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I have a newish build bike, with a 12s SLX mech I bought used from Merlin (via ebay) which as advertised as having had the clutch serviced.
It has been fine for a few rides but today I noticed the chain was skipping and loose, and on investigation the mech isn't taking up slack like it should. If I push it forward it doesn't spring back. Same behaviour with the clutch on or off.
Any ideas on where to start looking? Bike hasn't done many miles so it's unlikely to be merely dirty I think.
I've seen this a few times and for me it's not been the clutch that's been the issue - it's the pivot between the lower cage and the parallelogram that has got full of crap and has too much friction for the spring to overcome.
There's a good guide to stripping a Shimano mech here:
the clutch might well have been serviced but I found this Video really useful.
Its a really easy job and made a huge difference
edit.. link didn't attach but its that one there ^^
Nice one, thanks folks. I agree it feels like the pivot joint isn't as free as it should be: it moves ok if I move it, but not otherwise.
I will look at stripping the mech as a starter for 10 👍
Could be the main pivot, but could also be the clutch. Or both. First time I had to do it the clutch was fine and the pivot needed love, second time just recently the clutch was rusty and the pivot still running fine without it. Take it apart and rebuild with decent grease in the right places- I found this helpful:
https://nsmb.com/articles/shimano-derailleur-clutch-service/
An Important Update for those waiting breathlessly for news of the patient...
I made a bit of time to strip the mech yesterday, and it was indeed the pivot joint which was full of muck and tat. The poor old spring was apparently mostly made rust and bad dreams. It had also somehow twisted itself out the little hole on the back of the mech cage, and I think that's why I had no tension.
Anyway, lots of WD40, regrease, reinstall, and it seems OK for the time being at least. [Side note: Merlin's "fully refurbished" seems a bit optimistic in retrospect :-(].
One potentially useful note for Googlers From The Future: when reassembling the clutch note that the cam roller part has a hole on one plate which needs to mate up with a little peg on the base of the housing. If you get it upside down the roller assembly won't drop far enough into place and the cover won't go back on nicely.
Apologies to Doddy if he said that in the video -- I may have missed it 😀
Annoyed now, I lobbed an XT mech that I thought had a dodgy spring, I bet it was this.
I had to do this the other day but couldn't be arsed to go as far as you. Just fired loads of lube in there for now.