I have a '97, 5-speed with the "auto/4HI/4LO switch.  The 4WD engages
itself during turns on dry surfaces (roads, parking lots, anywhere).  At
the minimum it causes the truck to jerk back and forth as you turn. In one
instance, it snapped the drive shaft within the transmission right in the
middle of oncoming traffic in an intersection, stopping the vehicle and
necessitating replacement of the tranny, transfer case and clutch.  Within
months it was doing it again and I had Ford run a diagnostic.  They want me
to replace the whole drive system again because their computer says there
is nothing wrong with the Explorer's computer therefore it must be in the
mechanical parts.  However a mechanic I trust tells me that he believes
either the Explorer's computer or the 4WD wheel sensors are faulty and
telling the 4WD drive motor to engage.  Every other Ford service
department (6 total) I have spoken with has a different answer.  All of
them swear they've never seen this problem before.

Does anyone have an idea or a possible solution short of replacing the
drive chain?