When I bought this truck one of the hubs was slightly hanging out so I knew I would need hubs so I had a shop replace both hubs they found a vacuum line leak that they patched and said 4x4 worked. I picked up in the fall and didn't get a chance to test it but recently when I tried the HVAC went from vent to defroster and I didn't notice any changes in the steering effort so I knew it wasn't working (vacuum leak). The shop told me to just put the auto hubs in manual and that there is probably a vacuum leak in the front axle seals. I did that and found out that I still had to put the dash switch on 4x4 to engage. I tried it in a snow filled lot and could tell the difference. What does the dash switch do?What happens in the hubs to engage 4x4?What else is engaged/turning in the front driveline when in 4wd compared to 2wd?Is I harmful to drive with the hubs locked and the dash switch on 2wd?What wears or what damage happens if it is driven in 4x4 on dry surfaces? Does driveline binding only occur in sharp turns?

Will not hurt anything to keep the hubs locked. Sounds like you still have a vacuum leak. I would replaced the hoses on the front axles and also check the black box by your battery. A lot of times one of those lines will come loose and that will make you A/C come out the defroster vents and not the dash.

The dash switch send vacuum to the front hubs to lock them and also hooks the front deferential to the transmission. The vacuum that goes to the front hubs only lasts about 45 sec. And then stops, the same thing happens when you turn the 4 X 4 off. There is more then likely a vacuum leak in the hub itself. Ford made a few 4X4's with no way to unlock the hubs so I guess you can leave them locked

On my F350 I had to aslo manually lock the hubs as the auto would not work. Vacuum leak in the hubs. My owners manual said not to leave in the locked position except when 4x4 is engaged. Ckeck your manual to be sure, mine was an 06.

You are not getting vacuum to the hubs. On the passenger side inner fender there is a solenoid that is actuated when you turn the switch on on the dash. This is what sends the vacuum to the lines going to the hubs, It is very common for that valve to go bad. You need 2 people to check it easily. First start the engine and reove each line one at a time to tell which is the line from the engine...a suction when you place finger on the lines end. Next with the line going to the hubs and the engine running have someone turn the swith to 4 wheel high and see if you feel the suction at the valve nipple. I bet you don't. The valve is a dealer item only and costs about 65.00 bucks. And do NOT leave the hubs engaged all the time.

Sounds, like others have said, either a vacuum leak or like mine, a bad PVH soleniod(located on right fender under hood and pictured here) around $60

Ford SD/Excursion 4x4 Driveline Questions | Good Sam Community

15 Replies

nremtp143
Explorer
Jan 01, 2014
Sounds, like others have said, either a vacuum leak or like mine, a bad PVH soleniod(located on right fender under hood and pictured here) around $60
spadoctor
Explorer II
Jan 01, 2014
You are not getting vacuum to the hubs. On the passenger side inner fender there is a solenoid that is actuated when you turn the switch on on the dash. This is what sends the vacuum to the lines going to the hubs, It is very common for that valve to go bad. You need 2 people to check it easily. First start the engine and reove each line one at a time to tell which is the line from the engine...a suction when you place finger on the lines end. Next with the line going to the hubs and the engine running have someone turn the swith to 4 wheel high and see if you feel the suction at the valve nipple. I bet you don't. The valve is a dealer item only and costs about 65.00 bucks. And do NOT leave the hubs engaged all the time.
Halmfamily
Explorer
Jan 01, 2014
On my F350 I had to aslo manually lock the hubs as the auto would not work. Vacuum leak in the hubs. My owners manual said not to leave in the locked position except when 4x4 is engaged. Ckeck your manual to be sure, mine was an 06.
K_Charles
Explorer
Jan 01, 2014
The dash switch send vacuum to the front hubs to lock them and also hooks the front deferential to the transmission. The vacuum that goes to the front hubs only lasts about 45 sec. And then stops, the same thing happens when you turn the 4 X 4 off. There is more then likely a vacuum leak in the hub itself. Ford made a few 4X4's with no way to unlock the hubs so I guess you can leave them locked
cpaulsen
Explorer
Jan 01, 2014
Will not hurt anything to keep the hubs locked. Sounds like you still have a vacuum leak. I would replaced the hoses on the front axles and also check the black box by your battery. A lot of times one of those lines will come loose and that will make you A/C come out the defroster vents and not the dash.

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Ford SD/Excursion 4x4 Driveline Questions

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