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Will Shimano 9 speed STIs work with 8 speed rear derailleur?

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Will Shimano 9 speed STIs work with 8 speed rear derailleur?

Old 02-28-15, 09:46 AM
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rjhammett
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Will Shimano 9 speed STIs work with 8 speed rear derailleur?

I have a set of Dura Ace 7700 STIs (9 speed) and I want to know whether they will work with a Dura Ace 7400 rear derailleur (8 speed). Obviously I will be running with a 9 speed cassette and chain. Is there enough range on this derailleur to get 9 speeds out of it? Thanks.
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Old 02-28-15, 12:36 PM
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HillRider
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I don't think it will directly but only because the rear derailleur is 8-speed Dura Ace. All other 8-speed era Shimano rear derailleurs will shift fine with 9-speed STI (assuming a 9-speed cassette and chain) but pre-7700 Dura Ace had a different cable pull and geometry than the other groups. There is a way to reroute the shift cable attaching point to make this work and Sheldon Brown's web site has the details.
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Old 02-28-15, 03:17 PM
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HillRider is correct. Usually you'd be able to use any 7/8/9/10 speed RD in this case but DA7400 is special. You can try the alternate cable attachment but in my opinion you'd be better off with a something other than a DA7400 RD.

Edit: I just remembered, there's an additional thing you could do in this situation. Dura Ace 8-speed shifters pull the same amount of cable as normal Shimano 9-speed shifters. So if you want, you could use your 9-speed shifters, your DA7400 RD, and a Shimano eight speed cassette.
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