Max tow axle -- is this the normal position?

[Ed21]

Does anyone know if this is the normal position of the axle? Or has it moved into the differential before the bolt breaking. Noticed all of the broken bolt pictures look this way. I know that by the location of where the bolts are broken that it would indicate that the shaft is in the shown location. Just wondering if the bolts loosen before breaking. Seems shaft should be flush with hub to eliminate any stress or flexing between the washer behind the bolt and the axle face. Also, if it does move into the differential can it cause damage? Disclaimer: I’m not an engineer, I just play one in my sleep.

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[Ed21]

Also, what’s the difference between this design and the 2020 max tow axle?

 

[Old Bear]

I haven't had this happen to me, but I do know that the half-shaft is not flush with the hub as designed. I do not recall anyone specifying a measurement for how far down it is, but I do know that it is not flush. Yes, the danger is that over time the half-shaft will walk into the differential housing, eventually causing damage on both sides, leaving you stranded unless you also have 4-wheel drive.

 

[Bryan Simon]

I would not be concerned about the axle traveling inward.
The worst it’s gonna do is bump into the spider pinion pin.
Will do no damage whatsoever.
The only difference in this rear vs all the others is that the axle is not really load bearing/supporting.
The rear hub is doing the the load supporting, not the end of the axle.

 

[Buyer2021]

I would not be concerned about the axle traveling inward.

Just FYI, it's been documented (actual experience) that the axle shaft can migrate inboard far enough to lose engagement with the splines at the outboard (hub) end (or perhaps the engagement becomes too shallow and the splines strip-out under load).

While this does not appear to result in damage to the differential, it does result in sudden loss of complete rear-axle driving force. That can be a very real problem depending on the driving situation when it happens.

Yes, some have reported being able to move the vehicle by engaging 4WD and / or rear locker after that occurs.

 

[Ed21]

The only difference in this rear vs all the others is that the axle is not really load bearing/supporting.
The rear hub is doing the the load supporting, not the end of the axle.

Thanks for the replies, I was mainly wondering what the max tow axle difference is compared to the previous generation.

 

[RickBullotta]

This is the normal position for trucks with the max tow axle:

 

[hotrodmex]

Thanks for the replies, I was mainly wondering what the max tow axle difference is compared to the previous generation.

Previously (_-20) Ford still used a semi-float design with straight roller bearings. The axle shafts were 35 spline units, as opposed to the regular 34 spline units. The 35 spline axles stayed the same diameter the whole way, where the 34 spline neck down.

There was no visual difference on the exterior. I've seen lots of debate on the part number tags, but I don't think there was consensus.

 

[Ed21]

Previously (_-20) Ford still used a semi-float design with straight roller bearings. The axle shafts were 35 spline units, as opposed to the regular 34 spline units. The 35 spline axles stayed the same diameter the whole way, where the 34 spline neck down.

There was no visual difference on the exterior. I've seen lots of debate on the part number tags, but I don't think there was consensus.

Were they held in with a C clip in the differential as opposed to the bolt on the end? Just trying to get a little understanding on the change. I know of course the reason for most redesigns is $. Just trying to get a little knowledge in this thick skull of mine.

 

[hotrodmex]

Were they held in with a C clip in the differential as opposed to the bolt on the end? Just trying to get a little understanding on the change. I know of course the reason for most redesigns is $. Just trying to get a little knowledge in this thick skull of mine.

Yes, they were c-clip. Exactly the same design as the regular 9.75 with thicker shafts (as those are what fails by bending with vertical loads). This is a great graphic that has Semi, 3/4, and full float.

https://what-when-how.com/automobile/rear-axle-automobile/​

So you can see, one way to make the assembly carry more weight on a semi floating axle is to just make the axle shaft stronger, so it holds up against the bending.

 

[Ed21]

Great, thanks! I have a better understanding of it now.

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