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Old 11-20-09, 12:22 AM   #1
agealy
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Chain dropping -- front or rear derailer?

I recently bought a 1984 trek 610 with a shimano 600 groupset. The rear cogs were pretty worn so I replaced the freewheel with a 13-28 hyperglide. The chain has been dropping off of the chainwheel intermittently. I've done some careful shifting and it seems to happen when I'm shifting up to the bigger chainwheel. The chain falls off on the outer side, so in between the large chainwheel and the crank, but held up by the front derailer. Upon further inspection, it appears as if my rear derailer may be bent,. Not the whole thing, however, just the jockey pulley and perhaps the linkage between the jockey pulley and tension pulley. I'm guessing that the problem lies either with front derailer adjustment, or the possibly bent rear derailer.

Here's an ad from the previous owner: http://slo.craigslist.org/bik/1440640877.html

And a ****ty cell phone picture of the rear derailer: http://i154.photobucket.com/albums/s...y/derailer.jpg
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Old 11-20-09, 12:26 AM   #2
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If it's dropping to the outside, the H screw on the front derailleur needs to be dialed in more. Assuming the rest of your derailleur is actually set up properly.
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Old 11-20-09, 01:02 AM   #3
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Also you probably need to move the front derailleur clamp down a bit. Based on the photos in the listing it is way too high. When shifted to the large chainring there should only be about 1mm between the bottom of the cage and the chainwheel teeth. Based on the photos there is going to be an awful lot of space between the top of the cage and the chainring, which could also explain the chain dropping off. Once you have that right then you should also adjust the limit screw as recommended in the previous post, so that the chain just isn't rubbing on the cage when the small cog is selected at the rear.
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