# Rear derailleur adjustment for chain rattle in big gears



## nate (Jun 20, 2004)

First, I know very little about maintenance but I'm trying to learn. I've read about adjusting the rear derailleur online, but I don't want to try adjustments willy-nilly without finding the answer for my specific problem.

I recently stopped into my LBS and had the mechanic show me how to use the barrel adjuster on the rear derailleur to compensate for some cable stretch I'd had. It worked beautifully, as I no longer was experiencing problems with unwanted shifting when I was accelerating or out of the saddle.

However, less than a week after that, I noticed that I'm getting a very bad chain noise when I'm in my two highest gears (large chain ring on front and two smallest sprockets on rear). I am also getting some louder than normal noise when I'm in the lowest gear on the bike, though it is not nearly as bad as the high gears. 

On my normal rides I rarely get into those huge gears because there just aren't that many big or long downhills, but I noticed because I was running through the gears after cleaning and lubing the bike. I don't know for sure when this started, so I'm interested to know whether the adjustment for cable stretch could have caused this or whether it was probably something else that is unrelated.

Also, of course, I want to know how to fix it.


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## Fredrico (Jun 15, 2002)

*Try tightening front derailleur cable.*

If that doesn't work, try loosening (a quarter turn) the limit screw that prevents the chain from overshifting off the large chainring.

The noise is probably the chain rubbing on the outer cage of the front derailleur. You could see that with the bike in a stand. Once in awhile, the bolt that clamps the derailleur onto the seat tube comes loose or wasn't tight in the first place, and shifting pulls the derailleur out of parallel with the chainrings. The cage should be aligned so that when the chain is all the way in, on front and rear gears, and all the way out, front and rear, it doesn't rub on the derailleur cage.


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## Kerry Irons (Feb 25, 2002)

*Post in different forum*

This should be posted on the Components forum. Your noise could be as simple as the chain telling you it needs to be cleaned and lubed. It could be, as Frederico suggested, the chain rubbing on the front derailleur cage. You should be able to see this visually - shift into the problem gears and see if the chain is touching the cage. This might be adjustable with the barrel, but it also may require you to change the limit screw settings. You can tell which screw controls which limit by looking at the derailleur when it is all the way up or all the way down. Go 1/4 turn at a time on the screws, and remember where you started.


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## nate (Jun 20, 2004)

Kerry, I didn't notice until it was too late, and I didn't see a way to delete the thread so I could put it in the correct forum. (see my edit note in the opening post)
I don't remember for sure where the sound was coming from, so I'll double check. Unfortunately, I don't have a workstand yet.
If the LBS just recently helped me position the barrel adjuster to fix unwanted shifting (in the middle sprockets on the back), does that mean it's probably the H and L screws or I should still try the barrel adjuster first? From what I've read online, it seems the the H-L screws should seldom need adjustment once they're positioned correctly. Is that correct?

Thanks for the help.


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## Kerry Irons (Feb 25, 2002)

*Limit screws*

"it seems the the H-L screws should seldom need adjustment once they're positioned correctly. Is that correct?"

Yes that is correct. However, they may have not been set right. Sometimes, the derailleur is set up so that it relies on the "clicks" in the shifter to serve as upper and lower travel limits. When you changed the barrel adjusters, you may now be finding that the limit screws are set wrong. The way to find out is to shift into the noisy gears and then inspect closely. You can easily see if the cage is rubbing on the chain.


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