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So I put together a bike a couple months ago. New chain, new chainrings (3 speeds), and new rear cassette (8 speeds). Used front and rear derailleurs from a bike co-op. The free wheel is old but seems to be working fine. All components are Shimano.

It had been plugging along just fine until recently. Now any time I stop pedaling, such as at a stop light or a bump, when I start again, the chain "skips" or "jumps". I'm not trying to change gears, it just feels like the chain is disengaging and then reengaging. It's infuriating and I think pretty dangerous.

When I'm pedaling continuously on a trail, no problem. When I'm standing up on my pedals going up a hill in 2 (front)/7 (rear), no problem. This info, combined with the fact that the entire drive train has to have less than 500 miles on it, and the fact that I went into another bike coop and the tech there measured my chain for wear and found that it wasn't worn makes me think this is not a worn drive train problem.

My guess is that the rear derailleur is properly keeping cable tension when I stop pedaling, which is somehow (?) causing my issue.

Any help is greatly appreciated, it's really my only form of transportation and it's getting to the point where it's unrideable.

  • What's happening, at the most basic level, is that the chain is going slack and when that happens some sort of maladjustment/mismatch in the drive train causes the chain to get slightly off one of the sprockets (most likely the front). In the case of a well-used drive train one might suspect worn sprockets or chain would be at fault, but if they are all new then that's not it. So probably you should simply go through the adjustment process again -- it's normal for it to be needed after a "break-in" period on a new bike. My guess is that the front derailer is out of adjustment. – Daniel R Hicks Apr 6 '17 at 2:51
  • Also, you should make note of which gears exhibit this problem. Likely it's more common when the chain is fairly slack. (It may be that your chain is a hair too long, among other things, or the rear derailer does not have enough "tooth capacity" for your drive train.) – Daniel R Hicks Apr 6 '17 at 2:54
  • From what I can tell, it happens on pretty much any gear I've tried. I just went through the rear derailleur adjustment process, and I actually removed one link from my chain as well, and I'm still having this issue. It's actually worse now. But both rear and front derailleurs are shifting just fine. Could a derailleur that's shifting well still cause this problem? – Jon Apr 6 '17 at 3:07
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    I'll definitely look into that. Did some more experimentation. When I put the bike in a stand and manually roll the top jockey wheel on the rear derailleur toward the back of the bike (to move the chain in the direction it moves to power the bike forward) it doesn’t catch the chain reliably. Am I correct in thinking that could be the issue? – Jon Apr 6 '17 at 5:29
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    Also, if you have a chain whip tool: remove the rear wheel, put the chain whip on the cogs, and try turning them back and forth with the tool. If you can make it skip that way, then it's definitely the freewheel. (Watch your knuckles!) – Mike Baranczak Apr 6 '17 at 19:44
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Posting this to help others who may stumble upon this.

Took my bike into a local coop, armed with my roommate's hunch about the freehub body, and I removed it, and the guys there said that it had too much play and wasn't ratcheting correctly. Either damage to the pawls or gunk.

Put a new freehub on, and it's as good as new. The take away here for me was: if you're able to stand up on your pedals while going up hill no problem, and your chain only feels like it's skipping after the freehub disengages (coasting) and then reengages (starting pedaling again), it's probably not the chain or cassette/chainrings.

I think this is a weird problem since I had brand new gears and chain, but a very old freehub, which I doubt happens too often, but this worked for me, for what it's worth

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I'm just going to assume here that as you say your freewheel is ok,.. that it doesn't have worn pawls etc. Turn your bike upside down and pedal it slowly in reverse (not driving the rear wheel) whilst your doing this look and listen closely as the chain travels over the freewheel. You are looking for any tight links in the chain here which can cause the issue you describe. If you find any tight links.. use a chain link tool to adjust the relevant tight pins.. This will free up the tight spot.

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