When shifting gear on my mtb sometimes the chain sticks between cogs and other times it does not move immediately .Would be glad of any advice as it is very annoying I managed to stop to have a look and the chain sort of balances between the cogs.It will eventually fall on to the cog with a clunk although sometimes when I move the lever nothing happens at all and when I move it again it changes two gears.This is always on the smallest or second smallest rear cogs and usually changing up
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The chain gets stuck in between the freewheel gears or when you click to the next gear the chain clicks but won't shift? Does it happen when shifting up or down or both? – David D Feb 11 '21 at 14:21
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1Better description needed. – Daniel R Hicks Feb 11 '21 at 14:35
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ive added to the post to explain it better – Keith Bruford Bennett Feb 11 '21 at 20:28
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2This is still too unclear, there could be plenty of different reasons for this. More information needed. – leftaroundabout Feb 11 '21 at 20:32
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Feels like indexing needs a tweak. Is anything damaged ? – Criggie Feb 11 '21 at 20:38
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Is it a shimano 9speed system from 2013 or so? – Noise Feb 11 '21 at 20:44
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I would not be surprised if there were more than one problem involved, such as low tension in the derailleur cable plus misadjustment of the barrel adjuster. – Adam Rice Feb 11 '21 at 21:04
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Could be a cable that is sticking. – Daniel R Hicks Feb 11 '21 at 23:47
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nothings damaged or been knocked it just suddenly started.its a shimano tourney 8 speed – Keith Bruford Bennett Feb 12 '21 at 14:57
2 Answers
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Best guess is bent derailleur hanger. It's a quick and inexpensive repair for your bike shop. It does require a special tool.
Mike Smith
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From what you describe, the problem could the B-screw (derailleur tension screw).
If the derailleur tension is set too low (screw too tight), the chain sits too far from the sprockets and it can have trouble jumping from one sprocket to the other, especially on the smaller ones. Otherwise, if the screw is too loose, the upper pulley can be too close to the sprockets and shifting to the biggest sprockets could be a problem. Remember, the derailleur upper pulley should sit close enough to the smallest sprockets, but not so close to touch the cassette when the biggest sprocket is set. The more speeds the cassette has, the bigger the gap can be: it can be 2 mm on 7-8 speed cassettes, or even 6 mm on 11-12 speed cassettes (obviously the more the teeth on the bigger sprockets, the more the gap is)
Another problem that can cause similar symptoms is when the chain has too many links or if it's too worn out: if the chain is too long, it will have trouble sitting near enough to the cassette, no matter how much you adjust the B-tension screw.
Andrea
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