I believe that it is a planetary transfer case with an internal clutch pack, that delivers 30% of the engine torque to the front wheels, allowing for slip for cornering. When the van is driving normally, the planetary gears rotate as a unit but if the rear wheels start to slip, the planetary gears start to turn out of sync with the rest, a sensor detects this motion, and an electric solenoid locks the clutch pack together. After four seconds the solenoid releases, and if the tires slip, the cycle starts again.
no
Yes, the 247 will bind in corners if the proper fluid is not used.
chain drive
no
aerostar 3.0, 4.0 mustang 3.0, 4.0
The problem is most likely in the transfer case or the linkage. The transfer case is bolted to the rear of the transmission on that truck. The linkage could be misadjusted, there should be three distinct positions for the transfer case, Neutral, Low and High. If you suspect the linkage disconnect the linkage and manually put the transfer case in each position and try it to see if it works, if it does it's the linkage if not the problem is in the transfer case itself.
check fuses
The Transfer Case chain is located inside of the transfer case. The transfer case is the gearbox located just behind the transmission. It sends power to the front wheels when 4-wheel-drive is selected. To remove the transfer case chain, the transfer case must be removed from the truck, by removing the front and rear drive shafts and unbolting from the transmission (also various connectors for speed sensors, if equipped). The two halves of the transfer case cover housing must be split by removing all the bolts, and several spring clips must be taken off. Unless you have worked on one before, you may want to have the pro's work on this.
yes
Work is the transfer of force
most definatly
any gear oil or atf will work to