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Discussion Starter · #1 ·
Looking for some ideas here. I have a SRAM PG-970 cassette (12-26) on my commuter. The chain jumps and rattles, but only in the 12-tooth cog. The rest of the cogs are nice and quiet. Everything shifts fine, so I'm thinking it's not a cable tension issue. The jockey pulley seems to be properly aligned below the 12 when in that gear.

Any ideas? Anything I'm overlooking? I don't often need the 12 on a bike that weighs 30+ lbs. fully loaded, but it's bugging me that it's not right.

Thanks in advance for your help!
 

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info..

A stiff chain link or a wipperman connex link installed upside down will cause this sort of problem. You might also need to adjust the RD limit screw, if you have not already tried that.
 

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I was going to suggest limit screw, too. I'm not sure what "jumping and rattling" is, but it could be catching on the next cog because the derailleur isn't moving out quite far enough. That can show up under tension even if the jockey pulley appears to be in the right place.
 

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+1 on the limit screw adjustment. A tight limit screw might be keeping the RD out of ideal trim and causing the grief.

You didn't say how old the bike is, so another cause might be chain stretch. A stretched chain might be running fine on the cogs you generally use, and which it has worn to match it's condition, but not run well on the less used 12t cog, especially because of the small amount of engagement. It's analgeous to using a new cassette with a worn chain.

First check the limit, if that doesn't help measure the chain.
 

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Discussion Starter · #5 ·
"Jumping and rattling" = chattering, noisy, whatever you want to call it.

I've never used a Wipperman link before, and this is my first experience with a SRAM Powerlink. Can a Powerlink be installed upside down as well?

I'm planning to take a second look at cable tension tonight, as the bike and I are both at the office and I have no good way to suspend the rear wheel for tinkering. I'll also take a look at the high limit screw again.

Thanks for the ideas!
 

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Becky said:
"Jumping and rattling" = chattering, noisy, whatever you want to call it.

Can a Sram Powerlink be installed upside down as well?
No, Sram powerlinks are symetrical, whereas the Wippermans are not.

BTW- it shouldn't be a cable tension issue because if that needed adjusting it would affect trim in all gears. Check the limit screw - which only affects the high gear position - first.
 

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One other possibility

Becky said:
"Jumping and rattling" = chattering, noisy, whatever you want to call it.

I've never used a Wipperman link before, and this is my first experience with a SRAM Powerlink. Can a Powerlink be installed upside down as well?

I'm planning to take a second look at cable tension tonight, as the bike and I are both at the office and I have no good way to suspend the rear wheel for tinkering. I'll also take a look at the high limit screw again.

Thanks for the ideas!
Basically agree with everyone else that the first thing to check is the limit screw. As another possibility, check that the chain is not hitting the frame at any spot. Also, you don't say whether this takes place on both large and small (or middle) chain rings, but if you are on any other than the large chainring when using the 12, you are cross-chaining and you shouldn't do that. If you are cross-chaining, it could be that the chain is rubbing on the larger chainring and that might be a source of the problem if the chain is catching on a shifting pin.
 

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Are you sure that you have the 12 on the spline correctly? If not, it will go on cocked, and will cause chain jumping.
 

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I'd think chain stretch, limit screw, chain needs lubed, or just the typical noisiness of SRAM cassettes.
 
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