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new bigger cassette now rear mech issues

acidstratoacidstrato Posts: 945
edited September 2009 in Workshop
I've fitted a 12-27 cassette to replace my old 11-25, only now when on my granny chainring the upper jockey wheel on my rear mech is too close to the 27T ring. its fouling on it and making noises I tried adjusting the B screw but it doesn't seem to change anything (i know what its meant to do but i cant see how its meant to make any difference? something missing maybe?)

on the top crank chain ring everything seems to run fine as the extra tension pulls the cage down away from the cassette. I've adjusted the H/L screws and the barrel cable adjuster and on the stand (turbo) it changed up/down alright.

its a Giant SCR 1.5, tiagra compact 9sp groupset now fitted with an ulteggra 12-27 cassette and HG73 9sp chain with a powerlink. did cross my mind that the chain seems slack

this is karma for me stating earlier that the giant had been reliable lol
Crafted in Italy apparantly

Posts

  • nicklousenicklouse Posts: 50,675 Lives Here
    screw that B screw in.

    you did fit a new chain? (needs to be a tad longer).
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • acidstratoacidstrato Posts: 945
    yeah chain replaced with cassette

    B screw all the way in?
    Crafted in Italy apparantly
  • whyamiherewhyamihere Posts: 7,678
    Did you check that the chain was the right length, or just put it on as it came out of the packet?
  • amck111amck111 Posts: 189
    check out http://www.parktool.com/repair/readhowto.asp?id=64 regarding the B screw. Though it sounds like the chain is too short.
  • acidstratoacidstrato Posts: 945
    uhhh....i assumed being the correct speed fitment made it the correct length???

    other than swapping one link for the power link, the chain went straight on out of the packet
    Crafted in Italy apparantly
  • acidstratoacidstrato Posts: 945
    looking at the pictures there something is obviously wrong, the lower pully on the cage stretches far back, almost making the cage horizontal.
    Crafted in Italy apparantly
  • John.TJohn.T Posts: 3,698
    edited September 2009
    It sounds like the chain is too long. You can check the Shimano way which is to put the chain on the big ring and smallest sprocket and check the position of the jockey wheels. The should be lined up vertically.
    Alternately use one of the methods here.
    http://www.parktool.com/repair/readhowto.asp?id=26
    My Fleet.
  • acidstratoacidstrato Posts: 945
    tidy thanks for that, I suspect your right after reading about 'saggy' derailleurs I will have a go at sizing the chain tomorrow after work
    Crafted in Italy apparantly
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