Another broken Axle bolt

[Ed21]

The nut threaded on the end of the axle shaft would be more substantial imo.

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[FaaWrenchBndr]

So the MaxTow axle design is somewhat of a bastardized mix of a semi floating and a floating axle.

With a semi floating axle, the retainer plate holds the axle shaft in the housing. The axle shaft itself, supports the weight of the load and provides the torque to the wheel. A full floating axle, the hub assembly is retained directly to the axle housing by the flange. This in-turn, supports the load weight. The axle shaft slides through the hub and simply drives the wheel. The force of this axle torque is normally connected to the hub with a flange on the axle and bolts at the outer edge.

Ford’s MaxTow, the hub is indeed retained at the axle housing, supporting the load. The axle shaft simply provides the torque to the hub. The torque from the differential is transmitted to the hub through a set of spines. The spines meet with the hub at the outer end of the axle. The bolt that is breaking, simply retains the actual shaft to the hub. If the splines have the proper clearance, the bolt does nothing but retains outward pressure on the axle shaft at the hub meeting surface.

I believe the problem lies with the axle spines and the hub. Movement is creating a situation where the retainer bolt is stressed and then fractures. It’s a poor design.

 

[scott011422]

It would be interesting to see a cutaway of the bearing/hub assembly. Traditionally, semi-floating axles only use single row bearings. This is plenty to transfer axial load to the OD of the axle tube. However, the use of a single row bearing leads to increased play in the camber direction. Hence the forged axle shaft flange that is typically used. This keeps the bearing plane alignment perpendicular to the axle shaft, Single row bearing takes the weight load and all is good.

But if Ford is using a single row bearing, now all that camber load is supported by the spline. It makes sense that Ford is aware of this since they pressed the splined shaft into the bearing hub. Splines are traditionally used for rotational transmission only. They are not normally intended for side loads, That's why most are all slip fit.

Now it seems Ford has done this for awhile. So what changed?

What's really interesting to me is, From the pictures I see, Looks like a standard front wheel drive hub bearing. Those have been spline driven by CV shafts forever. Bearings (more than 1 in those hubs) takes all the loads, slip fit spline transmits the power, spline is retained by a bolt or castle nut with no problems. No Fretting, No wallowing, No stripping of splines, nothing.

So obviously, there is something going on with this axle to have all this spline problems on what should be a no worries system. Ford has this designed for basically no flex. I think something, somewhere is definitely flexing. Bearings, Axle tube, Something. Flexing would also explain the broken bolt. There should be almost no load in that direction. Couple that with the shaft no longer being pressed in when this bolt breaks. All so very odd.

Sorry for the ramble.

 

[FaaWrenchBndr]

Here’s diagram of it…..the MaxTow is on the right. A full float 3/4 is on left.

It just doesn’t show the bolt at the hub/end of the axle. This design uses one roller bearing, but the weight is suspended by the hub hub is bolted to the house flange.

 

[Deleted member 22921]

One would think that by now, Ford would simply stop using this axle bolt design.

 

[Buyer2021]

Here’s diagram of it…..the MaxTow is on the right. A full float 3/4 is on left.

It just doesn’t show the bolt at the hub/end of the axle. This design uses one roller bearing, but the weight is suspended by the hub hub is bolted to the house flange.

I respectfully suggest that the details are critical and the depicted diagram has so many inconsistencies compared to the Max Tow hub assembly (more than just the missing end-bolt) as to make it useless for assessing the the actual Max Tow configuration.

You may consider these inconsistencies and omissions 'minor details', that's your prerogative, but IMO they are the devilish details which require accurate depiction to gain real understanding of the Max Tow axle and its behavior.

Perhaps of interest are the pics of an actual Max Tow axle shaft and hub posted here.

Aside, the list of "...everything else that's included in the new 2021 Ford F150 maximum towing trailer axle...", though from a Ford retail website description, omits reference to the larger diameter / thicker rear brake rotor included with the Max Tow axle per the Ford e-Sourcebook specifications applicable to the 2021 F150.

 

[Ed21]

Here’s diagram of it…..the MaxTow is on the right. A full float 3/4 is on left.

It just doesn’t show the bolt at the hub/end of the axle. This design uses one roller bearing, but the weight is suspended by the hub hub is bolted to the house flange.

 

[Ed21]

Sorry for the screw up on the quote but as far as the full float being overkill for a half ton. My truck has almost 2000# payload. I would imagine most new F150’s have well over 1000# payload.

 

[HammaMan]

Neither axle has ball bearings -- They're both roller bearings, one has twin conical.

 

[FaaWrenchBndr]

I respectfully suggest that the details are critical and the depicted diagram has so many inconsistencies compared to the Max Tow hub assembly (more than just the missing end-bolt) as to make it useless for assessing the the actual Max Tow configuration.

You may consider these inconsistencies and omissions 'minor details', that's your prerogative, but IMO they are the devilish details which require accurate depiction to gain real understanding of the Max Tow axle and its behavior.

Perhaps of interest are the pics of an actual Max Tow axle shaft and hub posted here.

Aside, the list of "...everything else that's included in the new 2021 Ford F150 maximum towing trailer axle...", though from a Ford retail website description, omits reference to the larger diameter / thicker rear brake rotor included with the Max Tow axle per the Ford e-Sourcebook specifications applicable to the 2021 F150.

Ok…….guess this is a flawed depiction.
Apologies

 

[Buyer2021]

Neither axle has ball bearings -- They're both roller bearings, one has twin conical.

Maybe I'm misunderstanding ... Are you saying you know for certain that the Max Tow hub assembly contains some configuration of roller bearing(s)?

If you have any fact data on the configuration of that hub's internals, please enlighten with details and share your source. I'd desperately like to know what's in there but have not found any instance of authoritative (IMO) diagrams or pics of an actual 'dissection' of the Max Tow hub assembly.

 

[HammaMan]

Maybe I'm misunderstanding ... Are you saying you know for certain that the Max Tow hub assembly contains some configuration of roller bearing(s)?

If you have any fact data on the configuration of that hub's internals, please enlighten with details and share your source. I'd desperately like to know what's in there but have not found any instance of authoritative (IMO) diagrams or pics of an actual 'dissection' of the Max Tow hub assembly.

Without tapered roller bearings in place there's no way to handle axial loads on the hub. The standard 9.75" rear end transfers axial forces to the differential's tapered bearings while using a healthy sized roller bearing at the end of the axle tube.

 

[FaaWrenchBndr]

Without tapered roller bearings in place there's no way to handle axial loads on the hub. The standard 9.75" rear end transfers axial forces to the differential's tapered bearings while using a healthy sized roller bearing at the end of the axle tube.

Thanks for explaining, looks like I found some bad info and diagram on the axle setup

 

[scott011422]

Without tapered roller bearings in place there's no way to handle axial loads on the hub. The standard 9.75" rear end transfers axial forces to the differential's tapered bearings while using a healthy sized roller bearing at the end of the axle tube.

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

 

[astro_fusion]

It's a full fluffer, they just cheaped out on the axle and hub, usually full floaters use a big drive flange that bolts to the outside of the hub body to transfer rotational torque. Ford "simplified" that and just gave you guys a center bolt plus washer. So they saved all that material on the end of the axle, and all the extra machine work on the hub for the attachment drive flange that would normally deflect and keep hardware out of tension. In the offroad world full floaters usually don't have bolts in the center of the axle to retain them, sometimes they are threaded but just for extraction purpose. The axles (sometimes hollow and gun drilled) simply float and bump between the drive flange (or hub cap) and the center pin in the diff carrier. Drilling and threading heat treated splined axles to locate them is a big no no, the axles twist, and when they do their length changes. Fix and add torque to both ends and you get bolt elongation failures.

Even worse it's a unit bearing full fluffer. Can't even check or add preload to the hub assembly?

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