2004 Ford F-350 Front axle hubs do not lock in automaticall

Yes the front hub seals will not hold vacume if they are damaged or old. They sit on the axle shafts and need a ford tool to installl them. There are some other things to check first, does your vacume pump operate normally, does it shut off. Does only the defrost setting on your heater work. The hubs on these trucks need 15 inces of vacume of engage so if you put a gauge on the one side while blocking off the other you can see it do that. Here is the most likely problem if you take off the retaining ring that holds the hub on and pop off the hub, look in the bottom of it can you see grease marks where the axle shaft has made contact with it. If it has the hub, seal and there is this grey plastic washer they all have to be replaced on the one side, then check the other side, if no contact with the hub has bee made replace the seals and the washers, make sure the vacume line that goes into the knuckle is clean and there is no stuff inside of it and you will be ready to go.