AWD 97 Safari

Greetings All.
A question involving the transfercase of the AWD Safari. Rear wheels are turning and front are not. Is there some sort of shear pin that has blown? Doesn't sound like the gears are all mashed up-it still drives. Any thoughts?
Thanks for any/all input.

If there is a switch on the dash to engage / dis-engage AWD, there is more than likely a problem with the actuator motor on the transfer case, or the circuits controlling it. If there is no switch on the dash, (full time AWD), the problem lies either with the transfer case, front driveshaft, or front differential.

Thanks ... it's a buddy's van- I'll have somewhere to start.