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Feb. 16, 2021, 2:20 p.m. -  Jan

re: sticking derailleurs. In a bout of winter bike overhauls I recently rebuilt an M8000 RD and a M7100 RD. My 11s needed jockey wheels and my 12s group had been suffering from a "sticking" mech, or inability to upshift from the 51T. After replacing the 12s' cable and housing, chain, and tried friend's GX10-50 cassette for comparison - nothing was successful to fix my upshifts.  AFAIK the clutch mechanism in Shimano 12s is the exact same as the 11s groups. It's three screws and a dab of grease and you're on your way. What was different was the exposure and wear on the plate axle. There was significant corrosion on the M7100 mech (3 months old) while the M8000 mech looked fine (3 years old).  This is where I believe the shimano 12s mech design is flawed. The "sticking" can be solved (on a surface level) by loosening or fully turning off the clutch. The clutch however is not the culprit. The corrosion on the plate axle prevents the desired movement from the parallelogram (see page 35 of Shimano service doc DM-MARD001-03) . I took some light sand paper to the corrosion, soaked it in fluid film and it has been great ever since. I haven't read any "long term" review mentioning this issue in any major MTB publication, but I also know my experience is not an isolated event. N.b. "flawed" is perhaps the wrong word because I probably spray my bike off with too much pressure. mea culpa.

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