New to the forum!
I've been trying to figure this out for the past 2 weeks with no explanation! Ive looked and looked but nobody seems to have a answer or at least guess at it. I'm guessing tcase is toast.
I have a 2002 zr2 blazer with the nv236 tcase (4 button). The front vaccum/diff is engaging properly like it should. The 4x4 buttons are all working and the tcase is making a clunk and engaging. With that being said I held the brake and was able to spin the back tires in 4low but didnt do anything up front. So I put the truck up on jack stand and all 4 wheels spun! BUT when its back on the ground the front wheels again do not. I then raised the back wheels off the ground, locked in 4x4 low gear and attempted to pull the truck forward using the front wheels.. No luck, the front driveshaft doesn't turn at all while the back are spinning normally.. It seems like its trying to but just doesn't have enough power going to the front driveshaft, like maybe something is slipping or not fully engaged inside the tcase?? But is making no weird noises. If anybody could be of any help I would greatly appreciate it. My research has led me nowhere..

 

Anybody?

 

It could be a couple things.
I believe the 4 button transfer cases have a clutch pack inside which could fail just like an auto transmissions clutches. (I would bet this clutch pack is worn and slipping if you dont have any odd noises)

I have also seen T-Case chains get worn enough to skip on the gears inside the transfer case but they are noisy and click when they skip teeth.

 

Here is a video of a 246 tear down and you can see the clutchpack i am talking about at 9 min.
The 236 and the 246 are very similar in regards to the design of them.

 

Clutch packs were also the conclusion I came to. One thing that does confuse me is I've read and been told that the clutch packs are only used when in 4x4 auto. When 4 high or 4 low are engaged its suppose to be locked solid with no clutches involved?

 

Finally got around to tearing the transfer case apart. Clutch packs were for sure cooked. Also black silicone had pretty much stopped up the pump tube screen completely thanks to the previous owner I'm assuming. Got all my parts to rebuild the np246 on cobra transmissions website. Thanks for the help. You guys nailed it from the beginning!