Crankshaft snags and loses resistance while cycling 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.
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.