sapporoguy

Thanks! Now would you please convince my stoker of that?

EddyR

I will Monday afternoon . Football and doctors appointment first
Ed

EddyR

Sorry this took so long . All I did was a search on Google " dt swiss hugi broken axle" or "dt swiss axle break"
I do not remember which but both bring up axle problems going back to at least 2017.
I flipped over 700 Road bikes and do not remember seeing many broken axles, maybe four in 10 years. I was surprised how common it was in years past.
I had one break in my Dura-Ace 7 speed freewheel . I had never seen a Swiss Hugi and did not know anything about them.
All axles seem to break at the same spot. Bike axles do not turn so the load is always at a bearing surface. My Dura-Ace axle was to hard and it was brittle and had old cracking lines in it.
Swiss made a great effort to make a very durable hub and still light.. Quality control of a part over many years can lead to bad batches getting in. I see that these Swiss Hugi are used buy pro mountain bikers and they beat them to death. Also getting 15 years use on a heavy touring bike speaks well for the design.
When a bike axle is made it is turned down from a mild steel and when it is finished it is hardened. To hard or to soft and it may fail. I have seen a lot of bent freewheel axles on low end bikes that had very low end ,soft< axles. When machining the axle it is important not to have any sharp corners where the bearings sit as this will be a failure point. A small radius is needed and the bearing must have it also. Some replacement bearings may not have this and that will cause a premature failure.
I have seen bottom bracket spindle fail at the same spot.
Hope this helps
EddyR

base2 

The thing is EddyR is this is not a freewheel type hub. It is a free-hub type hub.

A free-hub wheel hub has 4 bearings.
The outer 2 bearings are immediately adjacent to the dropouts & the inner 2 by nature of design support the middle of the axle by deflecting any downward force exerted by the outboard bearings in the upward direction. The inboard bearings in the middle of the axle, literally the weakest point is supported by the hub shell. The effect is a net zero of unbalanced forces on the axle.

It is an exceedingly strong design that allows for very lightweight aluminum axles to be used for a very long time under very heavy loads.

That the OP broke one through fatigue is the reason the problem was not obvious. Failure of this mode is nigh unheard of with this type of design.

The cool thing is this hub is 100% rebuildable with readily available components & any home mechanic with a hammer, punch, & a dab of grease can do all the necessary parts replacements in minutes.

EddyR

Base 2 COME ON YOU KNOW I WAS TALKING ABOUT TWO DIFFERENT THINGS.
First The Swiss freehub and then comments about freewheel axle failures.
HOW LAME

sapporoguy

Thanks, Eddy. I do find at least one post on this forum with these search terms, and it does mention chain slap. I’m not sure why it didn’t show up when I was searching for chain slap (I didn’t know to search for a broken axle until I saw that was the problem). I’m trying to picture what the stress is at that point. There is a bearing there, but there are also the three other bearings in the assembly supporting the axle, and the QR shaft running inside (which helps explain why I could ride even with a cracked axle.)

sapporoguy

Update from OP.
I installed the new axle.
No more chain slap.

CroMo Mike 

It's a good idea to check your QR rod for damage at the point that corresponds with the break in the axle, too.

Bike Gremlin

I agree. Poor design.
In addition to the bearing's position, the axle's diameter is sharply/abruptly decreased at that point - creating stress in that area.
Correct me if I'm wrong in saying that train axles had that problem over a hundred years ago and it was solved by tapering the transition (sorry about my Tarzan English, not sure about the exact technical terms).

sapporoguy

Makes sense! I will do!

sapporoguy

New axle vs old. It was surprisingly easy to put back in, including driving a new bearing in on the side I pushed it out.

CliffordK

The frame is attached solidly to the axle, which then transfers the weight to the hub shell.

So, the majority of the weight is born by the axle, and the two bearings under the hub shell. With the longest part of the axle on the right side.

It is likely the symptom that the OP experienced was drag at the freehub, because with the tight skewer, it pushed up on the axle right at the break between the shell and the freehub, causing the freehub to bind.

The freehub, and skewer gave some stability to the system, and allowed them to "safely" ride the bike back home.

If it was a freewheel, the break would still be just to the right of the hub shell, but there would be less to stabilize the axle, and it might not have been rideable.

The weight of the rider load isn't typically borne by the freehub.

The two freehub bearings transfer pedaling force to the wheel. Now, pedaling in the lowest gear, going up a hill could put a significant amount of force on that inner freehub bearing, and also transfer to that as a bending force on the axle.

So, the axle is pulled every which way causing fatigue.



The break occurred right at the shoulder on the inside of the bearing. I would have expected it to be on the outside of the bearing. But, that likely had a sharp angle, which would have caused a naturally weak spot for the fracture to originate.

Ideally the inner bearing race would be ground with a quarter round matching a quarter round on the axle where the bearing sits. And, thus no right angle needed, and no focal stress point.

Some tandems have a stepped 12mm axle for QR, or 12mm thru axle.

sapporoguy

snipped:
Thanks for the thoughtful analysis! We spent a lot of time this summer on our cross-country pedaling in our lowest gear (24 x 36 for about 18 gear inches) fully loaded on our tandem going up mountains and hills, so it doubtless took quite a lot of stress.

fooferdoggie 

no one is a miracle worker.

Racing Dan

Not sure this analyses is valid. Lots of reports of broken mtb hubs, that break in the same way as the OPs. Not to mention even more reports of ratchet mechanisms with obvious signs sign of rubbing, likely caused by the axle bending under load.

base2 

So many engineers...
The allowed bending is caused by the triangulation of forces between the axle thickness and the distance from the inner bearing to the sxle end. An under tightened QR skewer allows the axle to come out of compression & thus develop the potential for fatigue.

The larger the big cog, & the more towards the center of the axle the big cog is located, the weaker the design. Axles have bracing angle issues just like wheels do. An acute bracing angle carries less torsional load than does a more perpindicular angle. It may be hard to see because the load path is all contained within the geometry of the axle itself & not plainly visible as dishing of a wheel is.

But, if you'll bear with me...
It's about 45mm-ish from the drive side axle end to the inboard freehub bearing. The OP's axle is 15mm thick & 135mm long. Draw a rectangle of those dimensions. Half the axle thickness is a 7.5mm radius. Draw an acute triangle 45mm long & 7.5mm across ½ the base...Now do the same for the 90mm long non-drive side. That's a pretty steep bracing angle with in the axle to keep the forces safely contained within the axle & the axle under compression. When those forces start to leave the axle, the axle starts to yield (bend.)

Bent axles weren't even really a thing even with nutted axles under tension until 6 speeds & the necessary 126mm to make room for the extra cog. (Discounting Ultra 6 which fit into 120mm spacing) It wasn't until then a new design had to be come up with. In case you hadn't noticed, it wasn't until the last decade or so that the biggest cog available was a 32 & the widest hub was about 135mm & the higher quality among them were not nutted 1:1 gearing or just a bit lower was about the limit. Currently, we're at 51 teeth and 157mm with Super Boost...With axles that are 12mm & .5-.75:1 or lower gearing being the norm?

The internet pics you are seeing are because we're back to the same limits the engineers of long ago designed themselves out of. The modern truss is 24% longer & 17% larger diameter than the old (freewheel) design with ~50% more pedaling load. Have you ever wondered why higher quality hubs have larger diameter hub shells? Much of that load bourne by the hubshells rigidity supporting the center of the axle with extra bearings lessening the bending moment upon the axle.

The reason for all this is to keep the axle aligned & under compression with available clamping force. A compressed part does not crack. The OP's axle did crack. Therefore the axle was allowed to come under tension. Period. A transient cyclical loading force was applied by large cogs near the center of the truss combined with excessive static weight beyond what the QR skewer & hubshell could keep aligned & under compression within the axle body is the cause.

For the OP's 135mm wide 15mm (large) axle diameter Hugh240, this is rare.

Racing Dan

Sure, argue its a great design all you want, but it wouldn't have happened with a Shimano style hub, with the right hand bearing all the way to the right. Something else might might have broken, but not the axle.

sapporoguy

OP here. I'm totally out of my league in this discussion, but: By right-hand bearing all the way to the right, do you mean farther right than the very right end inside the splined thingie that the cassette fits onto? My DT Swiss Hugi has 4 bearings, one at the left end of the hub (the disc-rotor end) right about where the spoke flange is, one at the right end of the hub where the spoke flange is, one at the left end of the splined thingie that the cassette fits on, and one at the very right end of the thingie. So my right-hand bearing is pretty near as far right as I can imagine its being.
It's hard to see where a bearing would fit anywhere further right. All these bearings are 6000s, so the axle engages all 4 of them.
Or do you mean a bearing all the way to the left? In my DT Swiss, the break happened at the far-left bearing, from where a quite a bit of axle continues, unsupported by any bearing, to the left-hand dropout. Does a Shimano hub have a bearing near the left-hand dropout? Somewhere at the left end of the disc rotor mount location?

Racing Dan

Im not aware of every single DT design out there, but the one in this thread, that is similar to most other rear hubs, has the right hand hub shell bearing behind the right hand spoke flange. The free hub, has two bearings as well with one all the way to the right and one close to the right hand hub shell bearing, but, the freehub doesn't support hub shell. That is the reason they tend to break or bend in that particular spot.- Between the right hand hub shell bearing left freehub bearing. Of course you can brute force a solution with a thick axle, but that doesn't make it a great design.

A shimano hub is quite different. Its too much to write here how it works, but look up some pictures and it should be obvious what's the difference.

CliffordK

Is that the correct size? I assume the axle is from 2005. 9-speed cassette.

That would have predated the move to thru axles and 11-speed.

Looking at the photo in post #13 showing the endcap, I'm guessing that axle is slightly oversized. Perhaps 12mm.

Yes, the inner freehub body is solidly bolted to the hub. And, the right axle bearing is inside this inner freehub body, which effectively moves the bearing out as far on the DS as the NDS. There are still bearings between the inner and outer freehub body shells.

I'd think that the freehub bolt would be under stress, but I haven't seen many reports of it breaking.

The 11 speed Ultegra/Dura Ace hubs started using oversized aluminum axles. And, similar axles may have been put into the m8000 and m9000 series hubs. I'm not sure if they are making overized steel axles. Perhaps in the Shimano Saint series.

I'm not sure if Shimano is making new Tandem hubs though.

Racing Dan

Im not up to speed regarding newer Shimano offerings, but it is true they now sell hubs that somewhat resemble DT hubs, with the right hand hub shell bearing deep in the hub shell and a disc style ratchet mechanism. They are however (mostly) through axle designs. In that system a properly sized through axle bolt can support a hollow hub axle, preventing it from bending to any significant degree, even if its made from thin wall alloy tubing. - I still assert this bearing arrangement isn't great, but it might be necessary to make room for a stronger ratchet mechanism to cope with the torque from the dinner plate size cogs*. In the older Shimano hubs the ratchet is inside the free hub. Not a lot of room in there. Not to mention the micro spline free hub body is even smaller, to make room for at 10t cog. On the road side of things it appears things are mostly the same as ever.

*EDIT: And ever more powerful e-bike motors.

base2 

Racing Dan
The right hand bearing is all the way to the right. Nearly at the dropout.
The left hand bearing is all the left. Nearly at the dropout.
The wheel drive-side hub flange bearing is under the hub flange.
The inboard freehub bearing is on the inboard side of the freehub.
The ratcheting mechanism is 2 spring loaded donut shaped rings in an over running clutch style configuration. Each ring has (18?) teeth that interface all of the other rings (18?) teeth simultaneously. Each ring is splined to it's respective body/shell to transmit the relative difference in motion to the other.
All the bearings interface on a common axle.
All components slide apart via a good tug & a little persuasion with a bearing press.

It is different than the common Shimano design. There is no hollow freehub fixing bolt to attach the freehub to the shell to allow for cup/cone design. There are no ratchet pawls to wedge.

(Edit: I just read your last post, I think you've got it)

CliffordK It is a 15mm axle external diameter. I own the OP's exact hub & made measurements with digital caliper before I submitted the reply. The axle is hollow. The interface with the bike is made by what ever end cap the end user wishes to use. Accounting for the thickness of the axle walls, a conventional 12mm through axle to interface with the bike would barely fit inside. So, yes, you are correct.

For a point of humility, I have never disassembled a new Shimano Microspline hub. I don't know exactly what goes on inside there yet. Given that it is thru-axle in design, I suspect it must operate under similar principals to the DT 240 but I will gladly defer to whoever has experience with one. Shimano isn't one to pass up a good design.

Anyhow all, this has been a good thread. The kind of thread I come to BF for.

reburns

Perhaps a picture would help:

sringlee

I have a 2002 CoMotion Speedster with a nearly identical rear hub. We replaced all the bearings and inspected the axle which still looks good (although in retrospect I should have magnafluxed it to identify incipient fatigue cracks.) I carry a spare axle, sourced from DT (thanks for carrying the part!) for just this occasion so I can fix things on long trips. One thing I would like to replace is the drive side end cap v-seal o-ring which is gradually wearing out. I can't find these online. Does anybody have a source, or should I go back to DT? All I see are later versions which are perhaps 28mm in diameter when mine is only 14mm or so.