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Rear derailleur - guide pulley rubs largest sprocket...
Hi all,
I am building a road bike with Ultegra parts. I have a 9 speed rear derailleur that I've set and am trying to adjust. I've got the chain on fine, I've adjusted the the H and L limit screws and they are giving me no problems. It shifts through all the sprockets just fine.
However, the guide pulley is rubbing on the largest sprocket pretty badly. I've tried to tighten the B adjustment screw, which helped a lot, until I tightened it as far as it would go. The guide pulley is still rubbing the sprocket.
I noticed that when I pull down on the chain a bit, the guide pulley comes off the sprocket and the problem goes away. Could it be that my chain is a link too long? I wanted to ask before I removed a link and possibly made the chain too short (I know this could do damage to my components).
Any help would be greatly appreciated!!

Your chain might be too long. I'd check the length and take out any links needed. If that isn't it, it might be a compatibility issue between your derailleur and cassette.

Hi Alex,
Thanks so much for the advice and the whole site. It's been an invaluable resource during my project!
I remeasured the chain, and it was a link too long. Removing the link has helped even more, but there is still a tiny click when the chain is on the largest sprocket. According to their specifications my derailleurs and cassette should match, so I'm not sure what else could it could be.

Does the click occur each revolution of the cranks, each revolution of the wheel, every 2-3 revolutions of the crank (each time the chain goes around fully), etc?
It might be a stiff link where you joined the chain.

I agree with Dave, it could be a stiff link. Here's how to check.

I actually hadn't lubed the chain yet because I didn't want it making a mess. After I did, I don't hear the click anymore. Thanks Dave and Alex!!

I have this same problem on a Rocky Mountain ETSX-70 mountain bike with an XTR rear derailler. The previous owner replaced the chain so I'm suspecting the length is wrong. I have the B-tension all the way in and the guide pully still rubs the largest sprocket while I'm riding but not when on the bike stand. Do you think the determination of chain length in the video applies to full suspension bikes?

See my previous post. After putting up with the noise and mostly avoiding my small chainring for the last couple months, I finally fixed that clicking/derailleur bobbing problem I had while climbing. It only looked like the derailleur was touching the sprocket, but it wasn't. Turns out it was the smallest chainring up front. To find it I put my bike in the stand, took a strap and tightened the seat down, compressing the shock to simulate riding weight, then strapped the brake lever partially engaged to simulate climbing....turned the crank by hand and watched the chain. It wasn't releasing smooth off the smallest chainring like it should. Each tooth had a bit of a hook shape worn into it on the leading edge. I took my dremel tool and filed each tooth down. Problem solved. That was to find. Turns out the previous owner had replaced the middle and large rings, but not the small one. Hope this helps someone else!

"Each tooth had a bit of a hook shape worn into it on the leading edge"
That means it is worn (badly) and should be replaced. Probably along with the rear cassette. See e.g. the article on chain wear or . If you continue riding the worn sprockets with the new chain, you will wear out the new chain very fast.


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