Why won't these (old) gears index?

Discussion in 'Bicycle Mechanics and Repairs' started by KneesUp, 13 Aug 2019.

  1. KneesUp

    KneesUp Veteran

    The kid's bike is a bitsa bike. She's only recently started using the gears on it, and hence I've discovered they do not index. On closer inspection I thought I'd diagnosed it straight away - I'd inadvertently fitted a 6 speed grip shift (because she likes grip shift) with a 5 speed cassette (because I evidently miscounted)

    So, I've swapped if for a five speed thumbie today, having convinced her that they are better, and it still won't sodding index.

    I got it so it would go from 1 to 5, but then it wouldn't shift one gear per click going up again, so I gave the barrel adjuster a little tweak, and it moved up and off the end of the cassette after gear 1, so I tweaked the limit screw and it popped out of 1st on the thumbie (which was very hard to get to gear 1 anyway - not at all sure the kid could do it - it gets stiffer the lower gear you select)

    I think it might be too much friction in the cable, and / or too tight a curve leading to the derailleur, but any other thoughts appreciated. (And yes, it got paint spilt on it in the shed and I need to sweep under the guinea pigs!)

  2. Crackle

    Crackle Squatter

    My suggestions as a starter for 10...

    Put it in the lowest gear and check the cable tension again, no slack but not too much tension.

    Check the cable is moving freely in the housings.

    Try adjusting the b screw and whilst mentioning that, that chain looks right on the limit of being the right length for that gearing i.e too short.
    Cycleops, KneesUp and dave r like this.
  3. Tigerbiten

    Tigerbiten Veteran

    Both "standard" 5 and 6 speed cassettes have a distance of 5.5 mm between sprockets.
    The extra sprocket was add by making the cassette wider not by narrowing the gaps between sprockets.
    So your 6 speed shifter should work with a 5 speed cassette.
    I'd change the cable and try again.
    I'd also take a look at your derailleur hanger to see if it obviously bent as this can also alter the shift.

    Luck ....... ^_^
  4. OP

    KneesUp Veteran

    Chain is a tad short, agreed - I took a stiff link out (she doesn't use it much, it had paint on it ... ) and also swapped to the mid-cage mech as shown because I tough the short-cage that was on might have been the issue so it needed a longer chain if anything.
  5. Cycleops

    Cycleops Guru

    Accra, Ghana
    Change the cable making sure you grease it and get a chain of correct length. Move the mech by hand without the cable to check hi low adjustment. Connect everything up and it should work as intended.
  6. Spiderweb

    Spiderweb Not So Special One

    North Yorkshire
    Could be an issue with compatibility of parts?
    Old 5 speed block.
    What looks like a Shimano 2300 rear mech designed for closer ratio 8 speed.
    Indexed 5 Speed Thumb shifters not compatible with an 8 speed mech.
    raleighnut likes this.
  7. Cycleops

    Cycleops Guru

    Accra, Ghana
    Should work, the 2300 mech if adjusted should be fine, it's not the mech but the shifter that does the indexing.
    sleuthey likes this.
  8. Tigerbiten

    Tigerbiten Veteran

    I'm also starting to think it could be a compatibility issue.
    The new mech moves the wrong distance with the right amount of cable pulled by the shifter.
    With the chain off, line it up by eye with small sprocket and then shift it to the large sprocket, is it still lined up ??
    If it's way off, then that's your problem.
    If the old mech still works, you could try it and see if it moves the right amount.
  9. raleighnut

    raleighnut Guru

    On 3 Wheels
    Ditto, that's not a 5-6 speed mech, pull ratio will be different.
    gbb and C R like this.
  10. OP

    KneesUp Veteran

    I thought the indexing came from the shifter, like @cyclops i.e. when I move the shifter it pulls enough cable to move one gear on a 5 speed because it's a 5 speed shifter. However, I guess it also depends on how much the shifter moves per mm of cable pull - I thought that didn't change until 10 speed?

    I think I have the old derallieur in a box somewhere, I changed it when I changed the shifter to a twist grip at the kids request.

    Would this also explain why it gets really hard to move the shifter from 2 to 1?
  11. Crackle

    Crackle Squatter

    I would have thought the 2 to 1 difficulty is the chain being on its limit. I also would have thought that dérailleur would work but it can be a bit hit and miss when you use different parts, hard to say without trying something else.
    raleighnut likes this.
  12. DaveReading

    DaveReading Veteran

  13. andrew_s

    andrew_s Guru

    Nothing on there about how much the shifter moves per mm of cable pull.

    Kneesup is correct, in that all Shimano rear mechs move the same distance (1.7 mm) per mm of cable pull, with the exception of old Dura-ace (6/7 speed) and recent 10-speed MTB.
    Last edited: 15 Aug 2019 at 00:41
  14. DaveReading

    DaveReading Veteran

    So how does the shifter know that you have swapped the cassette for one with a different spacing between the cogs ?
    DCBassman likes this.
  15. OP

    KneesUp Veteran

    Because you move the shifter further between gears. So say you need 10mm cable pull per gear on 8sp and 12mm per gear on 5 sp. An 8 sp shifter pulls 10mm per click and a 5sp pulls 12mm per click. That’s how I thought it worked?
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