Have the shift on the fly 4x4 and at a point I need just a little advise.

Vacuum gauge has narrowed it down to the hub or a seal? I replaced the bearing two days ago and with it an o-ring around the bearing body. The actual hub has a o-ring around it, greased it as I checked it for damage. Both those o-rings look good, not damaged or rolled/pinched. A vacuum gauge attached to the hose feeding the hub doesn't build any vacuum. If I pinch the hose, the remaining vacuum hose leading to the left wheel and the pump are good, it holds stead vacuum and engages the left hub and transfer case.

I'm going to switch hubs, can do it without removing any wheels, just un-clip it and swap. If that doesn't reveal the issue at the actual hub or the o-ring... that would mean its the seal inside the axle?

Now my question, not having a schematic to work from, I'll assume the axle seal in near the diff or is there one near the bearing I'm missing?

Can I go without the seal or do I run the risk of early bearing failure from water or something like that? The left bearing was done last month and I never noticed any extra seals or something like that near the bearing when I took it apart. The axle slides thru the center of the wheel bearing, any seals there I may have missed?

I can turn the hub in to make 4x4 work, did it last year a couple times I used it, just gotten used to turning the hubs before I need them with my old truck. The hub will engage if I turn it, it's not the hub, its definitely a vacuum issue... is the area of vacuum between the bearing o-ring and the hub o-ring or deeper in the axle?

Thanks!

 

Where did you hook the vacuum to , at the line going straight into the hub in the wheel well or up in the engine bay?

 

On my 05' there is a fairly large seal that gets installed on the axle shaft and into knuckle and yes it is behind the bearing. They are around $50 each and you need the proper seal install tool or some appropriate sized PVC fittings. If you think you are due for ball joints you might as well do them while your at it as the axle and seal needs to be removed to do them. There should be enough if the seal left to keep out debris for awhile. As long as you aren't submerging the front end in water.

 

I replaced both lines going from the wheel well to the hub because they were soft and had the highest possibility to leak. Hooked vacuum pump to the line going directly to the hub, very easy to see if the hub will hold vacuum or not. The other end of that line is right off the canister. Only two lines for vacuum, A/C and the hubs.

My ball joints are solid.

 

Here's a link to a complete ball joint replacement.
Ford Super Duty Ball Joint Replacement Procedure | Superdutypsd.com
It's way more info than you need but it shows some pretty good pics of the axle seal. Unless it's in really bad shape or been disturbed it shouldn't be bad. Swapping the hubs is a good idea since you have a known good one. If you need to tear yours apart for a good cleaning and reseal here's a link to a "how to"
Welcome to guzzle's 4x4 Autolock Hub Lubrication Maintenance Web Page