Do hubs vacuum has anything to do with kingpin?

Recently, I noticed a leak on my right kingpin. Just before that for a while I was not able to engage to 4wd. (Some noise from under the car 4wd icon flashes and goes back with same reverse sound to 2WD)
While checking some youtube videos I have just learned that one of that it might fail to engage when vacuum is lost. 

I was in a sandy mud for a while before the last time it engaged, but nothing so dramatic or harsh. Light offroad. 

Just wondering if those two related deeply like the vacuum has to do with greasey joint, or is it the sand destroyed both? 
 

Chances are that the oil and grease mess inside the knuckle is probably causing it so cleaning it thoroughly when replacing the bearings will fix it, orrrrrrr it's a coincidence and there is a separate vacuum leak on one of the lines.

The vacuum passes though the wheelbearing (disengage- lock moves out) and through the space between the CV joint splines and the hollow stub axle (engage-lock moves in).
It needs the seal round the CV joint behind the wheelbearing to be in good order, or the hub won't engage.



 

It looks like the shaft oil seal has gone, most likely by wear on the kingpins. You can check the kingpins by jacking the wheel and try moving/rocking the wheel in both the vertical and horizontal. There is an article in the wiki about this.

As Lambert says if the shaft oil seal has gone it might have filled the knuckle with sludge and this could have blocked one of the vacuum lines, but vertical movement is kingpins and horizontal movement is steering or wheel bearing, I think.

I had a lot less oil than this and could feel vertical rocking in one wheel, but very little in the other, although both kingpin bearings had gone. The lower bearing in mine was stuck in place and took some shifting, it was very rusty when it came out.