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

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.
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
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.
spadoctor
Explorer
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.
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
Ivylog
Explorer III
Jan 01, 2014
Before I'd pay Ford $60 for a $15 part I'd rig something like this.
ScottG
Nomad
Jan 01, 2014
The fact that your HVAC went from vent to defroster is tell-tale to me. That would suggest the vacuum canister isn't working for some reason. Since the lines are pretty robust, I would look at any other work that has been done. I once fixed something like this after finding someone had replaced a battery and gotten the vac. to the storage canister pinched under it. After a while the line wore through and caused similar symptoms. Also look for anyplace where any line may be chaffing or rubbing against a sharp edge.

Good luck.
Scott
MFL
Nomad II
Jan 01, 2014
I asked my dealer, why the hubs were manual locking, when I had shift on the fly. He told me, if you drive in a corn field, you could damage the vacuum lines, but you could still lock the hubs manually I laughed and said, we both know I won't be driving in the corn!

He said you'd be surprised how many that do, and damage those lines.

Jerry
rowekmr
Explorer
Jan 01, 2014
Thanks for all the info! We are enduring a little snow now and will probably leave it locked for now and use the switch to turn it on/off for my errands. Will driving straight down the road in 4x4 bind anything if it is dry? I will check it out when the weather subsides or take it to an independent shop.
K_Charles
Explorer
Jan 01, 2014
Take it out of 4 wheel drive when you are on dry pavement. The hubs can be left locked for the trip to the store or what ever but turn on 4 wheel drive only when needed. When the storm is over, unlock the hubs.