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My b-tension screw does absolutely nothing…

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  • March 21, 2018 at 2:52 pm #28273
    AfterPeak

    So I have built a bike with ultegra rear derailleur and have a 11-25 cassette. Never touched the b-tension screw from new just installed the derailleur. Anyway I thought I would have a play with it to increase the crispness of my shifting and noticed it does nothing if screwed all the way in or out. Is that normal/possible?

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  • April 12, 2018 at 12:18 pm #915245
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    AfterPeak

    kil0ran wrote:

    kil0ran wrote:
    I usually request a spare hanger. Having said that my LBS has a hanger encyclopedia so as long as it isn’t completely trashed they can find one that’s a reasonable match, and then fettle accordingly

     

    Ordered one. Had to go back to tifosi to get one so I imagine I would have been stuffed in a couple of years time as they are not easy to get hold of

    March 31, 2018 at 5:00 pm #915243
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    AfterPeak

    OK I have finally got the
    OK I have finally got the bike on my work stand to have a good play with the screw.

    With the advice above (pedal backwards + shift up and down the cassette between adjustments) I can now see a small movement. I certainly can’t get the gap less than 5mm but it’s close to that so I am happy.

    Thanks everyone. I am going with mystery solved.

    March 27, 2018 at 10:49 am #915241
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    AfterPeak
    Peowpeowpeowlasers wrote:
    Pedal backwards.  You’ll see the change in position.  Postion the screw so the chain stays at least 5mm away from all the cogs.

    The screw on a Shimano derailleur simply adjusts the tension on a very large, fat powerful spring wrapped around the bolt that secures your derailleur to your hangar.  You can’t see this spring unless you remove the surclip from behind the bolt and then push the bolt out.

     

    Cheers I will give it a go. FYI never try and service that spring. Pain in the backside to get that surclip back in and hold the spring wound. throw in the bin and buy a new derailler 🙂

    March 27, 2018 at 10:42 am #915239
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    Accessibility for all

    Pedal backwards.  You’ll see

    Pedal backwards.  You’ll see the change in position.  Postion the screw so the chain stays at least 5mm away from all the cogs.

    The screw on a Shimano derailleur simply adjusts the tension on a very large, fat powerful spring wrapped around the bolt that secures your derailleur to your hangar.  You can’t see this spring unless you remove the surclip from behind the bolt and then push the bolt out.

    March 27, 2018 at 9:41 am #915237
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    Grahamd
    stenmeister wrote:
    ktache wrote:
    I have been adjusting my b-screw with my JIS 2 screwdriver,  it fits beautifully and doesn’t put stess on the grooves in the head.  Proper tool, proper job.

     

    Top recommendation Sir, I’m getting one of these.laugh

    Wholeheartedly agree, embarrassing that it took me years to order one. Got mine from Amazon, about £7 , so no nonsense with import duty / tax.

     

    March 27, 2018 at 9:32 am #915235
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    stenmeister
    ktache wrote:
    I have been adjusting my b-screw with my JIS 2 screwdriver,  it fits beautifully and doesn’t put stess on the grooves in the head.  Proper tool, proper job.

     

    Top recommendation Sir, I’m getting one of these.laugh

    March 27, 2018 at 9:06 am #915233
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    Judge dreadful

    Make sure the derailleur

    Make sure the derailleur hanger is butted up against the screw, when it’s wound as far out as possible, before you start. I’ve had lots of bikes where the hanger has been fitted badly, in relation to the derailleur, rendering the b screw adjustment limited, or useless.

    March 24, 2018 at 7:42 pm #915231
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    matthewn5

    Give the derailleur a wiggle

    Give the derailleur a wiggle after adjusting it. It does move (or at least, my Ultegra rear mech used to).

    If you really want to sharpen up the shifts, replace the upper pulley with one of those alloy ceramic bearing jobs you see on Ebay. Shimano upper pulleys have sideways movement built in to dull down the shifting — as the cage moves across, the pulley doesn’t completely move until the right part of the cassette comes around. Putting a pulley that’s rigid laterally makes a big difference. Whether you’ll like it or not is another matter! But certainly worth a try.

    March 23, 2018 at 7:48 pm #915229
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    AfterPeak

    DaveE128 wrote:

    DaveE128 wrote:

    SteveAustin wrote:
    It mightnot do anything if under tension, ie the cable is attached and tightened, and occasionally the chain in place can cause it to look like it isnt doing too much. so disconnect cable/chain, and then try it.

    i built a bike with a dura ace mech and that never looked like it was moving much tbh. never affected the shifting if it was in or out

    Uh… I think you may have misunderstood what the B-tension adjustment does. Unless it’s a shadow mech, if you don’t have a chain on you will not see the effect. Whether the cable is attached or not is irrelevant.

    The B-tension setting changes the angle that the main mech body sits at, and therefore the vertical distance between the upper jockey wheel (guide pulley) and the cassette sprocket. It does this because the angle is set by the balance between cage tension and b-tension. If the cage spring tension is higher, the cage moves up towards the cassette. If the b-tension is higher the cage moves down away from the cassette.

    The actual reason you may not be seeing the difference is friction in one or both pivots.  To find the equilibrium between the two springs, you might need to induce some movement by shifting across the whole cassette and back.

    So adjust up and down cassette and repeat? Still see nothing

    March 23, 2018 at 1:10 pm #915227
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    DaveE128
    SteveAustin wrote:
    It mightnot do anything if under tension, ie the cable is attached and tightened, and occasionally the chain in place can cause it to look like it isnt doing too much. so disconnect cable/chain, and then try it.

    i built a bike with a dura ace mech and that never looked like it was moving much tbh. never affected the shifting if it was in or out

    Uh… I think you may have misunderstood what the B-tension adjustment does. Unless it’s a shadow mech, if you don’t have a chain on you will not see the effect. Whether the cable is attached or not is irrelevant.

    The B-tension setting changes the angle that the main mech body sits at, and therefore the vertical distance between the upper jockey wheel (guide pulley) and the cassette sprocket. It does this because the angle is set by the balance between cage tension and b-tension. If the cage spring tension is higher, the cage moves up towards the cassette. If the b-tension is higher the cage moves down away from the cassette.

    The actual reason you may not be seeing the difference is friction in one or both pivots.  To find the equilibrium between the two springs, you might need to induce some movement by shifting across the whole cassette and back.

    March 23, 2018 at 9:27 am #915225
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    Anonymous

    I always used to go to

    I always used to go to GearMechHanger.com -[url=http://gearmechhanger.com/epages/950018694.sf/en_GB/?ObjectPath=Categories]Gear Mech Hangers [/url] for any replacement hangers. It was something I used to require pretty regularly and for some pretty esoteric frames; they always came up trumps.

    March 23, 2018 at 7:11 am #915223
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    AfterPeak

    kil0ran wrote:

    kil0ran wrote:
    I usually request a spare hanger. Having said that my LBS has a hanger encyclopedia so as long as it isn’t completely trashed they can find one that’s a reasonable match, and then fettle accordingly

    I think I am going to request one now. I always thought LBS could make you one.

    March 22, 2018 at 5:16 pm #915221
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    kil0ran

    I usually request a spare
    I usually request a spare hanger. Having said that my LBS has a hanger encyclopedia so as long as it isn’t completely trashed they can find one that’s a reasonable match, and then fettle accordingly

    March 22, 2018 at 4:22 pm #915219
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    AfterPeak
    kil0ran wrote:
    SpikeBike wrote:
    Grahamd wrote:
    Zooming in on the photo, there appears some swarf as though the threads could have been stripped. 

     

     

    Thats just threadlocker. It comes pre added to the screw when it arrived. I did read that you should pull the cage away when you screw it in to stop pressure on the hanger but that just makes the job more fiddly

    I learnt this lesson the (not too) expensive way when my B-tension screw bored a hole in my hanger – clearly sharper/harder than the hanger. Since then have been extra cautious particularly as one of my steel frames doesn’t have a replaceable hanger.

     

    kil0ran out of curiosity what happens if you cant get a replacement hanger? Is it worth buying a spare hanger when you buy a new bike? 

    March 22, 2018 at 12:28 pm #915217
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    kil0ran
    SpikeBike wrote:
    Grahamd wrote:
    Zooming in on the photo, there appears some swarf as though the threads could have been stripped. 

     

     

    Thats just threadlocker. It comes pre added to the screw when it arrived. I did read that you should pull the cage away when you screw it in to stop pressure on the hanger but that just makes the job more fiddly

    I learnt this lesson the (not too) expensive way when my B-tension screw bored a hole in my hanger – clearly sharper/harder than the hanger. Since then have been extra cautious particularly as one of my steel frames doesn’t have a replaceable hanger.

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