Kontact 

That is the reason, and it works. But we're not talking about axles breaking but failures of the spot where the freehub meets the hub body.

Kontact 

Are the OPs axles breaking?

Kontact 

And that's a problem, why? These hubs don't break axles yet are lighter than Shimano.

OldBike876

I got the freehub off and apart. Nothing looks worn (this thing is only 4 months old, of course), no shards of anything, no cracks... nada. It doesn't freewheel well, though, and in the two weeks of this thread it has developed one hell of a creak.

So, it clearly malfunctions in use, but I can't find any obvious faults upon inspection. Weird.

OldBike876

Well, to close this out, it's "fixed" but maybe not for good.

I splurged on a fancy new wheel. I bought it online and fellow I dealt with had some good advice to measure the frame. I did so, and there was a less than 1.5 mm difference at worst. I measured it several times, and would repeatably measure than 1mm difference left to right. The dropouts are square to each other, and I could not find any evidence of frame damage (wrinkled paint, cracks, distortions...)

The new wheel is very nice. I installed it and it was immediately obvious that it does not "drag" like the last one. It's a stark difference: I was coasting down the parkade to bed in the new brake, and it rolled MUCH faster (and I am using the same tire and casette). Also, it's clearly much stiffer than the old wheel.

But.... very occasionally I can hear what I think is the chain hitting the chainstay. That was one of the symptoms that started all of this. It's now a faint, a one-off, and only happens maybe every other day, but only when I transition from pedalling to coasting. It's significantly better.

I guess this means that the problem was unlikely to be in the old wheel, but the new wheel makes it less likely to happen. Anyway, I can live with it, and I'll wait to see what happens next.

Thanks for the theories and advice, as always.

masi61

Any chance this chainstay slapping of the chain is related to chain length or in someway connected to rear derailleur cage not doing its job properly (and nothing to do with the freehub)?

CliffordK

So far I've had absolutely no problems with Shimano style hubs. But, not quite the same weight as the OP, I don't think. However, I've done some loaded touring.

I don't have the FH-M8000. When Shimano moved to 11s, they started using an oversized axle on some of their hubs which I think the M8000 got, even though the freehub body appears to still be the shorter 8-10s freehub.

I would think the oversized axle provisions would make things better, but perhaps not as it may mean all internal freehub components got smaller.

Something like the Shimano XT FH-M756A is dirt cheap, and uses the older style freehub that has had decades of bombproof use might be worth considering trying. Of course, much of the expense is building the wheel.

If the OP wishes to continue with the M8000 hub, it might be beneficial to learn to change the freehub oneself, and replace bearings, check cones, grease up and set the cones. Not a hard job, but a bit tedious.

The NuVinci Continuously Variable Transmission (CVT) hubs are very popular with bikeshare bikes, and are supposed to be very durable. It might be worth considering, although it would be a major upgrade and not cheap.

OldBike876

I do not think so, as the chain slap is from it bunching up between the casette and chainring.

OldBike876

Before deciding on a new wheel, I spoke to a mechanic at the bike store about a supply of freehubs. He said they would sell me whatever, but he recommended against just fixing it endlessly. He said that diagnosing the problem in his shop would mean a thorough inspection and then trying the wheel in another bike before trying a shop wheel in my frame. He figured it was likely a problem with the wheel, but that was just based on my description and him seeing the chain bunch up in his shop.

Tusk

For what it is worth, I have Shimano 6800 hubs on my go to bike. At 250#, I have never had an issue.

You may want to start looking at Internal Geared Hubs for your next build. Shimano makes one that is very cost friendly.