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Hey All,
I have recently replaced my rear derailleur (because I knocked it off) and I went through the steps to tune the gears. The gears are changing silently and quickly with no issues at all. However when I am on the smallest cog I am noticing it will skip intermittently. It appears to do it more when it’s under a greater amount of pressure but it’s not predictable and I can easily go for long stints without it doing it, particularly if I’m just peddling on downhill sections. Any suggestions? I was wondering if it might be the lower stopper, but it all looks aligned. Its a shimarno XL 12 speed if that makes a difference (with Shimarno XL chain).
Thanks
You'll have bent the hanger or even the dropout if you hit it hard enough to damage the mech.
Cheers, from what I see and test with a stright edge that is all lined up nicely, it was my first concern when I was replacing the part, though never hurts to check again 🙂
Possible stiff link in the chain?
I'd also unwind the limit screw 1/8th of a turn as it may just be a very marginally limit issue.
Give it a good clean.
If you spin the cranks and watch as the chain goes around the smallest cog you can usually see a stiff link lift off a little bit from the cog.
Do you by any chance have a wheel set that uses a DT Swiss star ratchet freehub?
I do and what you’re describing is exactly what I felt/experienced when the free hub started slipping. Random/occasional skipping when under power in the higher gears. A quick strip, clean and regrease (with a tiny amount of an appropriate grease) sorted it right out.
I would TRIPLE check that the gear cable is routed correctly through the mech…
On the subject of cable routing, did you shorten the cable at all? I’ve had similar in the past where I’d replaced the gear cable but it was too short, routed under the bottom bracket and when the suspension went past about 60% activated the BB pushed on the cable and caused some ghost shifting. Took me ages to work it out!
Have you adjusted the b screw to move the jockey wheel away from the cog?
Have you routed the chain over the guide on the cage? I've done that before 😅
Is your chain stretched and it doesn't like the new jockey wheels?
Get the gear mech hanger checked/realigned with a proper tool - visual isn’t enough these days as 12 speed drivetrains are really pernickety - even brand new bikes out of the box sometimes need a tweak.
Is the magic chain link the right way up ? With SRAM there's definitely a right and wrong way due to one edge being kidney shaped and the other flat. If that's the wrong way around, it will definitely skip intermittently in the smallest cog.
It might not be the only issue, or even the cause of this specific problem (doesn't really sound like it TBH) but I would still get a hanger alignment tool on it. Visual check is nowhere near enough IMO. Having experimented a bit, I reckon shimano's 4mm at the rim tolerance is too wide for 12s and you want it as good as you can get and quite a lot better than that for good shifting. And you want to do that as the first setup step really.
I've had various problems with 12s and although they weren't all hanger alignment issues specifically, it was never really right without this being bang on. So I tend to align the hanger before assessing what else I've got going on.
The gears on my wifes bike have been skipping for months, I've tinkered with them endlessly and eyed up the hanger many many times, it always looked fine. Finally bought a DAG-2.2 from Park and was amazed at how far out of alignment the hanger was (horizontal and vertical). Straightened that out and reindexed the gears and everything seems ticketyboo (for now!).
I bought the tool as my kids are starting to jump so figured I'll have lots to fix over the next few years.