Wobbling when in 4wd

My 94 Explorer starts wobbling when I engage 4wd. Had the front wheel bearings changed a couple of months ago, and have had the problem since that. I also have problems of disengaging the front hubs (by going in reverse for some yards). Sometimes I hear the "click" when the hubs disengage but when I make a sharp turn, the wobbling starts again.

Someone please help....