NHTSA Safety Recall (23V-896) on 113,000 F-150 Trucks with Trailer Tow Max Duty Package

[Snakebitten]

'Reasoning / validity' of any of that, or its potential role in failure (?) ...... nope, not gonna go there!

But it's a forum!

While I would never take you as someone to conspiracy-orize, I think you've more than earned the privilege to speculate!

By the way, although it hasn't been many months and many thousands of miles, I did note that only the head of the bolts I used showed even a hint of exposure to the elements. The threads are well protected from mother nature.

So what's up with the heavy galvanized anyway? Caliper bolts don't seem to be so corse. And I haven't held the 4 bolts that actually hold the hub to the axle tube, but they don't appear to be so corse either.

It's going to be so interesting to finally see what exactly Ford changes with the TSB.

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[Snakebitten]

By the way, if I haven't made it clear what I personally believe is the problem with the OEM bolt, I think they are, or can be, over-torqued.

I'm more than willing to admit that is pure speculation. But if you hold your hands on the torque wrench you have used many times before, and you then go to torque a bolt that size, (M12, in this case) that little voice in your head starts to whisper "are you sure you wanna do that?" even as you approach 84 ftlbs. It just feeeeels like that should be enough.

 

[Buyer2021]

'Reasoning / validity' of any of that, or its potential role in failure (?) ...... nope, not gonna go there!

But it's a forum!

While I would never take you as someone to conspiracy-orize, I think you've more than earned the privilege to speculate!

OK, speculation du jour .....

1. The bolt isn't the problem, its failure is only one consequence of the underlying problem
2. The underlying problem is some weird, unanticipated, and yet unknown (or at least yet un-published) phenomenon / phenomena which causes the axle shaft to try to 'extract itself' from the splined hub with extreme force
3. Absent (2) the OE bolt ('coarse', galvanized, etc) would do the job it's intended to do
4. Given (2) a 'stronger / nicer looking' bolt defers the bolt-failure consequence of (2) but doesn't mitigate the underlying cause or its other consequences.
5. A truly effective 'final' remedy must eliminate the extreme force inherent in (2)

I have no idea, not even speculative, regarding the form that a truly effective 'final' remedy might take. Really, no idea whatsoever!

 

[Snakebitten]

OK, speculation du jour .....

1. The bolt isn't the problem, its failure is only one consequence of the underlying problem
2. The underlying problem is some weird, unanticipated, and yet unknown (or at least yet un-published) phenomenon / phenomena which causes the axle shaft to try to 'extract itself' from the splined hub with extreme force
3. Absent (2) the OE bolt ('coarse', galvanized, etc) would do the job it's intended to do
4. Given (2) a 'stronger / nicer looking' bolt defers the bolt-failure consequence of (2) but doesn't mitigate the underlying cause or its other consequences.
5. A truly effective 'final' remedy must eliminate (2)

I have no idea, not even speculative, regarding the form that a truly effective 'final' remedy might take. Really, no idea whatsoever!

You weren't difficult to draw in at all! ?

If #2 is in fact the REALITY of the problem, and it shouldn't be a surprise if it is, I'd be tortured forever wanting to understand the source of the "force".

I think when the truck is parked, sitting still, the bolt is not subject to any measurable force beyond the torque it was tightened to. And as ridiculous as it might sound to point out, I don't think the bolt would ever shear in 100 years just sitting there.

So whatever force there is that can and has managed to shear the head off of the shank of the Bolt, it only exists while the truck is in motion.

I'm stating the obvious. But I think it matters to progress along the possibilities.

On paper, with the hub behind bolted rigidly to the axle tube, there's zero "flex" between those two elements. So only the hub/wheel bearing would introduce any play, which very well can create-generate forces on and/or against the bolt.

This fits perfectly within the context of what you (and Hammerman) you propose in #2.

I'm trying to imagine what that play would look like if it was exaggerated, just to make a visible illustration.

Wouldn't it be a bow in the splined axle itself since the 2 splined ends are the only contact points, and the flex/play of the hub bearing would allow those two splined ends to NOT be in a perfectly straight line?

If my imagining is accurate, the force that would create that bow would increase the torque on the bolt head, but since the other end of the splined axle is free to "slide" in/out from the center diff, my brain says the flex-force wouldn't be concentrated on the bolt.

I apologize for the rabbit holing. But not really. Lol

 

[scott011422]

Here is a good illustration. I believe the side load example on the 3/4 section is the problem. I don't think that pressed in spline is up to that particular challenge. Sounds like a few others are on this same line of thinking.......

 

[HammaMan]

Here is a good illustration. I believe the side load example on the 3/4 section is the problem. I don't think that pressed in spline is up to that particular challenge. Sounds like a few others are on this same line of thinking.......

I think what the diagram doesn't illustrate well is that in the F150, both axle wheel bearing configs have the bearing/s in the same place. The 3/4 "HD" design has shorter axle tubes on the diff housing that's then made up with its hub. This places both designs bearings in the same place, inboard of the wheel flanges. Both bearings end up just inboard of wheel center, but still within profile of the wheel itself (though both do try to get near the center of the wheel). I believe their intentions with the "HD" design is that moment loads get imparted into a V pair of tapered bearings instead of the opposite edges of the roller bearing. Both are still supported with the axle shaft. The difference being where axial loads are countered.

In 3/4 float axial loads are taken up by the wheel bearings while the axle shaft itself can float in and out of the diff. In the standard config the differential pinion shaft acts as the stop for inboard/compression forces, imparting its force into the diff housing / flange bearings, whereas tensile forces are imparted into the C-clip (or is it a U clip?)

Pinion shaft

C clip aka "axle shaft retaining washer"

Seems the 3/4 per the manual is claiming the hub is pressed onto the axle. The axle bolt itself is TTY. Seems strange to require both. @Snakebitten have you made any attempt to see if the axle is free floating in there when you remove the bolt? I don't recall you commenting on that. We've seen instances of the bolt failing and then the axle becoming free floating to slide out of its splines on the wheel hub and into the diff.

Curious if torsion loads aren't causing the axle to flex slightly creating a balance issue that it could just sit in causing it to fatigue the bolt until it gives up seeing as it's already yielded? That's also a lot of shaft to leave unsupported if it's not mating with the wheel hub perfectly as well. Lots of theories that don't really get anyone closer to resolution
?‍

The manual does state explicitly that the hub is held into place with the axle, its inner washer, and the bolt, while also stating the hub and its bearings are serviced as a single piece indicating it's pressed into the bearings (though not likely clipped into place).

 

[Snakebitten]

@Snakebitten have you made any attempt to see if the axle is free floating in there when you remove the bolt? I don't recall you commenting on that. We've seen instances of the bolt failing and then the axle becoming free floating to slide out of its splines on the wheel hub and into the diff.

I did check thoroughly, when I removed the bolts. And commented that the pressed fitting still was intact, as well as the absence of fretting materials. (dust)

 

[Buyer2021]

Here is a good illustration. I believe the side load example on the 3/4 section is the problem. I don't think that pressed in spline is up to that particular challenge. Sounds like a few others are on this same line of thinking.......

Useful diagrams, IMO, but in the case indicated below, aren't the text explanations reversed in error?

 

[scott011422]

Useful diagrams, IMO, but in the case indicated below, aren't the text explanations reversed in error?

Good Catch!

 

[Chad_Cole_311]

2021 Ford Powerboost with max tow - I'm on my 7th rear axle replacement going in with the 8th new axle.

20k miles - Passenger-side failure February 4th, 2022

26k miles - Driver-side failure December 5th, 2022

29k miles - Passenger-side failure (again) February 5th, 2023

40k Miles - Passenger-side failure (again) July 18th, 2023

47k miles - The driver-side has leaked all rear oil out, assuming the axle has failed again. February 2nd, 2024 - Dealer replaced both rear axle's.

56K miles - Driver-side failure (again). I am waiting to get the truck into the dealer next week.

 

[PatchManager]

I recently received the notification of the PCM programming recall, so I decided to call and get the axle bolt looked at as well even though I recently checked the axle bolts and found that they were still both firmly seated. The service advisor stated they would replace the axles. I questioned her about this because it was my understanding that they would just check the bolts and only replace the axles if the bolts had broken. She said the note that she read stated the axles would be replaced. Is she misreading this or has Ford changed the process? The appointment isn't until FEBRUARY, so my thought was to keep the appointment and maybe the final fix will be in place by then.

 

[Fox146]

2021 Ford Powerboost with max tow - I'm on my 7th rear axle replacement going in with the 8th new axle.

20k miles - Passenger-side failure February 4th, 2022

26k miles - Driver-side failure December 5th, 2022

29k miles - Passenger-side failure (again) February 5th, 2023

40k Miles - Passenger-side failure (again) July 18th, 2023

47k miles - The driver-side has leaked all rear oil out, assuming the axle has failed again. February 2nd, 2024 - Dealer replaced both rear axle's.

56K miles - Driver-side failure (again). I am waiting to get the truck into the dealer next week.

Why don’t they just replace the entire diff . Maybe it wasn’t manufactured correctly or something. That’s nuts

 

[Gros Ventre]

The NTSB called out fatigue as a related cause. In my mind poor heat treating by the manufacturer of the bolts themselves may have been the cause. If they were therefore brittle that made them more susceptible to fatigue and then under normal loading could fracture. That alone could satisfy the #2 item above a few posts.

 

[Snakebitten]

I recently received the notification of the PCM programming recall, so I decided to call and get the axle bolt looked at as well even though I recently checked the axle bolts and found that they were still both firmly seated. The service advisor stated they would replace the axles. I questioned her about this because it was my understanding that they would just check the bolts and only replace the axles if the bolts had broken. She said the note that she read stated the axles would be replaced. Is she misreading this or has Ford changed the process? The appointment isn't until FEBRUARY, so my thought was to keep the appointment and maybe the final fix will be in place by then.

Unless she has a different document than my dealership and the NTHA, she is misreading. In fact, Ford will deny the parts order without an attached photo of the sheared bolt on at least one side. They do allow for replacing both sides if only one side sheared.

Just my opinion, but the reason they replace the whole assembly is because the labor is so little in doing so, rather than attempting to extract the broken bolt. And since I'm only stating my opinion, I think the bolt and the original torque specification is the culprit. But emphasis on opinion, based on viewing and messing with a faulty axle/bolt and then the same with a the replacement.

I'm ready to eat crow if/when Ford ever divulges sufficient information.

 

[Buyer2021]

I'm ready to eat crow if/when Ford ever divulges sufficient information.

Good qualifier, methinks crow is not foreseeably in your diet.

I don't expect we'll ever get an explanation of the underlying problem from Ford, even when (note I optimistically didn't say "If" ) the 'permanent' recall remedy is promulgated.

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