Forum menu
M8120 mech (12 speed) has started sticking and returning slow, leading to the chain skipping on the smallest sprocket (worse when the clutch is on).
Tried the normal relube of the clutch mechanism itself, which helped for a couple of rides, but the problem is back now.
Couple of questions before I strip the bugger down using the instructions here:
https://si.shimano.com/#/en/iDM/MARD001/maintenance/toc_task_x4l_jjn_j2b_kt
(I want to remove and regrease the plate axle)
Clutch is only about four months old, although it's done more than 1000 miles. Warranty job or expected maintenance at that point?
Shimano specify a particular grease - the mobil marine type stuff I normally use will be too thick, but I have a tiny pot of much lighter DT Swiss ratchet grease - would this be suitable?
Finally, has anyone done this on their clutch mech, and is disassembly/reassembly an OK job, or will it explode into a million pins and springs if I even look at it?
It's not a hard job, just a little bit fiddly working with small parts. Some mechs come really dry from the factory so yes, not uncommon to have to relube so soon.
I've always used the hub grease shimano recommends so can't comment on anything else unfortunately.
Thanks Devash
Right - I've stripped it down and cleaned/regreased the plate axle, which was notchy before. Now it's buttery smooth, but the chain is still skipping under pedalling load on the 10t sprocket, regardless of clutch on/off. It's not doing it in the stand, just when ridden.
It's only on the 10t. Has the mech spring failed, or is there anything else I should be looking at?
How old is it? Shimano warranty is 2 years (3 on XTR)
https://bike.shimano.com/en-EU/information/warranty.html
Less than six months. Will definitely be inside warranty period, just wondered if I'd missed anything obvious before I bother the retailer.
Sounds like something is up. I'd get it warrantied. My experience of Shimano's warranty is that the retailer will just send you a new one from their own stock.
I had similar slipping with just the smallest cog on a 10 speed set up. Tried loads of different stuff including a goat link. Eventually seem to have sorted it by tightening up the cassette lock ring. Might be worth a try.
Thanks. Now started to think back to what the last thing I did to it, which, to be fair, is normally the root cause.
I removed and reinstalled the PF BB while on a squeak hunt. Could a missing BB spacer (moving chainline slightly inboard) be the culprit here?
Nope, that's not it, BB shell is definitely 92mm and there are no spacers there. Think I've tried just about everything now.
What longevity are folk getting out of a 12spd XT cassette?
If you ride in the 10 a lot it could be worn?
I don't think I do! Cassette has done probably less than 1500 miles since spring, mostly in very good conditions. I've ordered an Slx mech which will turn into the spare if that doesn't turn out to be the problem.
More likely to be a stiff link or hanger alignment issue I’d have thought. Dodgy clutch won’t cause it to skip on a particular sprocket.
Pretty sure it's mech-related now.
Put a brand new chain on it, no improvement (or skipping on the other sprockets, which I'd expect on a worn cassette.)
Tried an older wheel with a SRAM Eagle cassette, did the same just on the 10t.
Swapped the mech for an 11spd one, no skipping even under load..
So either the mech or a very slight chance it's the hanger, as the 11 spd mech used a different one. I'd expect a bent hanger to throw out shifting elsewhere, and it's shifting perfectly.
Sounds like you've narrowed it down to the mech. But I did find the smallest XT 12 speed cog is quite easy to clock wrongly. The cutouts on the back sort of look like there are two ways to mount it but really one of those makes just enough difference for that gear to skip and shift bad.
I had the same issue and ended up buying a new clutch from Taiwan, took a few weeks but sorted it (sort of!)
Now just trying to figure out why as soon as it gets muddy my perfectly turned gears turn to utter rubbish! Any wet conditions and the gears start to grind and sound awful, also a bit more trouble shifting.
Maybe 12 speed still needs a bit more refining?!
The cutouts on the back sort of look like there are two ways to mount it but really one of those makes just enough difference for that gear to skip and shift bad.
Nearly had the cassette off to check that today, then remembered it was the other bike I'd stripped last weekend to grease the freehub ratchet, not this one. 🙂