CHAIN JUMPS PAST REAR GEARS

July 30, 2007

    I have followed the recommended way to adjust the rear dérailleur and it shifts okay—except in the center of the cogset the chain jumps past a cog as I shift to a lower gear. Starting from the smallest and counting toward the largest it happens about cog 5 or 6 and jumps to 7 or 8. It's a Campy Centaur 10-speed. Any help would be appreciated. Thanks.

Harold L.

Harold:
    As I've said before, walking someone thru diagnosis of an unobvious problem via the written word has problems of its own. But I've geared up for this one.
    I suspect one of three things: (1) a bad derailleur cable and/or housing; (2) excessively worn teeth on one or more cogs; or (3) a bad angle or tension of the rear derailleur.
    Number (1) you can address most easily. Try replacing the cable and its housing. If the problem persists, lay the bike on its side (gears facing up) under really good light and inspect the teeth on the middle cogs. Each tooth should have sharp corners, not rounded. Rounded teeth means you should replace the entire cassette (or freewheel); when you do, you must also replace the chain.
    If the teeth pass your check-up, you might check the angle of the derailleur relative to the cogs. I could try to explain that, but, as we often find, the folks at Park Tool have it covered pretty well.
    Failing all that, the derailleur might have a more subtle problem, like a bad spring, misaligned jockey wheel, or a loose bolt. (Some might even blame the shifter.) For these sorts of things I'd seek professional (I mean, well-paid) help.

Mr Bike

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