I'm about to pursue a project on my 2011 F350 and I'm wanting to make sure I have a decent basic understanding of the system. My emphasis is on the parts in and around the steering knuckle. I was hoping to describe my understanding of the system and if anyone catches anything I don't understand, I would appreciate correction if you have the time. So, starting at the transfer case:

Front output of transfer case connects to the front drive shaft. When the electric actuator that shifts the transfer case puts the transfer case in 4wd, power is transmitted from the front output shaft of the transfer case to the front differential.

The front differential divides that power as appropriately as it can to the axle shafts that come out of each side of the differential. There is a carrier bearing on the inside of each axle shaft (I think?). Is there a seal in there to keep oil from going into the axle tubes?

On the outside of the axle tube there is just a dust cover of some sort? Then there is the u-joint (not a CV-Joint?). On the other side of the joint is a stub shaft that goes through the steering knuckle and hub/bearing.

From this point on out I think I understand how stuff works because I have replaced the wheel bearing/hub assembly. What I don't understand is:

How is the stub shaft retained and stabilized within the steering knuckle?

As I recall, the only thing that holds that stub shaft into the hub/wheel bearing is a very heavy duty snap ring. How does that keep the stub shaft, u-joint and outer end of the axle shaft stabilized?

I was examining my pickup and it was easy to move the u-joint quite a bit. My brother went and looked at new ones on the Ford dealership lot and they moved about the same amount. So apparently the wobbling is normal? How do the splines on the stub shaft stay properly engaged if there is that much play?

It sounds like the back seal on the knuckle needs to be intact and very precisely installed so the orfice for the vacuum does not get blocked and so that the steering knuckle/hub/bearing/locking mechanism is air tight, enabling the vacuum actuation of the hubs to work properly?

All of these questions are because my hubs are not engaging while in auto. If I pinch the vacuum line on the right side, the left side will engage fine. If I remove the line going into the passenger side knuckle and try to pull vacuum on the steering knuckle with a vacuum pump I am unable to pull a vacuum.

I have a spare locking hub mechanism so I replaced that as a test and it made no difference. Right now I am suspecting the seal at the back of the steering knuckle. With as much play as there is back there, I cannot imagine how any seal could retain a vacuum but it must work if the seal is in good shape because the new ones are that way too.

Any thoughts would be much appreciated. Thanks

 

Your description and understanding of everything is correct. The inner vacuum/knuckle seal could be shot. Mine disintegrated when I took it out at 100k miles.

 

Thanks. I am reading about vacuum pulses but it appears that is on the older style hubs. It appears to me that the current hubs release when I release vacuum pressure and engage when I apply vacuum pressure (at least on the side with no leaks).

I am not finding anything on the forum about the new style hubs. Am I correct in how they work as well? Thanks.

 

Are you having any of the common vacuum leak issues like air only coming out of your defrost vents?

 

This is another reason that I'm wondering if the 2011 and newer Super Duty trucks are different. The line that goes from the vacuum reservoir down to the hubs was completely broken in two shortly after the vacuum reservoir before I started working on this.

When that was the case, there were not symptoms like air only coming out of the defrost vent while the 4wd was engaged. Also, my hub locking mechanism is totally different from all of the tutorials I see for replacing the hubs. I know my hub locking mechanism is not aftermarket because I have purchased a replacement one and it's exactly the same.

When I apply vacuum to the left steering knuckle with a Mighty Vac pump, it engages the hub (when the hub is in auto). When I release vacuum with the Mighty Vac pump, the hub disengages. The way I understand it, i should require a strong vacuum signal to engage it and a weak vacuum signal to disengage it if it works the same as what all the tutorials and YouTube videos describe.

Finally, ALLDATA mentions to make sure not to accidentally install a "yellow dot" hub locking mechanism for pulse vacuum and to instead install the "magenta dot" mechanism if you are replacing the hub locking mechanism.

I don't have access to ALLDATA right now so that's not word for word, but that was basically what it was saying.

Anyway, I guess I'm wondering if Ford has changed things around enough that the diagnostics and repair are a little different than they used to be? I think the basic concept is still the same, but either I'm not understanding something or there are some difference to how the system works now.

 

Also, thank you for your service.

 

Here's what ALLDATA says:

 

I finally found a thread referencing CVH (Constant Vacuum Hublocks) that are on the 2011 and newer trucks vs PVH (Pulse Vacuum Hublocks) that are on the 2010 and older trucks.

ESOF Clarification - Diesel Forum - TheDieselStop.com

Edit: This link will not work with an iPhone (and perhaps not any mobile device). It has something to do with their enhanced mobile view. To see the link you would have to use a device that does not use the enhanced mobile view. I don't know how to get around that.

 

For what it's worth, I have looked at pictures of the hublocks from 2006 to 2010 on Google and I can detect no visual difference between those hublocks and what are on my F350. Must be something in the part that cannot be disassembled that makes them different.