ok i am trying to understand the 4wd on my jeep which is an 89 cherokee 4.0 I6. so when it is in 2wd one of the back tires spins or both? when i switch to 4wd does the front driver tire spin ( i have a posi-lock on the front axel) or will the front passenger tire spin? if it isnt locked with the fork neither of the tires spin in the front? the reason y i am wonderin i rescently had probs with the front axel not really ingaugin. n e advice on how it works will be greatly apreciated thanks in advance

 

Check your vacuum line to the axle its probably leaking this has been covered like a million times for that year XJ.

 

The posi lock disengauged will make the front not work in 4wd, engauged with an open diff (guessing you don't have a locker) the tire with the least resistance like in mud or off the ground gets the power and will spin, rear works like this as well.

 

so if the posi-lock is not engauged neither tire will spin (in the front) because the front right tire is not engauged and the inner shaft is just spinning? if i dont have a locker in the rear it just spins the tire that can spin?

 

Yes.

 

This should answer your questions. Google is an amazing resource.

http://auto.howstuffworks.com/four-wheel-drive.htm