4x4 possible issue, any help?

[fordfan1984]

I have a 2003 E/B 4x4. Yesterday I noticed a new sound coming from the front end. It sounds kind of like knobby tires going down the road(deep whirring sound). I do not know if it is the front diff or one of the hubs not disengaging. I am not to familiar with the Expedition 4x4. I have had 4x4s in the past but I always have to get out and manually lock the hubs and shift the lever in the cab. Not used to shift-on-the-fly so if anyone can explain it in full and give me something to look at to find my issue I would be appreciative.

 

[fordfan1984]

i lifted up each side of the front and spun each front wheel individually and when i spun the wheel the axle shaft and front drive shaft would spin for both wheels. could this be a vacuum issue to the front hubs?