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Why wont 7-speed derailer work on 9-speed?(10 posts)

Why wont 7-speed derailer work on 9-speed?Kaboom
Nov 3, 2003 2:48 PM
i was thinking right now and i came up with a question i cant answer. If the hub width is only marginally smaller on a 7 speed bike (which can be made up for toying with the H/L screws anyway) is there a reason for which a 7 speed shimano derailer shouldnt work for any of the new 9-speed drivetrains?

It will, it just won't index,TJeanloz
Nov 3, 2003 3:04 PM
In friction mode, a 7 speed derailluer should be able to shift a 9 or 10 speed cassette. Once you introduce indexing, a problem occurs. The throw of the derailluer arm is different for the different speeds (more or less cable is pulled to achieve the same shift), thus the indexing will be all wrong, and will cause the combo to not work.
not quiteRusty Coggs
Nov 3, 2003 3:19 PM
The only place he would get in trouble is trying to use a pre 9 speed DA RD which does have a different throw ratio.The difference in cable pull is in the shifter,not the deralier.
that's what I thought...gtx
Nov 3, 2003 3:22 PM
in the opposite new 9 speed DA der indexes like a champ with my 7 speed DA freewheel and 7 speed DA shifters...
A derailer is..............Mike Tea
Nov 3, 2003 3:29 PM
.....a dumb animal and does what the shifter tells it. There are no indexing detents in a derailer.

Unless it's a different "actuation ratio" like a SRAM mtb derailer that will only work with 1:1 ratio SRAM mtb shifters then you are ok.
A derailer is..............Gripfer
Nov 3, 2003 4:42 PM
Agree. I've used a 7 speed LX with 9 speed Sram and Rapidfire, both worked fine.
Should workAl1943
Nov 3, 2003 6:10 PM
I converted a friends 7-speed STI RSX to a 9-speed 105 shifters & hub, Ultegra 9-speed cassette, both derailleurs are the original 7-speed. It shifts perfectly and has for two years with no adjustments.
Older 7 speed changers are too sloppy to work with 9 speedsMR_GRUMPY
Nov 3, 2003 6:17 PM
The newer changers are made with a lot less "slop" in them. The pivot points have to be precise. Not so, when you have large spacing between cogs. The "pull" on all Shimano changers, except 7 & 8 Dura Ace, is the same. An old six speed changer would work on 9 or 10 speed IF it didn't have built in slop. Grab the lower pulley of an old changer and pull it in and out. You will see the slop.
Older 7 speed changers are too sloppy to work with 9 speedsRusty Coggs
Nov 3, 2003 7:04 PM
Doubt that it matters.The slop you see may be dependent on the deralier model too.I have new 9 speed DA and ultegras that have minimal or no slop,a 105 has alot, and is about the same as both 7 speed and an old 6 speed sis deralier. Sheldon Brown and others with as much knowledge said a number of times it works.I'm good with that.
it will work fine..dotkaye
Nov 4, 2003 3:00 PM
derailleurs (except old 8spd DA) are agnostic about the number of speeds.. I'm using a 6spd der in an otherwise Ultegra 8spd drivetrain and it shifts perfectly well. If I ever go to 9spd I confidently expect it to work there too. Though by that time I may have succumbed to a 9spd der sale..