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Poor shifting - jumping sprocket

earthearth Posts: 934
edited August 2015 in Workshop
Following on from the other threads about cassettes and cables, I learned that the rear derailleur hanger can become bent and the rear mech will never shift properly.

I got the tool for straightening the hanger and found that it was indeed out of shape. After a few minutes I figured out how to use the tool - bend the hanger to reduce the difference by half and retest until it is straight.

So I now have a hanger that is very close to straight and a lot close that it was. I hoped for success but sadly it has made no difference whatsoever. The mech still jumps a sprocket and by turning the barrel adjuster I can affect which sprocket is jumped but I cannot stop it happening.

I have cables to try as well.

Posts

  • have you checked the chain and cassette for wear?
  • earthearth Posts: 934
    Chain is fairly new and always spotless and the chainlength tool shows it has not stretched. I asked about the cassette in a previous thread and although it has a few shark fin like teeth on the larger sprockets it has only done about 3K miles and those sprockets may apparently be shaped to improve shifting.
  • earthearth Posts: 934
    I recabled everything today and had another go with the derailleur hanger adjustment tool. I'm happy to say all shifting problems are gone. Must have been a combination of a bent hanger and sticky cables. But it is not just shifting properly, it is much better than before. The shifting to bigger sprockets on the rear mech used to be an increasing effort. Now it is as light as a feather. The shifting to the big ring on the front mech is very light and snappy as well but still requires a positive lever stroke to achieve it. I think this is more to do with the range of movement of the mech than the cables. Brakes feel about the same but they only pull a few mils of cable at most.

    The polymer cable might have contributed or it might be that the old ones were just too dried up and frayed. But I did notice the polymer surface gets damaged easily. Where the cables go under the bottom bracket and through the plastic cable guide is a magnet for dirt and grit. I can't see the coating lasting long there. To make matters worse, my front mech cable then goes through a small hole in the BB shell and comes out of a small hole at the bottom of the seat tube. Both holes have sharp edges and the cable rubs the edge.

    EDIT - The other thing I noticed was the polymer cable in the kit was not lubricated. Does the outer casing have lubricant inside?
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