Join Date: Nov 2003
Bikes: Leader home built hardtail, Diamondback Response
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The b screw is a dynamic adjustment. It works with the preload of the spring in the derailleur mount to ballance the fore/aft angle of the derailleur against the tension of the chain when peddling. To see the results of the adjustment you need to have the bike on with the drive train moving. If the b screw is contacting the notch on the derailleur hanger, you can observe the adjustment by watching the gap between the top jockey wheel and the cassette cogs increase (b screw in) or decrease (b screw out). If nothing seems to decrease the gap, your chain may be too long. If you cannot get away from the cogs, then you may not have the proper derailleur for the size of the cogset.
Sometimes when installing a derailleur, the b screw is pinched against the side of the derailleur hanger instead of set into the notch. This will result in improper adjustment and or a bent b screw.
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