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Old 08-19-14, 09:15 PM   #1
invasionusa
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Switching from 11-23 to 11-28 cassette and chain length/derailleur questions

I just switched my cassette from 11-23 to an 11-28 and I am having a really hard time trying to get my rear derailleur to shift correctly, it skips gears throughout and I can either not get it to shift all the way to the 28 or to the 11 depending on how it is adjusted. Would the length of my chain have anything to do with this? The chain is brand new, but when I got it put on I still had my 11-23 cassette on there, so it was lengthened for that, but I bought a new cassette a couple days later with the bigger gearing. I am not a very good mechanic, but I want to do this myself so I can get better. Any advice would be greatly appreciated.
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Old 08-19-14, 09:18 PM   #2
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Not to sound silly, but are they the same speed cassette? You didn't accidentally buy an 11 needing a 10 or vice versa did you?

I go between a 12-23 and an 11-28 often. No difference in chain length required. However, it was sized for the 28 originally.
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Old 08-19-14, 09:26 PM   #3
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The fist thing to do is shift (off the bike, carefully and at low speed) into the big/big combination and see if the chain is long enough to loop it with at least an inch to spare. Do this very carefully because if it does shift, and the chain is too short, you'll bend the axle, so gently ease into the shift.

If the chain passes this test, it's long enough, if it doesn't do not ride the bike until you correctly size the chain.

Another factor is the height of the RD upper pulley. The larger sprockets may require that you push the RD down. This is done either with the B-screw on the upper body (pre-2001) or with the worm gear screw between the lower body and cage.

The rest is basic textbook adjustments.
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Old 08-19-14, 09:27 PM   #4
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If the chain is sized minimally for a 23T largest cog, you will need 3 additional half-links to make it work on the 28. However, since links have to be added in pairs, you will need 4 more or 2" of additional length. However, the shifting problem doesn't sound related to chain length and I'll also ask if the two cassettes are the same "speed".
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Old 08-19-14, 10:53 PM   #5
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Originally Posted by brianmcg123 View Post
Not to sound silly, but are they the same speed cassette? You didn't accidentally buy an 11 needing a 10 or vice versa did you?

I go between a 12-23 and an 11-28 often. No difference in chain length required. However, it was sized for the 28 originally.

Yes, they are both 10 speed cassettes.
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Old 08-19-14, 10:56 PM   #6
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Originally Posted by FBinNY View Post
The fist thing to do is shift (off the bike, carefully and at low speed) into the big/big combination and see if the chain is long enough to loop it with at least an inch to spare. Do this very carefully because if it does shift, and the chain is too short, you'll bend the axle, so gently ease into the shift.

If the chain passes this test, it's long enough, if it doesn't do not ride the bike until you correctly size the chain.

Another factor is the height of the RD upper pulley. The larger sprockets may require that you push the RD down. This is done either with the B-screw on the upper body (pre-2001) or with the worm gear screw between the lower body and cage.

The rest is basic textbook adjustments.


What do you mean by loop it with an inch to spare?
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Old 08-20-14, 04:43 AM   #7
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What do you mean by loop it with an inch to spare?
Separate the chain first, then run the chain over the big-big gear combination without going through the rear derailleur (bypass it), where the two ends come together, you need an inch of excess chain.
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Old 08-20-14, 05:13 AM   #8
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"What do you mean by loop it with an inch to spare?"

Follow this link and scroll down to the "Chain Length section. Derailer Adjustment

There are other helpful hints for derailleur adjustments on that page, but I prefer the procedure on the Park Tool site: Park Tool Co. » ParkTool Blog » Rear Derailler Adjustments (derailleur). Follow the instructions there from the beginning, without skipping any steps.
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Old 08-20-14, 08:57 AM   #9
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Separate the chain first, then run the chain over the big-big gear combination without going through the rear derailleur (bypass it), where the two ends come together, you need an inch of excess chain.

Got it, thanks.
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Old 08-20-14, 08:57 AM   #10
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Originally Posted by dsbrantjr View Post
"What do you mean by loop it with an inch to spare?"

Follow this link and scroll down to the "Chain Length section. Derailer Adjustment

There are other helpful hints for derailleur adjustments on that page, but I prefer the procedure on the Park Tool site: Park Tool Co. » ParkTool Blog » Rear Derailler Adjustments (derailleur). Follow the instructions there from the beginning, without skipping any steps.

Thank you
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Old 08-20-14, 09:36 AM   #11
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Who put the cassette on and is it mounted correctly?
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Old 08-20-14, 10:23 AM   #12
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It is not necessary to open the chain or remove it from the derailleur to test for minimum length.

The lower pulley of the RD has enough travel to pass above a straight line lower loop. Simply try to shift to the big/big combination (carefully in case the chain is too short. If it shifts in OK, and there's enough slack for you to pull the lower loop forward about an inch or so, it's a pass.

OTOH, if the chain begins to jam because it's too short, that's a fail, and you don't want to force it.

BTW- it's very easy to test in advance and predict
if you'll have enough chain for a larger cassette.

You'll need 1" of chain for every 4 teeth, so shift to the big/big combination and see if you can pull enough chain forward, including the minimum 1", so if adding 4 teeth, you need to be able to pull 2" or 4 links forward.
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Last edited by FBinNY; 08-20-14 at 10:28 AM.
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Old 08-20-14, 04:29 PM   #13
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Who put the cassette on and is it mounted correctly?

I put the cassette on and yes it is mounted correctly.
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