i have a 98 xplorer 400, when i put it into 4 wheel drive it pulls hard to the left.
then it makes a loud snap in left front, after the snap it free's up.
i was thinking maybe a u joint???? anyone ever had that problem. thanks

 

just jack up the front end and w/ it off try moving that tire and check to see if the joint is bad. by the sounds it should be easy to tell if its that bad.

 

Sounds like the left front magnet is the only one engaging. Thr right one might not be for variopus reasons. Put it up on stands and see which ones are turning. The right one probably will not be, if it is pulling to the left. The loud crack might be the magnet releasing under a load.