I found some vacuum lines disconnected in the front wheel wells of my 2003 Ford F350 diesel. From the information I have found it appears they should go to the hubs for automatic locking hubs. I have a way to manually lock the hubs and it appears that they have been made so they could be locked manually or by vacuum. What is not clear to me is most information about these vacuum lines talks about ESOF (Electronic shift on the fly), but I don't believe I have this, I have a lever on the floor to shift into 4 wheel drive. My truck manual is not clear on this, it talks about ESOF with the auto-manual locking hubs, but does not say anything about the non ESOF. Were the hubs supposed to lock when the lever is shifted into 4WD?
if you have a floor mounted shifter and a hub that reads Lock-Free then theres is no way you have ESOF. Ford runs the line on all the trucks don't ask me why but they do.
1- remove the rubber line from the knuckle
2- remove steel nipple from hub
3- install a 1/4 pipe nipple (i used a stainless one i bought at Lowe's) use some type of pipe sealant on the threads also
4- remove rubber line from plastic fitting in the brake line holder and throw away
5- now this is up to you, either plug the plastic fitting with a rubber cap you can buy at any auto parts store, Lowe's etc. OR you can do like i did, remove the plastic vacuum line from the truck, its goes from the motor cross member up the passenger side and too a tee on the passenger side front fender next to the vacuum pump. When you remove it at the pump simply plug the rubber tee, i got a stainless bolt 1 1/2" long cut off the threads and stuck the smooth shank into the rubber tee. No more cracked unused lines hanging and the bolt will never rot or leak so you'll always have vacuum to run your heater etc in the truck