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EB
08-27-2020, 10:58 AM
This is probably on its way to the shop, but I wanted to check in here to see if anyone has encountered something like this with a Shimano hub before. I have a brand new Shimano XT M8130-B "SuperBoost" rear hub on the Evil. Like all Shimano hubs, it's a cup-and-cone bearing system.

Coasting, the hub is fine. When pedaling, it frequently emits a "grinding" sound as it turns. Also, it feels slightly draggy compared to the 148 hub I had on the old build,. though so many things have changed with this bike including the tires that it's hard to pin down whether that's the hub or something else.

It's extremely annoying after awhile, and definitely audible to riders near me. Very surprising to have this behavior with a brand new hub. The other data point is that I have washed this bike a few times with a gentle hose spray since the build was finished, but prior XTR cup-and-cone hubs I've had have had no issue with being washed from time to time.

jtakeda
08-27-2020, 11:02 AM
Hmmm. I feel like this doesn’t add up.
If it was the bearings in the hub the grinding should happen whether coasting or pedaling.

Does it happen in all gears? Is it possible the chainring is ever so slightly grinding on something?


My gut tells me this is crank/pedal/bb related if it only happens when pedaling.

Mark McM
08-27-2020, 11:17 AM
Hmmm. I feel like this doesn’t add up.
If it was the bearings in the hub the grinding should happen whether coasting or pedaling.

That's true of the main hub bearings, but the freehub bearings don't move when coasting. Unlike with earlier Shimano freehubs, the freehub body mounts directly to the axle. So if it only grinds when pedaling, the suspicion would be the freehub bearings or seals.

How do the bearings feel when you turn the axle by hand (off the bike)? Is there a difference when turning the axle vs. turning the freehub? How about when the wheel is in the bike, and the cranks are turned backwards with the wheel stationary?

EB
08-27-2020, 11:17 AM
It happens in all gears, but is much more audible in large cogs than in small ones.

I agree it may not be the hub, but I've managed to rule out the suspension and the cranks look fine as far as I can tell.

jtakeda
08-27-2020, 11:26 AM
It happens in all gears, but is much more audible in large cogs than in small ones.

I agree it may not be the hub, but I've managed to rule out the suspension and the cranks look fine as far as I can tell.

Have you checked the rear derailleur jockey wheels? I’m just throwing up possible guesses here btw. Maybe the bearings in the jockey wheels are worn and when the chain line is more at an angle it’s causing more bearing grind?

gdw
08-27-2020, 01:56 PM
It's probably the freehub bearings/design
You might find this thread useful. https://forums.mtbr.com/wheels-tires/multiple-xt-m8100-hub-failures-1139315.html