The reason is that the NP231 is a chain-driven transfer case. In a 4WD vehicle, your steering wheels travel further than your fixed wheels. Same concept as an axle differential with inside and outside on a turn, but you also have front and back. The NP231 is not a differential. The chain physically locks the front and rear driveshafts together. To avoid breaking things you must be on a slippery surface to let some of the tension release. Otherwise U-joints, straps, bolts, and chains break. Snow-covered roads are fine but any stretch on pavement that isn't 100% in a straight line (and wobbling the steering wheel to keep it straight doesn't qualify) will cause components to bind.

This is also covered in the owners manual.

 

Ok, thats all things I know, but why would someone put it in 4hi on pavement? which is the point im getting to. If conditions are to slick fordriving in 2wd then there should be no problem putting it in 4hi and driving down the road. Swapping to a different Tcase just so you can keep it in 4wd all the time seems crazy to me, it only takes 2 seconds to reach down and pop it backin 2hi if you see pavement. So, rather then trying to convert his xj to FWD just put it in 4wd..

And heck, I dont even get to see pavement for 6 or so months out of the year due to snow/ice. lol

 

Oh, the thing with that is with marginal ice on roads. With the sun and salt down here you end up with random ice patches. If it's dark out you won't be able to see it, so it's nice to have extra traction just available from the start.

 

You still got to admit the first generation didn't look like a Cherokee.
I have seen the newer style. Much better looking but sales were crap!