Strange gear shift problem

birdy247
birdy247 Posts: 454
edited March 2011 in Workshop
When I am on my small ring at the front and on one of the 4 larger rings at the back, my gears always slip.

When I inspected my bike, It looks like there is too much tension in the rear derallieur. The chain wants to jump back up to the bigger cog.

This only happens until I get past the 4th largest cog, then all shifts fine. (Not an issue when in the big ring at the front)

How would there suddenly be too much tension in the cables? I thought they generally stretched and needed tension added.

I cant loosen off the cables any more from the barrels, what's the best way to fix?

Thanks
www.turbotraining.co.uk

Comments

  • Simon Notley
    Simon Notley Posts: 1,263
    If it is too much tension then you just need to loosen the bolt that attaches the cable to the rear mech and allow it to pull a bit of extra cable through. If you reset the barrels to a neutral point before you do this you should be able to fine tune using them.

    Other explanations could be that your chain/cassette are worn out (would explain skipping, but not catching on a different sprocket) or perhaps the cable is sticking preventing it from moving as far as it should do. Remedy for this is a new cable or lube inside the outers.
  • Mister W
    Mister W Posts: 791
    Your description doesn't match your diagnosis. A problem with the tension in your cable would affect every gear. I suspect Simon is correct in saying that your chain/cassette are worn or your rear mech is sticking.
  • birdy247
    birdy247 Posts: 454
    Mister W wrote:
    Your description doesn't match your diagnosis. A problem with the tension in your cable would affect every gear. I suspect Simon is correct in saying that your chain/cassette are worn or your rear mech is sticking.

    When I turn the bike upside down, I notice that the rear mech arm occasionally moves (like its almost stuck to the chain).

    its a brand new chain, but cassette is older. Should I replace both at the same time?

    Thanks
    www.turbotraining.co.uk
  • Simon Notley
    Simon Notley Posts: 1,263
    birdy247 wrote:
    When I turn the bike upside down, I notice that the rear mech arm occasionally moves (like its almost stuck to the chain).

    Don't worry about that, it's pretty normal I think, just a little bit of friction between the chain and the jockey wheels.
    birdy247 wrote:
    its a brand new chain, but cassette is older. Should I replace both at the same time?

    That's a whole topic in itself! How old is the cassette? If we're talking five years plus with the same chain, it might be time for a new one (and soon before you wear out the new chain) but if it's only a year or two (or you change the chain every year or two) the cassette should be fine. In between these ages, it's hard for me to say without looking at it.

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