Yet Another Cycling Forum
General Category => The Knowledge => Topic started by: Paul on 30 December, 2023, 10:08:14 pm
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I have 3x8 set up on one of my bikes. In lowest gear, under load, the chain drops from 1st to second sprocket. It stays in 2nd fine ::-)
It runs perfectly up on the stand. However, there’s a little bit of play in the rear mech at the pivot. Is it just worn out or is there something I can do about it?
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Two thoughts:
If you have sideways play on the rear derailleur linkages/pivots that might be the problem with it "flexing sideways" under load
Can you tweak the cable adjustment a tiny amount to take the chain just a gnat's further onto the 1st sprocket (and check the limit screw isn't restricting the chain position on the sprocket)
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After my last ride I tweaked it as you describe but I haven't tried it in anger since.
In its original set up, when it would stay in 1st gear, the mech would sometimes ping on the spokes, which is probably not a good thing and which is why I adjusted it. If I can't find a sweet spot (and god knows I need that first gear!) I'm wondering whether there might be enough room on the hub to put a small spacer on before the first sprocket, without compromising the lock ring, or causing the chain (when it's on the smallest sprocket) to foul the stays.
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Hanger alignment?
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Ooh, that’s a good question. I don’t think so, but I’ll investigate. Is there a quick and easy method? Something about screwing something into the hanger and checking for parallel-ness with an axle?
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A rear wheel with a Shimano (10x1mm thread) hub is the same thread as a gear hanger.
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Is the sprocket flexing? Years ago I had a fancy titanium XTR 8 speed cassette where the larger sprockets were mounted on a spider. Whenever I pedalled hard while in the lowest gear the chain would jump to the next sprocket. I changed the cassette for a cheap and cheerful steel one and the problem went away.
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A rear wheel with a Shimano (10x1mm thread) hub is the same thread as a gear hanger.
I think I have a shimano axle - is that what I need?
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Is the sprocket flexing? Years ago I had a fancy titanium XTR 8 speed cassette where the larger sprockets were mounted on a spider. Whenever I pedalled hard while in the lowest gear the chain would jump to the next sprocket. I changed the cassette for a cheap and cheerful steel one and the problem went away.
I’ll add this to the list if other efforts don’t succeed.
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It is more accurate if you use a complete wheel, rather than just an axle.
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Other things to check:
Is the low gear stop adjusted a bit too tight, so bottom gear isn't fully clicked in at the shifter?
Is the shifter badly worn?
In the unlikely event that you're using a friction shifter, frame flex can tug the cable enough to move the lever*. This shouldn't happen with indexed gears unless the shifter is really worn out.
You can check hanger alignment with a long steel rule and calipers, but you should remove the BB, wheel, and mech first. This method also assumes the BB shell is in straight. You should check for inward/outward bend and twist. I have an old Cinder Cone MTB frame that had a visibly bent hanger, but after 20 minutes' careful tweaking it shifts impeccably.
*my old Thorn would always change to the middle chainring if I tried to sprint in the big ring
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Here's a YouTube link showing how to do the hanger straightening thing with another wheel
https://youtu.be/TnwreRrorIA?si=Pvff-gcV8idyeKiq (https://youtu.be/TnwreRrorIA?si=Pvff-gcV8idyeKiq)
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Here's a YouTube link showing how to do the hanger straightening thing with another wheel
https://youtu.be/TnwreRrorIA?si=Pvff-gcV8idyeKiq (https://youtu.be/TnwreRrorIA?si=Pvff-gcV8idyeKiq)
Brilliant! I get that now. :thumbsup: