Another broken Axle bolt

[HammaMan]

If the hub had tapered roller bearing, Wouldn't that make it fully floated?

But yeah, Without tapered bearings, Axial loads are taken up by the pressed in spline

I think you're mixing up hubs / axles.

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[scott011422]

I think you're mixing up hubs / axles.

Could you explain? Think there is some confusion somewhere.


On another note, Anyone wants to send me their old bearing, I'll autopsy that for the forum.

 

[Buyer2021]

On another note, Anyone wants to send me their old bearing, I'll autopsy that for the forum.

I'd love to see that but typically the interim remedy has been done under recall or warranty and the dealer retains the removed hub assembly and axle shaft (so no opportunity for the customer to take it and delve into the thing).

 

[HammaMan]

Could you explain? Think there is some confusion somewhere.

3/4 float is a lower cost design with the bearings closer together in a finished non-serviceable assembly, and the axle shaft provides some mass carrying capacity for moment loads as the bearing arrangement isn't sufficient enough on its own to counteract such forces in this application. Full floating preloads the bearings whose configuration is more analogous to a non-driven spindle. In lighter duty applications a 3/4 like arrangement would be sufficient on its own and is a common wheel hub configuration.

3/4 float design

Floating

The diagrams are generic representations for illustration purposes and don't represent any specific vehicle.

 

[scott011422]

Other than the assumption that Ford is using tapered roller bearings in the hub, I would agree with you 100%

I did say that "traditionally", 3/4 floating axles only use 1 bearing that transfers the load to the axle housing instead of the axle shaft. Who knows what Ford has inside that hub. But technically, if there are 2 opposing tapered roller bearings in that hub, that would in essence make that a fully floated axle.

And if thats true, I would lean more towards Astro-Fusion's theory that the spline is twisting in torsion, shrinking the length of the spline. That would explain the movement, sloppy fit over time, the fretting, even the broken bolt. Although I will admit that the splines look pretty straight on every photo i've seen. Could return after the torque is removed i suppose. That would lend itself to just a manufacturing issue.

 

[HammaMan]

In theory, yes it's constructed like a floating axle. When the axle bolt breaks and the axle slides inside, outside of no ability to transfer torque, the wheel and tire are fine. The issue with this bearing config is the authority it has over moment forces. It's supposed to use the axle shaft to do the lifting. If the bearing assembly / tolerances are outside of the engineered spec, or if it was just engineered poorly, it could be imparting more force onto the axle than was designed and popping its bolt head off. They're not sharing the causes so we can only speculate.

Speculatory fix is probably a thicker hub assembly to increase bearing spacing to reduce the forces that the axle shaft is expected to take. Since these have all been recall repairs, someone at a dealer may be able to get one. I don't see ford asking for the defective parts as it's just wasted cost. I don't believe the failure mode to be torsion related as we weren't able to determine any commonality of the failures. If it were owners who towed a bit it'd make sense. There's people who haven't towed and don't beat on the truck yet has had them fail. Poor / no preload on tapered roller bearings that then heat up and increase the spacing between them allowing the wheel to impart additional moment angle allowing for tensile forces on the bolt to increase. This could also be exacerbated by torsional forces in the axle twisting.

We're 2 years into this and as of yet I haven't seen anything on a final fix. IMO that points to it being a little more complex of a fix. Seemed to have showed up in the PBs first which suggests torque being a factor as they're heavier and have much more low end torque, particularly as a function of pedal travel. Torque alone though would suggest that the spider gears and their splines are receiving an equal amount of force and would have excessive wear where the axle splines interface. Popping the head off of that bolt requires a stupid amount of force that'd leave some evidence in the diff.

 

[Buyer2021]

Seemed to have showed up in the PBs first which suggests torque being a factor ....

Do you think that the PB's regenerative braking, which may result in more frequent and forceful reversal of the torque-load on the splines than most non-hybrid user's impose with their driving habits, may offer a clue in this?

Informal tracking data on the other forum suggests that PB's still predominate among bolt failures, even though non-hybrid variants are slowly gaining.

 

[hotrodmex]

Other than the assumption that Ford is using tapered roller bearings in the hub

 

[MikeyDog]

I personally have not experienced a broken bolt, but I thought we would have heard from Ford on what the recall remedy might be.

 

[FirstFord]

Ford's first letter said that they thought they would have a resolution 4th quarter 2024. Then a later letter pushed the time line back to sometime in 1st quarter 2025 (which we're still in). Even then, there is nothing binding to hold them to that - they could push the timing back again.

 

[HammaMan]

Ford's first letter said that they thought they would have a resolution 4th quarter 2024. Then a later letter pushed the time line back to sometime in 1st quarter 2025 (which we're still in). Even then, there is nothing binding to hold them to that - they could push the timing back again.

I've been suspecting they're hoping that they replace enough of them long enough for it to 'no longer be a problem'. Their recalls are hurting the bottom line.

 

[FirstFord]

I've been suspecting they're hoping that they replace enough of them long enough for it to 'no longer be a problem'. Their recalls are hurting the bottom line.

I can't say that that line of thinking has never entered my mind....

 

[UGADawg96]

That is possible except would the NHTSA sign off on a no-solution after the recall was initiated.

 

[HammaMan]

If ford is somehow able to tailor the data to show they've somehow figured out which ones were going to fail. Not sure how they were both able to continue to ship new trucks not part of the recall AND yet somehow not have a fix? That's not adding up.

 

[Buyer2021]

Not sure how they were both able to continue to ship new trucks not part of the recall AND yet somehow not have a fix? That's not adding up.

Yeah, that aspect of the situation is a bit of a puzzler

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