Ok i have a 2000 Ford F250 7.3 4x4 and im have some trouble here. I tried to place my 4x4 in high this week by the electronic four wheel drive and would not go. So i tried to place it manully and got this crazy jerking motion in the truck. It almost seemed if one side was in and the other side not. Now i tried to take it out of four wheel drive and the jerking motion persist in doing it and not stopping. Any ideas what this is and what i can do to fix it.

 

The diff is stuck locked in, that happends when they get worn, normally it fixes its self when you drive strait for a few feet so there isnt any strain on the diff.

 

Your vacuum hubs are shot, be it the line going to them or the seals inside the hub. I would check the vacuum lines first.

If you have not used the hubs it a while it will take a bit of backing up to get them unlocked sometimes.

Try manually locking and unlocking the hubs then with them unlocked back up a few feet.

 

You can tell if the vacuum valve mechanism is going bad by checking to see if your A/C only blows through the defroster vent or not.

The vacuum that runs the hubs is the same that switches the gate so that the A/C blows through the dash vents and not the defroster vents. The two are related somehow, I think its something like a proportioning valve that directs the vacuum pressure. This probably didn't help much.