How to fix rear derailleur on a certain sprocket

u0362565
u0362565 Posts: 17
edited June 2014 in The workshop
Hi all,

I recently made the rather rash decision to remove my derailleur's and give them a clean then reattach and set them up. I managed to break the rear derailleur shifter so i need to order a new one. But i'd like to at least set up the front derailleur. I've read that i should be on the smallest chainring and the largest sprocket to do this. However because i have no control over my rear derailleur its positioned so that the chain sits happily in the middle of the set of sprockets say sprocket 4 of 9. I want to move the chain so that its on the lowest gear, largest sprocket, how can i adjust the derailleur position manually so the chain will stay on the largest sprocket while i turn the pedals to test the front derailleur shifting? If i manually shift the chain to the largest sprocket the derailleur acts to try and shift the chain back to sprocket 4. I'm not an expert on derailleurs but i guess this is because there isn't any tension from the gear cable in the shifter to hold the derailleur spring under tension. I can hold the rear derailleur in position but i don't have enough arms to hold that and turn the pedals and make the necessary adjustment to the front derailleur!

Thanks for the help!

Comments

  • gbsahne001
    gbsahne001 Posts: 1,973
    If there's no tension on the cable then it should be sitting on the limit switch, which should in turn be the smallest ring on the back.

    Adjusting the lower of the 2 limit screws should adjust the trim at the lower end of the gears and the upper screw the top end of the gears. There's usually not enough adjustment in the screws to move it to the position you say it's in, which would suggest there is still some tension in the cable, possibly not sliding freely in the outer
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  • u0362565
    u0362565 Posts: 17
    Ok i have completely released the gear cable from the rear derailleur, set the chain by hand to the smallest sprocket then adjusted the high gear limit screw so that the jockey wheels are aligned under the smallest sprocket. As i have no rear shifter how can i shift the chain to the largest sprocket and make it stay there when i turn the pedals? I can shift the chain by hand but the derailleur position means its acting to shift the chain back down to the smaller sprockets.

    Perhaps i need to buy the new rear shifter before i can do anything. I'm just trying to set up the front derailleur until i can get the rear shifter. The video i watched showing how to align the front derailleur said to set the chain on the smallest chainring and largest sprocket at the back and this is an issue without shifter control of the rear derailleur.

    Thanks
  • desweller
    desweller Posts: 5,175
    How did you break the right shifter? They're normally the strong ones.
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  • u0362565
    u0362565 Posts: 17
    It wasn't shifting through all 9 positions so I opened it up to see how it worked but I clicked the shifter a few times with the casing open to see what was going on but didn't want to mess with it too much so put the casing back on but then when I was clicking through the gears something went snap and it was the little red plastic lever that tells you what gear your in so somehow I must have moved the lever out of place when I opened it and it must have caught on something and snapped. I won't be opening one up again unless I really have to!
  • desweller
    desweller Posts: 5,175
    Never mind, sometimes you have to risk breaking something to learn something! Does the shifter still pull cable correctly though? You could still use it if the escape mechanism is OK. Or you can unclamp the cable, push the derailleur to the desired position and then reclamp it.
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  • u0362565
    u0362565 Posts: 17
    Actually yes the shifter does seem to work so I've ordered a new one anyway but will try out your suggestion in the mean time, thanks for the advice!

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