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Chain makes a sound in the largest cog. What is causing this? Chain Length?

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Chain makes a sound in the largest cog. What is causing this? Chain Length?

Old 06-14-21, 11:30 PM
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Chain makes a sound in the largest cog. What is causing this? Chain Length?

My bike makes a noise in the largest cog when I pedal or backpedal. The noise seems to only be in the largest cog and not the others. When I backpedal in the largest cog smallest chain ring it makes this whirring sound as well. I've tried indexing and adjusting the limit screws and it doesn't seem to fix the issue. The other thing is that in the large chain ring and 2 largest cassettes the backpedaling motion isn't smooth at all. Any ideas on what the issue is? I'm curious if it's a chain length issue as when it is in the small ring large cassette the top pulley seems to be touching the cassette. Would appreciate some feedback.

Also, the rear derailler indexing adjustment screw seems to be all the way unscrewed, Does that matter at all?

Below are some photos in the smallest chain ring and largest cassette

Photos in the largest chain ring and largest cassette

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Old 06-14-21, 11:50 PM
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Big big will always have noise same thing with little little. It is called cross chaining and it stretches the chain to its limits which will cause problems. If you are coasting or back pedaling that noise is likely the pawls in your freehub not engaged acting like a prize wheel. That is a common noise as well and some hubs are prized for their freehub noise.

You could also be exceeding the maximum cog in the back and chain wrap.

I would probably do a drivetrain clean soon and get all the grit and grime out of everything.
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Old 06-15-21, 08:16 AM
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On a 9 speed 2x bike, I'd think you'd be able to adjust that out. But maybe not, I've never had a 9 speed bike.

Usually on the 10 speeds and 11 speeds 2x bikes I've dealt with I can get most of it out. Especially on on my Paramount that has ever so slightly longer chain stays than the other bikes I mess with.

I'm imagining that what you are talking about is the chain rubbing on the inside left edge of the front DR cage. If it's not that, then maybe there is a possibility that it can be something you can solve and not just put down to cross chaining.

Also, a lot of the newer Shimano front DR's have a wear pad on that inside edge that minimizes that sound a little. If it's worn or missing then that might explain a more noticeable sound now. Where you get these, I don't know. I think I brought it up casually once with a LBS mechanic and he said they didn't ever get any.

Many Shimano doc's show how to install them though. So I'd think it must be a part they sell some how somewhere. I've just never been motivated to google them.
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Old 06-15-21, 08:32 AM
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First thing I think of is "pulley knock". When the guide pulley is so close to the larger cog's underside there's not enough room for the chain to fit without the pulley being "pushed" away. The resulting noise as each link pushes on the pulley is what is heard. This Campy der has a cage pivot spring tension adjustment, reducing this pivot's spring strength will let the B pivot spring pull the der further away from the cog. It also looks like you might have enough chain length to remove one pair of links, this will make a big difference with guide pulley/cog clearances. Which way to go is easy. Do the cage spring tension reduction first as it's more easily reversed.

Hard to know about the whirring sound. It could be the ratchet making it's normal noise. Or there could be a "rubber" seal that wants lube. When was the last time this hub and freehub were overhauled?

I would thread back in the cable adjuster and re set the initial cable tension at the anchor bolt. Then go back to the adjuster for the fine tuning. I have seen many ders that when used with the adjuster completely out of it's threads have thread damage and sometimes need a thread chasing repair before the adjuster can be re installed.

BTW- It looks like you are running Al aftermarket pulleys. There's a reason why metal pulleys stopped being the factory spec decades ago. They make more noise. Andy
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Old 06-15-21, 09:11 AM
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Originally Posted by Andrew R Stewart View Post
BTW- It looks like you are running Al aftermarket pulleys. There's a reason why metal pulleys stopped being the factory spec decades ago. They make more noise. Andy
Metal pulleys tend to be noisier than the ones that came with your derailleur. Are those pulleys larger than the originals? That could also create clearance issues between the top pulley and the largest cassette cog
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Old 06-15-21, 09:17 AM
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Top pulley pinching chain against the big cog. Adjust the pulley cage spring screw. And yes, your chain does look 1 link too long.
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Old 06-19-21, 11:29 AM
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Originally Posted by cxwrench View Post
Top pulley pinching chain against the big cog. Adjust the pulley cage spring screw. And yes, your chain does look 1 link too long.
If you're gonna shorten the chain, adjust the B screw afterward.
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Old 06-19-21, 10:30 PM
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Also consider a longer derailleur hangar...
No matter where your at... There you are... Δf:=f(1/2)-f(-1/2)
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