Help: something is slipping or jumping

DonDaddyD
DonDaddyD Posts: 12,689
edited April 2009 in The workshop
Several times during my commute the crank on my bike feels like it's jumping, when it does this there is sound like metal banging/slapping against metal.

On top of that.
When pulled up and I push down on the crank or pedalling really fast - then coast - then pedal again the crank turns but the drive doesn't engage until further into the pedal rotation.

At first I thought it was the rear hub (as it doesn't make that Fulcrum noise) then I thought it was the bottom bracket. But I've been advised that its the chain slipping and both that and the rear cassette needs changing (I've had the bike since August 2008 is this normal?). The bike changes gear fine, its just when I'm pedalling so what could it be?
Food Chain number = 4

A true scalp is not only overtaking someone but leaving them stopped at a set of lights. As you, who have clearly beaten the lights, pummels nothing but the open air ahead. ~ 'DondaddyD'. Player of the Unspoken Game

Comments

  • itboffin
    itboffin Posts: 20,064
    Well you can check the chain by popping into a LBS and borrow a chain measuring tool, i'm sure they won't mind as it takes 5 secs and is very obvious when worn.

    I'd be more suspect about changing the rear cassette, I know people say you should chain them together but really unless I can see the wear I'm not chaining my cassette.

    I'd get that hub looked at ASAP just to be safe.
    Rule #5 // Harden The Feck Up.
    Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.
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  • Wooliferkins
    Wooliferkins Posts: 2,060
    It sounds as if your cassette/chain is worn. It's the mileage and how well you look after these things that mitigates how long they last. Have a look at the cassette teeth, are they pointy and wave shaped or do they still have a square tip to them? Does it slip in all gears?
    Neil
    Help I'm Being Oppressed
  • DonDaddyD
    DonDaddyD Posts: 12,689
    Doesn't slip in any of the gears, but the teeth on the third and forth ring(the ones I use the most) of the cassette does look worn.
    Food Chain number = 4

    A true scalp is not only overtaking someone but leaving them stopped at a set of lights. As you, who have clearly beaten the lights, pummels nothing but the open air ahead. ~ 'DondaddyD'. Player of the Unspoken Game
  • itboffin
    itboffin Posts: 20,064
    DonDaddyD wrote:
    Doesn't slip in any of the gears, but the teeth on the third and forth ring(the ones I use the most) of the cassette does look worn.

    I would have thought all that black muck on your drive train should have shortened the life a little :wink:

    If you can find a supplier those cassette rings are individually replaceable, I think SJS might sell them.
    Rule #5 // Harden The Feck Up.
    Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.
    Rule #12 // The correct number of bikes to own is n+1.
    Rule #42 // A bike race shall never be preceded with a swim and/or followed by a run.
  • biondino
    biondino Posts: 5,990
    Is it possible your rear derailleur wheels aren't springing back into place as quick as before, giving you a delay between starting to pedal and actually engaging the drivetrain?
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  • itboffin
    itboffin Posts: 20,064
    biondino wrote:
    Is it possible your rear derailleur wheels aren't springing back into place as quick as before, giving you a delay between starting to pedal and actually engaging the drivetrain?

    Good call, lift the back wheel and turn the cranks backwards whilst shifting through your gears that'll highlight any sticking.
    Rule #5 // Harden The Feck Up.
    Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.
    Rule #12 // The correct number of bikes to own is n+1.
    Rule #42 // A bike race shall never be preceded with a swim and/or followed by a run.
  • Chicago Dave
    Chicago Dave Posts: 59
    how many kilo's ya got on the drive train?
  • crankycrank
    crankycrank Posts: 1,830
    Sounds more like the cassette hub pawls are not engaging properly. Could be worn or just needs a good cleaning and lube.
  • DonDaddyD
    DonDaddyD Posts: 12,689
    Went to te bike shop he did a half turn of the crank before the drivetrain engaged. Said it's probably the hub (cassette or wheel - are they the same thing?).

    Told me it either needs replacing or cleaning.

    The chain is strecthed (bike shop demonstrated).

    thanks guys for the advice.
    Food Chain number = 4

    A true scalp is not only overtaking someone but leaving them stopped at a set of lights. As you, who have clearly beaten the lights, pummels nothing but the open air ahead. ~ 'DondaddyD'. Player of the Unspoken Game
  • desweller
    desweller Posts: 5,175
    DonDaddyD wrote:
    Went to te bike shop he did a half turn of the crank before the drivetrain engaged. Said it's probably the hub (cassette or wheel - are they the same thing?)..

    The cassette has no moving parts. It's the term used to describe the assembly of sprockets. It fits onto the freehub, the term used to describe the assembly that allows freewheeling.
    DonDaddyD wrote:
    The chain is strecthed (bike shop demonstrated).

    Chains don't stretch so much as just wear in the sliding interfaces. If you've been riding in the winter then August is not bad going I'd say!

    Cassettes can look perfectly OK but they do wear with the chain, which will only be obvious when you change the chain and not the cassette (skipping under load).

    You can check the wear of a chain with a ruler if you don't want to splash out on a special tool - the pitch should be 1/2".
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  • fossyant
    fossyant Posts: 2,549
    New freehub, or remove and squirt some light oil in and see if you get away with it.

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