Plzz help!

I recently purchased a 1998 Eddie Bauer ford expedition.
It has 200,000km or 130,000 miles
When I engage my 4x4 hi or LO I can hear it click then clunk and it sounds like it's locking in. I do this process in nuetrul with the brake pedal pressed down like your supposed to. When it's in LO the RPMS raise really quick like they are supposed to and all signs show it's working...... Until I hit snow. I go Absolutly no where and the front tires do not spin or work ...... Does anybody have any tips or help for me it would be much appreciated. I bought this truck for the winter and parked my mustang bullitt cuz I needed something for the snow. Now it's turning out to have been pointless to buy this SUV

 

What does your owner's manual suggest? If you don't have one you can download one at www. Ford Fleet maintenance-owner's manual

 

It just tells me how to engage it and I'm doing it that way

 

This sounds like either a bad transfer case, or the vacuum shift motor