I have used the search feature, and have seen one after another problem with the ESOF feature. I have a 01 F250 CC 7.3 4wd. The problem I am having is the when I switch the ESOF switch into 4H or 4L it will not engage the front hubs. The transfer case is engaging though. When I bought my truck last summer the dealership installed 2 new hubs for me, so I know they should be fine. You can lock the hubs and the 4wd works fine. Also I do NOT have a problem with vents/defrost vacuum. I know the hoses going to the hubs look like there in good condition, so I am thinking possibly the PVH solenoid? What should I test or look at first? Thanks in advance.

Seayya

 

I had a PVH go out. It either works or it doesn't. Find the line coming off the PVHS that goes to the hubs. Just in case; the PVHS is mounted to the fender well directly above the passenger side front tire and below the hood lip. On mine there was a hose barb elbow less than a foot from the PVHS. If you have one, break into the line at that point. If not, disconnect the line at one of the hubs. Activate the 4WD switch and see if you can detect any vacuum. It's not much, but you can feel it. If you determine your PVHS is working you need start looking at your lines to the hubs again. If they're good you're back to what's inside the hubs. Isolate each hub and try pulling a vacuum to determine if a hub is leaking. They should be able to hold vacuum.

Check Guzzles signature for a link to instructions on tearing apart the hub if required.

 

Pic of PHVS

 

Well, I have been working on this thing off and on for hours now. I have 14" of vacuum after the PVHS during 4wd and 7.5" when I go back to 2wd. Now at the end of the hose at the spindle I was only getting about 5" at the start and down to 1" within about 20 seconds. So I replaced all the hoses from the PVHS to both wheels. Now I am at about 13-14" at the spindles, but the hubs still don't engage. I took both hubs out checked the O-ring and greased it up then reinstalled. Still no engagement. The hubs are new as of 6/07. Brand new OEM hubs. I very rarely use the 4wd, but I would like to use it from inside the truck when needed. I am really beginning to hate OEM hubs and the way they work. I had a Jeep Wrangler that the factory hubs would only work 1 out of 10 times. UGH!!!!

 

Hmmm. Sounds like a certain amount of progress. Your vacuum signals at the hub are right now. Check the text in the grey box at the top of the thread per the link below. I wonder if you have a knuckle seal leaking?? Were you able to draw and hold a vacuum within the hubs?

I'm interested in what you find as I am trying to find time to dig into my hubs for similar reasons. Good luck with it.

http://guzzle.rbmicro.com/nblube.html

 

Is the large yellow o-ring considered to be the knuckle seal? If so I know the one on the driver side is new because I just replaced it last week along with the wheel bearing hub assembly. That was a nice dent in the wallet. As far as holding vacuum within the hubs I am not for sure what you mean. Are you talking about putting a manual vac. pump with gauge on the spindle itself. I did put a vacuum gauge in line between the PVHS and the hubs and from what I can remember (did alot of changes and checking today) it would not hold steady. Thanks again.

 

The large yellow o-ring is not the knuckle seal. The knuckle seal is a large seal that's located behing the hub. If you had the hub out to replace the yellow o-ring, you were staring directly at the knuckle seal. It's what's on the axle stub, centering it in the knuckle. It's a large seal, just as big as the inner diameter of the knuckle where the hub goes in. If it's gone bad, your hubs will not hold a vaccum and they will not lock automatically.

It sounds like you've done a good job of diagnosing the system up to the point of the hub/knuckle assembly. Next you need to do as suggested and see if the hub/knuckle assembly will hold a vaccum. You are on the right track with your thinking though. Pull the line off the barb fitting on the knuckle and put your manual vac on there to see if it will hold a vac. I'm guessing it will not. You might even be able to hear the air leaking in from the back side of the knuckle, which is where the seal would be leaking.

If you find the knuckle seal is bad and causing a leak, it will have to be replaced to get your auto lockers to work. I'd actually replace it no matter what if it's leaking, because it also seals out dirt and water from getting into the bearings on the hub and axle stub. The seals are not cheap (for a seal anyway) at about $30-$35 a piece, however they can take a bit of time to replace. The lockers and hubs have to come off, then the axle half shafts have to be pulled out. The knuckle seal will come out on the axle when the axle is pulled. Luckily, the axles pull straight out and you won't need to tear into the diff to remove them.

 

I'm subscribing to this thread with interest. Keep us updated on anything you find.

 

Apparently I have a little job ahead of me from the looks of it, because they will not hold vacuum at the hubs. I am in the need of replacing upper and lower ball joints, so in about two weeks (first free weekend) I will replace the ball joints and the seals at the same time. I have to pull replace the seals that are at the end of the axle tubes as well, so I might as well replace all the seals. Then maybe they will work. I feel my wallet getting lighter as I type.

I thought I would atleast tell you where my first problem was with the hubs not locking. I bought this truck last June from my local Ford dealership and realized about 4 days later something wasn't right about the way it was running (this was my first PSD). At an idle it sounded like it was missing, as well as alittle smoking. Long story short: Two injectors were bad, so it killed those to cylinders (160-180lbs of compression vs the other 6 cylinders at around 400lbs or so). So after checking around to see how much to repair this motor with little to no warranty from repair centers. I got help from the dealership on replacing the whole engine from pan to turbo and I got a good warranty as well. They also installed the new hubs, changed all fluids and filters, and replaced the drivers side leather for no additional charge, and now $7200 later it runs GREAT! BUT during this swap out of the engine they got the vacuum line going to the driver side hub mashed in between the motor mount. I will shutup for now. Thanks again everyone. I will post my results as soon as I get the time to change everything.

Seayya

 

Glad you've got it diagnosed. Wish it could have been something simple.

Why do I feel my wallet get lighter somehow too?