Should I be able to spin the rear wheels freely when the back of the car is lifted off the ground?
Yes, if there is no limited slip differential. The opposite tire will rotate in the opposite direction, however, when you turn a wheel.
If there is a limited slip, No, not unless the vehicle is in neutral. Then both tires will rotate the same direction and the driveshaft will turn.
That’s what happens on my limited-slip 4WD truck. Not sure if transfer case was set to 4WD would change the situation. I’ve done that experiment with transfer case in 2WD mode.
OP, if your Jeep has limited slip rear diff, be cautious if only one rear wheel is lifted , b/c I think it is possible attempts to turn the lifted wheel could be transferred to grounded wheel, & cause truck to move off the jack.
Yes it would change. If the truck was in 4wd, the trans in neutral, a limited slip rear, and the fronts on the ground, nothing would turn. If the fronts were up, they would turn if a rear was turned.
4WD with no differential in the transfer case or limited slip rear will spin one front and one rear tire on a slippery surface. If the transfer case has a diff, it becomes AWD and only one tire will spin on slippery surfaces. Confusing? A bit.
Not as much as the recent thread about the modern car’s 3-position indoor lighting switch … lol …
This thread gives me a useful idea. Lubing the truck’s rear driveshaft seems like a simple-enough job, but access to one of the zerk fittings makes it quite difficult. Have to use a needle adapter to grease gun, and even w/that have to file one side of the needle flatter to get it to the zerk. And then only if the driveshaft is in the perfect orientation. Whew! … lol …
The way I do it is park the truck on the level in N and parking brake off, then I crawl underneath & push the truck slightly in the direction that brings the driveshaft into proper orientation. (Not recommending this method btw, could be unsafe.) Needed orientation is about +/- 2 inches pushing, very tight clearances involved.
Now I’m thinking a better way might be to lift both rear wheels, then should be able to orient the driveshaft to correct position just by manually turning one of the rear wheels.