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Eyeballing rear derailleur alignment

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Eyeballing rear derailleur alignment

Old 09-08-08, 08:02 PM
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kuan
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Eyeballing rear derailleur alignment

If I tension the RD so that the chain wraps around the cog, the teeth do not sit exactly in the middle of the chain. Does that mean that something's a little bit crooked?

I'm trying to figure out my chain jumping problem on my stock Surly LHT. It does not like to work in the smaller four gears.
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Old 09-08-08, 08:57 PM
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Chain jumping problems are almost always an indexing issue. Start from the beginning with your rear derailler setup. Remove the cable and set the high and low stop (manually push the derailler to the low [largeest cog] stop and verify proper alignment). With the derailler properly aligned at the high (small cog)position, install the cable and begin your tension adjustment. Shift through the gears and keep an eye on the jockey wheel to see if it stays aligned as you climb through the cassette. If the wheel starts lagging behind as you shift, add more tension. When you get to the largest cog, start downshifting. If it goes too slow, decrease tension.

In my experience, a misaligned derailler hanger will generally cause slow shifting necessitating a double shift to get certain gears, often accompanied by not being to get into the smallest cog.
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Old 09-08-08, 08:58 PM
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Check to see if you derailleur hanger is bent. Your local shop has a tool that can quickly check this so if you're in tight with a mechanic go get it checked out. If not, use an allen wrench to remove th derailleur from the hanger and use a long straight edge to check check the hanger alignment to the front, rear and bottom of the wheel. If it's bent you'll probably still need to make that trip to a shop so they can straighten it for you. It can be done without a shop tool but it really is easier if you have one.

Assuming that you hanger is good, shift your chain to the large cog and check that the chain is centered on the cog and on the upper pulley. Assuming that's good, shift to the smallest cog and check that the upper pulley is lined up with the outer edge of the cog. If that appears good then you should be able to correct your shift problem by adjusting the cable barrel. Try shifting onto one of the cogs that is having trouble and watch what the chain does. If you start from the smallest cog and the chain has trouble shifting up to the next few cogs then turn the barrel out 1/4 - 1/2 turn. If the chain shifts to the larger cog and rides up on the teeth as if it's trying to go one more then turn the barrel in 1/4 - 1/2 turn. Work with that a bit and you should be able to resolve your shift problem.

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Old 09-08-08, 09:05 PM
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Originally Posted by kuan View Post
If I tension the RD so that the chain wraps around the cog, the teeth do not sit exactly in the middle of the chain. Does that mean that something's a little bit crooked?

I'm trying to figure out my chain jumping problem on my stock Surly LHT. It does not like to work in the smaller four gears.
http://www.parktool.com/repair/readhowto.asp?id=64

Then take it to a shop and get the hanger checked.
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Old 09-08-08, 09:12 PM
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I forgot to add. It's a new bike and it's already been to the shop. According to the mechanic everything is fine. The problem does not show up on the stand. It shows up while I'm riding. Even a small bump is enough to cause the chain to jump. This time I'm insisting on them taking it for a test ride.
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Old 09-08-08, 10:03 PM
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If this is a new bike I'll assume that the hanger is straight. Mind you that's not really safe since it could easily have been banged around during shipment or by the shop as they assembled it out of the box.

However when I set the rear derraileur I like to check that it lines up with the cogs and that the chain is sitting evenly on the cog. To move it is just a twist of the barrel adjuster at the shifter or at the derrailleur. If you get it so the chain is running centered then likely the lower gears will shift fine and not jump. When you shift the gears while the pedals are spinning the up and down shifts should happen in about the same time. If one is lazy compared to the other direction then tweak the barrel adjuster so it evens out the shift times. The shifting depends on when it hits the assistance hooks so try it both ways a number of times when you're getting close. And check at both extremes of the cassete.

You COULD get the shop to do this but you may as well learn to adjust stuff like this now. Especially since the guys at the shop didn't seem all that helpful. If it doesn't help then no harm done and you can take it in and mention that the problem is still there, that you adjusted it around the issue without success and could they please check the hanger alignment since this should not be happening.
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