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b-screw does nothing

Old 07-05-06, 12:54 PM
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viva
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b-screw does nothing

Hi, I recently removed/replaced my rear wheel and decided to do a "tune-up". After adjusting the limit screws, I began to adjust the b-screw and noticed the jockey/guide wheels weren't moving, no matter how much I turned the screw in or out?? I've adjusted this before and had no problem - any ideas what could be wrong? Could I have a broken spring? This is on a Dura-Ace 10 speed rear derailleur. Thanks.
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Old 07-05-06, 02:55 PM
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urbanknight
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Do you have the shifter and cable on the loosest setting? If it's under tension, you won't see any movement in the limit screws.
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Old 07-05-06, 04:19 PM
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seely
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Are you pulling the derailleur out by hand when tightening it? Otherwise there is a good chance you are bending the collar/b tension screw if you are trying to tighten it down under load. Always pull the derailleur back, away from the crankset (towards you if you are standing behind the bike) to get the load off the b-tension screw before adjusting it. Adjustment with the b-tension screw is minimal and really has two settings--all the way in, or all the way out. You really shouldn't need to mess with it unless you are getting rubbing in the largest cog on your rear cassette. If you are, then just put that screw all the way in and you should be about right.
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Old 07-05-06, 06:08 PM
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wagathon
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Did you change (shorten) the rear cable housing? If so, the screw may not even be in contact with the dropout stop.
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Old 07-05-06, 11:53 PM
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The B-screw adjusts the spring-tension, not so much the actual position of the upper jockey wheel. That's because the chain-wrap and pre-load of the cage pulls the RD up & forwards. The B-tension then adjusts how much force is pulling back on the cage. To really see what happens with B-tension adjustments remove the chain and shift up & down into the biggest cog, you'll be able to see a difference then.
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