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Chain Skipping

Old 09-02-19, 12:51 PM
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124Spider
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Chain Skipping

Note--Problem solved; discussed below

Hi,

Our tandem has developed an annoying problem.

At first, it manifested itself by being an occasional slip when in the smallest (highest) gear in back (the bike has a three-speed front chain ring, and a 9-speed rear cassette).

Then it started skipping in the highest three or four gears.

I have replaced the rear cassette, and there is no change in the behavior. I believe that the problem started approximately when I put a new chain on.

I know it's skipping teeth, not shifting gears.

It only happens while riding, under some load; cannot be reproduced on the stand.

And I know it's not the timing chain, since both cranks remain synchronized.

I strongly believe (based on feel and noise) that it's happening in the rear, not the front.

The front chain rings are fine, showing no signs of wear. The bike has about 2500 mile on it, from new.

The chain does not have any frozen links.

The chain is correctly tensioned.

It generally (but not always) happens soon after a shift; sometimes there's just the clunk and the cranks move forward quickly for a bit. The cadence sensor shows that the cadence is not changing when this happens, which is why I am sure it's not skipping gears.

On the stand, all shifting is smooth and precise, no chatter, and the problem never occurs.

I'm at my wits' end.

Any ideas?

Thanks.

Mark

Last edited by 124Spider; 09-03-19 at 10:06 PM. Reason: Problem Solved
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Old 09-02-19, 01:13 PM
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My first inclination was that your smallest cogs are worn, especially as skipping would get noticeably worse after putting on a new chain. However, you say you replaced the cassette (at the same time as the new chain?) so that should rule out worn cogs. Seems you aren't exactly sure what is skipping though. I wont diagnose the problem as a loose lock ring, bent derailleur hanger (everyone's favorite), or slipping freehub; I will leave those for others. Is it possible to have someone that good at wrenching/adjusting gearing to ride behind or on the drive side of your bike during a test ride and see if they spot what is "skipping". Or have your stoker watch the drivetrain carefully to see of they spot what is "skipping". I would get this fixed soon as you don't want it to cause an accident. Good luck.
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Old 09-02-19, 01:26 PM
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I replaced the rear cassette soon after changing the chain.

I can't be sure, but it may be that the problem started soon after changing the chain. After it spread from the smallest gear in back to the smallest four in back, I changed the rear cassette. The new chain has 300 miles on it (including 108 this weekend, well after the problem started), and shows no significant stretch (and no frozen links). The new rear cassette has 108 miles on it.
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Old 09-02-19, 02:01 PM
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What chain do you have on it now?
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Old 09-02-19, 03:52 PM
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So, going under the assumption that the problem started with the chain-change, I spent some time thinking about what could cause this about a new chain (keeping in mind that changing the rear cassette did not help).

I thought that maybe the quick links could be a problem, perhaps snagging on an adjacent gear when going through the cassette. I examined them, and they clearly were thicker/wider than the adjacent chain links.

So I took them off, and they were labeled "8 speed." I have no idea why 8-speed links came with a 9-speed chain.

So I went out and bought a "9 speed only" set of quick links, and installed them; these were the same width as the adjacent links. Then we went out for a couple of miles and the problem did not occur (it has never gone more than a few hundred yards without occuring, since it started).

We won't have time for a longer ride until tomorrow, but I'm pretty confident that this has solved it; I'll re-post only if it didn't.

Thanks for your help.

Mark

Last edited by 124Spider; 09-02-19 at 05:11 PM.
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Old 09-02-19, 07:48 PM
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It could be a tight link, had it happen on a completely new chain, cog set and chainwheel, all Shimano.
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Old 09-02-19, 07:52 PM
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Bad pawls in the freehub. Put a new freehub on it.
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Old 09-03-19, 08:15 AM
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Originally Posted by ramzilla
Bad pawls in the freehub. Put a new freehub on it.
This.^
Sue sounds to me like the ratchet mechanism in the freehub is failing.

If you have another rear wheel, try it out and see if that changes anything.
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Old 09-03-19, 08:30 AM
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It could also be the chain "skipping" on the jockey wheel making you think it is skipping on the cassette. It sounds and feels similar. Make sure your derailleur hanger is not bent and that both jockey wheels are straight and aligned in relation to your cassette.
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Old 09-03-19, 03:14 PM
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We took the bike out for a 15-mile test ride, and it started doing the same thing in the first couple of miles; less frequently, I think, but still doing it.

So we turned around and returned home. I put an entirely new chain on, and out we went.

15 miles, and nary a problem!

My working hypothesis is that I previously had installed an 8-speed chain (instead of the 9-speed chain I know it needed, and which I thought I had installed), and it was too wide, causing the problem. I don't know at this stage whether it's because I stupidly picked up the wrong chain and never noticed, or because an 8-speed chain was packed in a 9-speed chain package, but there I am.

I'm just glad it's solved, and the bike is fine.

Mark

Last edited by 124Spider; 09-03-19 at 03:36 PM.
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