Gears work perfectly, except....

robgodd
robgodd Posts: 28
edited February 2009 in Workshop
Hi All,

I've recently put together my new road bike from a box of bits (so I'm reasonably adept), but I've got a problem with the chain / gears.

It's Dura-Ace 10 speed, and it works perfectly - very smooth and slick, no clicking or skipping when riding. The problem occurs when I stop: if I pedal backwards (when at lights, for instance, to get ready to start off) the chain will instantly jump down one or two sprockets.

I've tried adjusting everthing, but nothing seems to have an effect. Can anyone suggest anthing?

Cheers!

Rob

Comments

  • Al_38
    Al_38 Posts: 277
    Were they all new parts?

    I've only had that happen when using a worn cassette / chain / jockey wheels / chainring. Also found that it is worse when the chain is all gummed up with too much oil and grease
  • meagain
    meagain Posts: 2,331
    Just one sticking link in the chain?
    d.j.
    "Cancel my subscription to the resurrection."
  • robgodd
    robgodd Posts: 28
    All brand new parts.

    Seems a strange thing to have happen, and it's driving me mad.
  • topdude
    topdude Posts: 1,557
    Chainline :?:
    Should be easy enough to diagnose with the bike at home, rotate cranks backwards in each gear. Is it skipping when on the extremes of the cassette and ok in the middle :?:
    He is not the messiah, he is a very naughty boy !!
  • robgodd
    robgodd Posts: 28
    Thanks Topdude - I think that's it. The chain only skips over when it is on the big chain ring and the big sprocket.

    Is it OK to ride in this gear? I know it isn't a good idea on a triple, but the chain line is a bit straighter on a double. I won't be damaging the chain, will I?

    Cheers,

    Rob
  • robbarker
    robbarker Posts: 1,367
    Have you got the rear mech properly seated, i.e is the hooky bit properly behind the tab on the hanger?

    Have you sized the chain correctly?

    if so, try adjusting the B screw (the one at the back by the mech mounting bolt), to adjust the amount of tension the mech puts on the chain.

    Otherwise, a stiff link is the other obvious one.
  • disgruntledgoat
    disgruntledgoat Posts: 8,957
    I had a similar problem a while back and a worn jockey wheel was the cause. When using one of the "bad" gears (big to big/ small to small) the chain would unseat itself from the top jockey.
    "In many ways, my story was that of a raging, Christ-like figure who hauled himself off the cross, looked up at the Romans with blood in his eyes and said 'My turn, sock cookers'"

    @gietvangent
  • maddog 2
    maddog 2 Posts: 8,114
    running big ring-big sprocket is not really advised as the chain is having to 'bend' quite a bit from the outside (big ring) to the inside (big sprocket) and so the links will be under more pressure, will be noisier, and will wear more. Not a disaster but if you do it a lot then your drivetrain will wear faster.

    Going back to the original problem though - most new chains, and certainly Shimano ones, come covered in sticky grease which inhibits their flexibility and their ability to shift slickly for a fair few miles. When you're backpedalling, it sounds like your new chain just can't 'bend' enough and is trying to mount the next sprocket. You can either:

    - just ride it and it will improve as the chain beds in and the grease comes off
    - degrease it and relube it

    indeed some race teams degrease new chains for this very reason - out of the box the shifting is sub standard.
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • robbarker
    robbarker Posts: 1,367
    robgodd wrote:
    The chain only skips over when it is on the big chain ring and the big sprocket.

    I missed this crucial bit.. This is probably why it's happening.

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