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Sliping gears

RodmcRodmc Posts: 42
edited May 2009 in The workshop
When I move off in the granny gear or stand while in said gear the cranks slip a quarter turn. This obviously slows me down and a car nearly rear ended me this morning when it happened 3 times in a row.

Oh if I am already moving in then change down into that gear it doesn't happen. Only appears to happen when pressure is applied.

Has this happened to anyone, can you advise me how to fix the slippage please as this is causing a bit of a nightmare when the lights change.

Many thanks.

Posts

  • will3will3 Posts: 2,173
    How worn are your chain and cassette?
  • RodmcRodmc Posts: 42
    The don't seem to be to bad, though I have a feeling you are going to say they need replaced.
  • el_presidenteel_presidente Posts: 1,963
    is it really a 1/4 turn? could peotentially be your cranksetslipping on the square taper BB (though I have a feeling this would only happen once...)
    <a>road</a>
  • RodmcRodmc Posts: 42
    Thinking about it maybe a 1/4th was over the top, probably an 1/8th.

    How would I go about rectifying that el_presidente?
  • laughingboylaughingboy Posts: 248
    When you say the granny gear, I take it you are talking about the smallest chainring, rather that the gears at the rear wheel.

    It could be a number of things. Old chains get loose at the pivots, and get longer. Over time this can deform cogs and chainrings. You may or not be able to see this wear, but it is a well known problem with only one cure: replace chain and worn parts.

    Otherwise, you could have stiff links on your chain that show up because of the tighter circle of the granny gear. Test each link for bendiness.

    Or... basically, I am guessing. I won't go on.

    Tip: If you don't want to die when unexpected lack of traction puts you in front of a speeding car at a junction, take it to a bike shop to get looked at.
  • *attempted thread hijack*

    Similar thing happened to me this morning but on a new bike that's only done 270 km, so the gears can't be worn (can they?) and they've been excellent til now.

    I got to the bottom of a small hill, put it into a smaller sprocket, heard the usual click, stood up to power up the climb and perhaps half a rotation in I had a 'phantom gear change', no resistance to my pedals, foot came unclipped, almost came off the bike etc.

    From then on changing down or up, the click of the shifter would be followed by a rattle of the rear dérailleur and an eventual change of gear, even then sometimes I had to 'feel' it in.

    I've got it booked in next week at the shop where I bought it from but I would like to ride it in the meantime and surely only a minor adjustment is required to get it purring again, but I don't know what it is & I don't want to F*** it up.

    Assistance gratefully received.
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