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Can a 7 speed Derailleur work on a 8 speed cassette I have a extra 8 speed shifters? and a wheel that has a 8 speed cassette.

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  • You might work? Give it at try.
    – paparazzo
    Feb 18 '15 at 20:08
  • Are the rear derailleur and shifters indexed?
    – RoboKaren
    Feb 18 '15 at 20:23
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8 speed shifter and cassette, 7 speed derailleur? You'll be fine. There's no "probably" about it.

6-, 7- and 8-speed gear is all cross-compatible in terms of chain width.

The only time you'd hit a problem is if the shifter and the cassette weren't made for the same number of gears, for example you could imagine a scenario (e.g. 7-speed cassette, 8-speed shifter) where you might click past the edge of the cassette. That would negatively impact your day.

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  • Well, the shifter and derailleur need to have the same cable pull.
    – Batman
    Feb 18 '15 at 22:45
  • @Batman The cable pull per cog is the same. The derailleur stops need to be set, same as anytime you install one.
    – andy256
    Feb 18 '15 at 23:40
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    You can't stick a Shimano shifter with a sram derailleur and expect it to work cause the cable pull ratios of the shifter and derailleur are different.
    – Batman
    Feb 19 '15 at 0:03
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    Most of the incompatible cable pull problems started in the 9 speed era. Older SRAM derailluers have a 2:1 ratio the same as Shimano. This table covers all the details. en.wikibooks.org/wiki/Bicycles/Maintenance_and_Repair/… Feb 19 '15 at 19:27
  • That's a good link @FredtheMagicWonderDog.
    – PeteH
    Feb 19 '15 at 20:04
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yes it will work. I tested it already. 6/7/8 speed chains are all the same width. so meaning. the cassette's width is the same too.

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Probably. Depends somewhat on whether the shifter is compatible with the derailleur (Shimano 8-speed shifters generally will work okay with 7-speed derailleurs, but you can't usually do a Gripshift with a Shimano derailleur, to name a couple of examples.)

You'll have to adjust the limit screws and barrel adjuster, but you would have to do that any time you install a different derailleur.

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