1999 Jimmy with NV236 t-case with Auto4WD.
Bought it in March with 82K.
Drove it 12K. Now has 94K miles.
Runs great, quiet, no problems.

Put it on jackstands, drained the t-case.
Old fluid was dark with moderate amount of very fine sparkles that you can only see by stirring the fluid with your finger while shining a light on it.

Refilled with Auto-Trak II -- 2.4 quarts.
Still on jackstands - ran engine, tested 2WD and 2WD. Worked fine.
BUT - the T-Case started making a rhythmic scraping grinding whining sound after running for 20 seconds.

Next day - drove 20 miles. No improvement.

Put it back on jackstands, drained t-case fluid, came out very clean and bright with only ~15 very small particles of black specs and aluminum specs.

I suspect a bad bearing and maybe the pump is eating into the case or maybe the chain is rubbing something.
Gonna drop the t-case.
Found plenty of threads and videos.

Questions:
1 - after disconnecting battery, do I unbolt and remove the encoder motor from the t-case before dropping the case?
2 - in 2025, what are your favorite suppliers for internal t-case parts?

Thanks.

 

Update:

The best advice I found was big cushions on the floor.

The vehicle was on jackstands. We pulled the bolted crossmember and tranny mount. We did not remove any exhaust component.
We put a tranny jack under the tranny pan. Wiggled and jerked the t-case. It would not clear the tranny output shaft.

We raised and lowered the tranny while working the t-case back.
You will discover that there is a "perfect" position for the tranny: lifted only slightly higher than its resting position on the tranny mount.
In that position, the t-case is nearest to falling off the tranny output shaft.

At that point, I gave the t-case a really hard jerk backwards and it fell at lightspeed, landing on the cushion.

It took more time to remove the crossmember than it took to drop the t-case. The cushion was a lifesaver. I used a walmart boat cushion (square "life-preserver" with webbing straps). Perfect.

Inside my case was clean. The plastic retainer had fallen out of the rear output shaft bearing. That bearing only has 7 *****, and when the ***** all move to one side, it howls and begins to chew itself up.

Youtube has good videos on the 236 and 246 case. Disassembly was easy.
We cleaned and inspected everything.
The input bearing, planetary, clutch bearing, and the rearward sleeve bearing for the front shaft, were all good.
The clutch assy felt smooth and good, so i did not break it down. Same for the planetary.
When clean, the front output bearing was just a little bit catchy, so we decided to replace that one too.
And we decided to replace the small sleeve bearing for shift actuator shaft.
Note: If your actuator shaft does not have any slop and is not leaking fluid, then do not remove the actuator from the case body. The needles fall out of the sleeve bearing!
Mine fell out, I gathered them, cleaned everything, put a layer of grease in the bearing ring, and placed all the needle back in it. Then I tested it by hand. It felt sloppy. So I punched it out and bought a new bearing that has a retainer feature that prevents the needles from falling out. This bearing is also the seal. Be sure to install it with the seal on the outside, so that t-case fluid will lubricate the needles.

So our parts order was for three seals (input, output, output), three bearings, a pump saver plate, adaptor gasket, and three u-joints (front, rear, rear).
Total cost was less than $300.

The OEM rear output bearing was SKF BB1-1001-N/C3.
This bearing is no longer available.
Rock auto does not list the bearing anywhere in the t-case parts list.
The bearing is 35mm bore x 80mm OD x 23mm thick, with a snap-ring groove that holds everything snug.
You find replacements by crossing the oem bearing or asking a good shop.
These are good candidates: GM 12547400, NSK 573305D, National 307FFL5, BCA NB307FFL5, SKF 63072RSNRX, or Timken 307FFLS. We ordered the new SKF. If it doesn't work, I'll post back.

We laughed for a long time about how that boat cushion saved our ***.
You really want to put thick cushions down and be ready for the t-case to fall.
Dropping it on concrete would be a tragedy.
Benching it while also jerking it backwards seems pretty impossible to me, and I am a pretty strong guy.

Overhaul kits are available. They all seem to trace back to one supplier: BK333. Minnesota. Kit prices range anywhere from $180 on eBay to $300 on shop sites.
There is one other outfit called transmissionpartsdistributors.com who sells a nice-looking overhaul kit with all japanese bearings. I nearly bought one of those kits but the company has sketchy reviews, so we decided to go carte blanche at Rock auto.

IMO - New Process / New Venture made top-quality transfer cases for decades, BUT, the 236/246 is a real weirdo. Kind of a first-gen AWD.
IMO - all of the GM products with 236 or 246 will eventually fail, and probably during this decade.
The most common failures are as follows:
1 - the pump saver clip falls out, causing a very slow fluid leak that you never notice. The case runs dry in a few months and then burns up. Solution is install pump-saver before burn-up, or total overhaul of all parts and front case half after burn-up.
2 - the clutch bearing retainer clip and clutch bearing are the 2nd most common failure point.
3 - the rear output bearing with plastic retainer is the third most common.
4 - then it is either the actuator sleeve bearing, which locks the t-case in one position, which may be N, or 4L, or 2H, OR, it is the front output bearing which then tears up its opposing sleeve bearing. Remember, the front output shaft on a 236 is always turning.

I got this info from my local tranny shop when I took in my parts to get their opinion.

Good luck!

 

That's nice detailed info. Thanks for sharing.

 

Great writeup! I'll be saving this!