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Snakebitten

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Are these TTY? They appear to seal the axle and the hub together to mitigate gear oil leakage. My idea is a whole other configuration entirely, not just a washer.
I was just describing what you had pondered and the idea it planted in my mind, as feeble as that might be.

If it is NOT the over-torquing of the OEM bolt that is injuring the shank, and then leading to eventual shearing under additional stresses, then it must be solely those additional stresses on an otherwise healthy bolt.
(Unless the OEM bolts are simply crap?)

So my idea is just to cushion those forces in play on the bolt itself a little.

The hub/axle mating surface is what carrys the transfer of torque to the wheels. I don't think that design or the materials used aren't up to the task, as long as the axle is kept at the intended location relative to the hub.
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Oilberta

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Sudden shock load on the bolts? 🤔 Interesting thoughts gents.

Would it help if one applies buffer material between the washer and bolt as suggested…. Maybe the use a spring washer taking some of that sudden load out of the equation:

Ford F-150 NHTSA Safety Recall (23V-896) on 113,000 F-150 Trucks with Trailer Tow Max Duty Package 1708110638102
 

Snakebitten

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Sudden shock load on the bolts? 🤔 Interesting thoughts gents.

Would it help if one applies buffer material between the washer and bolt as suggested…. Maybe the use a spring washer taking some of that sudden load out of the equation:

1708110638102.png
I love it!
I need to find one that fits dimensionaly.
 

Oilberta

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I love it!
I need to find one that fits dimensionaly.
Dimensionally yes, there’s also a thickness = spring force ratio considerations, out of my realm but we use Fastenal(bolt suppliers…. Really good ones) up here in Canada, pretty sure it’s an American outfit. They really know nuts and bolts.
 

HammaMan

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Sudden shock load on the bolts? 🤔 Interesting thoughts gents.

Would it help if one applies buffer material between the washer and bolt as suggested…. Maybe the use a spring washer taking some of that sudden load out of the equation:

1708110638102.png
The tensile forces imparted on the bolt should be such that it can't flatten that washer for it to provide protection against any excessive tensile forces. If you calculate the clamping force the bolt applies (not difficult to calc), you'd need a washer that doesn't begin to deflect until those forces are at the point where the washer takes up the additional forces. The ultimate tensile strength of the bolt should be easy to approximate based on grade.

Think of it like a leaf spring suspension (but conical here) where deflection occurs when additional load is placed onto them. For example, a leaf spring at maximum deflection under normal loading has no give for additional flexing capability (like already sitting on the bump stop). It's no longer providing any benefit against additional forces as its capabilities have been exceeded.
 

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Big Dog Daddy

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Oilberta

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The shock load theory cooked up here may have some teeth to it.

Consider how many times the differential is changing output side to side for inner/outer wheels when turning and cornering. How many times does a wheel have no traction on ice/grass/wet pavement then suddenly have grip and the differential just immediate transfer torque to the other side when traction changes.

I’m no engineer or physics major, but my basic understanding is that the torque being applied from the differential will want to suck that axle shaft inward, and if there’s already some slop in there indicated by those with broken bolts what impact will that sudden torque increase do to the bolt trying to retain that axle in place.

Again I’m spitballing here, but the forces are there.

Now we need someone to drive in full diff lock mode 100% of the time to test, like those 100% sport mode guys 😁
 

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Another mitigation technique could be such that the axles are counterbored another 1/2 or so (as well as deepening the threaded area) for use with a longer bolt so that whatever additional tensile forces present, are absorbed by the additional length of the bolt. Increasing the free length of the bolt allows for it to better handle tensile forces by providing more shaft length to deal with excessive tensile forces.

Another option may be a slightly lower grade bolt allowing for more plastic deformation before failure such that it can absorb whatever play / forces are sheering these bolts. Here for example a grade 5 would continue to hold the axle in place after experiencing whatever force is failing the higher grade bolt. Torque value would be lower, but the grade 5 wouldn't break. Whatever forces are breaking these appears to be a high force, but the force required to keep the axle in place that can be moved by hand with bolt removed, which is the ultimate job of this bolt.

Ford F-150 NHTSA Safety Recall (23V-896) on 113,000 F-150 Trucks with Trailer Tow Max Duty Package 1708114207293
 

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HammaMan

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but my basic understanding is that the torque being applied from the differential will want to suck that axle shaft inward, and if there’s already some slop in there indicated by those with broken bolts what impact will that sudden torque increase do to the bolt trying to retain that axle in place.
The force would be equal inside of the diff itself on the spider gear and there's nothing retaining it there. While twisting would 'shorten' the axle, it may also imbalance it as well increasing the forces applied to the bolt. I'd put a few $ onto this being the failure mode.

There's no forces I can see that requires this bolt to be the grade it is. It's a floating axle after all, it's not holding the wheel on, it's job is to retain the axle into the splined hub. As soon as the torque is removed, a spring is more than adequate to pull the axle back. I don't see an issue with this method as a drive shaft freely moves in and out of the transmission as the rear axle moves about on its arc changing the exposed length of the drive shaft.

Need more images. Imbalance appears from this image at least to provide witness marks that one area of the bolt was receiving more force than the rest! If the axle is torqued and warped, that vibration would 'polish' or otherwise provide witness marks to this force and the vibration.

Ford F-150 NHTSA Safety Recall (23V-896) on 113,000 F-150 Trucks with Trailer Tow Max Duty Package 1708116067330
 
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Snakebitten

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Another mitigation technique could be such that the axles are counterbored another 1/2 or so (as well as deepening the threaded area) for use with a longer bolt so that whatever additional tensile forces present, are absorbed by the additional length of the bolt. Increasing the free length of the bolt allows for it to better handle tensile forces by providing more shaft length to deal with excessive tensile forces.

Another option may be a slightly lower grade bolt allowing for more plastic deformation before failure such that it can absorb whatever play / forces are sheering these bolts. Here for example a grade 5 would continue to hold the axle in place after experiencing whatever force is failing the higher grade bolt. Torque value would be lower, but the grade 5 wouldn't break. Whatever forces are breaking these appears to be a high force, but the force required to keep the axle in place that can be moved by hand with bolt removed, which is the ultimate job of this bolt.

1708114207293.png

The Dorman bolts, which I used, are the same 10.9 grade as OEM.

The other bolts pictured, in various lengths, are the next grade down. (8.8)

If/when I experience a bolt failure, I will be happy to try this theory out.

Ford F-150 NHTSA Safety Recall (23V-896) on 113,000 F-150 Trucks with Trailer Tow Max Duty Package 20240215_175913
 

Snakebitten

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:) Here you go! They have incredible compressive force. and the OD looks closer to what you may already have. Just check the dimensions. Let me know if you can't find them, I'll pick them up and mail them to you.

Steel Spring Lock Washer, Conical, DIN 6796, for M12 Size, 13 mm ID, 29 mm OD | McMaster-Carr
Does the OD need to be perfect?
Just so long as it's a little less than the OEM washer, wouldn't it be fine?

By the way, do I stack the belleville washer on the OEM? Or use it instead?
 

Big Dog Daddy

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Does the OD need to be perfect?
Just so long as it's a little less than the OEM washer, wouldn't it be fine?

By the way, do I stack the belleville washer on the OEM? Or use it instead?
No, the OD doesn't need to be exactly the same, but it does need to be large enough to engage with the hub and not fall through the middle. If its slightly smaller or bigger it wouldn't be a problem. The link I sent has the washer at 3mm thick judging from the photos it's probably about the same thickness as the factory washer. You could probably use this one as a direct replacement for the factory washer or with a longer bolt you could place it between the head of the bolt and the factory washer. Either way it will create a compressive tension.
 

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The Dorman bolts, which I used, are the same 10.9 grade as OEM.

The other bolts pictured, in various lengths, are the next grade down. (8.8)

If/when I experience a bolt failure, I will be happy to try this theory out.
Consider a grade 5 bolt as a test article, keep in mind it uses less torque. Before testing, devise a method for precisely measuring the bolts looking for any permanent deformation/stretching. Don't forget your loctite
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