Changed cassette and now gears need adjusting?

volké
volké Posts: 58
edited June 2010 in Workshop
I recently bought a 12-27 cassette for a particularly hilly weekend. The shop I bought it from fitted it and presumably set the gears up because everything worked smoothly.

Since I'll probably change between by 'normal' and 'hilly' cassettes a few times, and can't really go to my LBS each time and get them to do it, I bought a chain whip and lockring tool. I also have a second chain so I don't need to adjust the length each time as well.

Anyway, I've just switched back to my 12-25 cassette and original chain - but now the gears need setting up again. Does anyone know what I should be adjusting?

Also, its a DA 7900 setup if that makes any difference.

Cheers.
Racing Bike: Cervélo S2
Training/ Criterium Bike: Cervélo S1
Mountain Bike: Santa Cruz Blur XC

Comments

  • kettrinboy
    kettrinboy Posts: 613
    edited June 2010
    most minor tweaks can be done with the barrel adjuster at the handlebar end of the shift cable and/or the barrel adjuster on the rear mech , just turn the bike upside down spin the pedals and shift up and down the cassette while turning the barrel adjuster a fraction of a turn either way until the chain shifts smoothly on all the speeds, it shoudnt need much more than that with just a change of cassette.
  • Wheelspinner
    Wheelspinner Posts: 6,604
    Shouldn't need to swap chains going from 12/25 to 12/27 either, nor change the length of chain. Derailleur should accommodate that change with no problems...

    Otherwise, just tweak the adjuster on the rear derailleur, or the downtube stop one, should fix it.

    Assumption is that the cassettes are the same type? I vaguely recall there were some interchangeability issues with (early) DA7900 cassettes and other 10 speed Shimano ones, used different thickness spacers or something. Could be wrong though...
    Open One+ BMC TE29 Seven 622SL On One Scandal Cervelo RS
  • Buckled_Rims
    Buckled_Rims Posts: 1,648
    I used to regularly change wheels on my previous bike and it always required a slight adjustment on the RD barrel even though the cassettes were from the same family but different cogs.

    From a 12/25 to a 12/27 no chain adjustments needed. Just learn to adjust the barrel by a quarter turn and test - redo until selection is slick, then remember how many turns you take and what direction :wink:

    I ended up painting a white spot in the adjuster for ease of use.
    CAAD9
    Kona Jake the Snake
    Merlin Malt 4
  • volké
    volké Posts: 58
    I'd already completely mucked up the settings by adjusting everything in sight :roll:, so I took the chain off to set the top/low on the rear derailleur, put it back on, and have set the top/low on the front derailleur too.

    Given that there are no barell adjusters on the 7900 shifters, or on the cables (Internal cable routing), the only barell adjuster available is on the rear derailleur. So this must be the one I should turn to follow your advice. How exactly should I go about setting this up?

    The only other adjustment is the B-tension (Which I've also messed with) - so that will need setting as well. I've got it so its close to the large cog but not touching - though I don't know whether it should be closer to it or further away.
    Racing Bike: Cervélo S2
    Training/ Criterium Bike: Cervélo S1
    Mountain Bike: Santa Cruz Blur XC
  • Buckled_Rims
    Buckled_Rims Posts: 1,648
    CAAD9
    Kona Jake the Snake
    Merlin Malt 4