I just got a 2005 F350 last week. When we were test driving it I noticed the heater was stuck on defrost. Tonight I heard a humming noise from under the hood, so I started checking things out. The vacuum pump was running non stop, so I definitely have a vacuum leak.
I pulled the vacuum line from the pump and plugged it off with my finger, the pump stopped running. Removed my finger the pump started again. So, I pulled the line coming out from the reservoir, at the solenoid. Plugged that one up and about 2 minutes later the pump stopped, released my finger it started again. Unplugged the line that goes back toward the firewall and held my finger over that one and the line going down to the frame and the pump again quit.
SO, I am assuming my leak is down in the 4x4 area.
My questions, is there a common place where it will leak? I was looking with a flashlight, will look more in the daylight.
If I plug the lines going to the 4x4 under the front end and only use the pump for the heater controls what kind of bad things will happen?
If there is no vacuum to the hubs will the default to locked or unlocked? What I am wondering, if I plug that line off for now will my hubs be locked or unlocked? If they will be unlocked I can just use the manual hubs until I can get the parts to fix whatever needs fixed.
Finally, is it possible that one of the hubs itself is bad causing the vacuum loss?
I am just not sure where to start looking beyond the lines. Hopefully it will be as simple as a leak in a line, but the way my luck goes probably not.
By the way, I don't know if the 4x4 works or not. I should have flipped the switch on the test drive but never thought about it.

 

You can plug the vacuum lines to the 4x4 and nothing bad will happen. Put your hubs in the auto position and they should not be locked providing the hubs are in working order. You can leave it like this if you like. When you want 4x4 just turn the hubs to lock and then engage the transfer case by turning the **** to 4 hi or 4 low.

If I had to guess I'd say your PVH solenoid may be faulty. It should only apply vacuum to that line going to the frame and to the hubs (4x4) for a short period of time when the **** is turned to 4hi or 4 low, and then again for a short period of time when the **** is turned back to 2 hi. Otherwise the PVh solenoid should vent to atmosphere and not allow any vacuum to pass through from the reservoir.

 

OK. I unplugged the line coming out from the pvh solenoid and plugged it off with my thumb. After a minute or two the pump shut off. When I connected the hose again the pump ran constantly.
So, if I cap off the lines going to the hubs I am essentially turning the hubs into manual locking hubs? Do they go to the unlocked position when vacuum is removed, or do they stay in whatever position they were in when the vacuum was lost?

 

Yes...if you plug the vacuum lines you are essentially making the hubs manual hubs. Auto position is the unlocked position, and lock is obviously locked.
The way the vacuum hubs work is basically like this.....When you turn the **** to 4x4...the PVH solenoid( pvh= pulse vacuum hub) sends a vacuum pulse which locks the hubs. This pulse lasts for hmmm I think 20-25 seconds off the top of my head...and then the PVH vents to atmosphere, so no more vacuum going to the hubs. When you turn the **** to 2 wheel drive the PVH sends a shorter less strong vacuum pulse to the hubs to unlock them. After i think 12-15 seconds the PVH again vents to atmosphere. So basically there is never any vacuum in the lines after the PVH solenoid except for the short period of time just after you turn the **** to 4x4 or 2x4. Long story short...if you always have vacuum in the lines after the PVH solenoid....then it is faulty. Now will replacing the PVH stop the vacuum leak you have and fix the 4x4...yes and no. A new PVH will stop your current vacuum leak I'm fairly sure....However whether the 4x4 works as it should will depend on the vacuum lines being good after the PVH as well as the hubs, o rings and knuckle seals.

 

There should not be any vacuumed through the front hub control valve during normal operation, sound like you might have a problem with the valve or something else

 

OK, that makes sense now. I am heading out to check things out in the daylight.

 

Checked it out today. Here is where I am at.
I checked the hubs by turning the axle shaft. The drivers side is free, the passenger side if locked in.
I checked the vacuum at all connectors along the line and found both hubs may be leaking. I took the line off the drivers side hub and put my vacuum gauge on it and got nothing. I took the line off the passenger side and put my gauge on it and got nothing. I pulled both lines, plugged the drivers side and put my gauge on the passenger side and it built up pressure and shut the pump off. I am assuming that along with the PVH solenoid I also have a leak in both hubs.
What is the common problem when these hubs leak and how to fix it? It is a 2005, can the O-rings I have read about be replaced easily, or does it take special tools to get it done?
I have no problem running it without the auto shift on the fly, but with the passenger side locked in I am not sure what to do.

 

My 2005 didn't work when I got it. I used a hand vacume pump to check everything. Some small leaks at the hubs but bad. Everything checked ok but the control valve. I bought a new one from NAPA and installed. Everything works now

 

If I can get the passenger side hub unlocked I will just delete the vacuum part and go all manual. I am wondering why the passenger side is locked in but the drivers side is free.
By the way, both hubs turn easily with the manual *****. Do I just need to take the passenger side hub off and clean it up?
I might go ahead and change out the solenoid switch, it is obviously bad if it lets the pump run constant and vacuum to the hubs constantly, but even with the solenoid bad should it still build up vacuum pressure to the hubs?

 

I'll assume that when you manually turn the passenger hub it still stays locked? Have you turned it from auto to lock and back again and checked? You may have to pull passenger side hub and clean and lube it, do drivers side as well if they've never been serviced. If this doesn't help then you need to replace the passenger hub....keep in mind the Ford auto lock hubs aren't cheap so most just replace with say Warn manual locking hubs and write off the auto locking portion of the 4x4.
There are several seals that make the 4x4 work...first off there's a diaphragm in the hub itself, then there's the o ring that seals the hub itself in where it sits, third there's the wheel bearing o ring which seals where the wheel unit bearing seats in the knuckle assembly, and fourth there's your wheel knuckle seal which seals where the axle shaft comes through the knuckle into the wheel hub assembly. The hub and o ring are fairly easy to replace and just involve pulling the locking hub itself. The wheel bearing o ring requires removal of the brakes, rotor and the wheel bearing unit....once you're in this far all you have to do to replace the knuckle seal is to pull the axle shaft. Out of all this the knuckle seal is the only one that requires a special tool to properly seat it on the axle......clear as mud? lol

 

Yep, that does make sense.
I will check and see if turning it to lock and back frees the hub. If they are free I will just plug off the vacuum lines and run them manual. Hopefully it is just gunked up inside and cleaning will free it.
I will post back with what I find out! Thanks!

 

OK, turned the lock **** back and forth, no change. It is still locked in.
Now for a dumb question, how do I get the hub out? The last 4x4 hub I tore down was on my old '79 F250. There are 3 torx screws on the outer edge of the hub. I assume you just remove these and pull the hub assembly out? Can this be done with the wheel on, or do I have to take the wheel off?


Edit: just for curiosity I had my son sit in the drivers seat and turn the 4x4 **** from 2 to 4 high. When he switches it to 4 high I can hear the drivers side hub click in and it locks the hub. When he switches back to 2H I can hear it click and it releases the hub. Go to the passenger side and nothing. It makes no noise and stays locked in. Don't know if that has any bearing on the diagnosis of the problem or not. Although it won't hold vacuum pressure it does switch.
So, in my mind if I can get the passenger side to switch like it should and change the solenoid then it should all work fine. Maybe lose dash vents while it is switching to and from 4x4 but other than that it should work?

 

Yes just remove the torx screws and pull the hub...no need to remove the wheel.

 

No...any vacuum leak at all will prevent the hubs from locking or unlocking automatically. If drivers side locks and unlocks with vacuum.....then my guess is there is no leak and just the passenger side hub is sticking, so then yes changing your pvh solenoid would allow the esof to work as it should.

 

Thanks! Going to work on pulling the hub and checking it next. Hopefully it is just stuck and cleaning it will fix the problem.