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Rear Derailer hits largest cog in back...no b-screw adjustment.

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Rear Derailer hits largest cog in back...no b-screw adjustment.

Old 10-02-11, 11:37 PM
  #1  
vins0010
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Rear Derailer hits largest cog in back...no b-screw adjustment.

I recently picked up an old Trek 700 Sport hybrid for my sister-in-law to use for casual rides. It is pretty entry-level, having a triple upfront, grip shifts, 7-speed freewheel, and a Shimano indexed rear derailer (not sure what "line"...just says "SIS" on it). I tuned it up and the thing does not like to shift into the medium/large (upfront) and largest cog in back. When it does, the jockey wheel hits the largest cog. The derailer does not have a b-screw. I'm thinking the chain might be too short...but don't quite want to throw on a new chain without being sure. I do think all the parts (including chain) are original. The previous owner bought it new, said it was never used, and they're finally just selling it. From the condition of the bike, I believe him. Any ideas on anything else it could be or I could do?
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Old 10-03-11, 12:10 AM
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The following image shows gear combination's that Shimano doesn't recommend you use.

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Old 10-03-11, 08:03 AM
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vins0010
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I should be happy I get the second biggest on the back, while on the largest in the front! I know you shouldn't use those and they are iffy, generally. However, I still haven't had this kind of trouble using this combination on other bikes...wondering about the cause.
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Old 10-03-11, 09:12 AM
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As long as you can get into small chainring/big cog I think I'd call it good. Being able to have mid ring/big cog would be nice but it's not a deal breaker.

Rear derailer springs could be a tad tired making that shift difficult.
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Old 10-03-11, 10:19 AM
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[blind text based guess, lacking pictures.. ]
must have added a bigger cog on the wheel , but not changed the RD to suit.
need a RD that clears the bigger cog.. long ones will do , Mtb Type.
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Old 10-03-11, 10:39 AM
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Originally Posted by cobba View Post
The following image shows gear combination's that Shimano doesn't recommend you use.

Interesting.
Do you have a page with text that links to this picture?
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Old 10-03-11, 11:01 AM
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It's the "Which gear combinations..." question on this page: (Question before last)
https://cycle.shimano-eu.com/publish/...isc_faq_s.html
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Old 10-04-11, 08:46 AM
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I guess I would suggest you simply have a wrong derailer on your bike. It would seem to be either wrong or really old and almost all RD now have a "b" screw to adj the clearance between the jockey wheel and the largest cog.
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