Chain dropping down

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honesty
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Chain dropping down

Postby honesty » 19 Oct 2017, 6:11pm

This started a week or so ago when I had the chain on the middle ring and on the lowest gear bat the back, the chain would just drop to the granny ring for no reason. It’s not the front derailleur as the is not touching the chain at all. Today though it happened when climbing out of the saddle on a higher gear though. Sudden loss of grip was somewhat painful. Smashed my walnuts twice... what could be causing this?

Brucey
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Re: Chain dropping down

Postby Brucey » 19 Oct 2017, 7:30pm

oooh blimey, might I suggest that for safety's sake you confine yourself to riding in the saddle until this problem is resolved?

Could be worn chainring, bent chainring tooth, burr on chainring tooth, something jammed in a chainring tooth, worn chain, chain flapping about more than normal (a resonance effect brought on by something eg wear), stiff link, bent link, broken chain link, damaged chain link.

It could be a combination of faults, for example if the chainring is slightly hooked, the chain might start to 'suck' but then release on each pedal stroke. If the rear mech is also sluggish, and/or the freewheel is a touch draggy, this may allow the top run of the chain to go slack briefly and this might cause the chain to start to derail.

Suggestion; if you are in it for the long haul with this bike, you could start replacing things just to see if it makes any difference or not. Worst case is you have some spare parts that you can use later on when you really need them...? This way you can identify the culprit even if you can't see exactly what is happening.

cheers
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honesty
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Re: Chain dropping down

Postby honesty » 19 Oct 2017, 7:36pm

Everything was replaced for the drive chain 18 months ago... checking the chainring and it doesn’t looked hooked, but some of the teeth seem to be shorter than others. I think it’s the rear mech though then. Back peddling makes the chain stick.

Brucey
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Re: Chain dropping down

Postby Brucey » 19 Oct 2017, 7:42pm

could be. Worth checking that the freewheel isn't draggy too.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Samuel D
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Re: Chain dropping down

Postby Samuel D » 19 Oct 2017, 7:47pm

honesty wrote:It’s not the front derailleur as the is not touching the chain at all.

How far is the derailleur laterally from the chain on the middle chainring and largest cassette sprocket?

MikeF
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Re: Chain dropping down

Postby MikeF » 19 Oct 2017, 7:47pm

honesty wrote:Everything was replaced for the drive chain 18 months ago... checking the chainring and it doesn’t looked hooked, but some of the teeth seem to be shorter than others. I think it’s the rear mech though then. Back peddling makes the chain stick.
Some chainrings have certain teeth shorter than the majority. Could it be problems with the freewheel part of the hub? If the ratchet slips ie teeth don't engage properly then the sudden forward motion might make the chain drop onto the granny.
"It takes a genius to spot the obvious" - my old physics master

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honesty
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Re: Chain dropping down

Postby honesty » 19 Oct 2017, 8:04pm

I hope it’s not the freewheel... the hub was rebuilt, new freewheel and new bearings

Brucey
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Re: Chain dropping down

Postby Brucey » 19 Oct 2017, 8:15pm

IME if the lubrication of the freewheel mechanism was of the usual type (i.e. virtually non-existent) then it might well have gone bad even though the bits are new(ish).

Remember that if you actually ride your bike much, and/or in all weathers, then you are not an average cyclist, and you may have to do more/better maintenance than is usual.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~