Derailleurs: Limit Screw and B-Screw adjustments
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  1. #1
    RoadBikeReview Member
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    Derailleurs: Limit Screw and B-Screw adjustments

    Hello all!

    I have a brand new Allez Sport. I'm a noob to the sport but love to tinker. I was watching videos on tuning the front and rear derailleurs because 1) I'm trying to get rid of as much cross chain rub as I can, and 2) I refuse to accept that my friends BD bike with Shimano 2200/2300/Sora parts shifts smoother than my bike with full Sora parts (except crank).

    I've gotten the shifting really smooth, maybe 95% there, but I do feel like I can make it even smoother (without having to bring it to my LBS), so I have some concerns.

    1) I feel like my rear derailleur Low-Limit could be pushed closer to the spokes, but I've unscrewed the low limit screw to the point where it doesn't even make contact with the derailleur so it won't go any further. Any ideas?

    2) My B-Screw makes VERY little changes regardless of how tight or loose it is. I have to look VERY VERY closely to see any type of change when I'm adjusting it. On parktool.com, they recommend unscrewing the B-Screw to the point where the derailleur touches the cassette then screwing it back in until it backs off enough from the hubs. My derailleur will move at most 1-2mm at the full limits of the B-Screw. Any ideas?

    Thanks everyone for the input.

  2. #2
    RoadBikeReview Member
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    1. You may not have enough tension to check the low limit. What you need to do is pull on the cable running under your chainstay after backing out the lower limit screw. I haven't ever seen a RD that couldn't move into the spokes if the lower limit is backed all the way out.

    2. What chainring are you in when you try to adjust the b screw? You want to be in the smallest chainring so that there isn't too much tension in the RD. If the pulley doesn't touch the cassette in the small or large cog with the b-screw all the way out then leave it there that is the best your are going to get.
    Last edited by redlude97; 04-11-2012 at 01:42 PM. Reason: could->couldn't

  3. #3
    A wheelist
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    Quote Originally Posted by RyKnocks View Post
    1) I feel like my rear derailleur Low-Limit could be pushed closer to the spokes, but I've unscrewed the low limit screw to the point where it doesn't even make contact with the derailleur so it won't go any further. Any ideas?.
    You've got cable tension issues. Set the high and low gear stops with the cable disconnected. Use your thumb to move the derailer. Pedal by hand, push the derailer lower pivot (knuckle) and make the chain shift up a cog or two. Let go. Make sure it shifts back down cleanly without rattle in the gear. Adjust the hi stop to get this.

    Grip the top pivot (knuckle) with the fingers and push the lower pivot towards the spokes. Try to get the chain to shift over the top of the cassette. Push as hard as you can with that thumb. Adjust the low gear stop as needed.

    Let the derailer shift down into the high gear. Re-fasten the cable and adjust the indexing perfectly. Pull on the cable mid-span and shift the gears up & down a few times. Re-tension the cable if necessary. Re-set the indexing if necessary.

    You're all done.
    .

  4. #4
    RoadBikeReview Member
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    You'll get it, keep reading and adjusting, it's quite easy once you see how it all fits together. Sheldon is still the best resource. Derailer Adjustment

  5. #5
    WWU
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    Quote Originally Posted by Mike T. View Post
    You're all done.
    One of the easiest-to-follow explanations I've read in some time.
    "Use one hand to keep the chuck from popping off the valve, the other hand to pump. Switch hands every so often so you don't wind up looking like a fiddler crab." -Wim

  6. #6
    Happily absent RBR Member
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    Have you read the Shimano instructions for your derailleurs? They're all on Shimano's Tech site.
    Get a better saddle: www.kontactbike.com

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