Would BB play affect rear shifting

mclaren1986
mclaren1986 Posts: 23
in MTB workshop & tech
Hi, I haf a problem with my chain skipping on my cassette. so I changed my cassette and chain and stiff gear cables which did make an improvement but my gear is clunking changing down no matter how much I index. I have never had a problem indexing my own gears before.

I noticed that I have about 1-2mm play on my cranks which appears to be related to my pressfit BB. Could this be causing my issue? I have cleaned my jockey wheels which didn't help much.

Appreciate any help.

Comments

  • reaperactual
    reaperactual Posts: 1,185
    edited January 2021
    A tiny amount of play in the BB shouldn't effect chainring position enough and in turn won't have any effect on shifting.

    If there is clunking or hesitation when shifting from bigger to smaller cogs which can't be tuned out most of the time it will be some excess cable friction that could be the cause for various reasons.

  • mclaren1986
    mclaren1986 Posts: 23
    Thank you, I need to change my BB anyway because it doesn't spin very smooth at all but won't expect this to improve gear shift. Maybe my outer has too much bend.

    .
  • reaperactual
    reaperactual Posts: 1,185
    edited January 2021
    👍 I've seen worse bends on those sections of cabling. Lots of little things that could cause friction. Could the cut outer cable ends be pinched?

    Had first hand experience of a tiny kink in new inner cable that caused me a massive headache on one occasion?

    A hassle but could be worth a re-install of shift cable and re-index from scratch double checking all those little details that can easily be missed etc?

    If you go down the full re fit route take care of any fraying on inner cable ends as that would be more trouble than it's worth re threading though outers unless you have spare inner cables handy?
  • mclaren1986
    mclaren1986 Posts: 23
    Thanks for your advice. I was a bit lazy and didn't use the tool to open up the outer hole after cutting. I think I will replace inner and outer again :) it had a small fray but managed to cap it. Won't enjoy being pushed through an outer again.
  • reaperactual
    reaperactual Posts: 1,185
    edited January 2021
    Your welcome Pal.👌

    When fitting new inners/outers/both I usually put a thin layer of silicone grease on inner cables as I feed it through then wipe off on any exposed sections afterwards which helps with threading, shift performance and general usage.

    Reckon it's a 50/50 success rate reusing inner cables so would probably be best to fit a new inner but the outer could still be ok if it's new.

    Take your time and get the small things right and if by the tiny chance it is something else you will have ruled out 90% of the issues it could be.

    I'm sure you'll get shifting spot on with a bit of care and attention redoing the cables and indexing from the start again.😎👍

  • steve_sordy
    steve_sordy Posts: 2,453
    Check the tightness of the bolt securing the mech to the mech hanger; ditto the mech hanger to the frame. Twice that has been the cause for me of dodgy shifting. It is such an obvious thing once spotted that each time it was a head slapping moment! On neither occasion did the bolts look loose, but once grabbed hold of and twisted, it became clear.

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