Need advice adjusting rear derailleur when chain is on largest chainwheel

Discussion in 'Cycling Equipment' started by dvroberts, Jan 2, 2011.

  1. dvroberts

    dvroberts New Member

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    Hi Folks,

    First time posting here. I have a Bridgestone RB-T (1994 touring bike with Shimano RX100 derailleurs) that I am having trouble adjusting the gearing while the chain is on the crankset's largest chainwheel. I have 3 chainwheels on the crankset, and with the chain in either the smallest or the middle chainwheel I have no problem getting the rear derailleur to go through all 9 sprockets on the freewheel. But in the largest chainwheel, I can't get the rear derailleur to shift to either of the two largest sprockets. In fact, when I shift from the third-largest sprocket to the second-largest, the chain often gets stuck/jammed. When it's on the third-largest sprocket, the rear derailleur is almost horizontal, and looking from the back of the bike, the rear derailleur looks too far to the right. I am at a loss for what to try. Any advice would be much appreciated. I'm about to throw in the towel, admit defeat, and take it to my friendly bike shop./img/vbsmilies/smilies/frown.gif

    P.S. I posted this on bikeforums.net as well, so if you see this as a cross-post, please don't roast me! I'm just not sure which forum is more active.

    Thanks,

    Doug
     
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  2. oldbobcat

    oldbobcat Well-Known Member

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    It sounds like the chain is too short. There just aren't enough links to span the large ring, the chainstays, the largest rear cogs, and the derailleur pulleys, or the chain is pulling the jockey pulley so far forward that it does not clear the the big cogs. But either problem should be cured by using a longer chain.

    My method for determining a workable chain length is to switch to the smallest ring and the smallest rear cog and break the chain so that it just clears itself as it runs through the derailleur pulleys. The other method is to shift into the largest-largest combination and break it so you get a shallow s-curve through the pulleys. My method usually results in a slightly longer chain.

    By the way, on most 7-, 8-, and 9-speed bikes, and especially bikes with wide cassette ranges, the large-large combination is not used. This is because the acute crossover creates excess friction and stress on the cogs and chain. On 10-speed road bikes, the small-small combination is usually not used because the chain will rub on the inside of the large chainring. Also, many road riders will never use the large-large combination, but I say 10-speed chains are very flexible and if the chain is long enough and you do it for only short periods, there's no harm done.
     
  3. alfeng

    alfeng Well-Known Member

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    Did the problem occur after you put a new chain on the bike OR is a situation which has existed for a long time?
     
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