trusted tech does not make sense. The first tsb does not apply to your vehicle it applies to compact s10 and s/t vans. The second I believe was rescinded by 2009 but likely much sooner. There is nothing special about the transfer case it was simply the next design update for the t-case. What is this special part you are talking about? It honestly sound like it had the wrong or low fluid level in it and killed itself as a result. they just don't blow up like that. Even if the clutch pack inside it was jamming while in 4wd you would have noticed binding in the system. And for it to simply and suddenly lock up because of a misread sensor or just not correct it seems.
It can go into 4hi and out at any speed with no issues and the tccm has to see that the transmission is in neutral on a separate circuit before it would respond to a 4lo switch depress. I think you just had some bad luck and something failed. When you get back plug everything back in and drive slowly with help around to see if something is still wrong and report back here. Otherwise repair what is broken and leave it alone. For the slip joints and shafts, get some pics so we can verify everything is as it should be.

 

[BRUTUS_T_HOG]

Yeah I bet there was a pinhole in the case from the common oil pump wear site. Ran out of fluid and blew up.

The case you'll be taking out is overall reliable and durable. I wouldn't even think to hackify the vehicle.

 

[novamodeler3]

Honestly your trusted tech does not make sense. The first tsb does not apply to your vehicle it applies to compact s10 and s/t vans. The second I believe was rescinded by 2009 but likely much sooner. There is nothing special about the transfer case it was simply the next design update for the t-case. What is this special part you are talking about? It honestly sound like it had the wrong or low fluid level in it and killed itself as a result. they just don't blow up like that. Even if the clutch pack inside it was jamming while in 4wd you would have noticed binding in the system. And for it to simply and suddenly lock up because of a misread sensor or just not correct it seems.
It can go into 4hi and out at any speed with no issues and the tccm has to see that the transmission is in neutral on a separate circuit before it would respond to a 4lo switch depress. I think you just had some bad luck and something failed. When you get back plug everything back in and drive slowly with help around to see if something is still wrong and report back here. Otherwise repair what is broken and leave it alone. For the slip joints and shafts, get some pics so we can verify everything is as it should be.

I wish I could offer a better explanation, but I'm just passing along what I'm hearing from back home. As for "special", my father in law told me that the replacement transfer case tail section was too long, requiring the rear driveshaft to be cut to fit. The replacement t-case was removed out of a 99 Yukon 4dr 4WD. The way he explained to me, the factory t-case in My Hoe was a different part number (cant remember for the life of me what he had said) than the *usual* t-cases of the general populous of 4WD GM trucks. He said that the "AUTO 4WD" setting was the kicker in this being a different part.

Reading this though, regarding the way the system *should* work, I still scratch my head about the bucking at speed, and the grinding while backing out of the driveway. Also, only twice did I experiencing a very unsettling grind/bind at speeds of 65 mph. Sounded JUST like I was trying to select a gear without the clutch (in a standard transmission application). Big ugly noise, and I couldn't remedy it until I put the vehicle into Neutral, pulled off the interstate, sat for about 10 seconds, and back into Drive. At that point, everything was fine. Like nothing happened.

I'm thinking of chasing the diagram and replacing some cheap items in the circuit. The cab switch, sensors, and repairing any obviously damaged or worn wiring. I don't wanna hack it up, I just want to take the right measures now to ensure I don't run into this again.

I will get some pics and provide good part numbers, etc for everyone here to leave their input once I get back. As for now, a lotta $$$ later, the wife has it back and it's out of the shop. Will have to do until I can get into it.

Thanks for all the input and help. Good to know that a lot of knowledge is available at a mouse click, and I appreciate everyone taking their time and sharing their information.

 

[1998Suburban]

I just finished rebuilding the NVG 246 AutoTrac transfer case in my '98 Suburban (RPO NP8). It sounds like you tried to put in the NVG 241 transfer case which, as you discovered, is vastly different.
I don't think you can (easily) splice in toggle switches to control the positions of the 241. The 246 uses an encoder and a Transfer Case Control Module (TCCM) to actively control clutch pack engagement when in Auto.
I have a pretty good Word document with pics of the rebuild if you're interested in seeing how the thing comes apart/goes together. I'm not sure how to post the .docx file. It would probably be a good "how to."

Here's what the front case half of a 246 looks like completely stripped:


I assume this is your transfer case: