Mysterious Shimano 12-Speed Rattle

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Mysterious Shimano 12-Speed Rattle
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Posted: Oct 16, 2019 at 21:10 Quote
Most noticeable in 11th and especially 12th gear , there is a significant rattle / chatter when coasting over bumps, ie, no tension on the drivetrain.

Already checked chain length, derailleur B tension, chainstay internally routed cable, all bolts, cassette lockring, and DT350 freehub ratchet. Could it be something with the derailleur clutch system or perhaps the nesting 11&12 cassette cogs?

This is a brand new XTR derailleur and XT cassette.

Going insane on rides and at my workbench. Please help!

Posted: Oct 17, 2019 at 0:38 Quote
I have a pretty similar setup (SLX cassette instead of XT, but same derailleur and hub), and nothing.

I would probably disassemble the whole thing and check again ?
On a side note, what chainring do you have? The 12s Shimano hyperglide chains have a smaller inner width than SRAM 12s cassettes, and most of the regular narrow wide chainrings are not compatible with the Shimano 12s chain. Tried a RaceFace and OnOff chainrings I had on hand, and there are quite a few reports of people having big chain suck (or the chain "struggling" to get in the narrow wide)

Might be worth checking ? If you have a Shimano crankset and chainring, it shouldn't come from that...

Posted: Oct 17, 2019 at 7:29 Quote
Thanks for chiming-in, Ploutre!

Crankset/Ring is RaceFace Aeffect2, straight from an OEM build. Shouldn't be the issue. Sound is definitely local to the rear hub/cassette/derailleur area.

Also removed the pads on the brake to eliminate that option.

Posted: Apr 18, 2020 at 13:26 Quote
I've got an SLX 7100 mech, SRAM cassette, chain and ring.

I noticed when I back pedal, the chain goes very slack when in the small cogs. It's like the mech isn't putting enough tension on the chain to overcome the inertia when getting the big cogs turning backwards.
After a wet uplift day I noticed it got worse and also it would not shift from the biggest sprocket to the second one. The mech was stuck.
I took the clutch mechanism apart and cleaned and regreased it. When I put it back together it was smooth with the clutch off, but still not perfect with the clutch on. The backpedalling problem was still present but not as bad. The shifting problem was still present.
Next I took the wheel out and just went at it with Muc Off clean and protect spray. This did the job on the shifting.
It was still noisy though and today I noticed that there was no tension on the first 2cm of derailleur cage movement even with the clutch on. I was showing my daughter and it fixes itself - very odd.
After another clutch strip and rebuild, plus a good lube of everything, I have found that the clutch only works properly when changing down the box (from smaller to bigger sprockets).
Let's say I want gear no.10. If I change from 9 to 10 (bigger to smaller) there is 2cm of play on the derailleur cage. If I change from 11 to 10, stretching the chain out to reach over the bigger sprocket, the clutch is engaged from the start.
I am going to give it a go tomorrow and see if that quietens down the chain slap.
Not very good, to be fair. My previous XT M8000 never had that fault.

Posted: Jun 15, 2021 at 19:11 Quote
Did you ever figure out what was causing this @jaame? I am having the exact same problem in reverse (keeps tension when going from small cassette cog to large but not vice versa) with my new xtr 12 speed and it is annoying to say the least. Rebuilt the clutch twice and checked everything twice as well. I really don't want to have to use it as is or buy a new one. Any tips?

Posted: Jun 15, 2021 at 23:32 Quote
Worn or dirty clutch, the wrong grease in the clutch, and the bushing on the shaft that holds the derailleur arm onto the B knuckle. Especially that last one. It needs a good clean and rebuild every so often. Apparently one should use roller bearing grease in the clutch also, not normal grease.
I’ve switched to Sram now.

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