Broken metal peeps

Bike N Gear

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Anyone care to guess what could have caused this axle to break?

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Karate Monkey

Well-Known Member
Loading on the freehub. Ie, somebody cased a landing/cumulative damage. Same thing that causes 7 speed+freewheels to break.
 

Santapez

Well-Known Member
Team MTBNJ Halter's
Looks like there's a major stress riser there where the diameter changes at a 90 degree cut with no chamfering where the break is. The inner bearing on the hub and inner bearing on the freehub are spaced outside of that stress riser so the play in the two will bend the axle right at that stress point.

It looks like they went for a larger bearing on the freehub inner probably to keep the interface between the two siffer, which would be OK but then makes that high stress point. Would have been a stronger axle to be straight without that change in OD for the larger bearing.
 

JDurk

Well-Known Member
What @Santapez said. I had that happen twice with a Hope SS hub. The thru axle shaft was aluminum and would break right at the edge of the hub body where the freehub sat flush. It's since been replaced with a stainless steel version.
 

Bike N Gear

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I think it's a poor design. Only had about 1100 miles on it. Waiting to here back from Specialized. Pretty sure they will tell me it's not a part they stock despite being their S/DT hub.
 

Santapez

Well-Known Member
Team MTBNJ Halter's
I don't see a machined radius where it changes diameter. That would make a stress riser, and cracks to develop over time.

There's the tapered portion, which doesn't go smoothly into the rest of the axle, but instead has a straight cut down to the OD, probably where the bearing sits for the freehub. Looks like there's a mark in the circled portion below the taper where a bearing sits.

Hard to really tell, but does this hub use 5 bearings? Looks like there's marks for two bearings on the top straight portion, a larger bearing on the thicker part of the taper portion, and then two smaller bearings, one that sits against the tapered portion.



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Karate Monkey

Well-Known Member
The wear on the tapered piece is likely from the able flexing/rubbing the sleeve on the freehub. The bearing looks like it is recessed.
 

Santapez

Well-Known Member
Team MTBNJ Halter's
The wear on the tapered piece is likely from the able flexing/rubbing the sleeve on the freehub. The bearing looks like it is recessed.

If a larger bearing doesn't sit on the large part of that taper, I'd say it's a garbage design. :)

It means all the force of the freehub sits on two bearings to the drive side of that tapered portion, which would put a lot bending stress on the axle.
 

Karate Monkey

Well-Known Member
If a larger bearing doesn't sit on the large part of that taper, I'd say it's a garbage design. :)

Well, yes. I think I said that, just not in as many words. We discovered collectively that that design doesn't work well with freewheels, hence the move at the time to Shimano's freehub with the axle bearings on the outsides.

The current Shimano design is similar, but with no step+an unsupported portion that is ~4mm. Time will tell if it is as robust as their original design.
 
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