Dura Ace 7900 b-screw extension for 30t cassette

petemadoc
petemadoc Posts: 2,331
in Workshop


I'm trying to push the limit of my 7900 rear mech to fit a 30t cassette.

It will work if I can get the b-screw to push the mech just a tiny bit further.

I bought a longer b-screw but it's sliding past the mech hanger as you can see in the picture.

Does anyone have a solution to this?

Comments

  • me-109
    me-109 Posts: 1,915
    Use a nut like a nyloc after you've run it through the mech, so the contact point is larger, or slot the (threaded) end with a hacksaw so you can wind the screw/bolt in from the 'wrong' side and then adjust with a bladed screwdriver.
  • petemadoc
    petemadoc Posts: 2,331
    me-109 said:

    Use a nut like a nyloc after you've run it through the mech, so the contact point is larger, or slot the (threaded) end with a hacksaw so you can wind the screw/bolt in from the 'wrong' side and then adjust with a bladed screwdriver.

    Genius! I'll give those a try.

  • lesfirth
    lesfirth Posts: 1,382
    Fit the B screw in upside down so that the head rests on the frame.
  • trevor.hall12
    trevor.hall12 Posts: 483
    Thread it through the opposite way so the wider head holds it on the hanger
  • lesfirth
    lesfirth Posts: 1,382
    trevor.hall12 said:

    Thread it through the opposite way so the wider head holds it on the hanger

    Do you read earlier posts?

  • trevor.hall12
    trevor.hall12 Posts: 483
    lesfirth said:

    trevor.hall12 said:

    Thread it through the opposite way so the wider head holds it on the hanger

    Do you read earlier posts?

    were they as pointless as this ?

  • dj58
    dj58 Posts: 2,223
    edited September 2023
    I think your problem may be that the screw is too long. If you read the post in this link
    https://forum.bikeradar.com/discussion/12952412/ultegra-derailleur
    you can see that although the poster is referring to a ultegra RD, the screw he used is a lot shorter than the one you are using.

    Of course there could be differences in the mech and hanger geometry that necessitates a much longer screw. The suggestion above regards reversing the direction that the B-screw is fitted should work. Do report back to tell us if you got it to work.

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