My Transfer Case Woes

[Colorado Yeti]

i just bought my 99' 2 Door Z-71 Tahoe about 1-1/2 months ago. It only has 54,000 miles on it and it is completely stock. I use the 4WD fairly often where I live and drove it to Eldora ski area last weekend during snowstorm. On the way back, I started hearing a horrible bearing noise coming from the middle of the vehicle that would go away when I would shift to 4WD. I limped back home and put it up on jack stands while running in 4WD. It sounded like a box of rocks was poured in the transfer case. I have a challenging new job and don't have time to work on my own vehicles anymore so I took it to my trusty local 4WD shop that I have known for the past 30 years.

When they pulled the transfer case apart, the rear main bearing fell apart in their hands. Multiple ball bearings were rattling around in the case. Luckily, all the gears were okay and the case is fine (miraculously). They are putting in new bearings, seals, chain & oil pump assembly and reinstalling it for a very good price. My fried Justin (who owns the shop with his dad) says that the previous owner had filled the transfer case with ATF and this particular case requires a very specific lubricant that is unique which was the cause of the premature failure.

Just posting this so others will be aware of this if they R&R their own New Venture 246 case. Every 4WD vehicle I have owned either uses 80-90W gear lube (aka DANA 20) or ATF. Not this one. You have to specifically buy the "Autotrac 2" fluid from GM directly. It's the blue shit.

 

[alpinecrick]

Yes. Suburbans and Tahoes 96/97 on up have AutoTrak and require the GM "blue" fluid. Some of the base Suburban/Tahoes came with mechanical shifters (on the floor) or "push button" 4wd without the AutoTrak feature. Trucks did not have AutoTrak. Any GMT400 without AutoTrak takes DEX III or better fluid, although I have read that GM recommended conventional over synthetic fluid in the those T-cases. I have 80k miles with synthetic fluid in my NP243 with a total of 245K and the transfer case is still tight with no play I can see in the output shaft bearings on the rear or front driveshafts. Hopefully your guy replaced the little plastic shoes on the shifter fork cause it seems those are the first things to wear out.

The firstest and mostest important thing a guy can do when buying a used truck is replace ALL the fluids in the vehicle--engine, trans, transfer case, diffs, power steering, and coolant with a flush.

At some point in their life, it's quite common for GMT400's to have the owner put green coolant in the vehicle that came with the yellow DexCool--bad ju-ju. Next most common it seems is the wrong fluid in the transfer case.

I spend a lot of time on the yuppie side of the mountain because of work in recent years, and because of I70 traffic this season have skiied Eldora more than WP or Copper combined!

 

[Colorado Yeti]

Me too brother. Just got back again today....wicked cold and windy. I stopped doing the I-70 nightmare on the weekends about 5 years ago and I have never looked back. I'll still go up on a weekday to Winter Park but that's it.

Also, I'm new to this Tahoe thing. What is the "GMT 400" thing?

 

[alpinecrick]

The GMT400 series was GM's designation for the 88 thru 98/99/2000 design of trucks and SUV's. The GMT400 Suburban/Tahoes started in 91 (IIRC) and ran thru 99. The Tahoes were designated GMT420, the Suburbans GMT410 (again, IIRC) The GMT800 series started with the 1500 trucks in the 99 model year and by 2001 all the pickups, Suburbans and Tahoes were the GMT800's.

 

[alpinecrick]

Here is the scoop: https://www.tahoeyukonforum.com/thr...g-a-91-99-obs-tahoe-suburban-look-here.61712/