Old 05-22-11, 11:55 AM
Retro Grouch 
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Join Date: Feb 2004
Location: St Peters, Missouri
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Bikes: Catrike 559 I own some others but they don't get ridden very much.

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Truthfully, I think that most any Shimano derailleur will work but, for the absolute best shifting, you should match the derailleur to the shifter. Here's why:

Shimano makes several different grades of components. The lower end ones use cheaper manufacturing processes and are less precise. To allow for that, the lower end components have a degree of "fuzzy logic" built into them. Lower end shifters, for example will let you overshift just a skosh, to make up for a lightly slopier derailleur. A Dura Ace shifter can't make a Tourney derailleur shift more crisply and a Dura Ace derailleur won't be be at it's best if it's paired with a low end shifter.

That all depends on everything else being in the default mode. On older bikes bent derailleur hangers are common. If your derailleur hanger isn't in the same plane with your cassette, the most precise and expensive components in the world aren't going to shift as quietly as you'd like. Try shifting your bike into a gear combination that makes your derailleur arm point straight down. Now prop your bike up so it's vertical and look at it from the back. If your derailleur arm looks like it's pointing toward the rear wheel - that's it. Get your derailleur hanger straightened and your shifting will quiet down.
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