1997 5.4 manual shift transfer case.

My truck has started shifting into 4x4 on its own. A couple of times in the past it has stayed in 4x4 but the indicator has shown it as being in 2x4. I suppose that the transfer case is in need of being replaced but I would like to see if anyone has any other ideas. Is there anything else that could be causing this?
And if It seems that I will have to replace the transfer case what is the best way to go? New or used? Where to buy?
Thanks
Darin

 

It could be that the front automatic hubs are sticking in the "on" position even though the transfer case is in 2H.

I can't remember now if it's a vacuum motor or electric solenoid which actuates the front diff. You may be able to check it with a vacuum gauge.

Lift up the passenger side front tire. If the front diff and transfer case are disconnected it should spin freely. If the front driveshaft turns there's a problem either with the actuator or the mechanism in the diff.

Automatic front hubs is a misnomer. Actually they are permanently on but one side of the ring gear is disconnected in the diff itself.

Perhaps someone else with more experience can explain it.

I suppose you've tried driving in reverse for a hundred feet while moving the steering wheel from side to side to help unlock the front diff?

 

Both times when it was locked in 4x4 I was able to get it out after driving it by mistake on the pavement. So that is not a issue at this time although it could be part of the same problem. The problem now is it will briefly shift in 4x4 on its own.
Thanks
Darin