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Discussion Starter · #1 ·
It's time for dinner, so I paused working on the bike and am posting for help. Here are the facts: Shimano 6700. New derailer hanger bracket -- even though the old one checked good. 2010 Cervelo RS. New 6701 chain. New 12-27 cassette. New cables. The bike has been hanging on the wall while I rode another bike, just got done recabiling and getting it ready for the road again.
Works perfectly except 12 tooth in back, big ring in front. Slow pedaling gives a clunk (a pretty loud clunk) every so often. Repeatable. Looks like the chain is jumping between the top pully and cassette when the clunk happens. This statement isn't fact, it is a possibility as I think I saw it jump right before the wife called me to dinner. Really fast pedaling and there isn't a clunk.
The rear derailer is a replacement purchased after a car took me out (the crash scrapped the original derailer, so I replaced it as I didn't want a scratched part on the bike (vanity), and this is why I also replaced hanger bracket even though the original checked fine). I am wondering if the derailer top pulley is defective in some manner? If the ebay derailer is defective in some manner? Right now, I think something is binding up then releasing, just not sure what it is.
Have some spare pulleys and the old derailer which I can try tomorrow unless someone can give me some words of wisdom here.
And before someone asks, I double checked the rear derailer adjustment as well as B screw adjustment.
I am sure it is something stupid that I am overthinking, but would sure appreciate any input you might have.
 

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I don't see where you mentioned checking your limit screws.

Whenever I have my chain off, I always take the opportunity to check my derailleur limits. Use your thumb to push it all the way up under the biggest cog and adjust the screw until it's centered, or just very slightly outside of the largest cog.

Then do the same with the smallest cog, letting it come just underneath, and maybe just slightly past the smallest cog.
 

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Discussion Starter · #3 ·
Good point. I did check and adjust limit screws before installing the chain as well as after. Also verified cable tension. This one has me baffled right now.
 

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Check for a tight link. In this gear combination a tight link will make itself know earlier than other combinations. I set the limit screw as follows: shift up one gear, tighten limit screw so you cannot shift down, while turning the crank loosen the limit screw until the chain shifts and then loosen 1/2 turn more.
 

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Check your jocky pully's from the rear, inspecting each cog. I had one that one of the cogs was out of alignment with the others. I tried to bend it back straight (it was plastic of some type), and it would just revert back to offset & I changed it out.
 

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Discussion Starter · #6 ·
Problem solved. Went out this morning (raining) and gave the limit screw for the 12 tooth a 1/4 turn to move the wheel outboard. Migen21 had it right. I can make excuses for how I missed this, but I won't bother.
 
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