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Old 11-20-11, 09:31 PM   #1
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Rear Derailleur Replacement Help

Hi All,

Looking to replace a broken rear derailleur on an old road bike I use as a commuter-12 speed Performance Vitesse-late 1980s, early 90s model. Old derailleur (Shimano Exage Sport) recently got destroyed by an errant plastic bag that got caught in my cassette.

I've been reading up some on rear derrailleurs and am trying to find a middle of the road replacement that will be compatible with my bike.

13T-28T, Shimano LightAction SIS Set

I've been looking at the Shimano 105 RD-any advice on what an acceptable replacement would be? Short cage or long cage? I'm looking to stick with Shimano.

Any input would be great appreciated. Thanks!
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Old 11-21-11, 11:53 AM   #2
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Sticking with a 12 speed? If not check out miroshift, good shimano compatible stuff
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Old 11-21-11, 12:01 PM   #3
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Any of the current long cage Shimano derailleurs will work fine, even the near bottom of the line TX-55 will perform better than your old derailleur. The long cage will work well with you 28T, some short cages will be okay, some will not. Of course, you can spend more.
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Old 11-22-11, 05:07 PM   #4
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I would go with something old but higher quality. Look on ebay or craigslist (if it is active in where ever it is that you are), you can easily find something in the $20 range that is good.
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Old 11-23-11, 06:56 AM   #5
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You need long cage if you have a triple up front. Otherwise short cage should be fine. This would also be a chance to change to an MTB rear derailer if you ever think you might want to run a rear cog bigger than 28. I put a new $22 Shimano Deore (it was on clearance and I forget the exact model number) on my commuter a couple of years ago (I run 7-speed SIS). I normally run 12-21 but change to 11-34 for loaded touring.
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Old 11-23-11, 07:51 AM   #6
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"12-speed Shimano SIS".

Check out how your derailleur attaches to your frame. Most frames have an arm that extends downward from the dropout that the derailleur bolts onto. Some frames require a "claw" on the derailleur that attches to the axle.

If your frame has the arm, and you buggered your derailleur with a plastic bag, your derailleur hanger alignment is probably buggered too. It needs to point straight down. On a bike with a 6-speed freewheel, you should be able to eyeball it straight enough so it will index. Be sure that you have a derailleur bolted onto the hanger before bending it or you might ovalize the derailleur mounting hole.

Most modern Shimano derailleurs will index with your shifters. Short cage is fine. If you're on the economy plan, I wouldn't worry about trying a used one.
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