I have a 91.5 d250 4x4 and my driver side hub is moving to the lock position. I can spin it back the free spot and after about 10 miles it's back in locked. Any help here would be nice, I just dont know about the hubs you have to lock, or unlock.

 

Sounds like your do for a set of hubs or find a used one, there are supposed to be a little detent in there that you here click when you turn them out thats what holds them out, sounds like it is worn down and or broken.