I own a 2000 Excursion Diesel and I have read all the posts about hubs not engaging. And yes, when i get the money, manual hubs are in the future but for now I have to deal with what I have. Here is the problem....
- I engage the 4x4 and more times then not the hubs will not lock in. It seems that if i cycle the switch i can get it to grab but it won't hold. I tried the method of the a/c vent (i'll tell you how i did it becuase i don't think i did it right). I started the X, turned on the a/c (air is now coming out of the vents, not the defrosters), i then engage the 4x4 ( light comes on) however the air continues to come out of the vents and does not go to the defroster. According to this technique, I do not have a vacume problem. SOO, I went and looked at the hubs. Both seem good. I then took a vacume gauge, went right to the input from the vacume hose to the hub and pumped it up to 10 inHg. It holds but then will slowly trickle down. THen did the same thing to the other side. This time it would not pump up at all. So, i then swapped hubs thinking maybe the hub is bad. The problem stayed on the same side. I then disconnected that hose and capped it. So now the hub that did work is connected the other one is capped off. Hooked up the vacume to the line going out of the relay in the engine compartment to the hubs. The system pumped up fine.
SO I ASK ALL OF YOU SMART GUYS - what the heck is going on? I am not familiar with what is inside that knuckle (don't know the technical term for the part) or hub that keeps the system tight.

 

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

There is a oring seal that is probably bad on yours.

 

I looked at the ones on the hub. Their good, also, i can swap hubs and they both work on the good wheel. Its something in that wheel. I need to know what else is in their that could cause it not to hold pressure.

 

Lock yiour hubs manually when you need 4 wheel drive, for now, until you can afford a set of replacement hubs.

 

I think i found it. Guzzlers website is amazing. In his "how to service your needle bearings" he talks about a common problem with the ESOF. The o-rings in the wheel housing itself go bad, which can lead to the vacuume system pulling dirt and debries into the assembly. Anyway, sounds like this is my problem.

Thanks

 

I have a 2006 F-250.
Is this the same service for 2005 + trucks?

 

There is an additional set of vacuum seals behind the hubs, they were replaced at a shop on a previous truck I had it, they were an $80 part.

 

my hubs weren't engaging on my '03 so i just took the hub assembly all apart, cleaned it up with brake parts cleaner, re-greased them, put them back in, and haven't had any problems since. did the same to my brothers '04 and no problems with his either.