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8-speed DA STIs, 9-speed cassette, 7-speed

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8-speed DA STIs, 9-speed cassette, 7-speed

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Old 01-18-11, 07:43 AM
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Barchettaman
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8-speed DA STIs, 9-speed cassette, 7-speed

Will this work? I have:

7400-series 8-speed STI Dura Ace shifters.

An Ultegra 9-speed cassette, with one of the sprockets removed, giving me a custom 8-speed block.

A newish 105 rear derailleur with standard cable routing.

The cassette will be mounted on an old (but still nice) freehub body originally for 7-speed.

What say you?
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Old 01-18-11, 09:51 AM
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Al1943
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The pitch should be OK for the cog spacing. D-A 7400 cable pull is the same as Shimano 9-speed.
I don't know how well the cassette will work on that particular hub.
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Old 01-18-11, 05:52 PM
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If you already have the parts, try it. Seems the only question mark is over whether you get to use 8 or 7 of your cassette.
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Old 01-23-11, 02:04 PM
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i tried that. didn't work. you're supposed to be able to do it if you file off the extra tooth on the inside of the cassettes, but the 7400 needs its specific locking outer cog and it just doesn't all fit. i wound up replacing the cassette body for about $80us
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Old 01-23-11, 02:45 PM
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Originally Posted by Al1943 View Post
The pitch should be OK for the cog spacing. D-A 7400 cable pull is the same as Shimano 9-speed.
I don't know how well the cassette will work on that particular hub.
No it isn't. Non Dura Ace changed cable pull ratios with 8sp, DA didn't change until 9sp. The alternate cable routing should fix the issue (this has worked for me in the past).
http://www.sheldonbrown.com/dura-ace.html
If you want to drop a cog from the cassette (probably required given the 7sp hub) you may have a tricky time getting it to seat. The upper cogs (I think) are on a carrier, so you can't drop one of them. Dropping the smallest cog may prevent the lock ring from working properly. Dropping an intermediate gear will result in a hole in your range, and the teeth will no longer be lined up across the new gap. It will still shift, but may do so a bit funny between those two cogs.
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Old 01-23-11, 04:13 PM
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Originally Posted by jccaclimber View Post
No it isn't. Non Dura Ace changed cable pull ratios with 8sp, DA didn't change until 9sp. The alternate cable routing should fix the issue (this has worked for me in the past).
I'm afraid you are confused. The D-A 8-speed cable pull is the same as all 9-speed Shimano. It is the RD actuation ratio that changed with 9-speed. The OP wants to use D-A 8-speed shifters with a later RD and 8 cogs on 9-speed spacing. That part should work. Mounting it on a 7-speed hub may not work.
I'll post more supporting info when I get to a real computer. Now on iPhone.

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Old 01-23-11, 07:26 PM
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^I may be. If the rear derailer ratio was changed, wouldn't you need to change the pull ratio or the shifter pull per gear? Sheldon used to have a chart outlining cog spacing and pull,but I can't find it at the moment.

Edit: Found it.
http://www.sheldonbrown.com/cribsheet-spacing.html
8sp is 4.8 mm center to center on the rear cogs. 9sp is 4.34 mm. Not all the info, and I'm still not sure how this works without the alternate cable routing unless Shimano was being smart and spaced everything just right (quite possible)

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Old 01-23-11, 11:19 PM
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Originally Posted by jccaclimber View Post
^I may be. If the rear derailer ratio was changed, wouldn't you need to change the pull ratio or the shifter pull per gear? Sheldon used to have a chart outlining cog spacing and pull,but I can't find it at the moment.
Edit: Found it.
http://www.sheldonbrown.com/cribsheet-spacing.html
8sp is 4.8 mm center to center on the rear cogs. 9sp is 4.34 mm. Not all the info, and I'm still not sure how this works without the alternate cable routing unless Shimano was being smart and spaced everything just right (quite possible)
I'll post some charts for you when I get home soon.
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Old 01-24-11, 07:44 AM
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Great, thank you.
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Old 01-24-11, 08:38 AM
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http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3946

I use a Nine speed Ultegra Brifter with s 7400 DA driveline. Nine speed cable pull and eight speed DA is the same.
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Old 01-24-11, 01:23 PM
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Thanks for the table. The numbers in the table don't quite line up, example 2.5 x 1.7 != 4.35. However, they do imply 8sp DA and 9sp Shimano to be very close. It looks like you'll be off by a tiny amount at the end, ie if you center everything in the first gear you'll be off enough to make some noise in the last one, which was my experience. I did find that if I centered everything up in gear 4 then it was close enough. Thanks all for the tables.
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Old 01-24-11, 02:48 PM
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Originally Posted by jccaclimber View Post
Thanks for the table. The numbers in the table don't quite line up, example 2.5 x 1.7 != 4.35. However, they do imply 8sp DA and 9sp Shimano to be very close. It looks like you'll be off by a tiny amount at the end, ie if you center everything in the first gear you'll be off enough to make some noise in the last one, which was my experience. I did find that if I centered everything up in gear 4 then it was close enough. Thanks all for the tables.
Here are some more;http://sheldonbrown.com/dura-ace.html scowl down to the tables
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Old 01-24-11, 02:55 PM
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Originally Posted by Kimmo View Post
If you already have the parts, try it. Seems the only question mark is over whether you get to use 8 or 7 of your cassette.
+1. The bottom line.

If I already own parts, I'll put whatever they are onto a bike and see if I can make it work to my satisfaction. If I'm buying new parts, I'm going to get stuff that matches.
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