Note that on the early CSP and the current recall dealer notices, in the 'Parts Requirements' section there's reference to LH & RH "Rear Axle Shaft Assy" as one PN each (and Caliper Anchor Bolts as one PN); I'm not seeing any indication of hub, axle, and axle bolt as separate PNs required for the 'repair'.
And I never thought of that.
But thinking about it now, could that be one explanation for the evolving suffix-letter in the otherwise consistent "Rear Axle Shaft Assy" PNs?
And that's why I suggested a little back to another poster there is no need to go to the dealer if your bolt isn't currently broke. It is easy to check at home.
I don't think any of us has yet seen inside the hub assembly to know the arrangement of bearing(s) and components within this specific Ford design (as a 'non-serviceable' / replace in its entirety assembly the internals are not revealed in the Workshop Manual), but whatever that is it retains the integral rotating flange to which the brake rotor and wheel are bolted via the wheel studs.
EDIT - just realized you're talking about welding the axle shaft to the hub assembly (not the hub assembly to axle housing connection) - no guess from me other than that would preclude service of the hub or axle shaft as separate components.
No guess from me.
There doesn't seem to be any correlation between usage and the failure. People that have a non-towing babied pavement queen have broken them while others that tow a lot haven't. The axle shaft itself isn't load bearing as that's the way it's designed.
The axle is held inside the axle tube because it is tapered, and only the splined surface at the outboard end is small enough diameter to the fit into "hole" in the hub.
You can't pull the axle through the hub. And if you look closely, the end of the axle can't even be pulled flush with the hub face. That's why I claim the infamous bolt is only tasked with "locating" (holding) the splined axle furthermost outboard. And it's why it is safe (relative) to operate the truck with a sheared bolt. Short term for sure.
This is the axle pulled as far outboard as possible:
This is it as far inboard as possible:
It's TRAPPED between two splined devices. You must remove the hub itself to get the axle out of the tube.
Seems like they could have just made a bolt with a shoulder allowing it to torque to the axle itself, kept the heavy duty washer head and just put a heavy duty rubber washer of sorts there to act as a light-duty spring of sorts (or possibly a conical spring steel design that takes up the ~2mm of space created by torqueing to axle, assuming tolerances allow). This would add a little bit of play between the axle and the hub, preventing the shear, while still holding the axle in place. It seems that the axle is able to ever-so-slightly flex/flop/move at the hub to the point where it fatigues the head off the bolt. Given that the axle is easily moved without the bolt retaining it, it shouldn't take much force to keep it in place.The axle is held inside the axle tube because it is tapered, and only the splined surface at the outboard end is small enough diameter to the fit into "hole" in the hub.
You can't pull the axle through the hub. And if you look closely, the end of the axle can't even be pulled flush with the hub face. That's why I claim the infamous bolt is only tasked with "locating" (holding) the splined axle furthermost outboard. And it's why it is safe (relative) to operate the truck with a sheared bolt. Short term for sure.
This is the axle pulled as far outboard as possible:
This is it as far inboard as possible:
It's TRAPPED between two splined devices. You must remove the hub itself to get the axle out of the tube.
