Truck: 2003Ford F-350 Lariat, 7.3L Diesel, 4X4 Electronic Shift on the Fly (ESOF), 136,400miles<o></o>

Scenario: I recently got stuck in some soft sand and when I tried to use 4-wheel drive to get out I found it was not working. With slight tension on a tow chain the 4-wheel drive activated and I was able to drive right out. A few weeks later I noticed a loose feel in the front driver side wheel and an intermittent squeal. Found my bearings going bad, so replaced both front hubs. The 4-wheel drive still did not work after replacing the hubs. I also found that after turning on the defroster and switching back to Max AC it took several seconds for the vents to open.

A local shop put “smoke” in the vacuum system and reported to me that smoke was “pouring”out of both front hubs and out of the Pulse Vacuum Hublock (PVH) Solenoid. They also found the Vacuum Pump was underpowered. I took the diagnosis and left.

I replaced the Vacuum Pump and still had no activity when switching the ESOF to 4H or4L. I found that after turning on the defroster and switching back to Max AC it still took several seconds for thevents to open.

I replaced the PVH Solenoid and still have no activity when switching the ESOF to 4H or4L. When I started the truck after replacing the solenoid my Max AC was blowing out of the defrost vents and it will not switch over to the proper vents.

I am guessing I may have a seal that needs replaced at the hubs since they were both leaking, but I am not sure where to go next….

I am a weekend dabbler, I am by no means a mechanic! Any advice is much appreciated!

 

There is a piece of vacuum tubing coming out of the top of each wheel bearing enclosure that runs up to a hard line on the frame, you may just need to replace that tubing, as it dries out and cracks. I would start there looking for vacuum leaks.

I will have to dig around, but I know there is a hub maintenance thread or link here somewhere on cleaning them.

the other option is to plug the vacuum lines and install Warn Premium manual locking hubs from Riff raff, he has a great price on them, that was the road i took when i had an auto hub fail. i think my 1 good one is now in WA with Tinywonder here.

 

Go with a set of manual locking hubs and be done with it and never have to worry about vacuum leaks again.
Try putting your hubs to "lock" instead of auto and see if it works then.

 

I'd like to try and repair what I have for now, but may look at the manual hubs in the future.

The shop said the lines are not leaking. I asked them to check the connectors near the hubs and hey said the leak was "in the hub." Any idea what that would mean?

How do I determine if a vacuum line is leaking?

 

I replaced my unit bearings and am having the same issue now. Put them in manual and they lock, Auto they don't...

I'm going to try this next, this is what they might have been talking about
Hub Service

 

I did not get a chance to try the "manual" mode today, but if I put them in manual will I always be in 4X4? What role does my ESOF switch play in the system when hubs are in manual?

 

With the hubs locked in manual the wheels will be locked to the front axle shafts and the wheels will spin the shafts as you drive. You will not be in 4 wheel drive though. When you place the switch in the cab in the 4x4 position the transfer case will engage and you will be in 4 wheel drive. When you turn it off you will be in 2 wheel again but still spinning the axles. Once you move the hubs back to auto you will no longer be spinning the axle shafts. They basically work like manual hubs when used this way.

The auto hubs have other problems if not maintained. Here's a link that may help with the hubs although I'm not sure if it will help with your vacumm leak problem. http://www.guzzle7pt3.com/allube.php

 

Alright, defrost/AC problem solved. Vacuum pump and new PVH Solenoid working correctly. So, now for the apparent vacuum leaks at the hubs....at this point 4-wheel drive seems to work intermittently with hubs in auto and using ESOF. Any ideas if there is an O-ring in the hub that I may have missed when replacing the hubs....?

 

Usually when you eliminate the default to defrost you fix the esof problem. Are you sure it's not working every time.