Hello to everyone, I just bought a '96 ZJ...

4.0L, selec-trac, automatic, Dana 35 rear diff

Well turns out I missed something on the test drive. When in 2 wheel drive taking a very tight turn (u-turn, cul-de-sac, any tight turn), the rear differential acts like it is locked. Similar action in 4Hi, 4Hi-full and 4-Lo.

Expected that in 4Hi and 4Lo, didn't expect in full time. Front behaves similarly in all 4wd.

Jacked up the rear, if I spin a tire, the other tire will move in the opposite direction (no surprise). If I hold the other tire the tire in motion will continue (no surprise). So I would say that it is not a welded diff.

Is there any vacuum actuation for the hubs or differential that I should investigate first? Any other ideas?

 

yep, we don't know much about jeeps or their 4x4 nuances. I participated in the above viewing with the above poster.
but anyway, wedge head was driving, I did the observing from outside the vehicle.
when turning tight turns the rear wheels were slipping & chirping similar to what you would expect with a locked diff on dry pavement.
The inside rear tire would turn but then spin faster than the road surface.
The outside rear tire would do the same, spin/chirp faster (which seems odd for a locked diff scenario)
when viewing from behind, the inside would spin, then the outside. appeared as neither at the same time.
As the tires moved through different arc length paths, they would would spin in spurts. best as I can explain at the moment.

by description, the 4wd part-time is with everything locked, right? So we supposed maybe when the OP tried out the various 4wd settings it became 'stuck' in the locked mode. Is that possible? What kind of mechanism is present on these vehicles to facilitate the locked and unlocked 4wd modes? some kind of vacuum operated locker? or?....

 

No vacuum disconnect on your jeep. Yes,the front and rear driveshafts are "locked" in part-time. First,make sure you are completely disengaging the t-case,the 242 can be tricky,if you're stopped run the shifter from D to R and back,if you're moving a couple of quick releases or taps of the accelerator should do it.

When you jacked up the rear and spun the tires did the driveshaft spin? Does the t-case shift smooth?

 

Swap to a NP231 t-case and Dana 44's and you'll be good

 

I think it may not have disengaged. I will try those tricks as well.

In neutral (transmission), if we spun one wheel and I held the other wheel in place, the driveshaft would move.

The t-case shifting does seem 'finicky' sometimes smooth sometimes requires a little effort.

Swapping out for a 231 and some 44s...maybe in the future!