4WD - verifying operation??

I have a new 2000 XJ w/ AW4 and NP242. After fixing my 4wd indicator light (frayed wire), I wanted to verify 4wd operation - I jacked up the front left and engaged the tcase. The front wheel locked up, when I put it in 2wd, it moved freely...I tried the same thing on the passenger side, but the wheel spun freely regardless of 2wd or 4wd...Is that normal, or do I possibly have a bad hub on the passenger side?

Also, is the front drive shaft supposed to always spin/rotate in 2wd? Mine does...

Thanks (and I searched, and searched, and searched, but no luck)

Easy question first, yes, unless your hubs unlock, which sounds like they don't (did any late XJ's have them?), the driveshaft will spin in 2wd. Its just like the rear axle with the trans in neutral. If you have an open differential in the axle, its possible to spin the wheels on the axle in opposite directions and NOT move the drive shaft, but both wheels spin in the same direction or one wheel is held still, then the drive shaft has to turn. If you have an LSD, then both wheels will want to spin the same direction/speed and the driveshaft has to turn with them.

Does NOT the NP242 have an open differential between front/rear? I thought it did, and thus, it should behave like the open differential in an axle. If your rear wheels are free to spin, they can spin the opposite direction of the front wheels without moving the input shaft to the transmission/engine. If the rear wheels are held in place, the front wheels can only turn if the input shaft to the trans/engine is able to spin.

When your passenger side wheel spun freely regardless 2wd or 4wd, did you happen to have the trans in neutral? Did you have both front wheels off the ground? You likely have an open differential on the front axle, and thus if both wheels are off the ground, they will spin freely without moving the drive shaft, because they will spin in opposite directions, the open differential allows them to do that.

Thanks for the input on the front drive shaft.

As to the left side spinning freely in 2wd and 4wd - No, it was not in neutral, and only one wheel was off the ground...

Just cant understand why the left would lock up, while the right wont??

If 3 wheels were on the ground, the trans in park and in 4WD, the one wheel off the ground should NOT be able to move.

If I'm correct about the NP242 being open differential, then if one of the rear wheels was off the ground, it could spin the opposite direction of one of the front wheels. As well, with an automatic trans, even in drive or reverse, the input shaft to the xfer case can turn letting the front wheel turn.

Your sure the other 3 wheels were on the ground, the trans/xfer was locked (in Park) and in 4WD?

Does the driveshaft for the axle turn with the passenger side wheel. If the driveshaft does turn, your problem is in the xfer case or further up. If the axle does NOT turn, with one wheel still and the other spinning, something is wrong in the axle. Since the other wheel worked as expected, I would suspect most likely the differential in the axle is fine, its either the hub, like you suspect or the driveshaft from the differential to the hub.

Before you start tearing things apart, I'd get a 2nd opinion. My XJ is 2WD and I've never owned a 4WD, I've helped friends and family with there 4wd and I'm more knowledgeable about differentials and dirvetrains than the average person, but you really want the opinion of someone that has a NP242 and has dealt with it a lot.

btt

easier way to check your 4wd. remove rear drive shaft. put t case in 4wd. and drive away. your tcase does have essentially a "open dif" but only in the full time 4wd mode. in the part time and 4lo youll have a solid lock between your front and rear drive shaft. when you go to test your 4wd do so in part time or 4lo

What about putting the jeep up on 4 jack stands, put it in 4wd and let it idle?

Sounds unsafe but if it falls you wont go flying forward while its just idling in D, or little throttle with a manual. Ive never done it, but I guess it beats removing drive shafts and whatever else....

Thanks for the input guys - I continued working with it (engaging/disengaging the part time 4wd, full time 4wd and 4low). It is working like it should. The right axle locks up now when I lift it off the ground and engage 4wd...(either side)

Also had a mechanic I trust look at it - he said it is working like it should...

The previous owner did not use the 4wd much (if at all, by the condition of the XJ). It just needed to get "broken in"...

Thanks for the help - this is THE XJ site...