I have a '79 K5, stock except 33" tires. It is full time FWD and has an NP203 transfer case. I heard some grinding/popping noise one day coming from the transfer case, turned around and went back to my house, parked the truck, and it hasn't moved since. I can put the truck in gear, with any position selected on the case, and only get noise. I looked under the truck while it's in gear and see my rear shaft spinning freely, front shaft doing nothing. Speedometer indicates I'm hauling ass. I pulled both drive shafts off, looking for anything obvious like a broken u-joint or something and they look fine. However, I can turn the rear shaft in my hand and hear a lot of grinding in the tailshaft(?) of the transfer case. I'm no mechanic, but I'm okay at working on intermediate level repairs. I don't understand why the shaft spins in drive but the truck deosn't move. Someone please tell me what is probably broken and I will have some direction to work in. Right now, I wonder if the transfer case AND the rear end are broken? Anyone?