shimano 10 speed 27-16 cassette and triple crankset transmission problems
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  1. #1
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    shimano 10 speed 27-16 cassette and triple crankset transmission problems

    G'day

    I use this cassete because I like close ratios for long distance Audax rides. I have changed the 16 cog for a 13.

    I know that this cassette is not recommended by shimano with a triple crankset. I am using a dura ace medium cage rear derailuer and a triple front derailuer. I also have friction downtube levers so I can fine tune the front and rear derauiluer.

    There is a lot of extra friction grating/mechanical/vibration noise when I use the 27 rear cassette with the middle chainring. I can see the rear derailuer shaking. The problem is less in the 25. There is no problem in the with the other rear cogs 23-13
    When I use the small chainring and the 27-25-23 I have the same problem.

    It must be putting extra stress on the chain because it broke recently. When I remove several links and rejoined the chain to get home the problem was reduced

    I have put on a new chain, a littel longer than the old one and the problem has increased.

    Today when riding on the 26 tooth chainring and the 27 rear cassette I could see the bottom of the chain was shaking sideways.

    Just to test this I have another wheel with a 27-12 rear cassette and when I use this there is no problem.

    I do not want to give up my close ratios without trying to solve/reduce th problem first.

    Any suggestions?

  2. #2
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    Sounds to me like you need to screw the "B" screw in more. The shaking that you refer to sounds like it is the upper pulley rubbing the 27's teeth. With the bike in a workstand and in this grear combination, try pulling back slightly on the rear derailleur. If the noise/shaking stops, then the B scre is your problem.

  3. #3
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    Quote Originally Posted by cyclust
    Sounds to me like you need to screw the "B" screw in more. The shaking that you refer to sounds like it is the upper pulley rubbing the 27's teeth. With the bike in a workstand and in this grear combination, try pulling back slightly on the rear derailleur. If the noise/shaking stops, then the B scre is your problem.
    Most likely the cause, but you would also be suited to go with a long cage. Make sure the chain isn't too short or long either.
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  4. #4
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    +1 on the "B" screw adjustment.

    It's critical that there is always a free section of chain between the jockey wheel and sprocket. On large sprockets the RD can ride too high and the jockey wheel engages the sprocket through the chain causing the type of problem you describe. In some cases there's enough force to push the RD backward damaging it of the hanger.

    BTW the "B" screw setting has to be checked with each large cog using each chainring. Shifting the FD effectively changes the chain length, affecting the angle of the RD cage, so a derailleur that clears correctly on one chainring, might touch with another. Adjust the B screw, and/or possibly change the chain length to get the best balance between clearance and shift performance throughout the range of usable gear combinations.
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