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  1. #1
    Senior Member autonoz's Avatar
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    B screw not touching



    Well hopefully you will be able to see what I believe is my dilemma. I have the chain on the large gear in the front and the large gear on the back but my B screw never makes contact with the stop. I am no expert but I believe it should be touching, am I correct? If so can someone give me an idea as to what may be wrong?

  2. #2
    Senior Member bikeman715's Avatar
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    Yes you are right , it should be. To fix do this , find a 6 or 5 MM hex loosen the derailer's mounting bolt so the derailer can rest against the stop , re-tighten the bolt and you be good to go.
    bikeman715

  3. #3
    Senior Member autonoz's Avatar
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    Quote Originally Posted by bikeman715 View Post
    Yes you are right , it should be. To fix do this , find a 6 or 5 MM hex loosen the derailer's mounting bolt so the derailer can rest against the stop , re-tighten the bolt and you be good to go.
    Thanks for the quick response. This is what I thought would fix the problem as well, but all the derailer does is push back off the stop. When I say push off I mean the spring pushes it back to the same position.

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    Push it back forward onto the stop and note the position of the upper pulley with respect to the sprockets, especially larger ones. I suspect it's riding super close or maybe touching (through the chain) in which case the sprocket will push the RD back until it clears.

    It's possible the largest sprocket is too big for the RD, or possibly the chain is too long. Check the latter by shifting to a typical low gear combo, and pulling the lower loop forward (while holding the crank) and see if the upper pulley drops away from the sprocket, and the Rd swings forward. If that seems promising, remeasure the chain by going to the big/big combo and seeing how much you can safely shorten the chain. (minimum length is big/big, with some room for the idler cage to give more).
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  5. #5
    Senior Member autonoz's Avatar
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    Quote Originally Posted by FBinNY View Post
    Push it back forward onto the stop and note the position of the upper pulley with respect to the sprockets, especially larger ones. I suspect it's riding super close or maybe touching (through the chain) in which case the sprocket will push the RD back until it clears.

    It's possible the largest sprocket is too big for the RD, or possibly the chain is too long. Check the latter by shifting to a typical low gear combo, and pulling the lower loop forward (while holding the crank) and see if the upper pulley drops away from the sprocket, and the Rd swings forward. If that seems promising, remeasure the chain by going to the big/big combo and seeing how much you can safely shorten the chain. (minimum length is big/big, with some room for the idler cage to give more).
    I can push it to the stop and the gears or chain do not hit. I did some chain length checking and I think it s like one half link long. Probably worn out. If my chain is stretched would it make it hard to fine tune the down shifting?

  6. #6
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    Ok we're missing something. The idler cage tensions the chain so there's a force pulling it forward. We need to find something pulling it back. Unless this RD has a sprung upper body it should always go all the way forward, unless a tight pivot held it. But I've never seen one spring back as yours does (except for those with upper springs).

    One other possibility but it's so obvious that I hesitate to mention it. Is it at all possible that the RD housing loop is short enough to pull on the adjuster?
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  7. #7
    Senior Member autonoz's Avatar
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    Quote Originally Posted by FBinNY View Post
    Ok we're missing something. The idler cage tensions the chain so there's a force pulling it forward. We need to find something pulling it back. Unless this RD has a sprung upper body it should always go all the way forward, unless a tight pivot held it. But I've never seen one spring back as yours does (except for those with upper springs).

    One other possibility but it's so obvious that I hesitate to mention it. Is it at all possible that the RD housing loop is short enough to pull on the adjuster?
    Ok, like I said I am no expert, and I am beginning to think I am an idiot. I have sixteen bikes in my garage and on everyone of them the spring pulls the derailer forward, except this one. It does have a spring in the upper pivot at the mount. I just purchased it used for my Premis. It is a Suntour 7000.
    Last edited by autonoz; 02-25-11 at 08:08 PM.

  8. #8
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    RDs with upper pivot springs are designed to pivot off the B screw stop, which is used only to limit their forward position. The angle depends on the balance between the upper and lower spring. If yours is working fine go with it. If you feel it's too far back and performance is suffering, see if either spring has adjustable tension (usually multiple holes for one leg) and see if you can later the balance favorably.
    FB
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    An ounce of diagnosis is worth a pound of cure.

    “Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

    “One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

    WARNING, I'm from New York. Thin skinned people should maintain safe distance.

  9. #9
    Senior Member autonoz's Avatar
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    Quote Originally Posted by FBinNY View Post
    RDs with upper pivot springs are designed to pivot off the B screw stop, which is used only to limit their forward position. The angle depends on the balance between the upper and lower spring. If yours is working fine go with it. If you feel it's too far back and performance is suffering, see if either spring has adjustable tension (usually multiple holes for one leg) and see if you can later the balance favorably.
    Thank you for sharing this with me. Knowing this, the derailer is probably working fine.

  10. #10
    Senior Member vredstein's Avatar
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    That appears to be a very short screw. Is there any chance it has been broken at the bottom?
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