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I have a hybrid (18+ years old) that I use for daily commuting which has developed a problem with the cranks. Every so often (perhaps 10% of the time) when I push down on either crank arm after free-wheeling, there is the sound of the cranks snagging/grinding on something internally, which can sometimes be felt through the pedals. The cranks then momentarily lose resistance and stop driving. This usually corrects itself within another complete 1-2 revolutions of the cranks (leading to further sounds of grinding metal), after which resistance is restored.

I'm not sure whether it's relevant but I recently had the pedals replaced on the bike, and the mechanic mentioned they were hard to remove. The cranks seemed to be fine before having the pedals replaced (no problems or noises). The bike also used to make a quiet "tick-tick-tick" sound when free-wheeled, but I've noticed this has stopped completely.

I suspect the bottom bracket needs replacing (the last time would be years ago, if ever), and we've had lots of rain recently so maybe some water found its way in. Everything else (chain, gears, pedals, etc.) are fine.

Are these symptoms consistent with bottom bracket failure, or something else? Does this explain why the "tick-tick-tick" sound has stopped?

Thanks.

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    Are you sure that your chain is ok and isn't slipping? The lack of a tick-tick may also be a freewheel problem.
    – RoboKaren
    Jan 18, 2016 at 23:03
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    Yes, I've monitored the movement of the chain carefully and it's behaving as it should. Thanks for the freewheel suggestion, I'll look into this.
    – greenback
    Jan 18, 2016 at 23:06
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    Unless the cranks/BB have a freewheel in them (rare but possible with a bike that old) it can't be that. It might be the chain building up slack along the top, if the freewheel has become harder to turn (so it pulls the rear derailleur tighter before it does that), or it might be that the freewheel has become worn or damaged and doesn't catch properly after freewheeling. Either way I'd take it back to the shop and ask them to have a look. They might have changed something and be able to change it back, or their work might have revealed a problem (or caused it, but that seems unlikely)
    – Móż
    Jan 19, 2016 at 0:13
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    When you say "loses resistance" I take it to mean the pedal you're pushing down on moves really easily, like its not driving the back wheel? When was the chain last changed? Can you take an up-close photo of the chainrings and the rear cogs? If you have an inches ruler, measure 12 links (24 half links) which would be 12 inches long when new. The chain is worn out if its too stretched, and 24 half links measures more than 12 1/8" Let us know what you find. I'm suspecting worn out transmission generally, and/or the freewheel/hub is tired.
    – Criggie ♦
    Jan 19, 2016 at 1:14
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    @Moz- Yes, from the replies I think it's most likely to be a worn freewheel. Will see what the mechanic says.
    – greenback
    Jan 19, 2016 at 22:02

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It's not the cranks or bottom bracket (though it sounds like the BB might need replacing anyway) if the chain is moving normally. The crank is fixed to the chain rings with bolts, so that can't slip.

It's much more likely that the ratchet mechanism in the rear hub is broken. Older ones work on 2-4 small spring loaded "palls" that engage a ramped gear. If the springs or the palls themselves rust and break, then the hub will no longer engage and you'll get that "no resistance" feeling. The grinding you are feeling is probably bits of pall, spring, freehub body and possibly bearing moving around in the rear hub. The lack of "tick-tick-tick" is because those palls are not being clicked into the gear by their springs.

Unfortunately, this probably means a new rear wheel. The freehub body is probably ground down into pieces, and those pieces will have damaged the inside of the hub itself. Technically, you could buy a new hub, and get your bike shop to lace that onto the existing rim, but it will probably be cheaper to just buy a whole rear wheel.

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    It is not strictly true that could be a free-hub problem. Years ago there was the Shimano Front-Freewheel System (FFS) which put the freewheel in the crank.
    – Rider_X
    Jan 19, 2016 at 3:00
  • You are right it could be a FFS system, but in all likelihood, that is not the problem.
    – brendan
    Jan 19, 2016 at 3:37
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    Thanks for the replies guys. I'll get the mechanic to take a look and post update with what he says. The chainset isn't original, I think I had the chain replaced about five or six years ago. The rear wheel and front chain rings were replaced about ten years ago, and I think the rear cassette is original.
    – greenback
    Jan 19, 2016 at 22:27
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    Update: as suggested, the issue turned out to be a worn hub. The mechanic also discovered play in the cranks and noted that the front chain rings and rear cassette were showing serious wear. The chain was slacking and gear cabling had also started to perish. The bottom line: new rear wheel, new crankset (Hollowtech II), new cassette and jockey wheels, new chainrings, new bottom bracket, cabling. £260 parts and labour. It has transformed the responsiveness of the bike and made it safe (and fun) to ride again, so well worth it. The rear mech and shifters were still in good nick so were retained.
    – greenback
    Feb 11, 2016 at 22:26

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