IZwack said:
The front driveshaft always turns while in Drive (unless you have a first generation explorer with selectable lockout hubs and transfer-case capability to go 2wd).
The reason for this is that the front passenger side wheel rotates an axle shaft which is splined directly to a set of spider gears of the differential (note that the vehicle doesn't selectable hubs on the wheels because the hub assembly is splined directly to the CV half shaftS). I believe your vehicle has a "vacum disconnect" on the passenger side axle shaft so the wheel on the passenger's side would not affect the driveshaft unless you are in 4wd (when the vacum disconnect is activated).
I have a slightly different theory....
The front driveshaft on a 2nd-gen does tuen, but the 95 and 96s used the center-axle disconnect as IZ mentioned. In theory, the system should act just like you described, i.e. the CAD would break the passenger side axle shaft, the front driveshaft would stop turning, and the spider gears inside the diff would spin, but the front driveshaft and carrier would remain stationary.
However, (and this is strictly my opinion) I believe that, due to the design of the transfer case clutch setup, there is enough friction from the clutches shearing the transfer case lube that the 'friction' of the oil between the clutch plates is enough to make the front driveshaft turn. (On a side-note, this would be similar to the way the engine oil would make a wet clutch on a motorcycle spin the primary even when in neutral)
Now, regardless of why it spins, the bottom line is that it spins to some degree all the time. The quick and dirty solution would be to drop the driveshaft. However, if you're going to do that anyways, that's half the job of replacing it, so may as well do it and get it over with IMHO. Better-off doing it now than after the joint snaps and drops the shaft on the freeway!
-Joe
