Seized front diff?
 

My 96 4runner won't move when it's in 4wd. I recently completed a manual hub swap where i installed new diff seals, cv axles, wheel bearings and hubs. The 4wd worked fine after this and i had been diving it through the snow just fine. Snow melted, i took it out of 4wd. next time I tried to put it in 4wd it made a metal on metal grinding noise and felt bound up. I took it out 4wd and tried it again and it wouldn't move at all. The 4wd indicator light comes on whenever shifted into 4wd.
​​​​​​
Since then i have deleted the ADD system, locking the actuator in the 4wd position. I changed fluid in both the front diff and T case. No shrapnel in either although the T case fluid had some moisture in it (looked milky, grayish). The car will move with both hubs locked in and in 2wd. Conversely it will not move forward with the hubs unlocked, in 4wd.

I know it's not the ADD system cause that's gone. Since the car moves with the hubs locked in it leads me to believe that the problem is the T case but I'm open. To any suggestions. Thanks✌️🤟

Since I haven't needed to really dig into my truck since buying it, my knowledge is starting to fade...but in 2wd with hubs locked in the front wheels are connected to the front diff gears. So if seized, it shouldn't move.

Without automatic hubs, all the transfer case shifter does is give you really low gearing. The t-case is always engaged, 2hi or 4hi/lo. Now what I'm not sure about with these newer trucks (the truck I did a ton of work on was an 83) is whether the front driveshaft is engaged when in 2hi. I think it spins freely in 2hi, no power going to the front diff. So while it would point to the front diff if you think "put into 4wd, t-case engages front diff...won't move, must be front diff", the fact that it will move when the front wheels are connected to the front diff, I think that rules out the diff.

So..t-case? Someone will definitely tear apart my reasoning if I'm way off...

Quick update: took off the front drive line and threw it in 4wd. Drives fine. Can feel the gear ratio drop in 4 low. So this narrows it down to front diff. too bad, I also thought that the hubs locking in and spinning freely pointed to the T case. With the drive line on I can put it in 4low and release the clutch and it will roll but it's very lurching and makes a lot of grinding, squealing noises.

The joints on the drive line are pretty sloppy and some of the zirc fitting won't take grease. Anyone ever heard of a drive line restricting motion?

Sounds like a u-joint in the front drive line is seized. If you can't do it yourself take it to a good drive line shop, or even just a reputable machine shop. They have the hydraulic presses and so on you really need to do it right.
I've replaced the U-joints on my pickup a few times now. For some reason, Toyota made them sealed, with no grease-zerts. My 87 4Runner has grease zerts all over the drive lines, and all the u-joints, as well as the double cardan, are still factory original. Keep em greased up real good and they last a lot longer than the sealed ones.
The weather warms a little more, and I'll be hitting the 99 with the grease gun. I figure that it's better to have a little too much grease than not enough. Not counting the slip joints. Those you can overfill. Be careful. The u-joints just throw the excess out all over the truck's underside, but it's a small price to pay.
Believe it or not, on a side note, guns work the same way. Over lube them a bit, and the first round gets rid of the excess. A little messy, but it works good. Just thought I'd mention it in passing.

Good luck to ya!
Pat☺

The solution.
 

I bought a newer diff out of a junkyard. Upon removing the old I found that the pinion flange was seized. Probably could have been repaired but the junkyard took a core charge and is gonna send it off to be rebuilt. Its still climbing mountains somewhere out there.