Adding disc to a older frame question- Mtbr.com
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  1. #1
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    Adding disc to a older frame question

    I am looking to add discs to an older frame. I have read and understand the how to, I am proficient at TIG and brazing. The brakes I am using are post mount so that part is pretty easy. plus my father in law is a home machinist so we have many tool options to complete this.

    I know the rear triangle needs added support due to the added leverage of the disc brakes. A simple reinforcement between the seatstay and the chainstay. So my question where does the reinforcement need to be located? I am guessing right below the upper mounting point for the caliper on the seat stay at an equal distance from the axle on the chain stay? I would draw a poor quality picture on ms paint but Im on my phone.
    Last edited by azimiut; 03-05-2018 at 07:01 AM. Reason: phone auto correct disc to disk
    Dont make me go all Jonathan Winters on this gas station.

  2. #2
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    Correct.

    -Walt

  3. #3
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    awesome. thanks.

    I was going to use similar diameter tubing as the seat/chain stays. does it have to be as rigid? I saw on the FAQ page under disc brake conversions that someone used a old rotor as the support. I was going to use the same diameter simply for aesthetics
    Dont make me go all Jonathan Winters on this gas station.

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    When a stainless rotor is used do you have to use silver to braze?

    Thanks, Brian

  5. #5
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    Quote Originally Posted by azimiut View Post
    I would draw a poor quality picture on ms paint but Im on my phone.
    win.


  6. #6
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    Quote Originally Posted by azimiut View Post
    I was going to use similar diameter tubing as the seat/chain stays. does it have to be as rigid? I saw on the FAQ page under disc brake conversions that someone used a old rotor as the support. I was going to use the same diameter simply for aesthetics
    Depending on how you angle things, the load the brace is carrying could be nearly completely under compression, so I wouldn't think it would much matter what diameter the tubing is. Having *some* thickness accounts for the brace not being completely aligned with the load. However, it shouldn't see much, if any, lateral load, which is why a piece of disc rotor should work just as well.

    Quote Originally Posted by calstar
    When a stainless rotor is used do you have to use silver to braze?
    Ag vs. brass? The simple answer is yes. You could also TIG. Or you can use some alloys of Ni-Ag (which really doesn't have much/any Ag in it) with the right flux. But if you know how to Ag braze, that's easiest. Personally, I would _not_ use it for the disc tab itself, but for the brace (see compression argument above), it's probably okay. YMMV.

  7. #7
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    I've seen people use a section of a rotor as the reinforcement -- it works and has a different look. And yes, if it's a stainless rotor, use silver (FilletPro works well). I have used a lot of 1/2"x.028" tubing from Aircraft Spruce for both seatstays and these types of reinforcements. It's in compression, so it doesn't need to be all *that* stout.

  8. #8
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    would you suggest TIG over Braze for the caliper mount? even though the brakes I have are post mount (magura MT8 I had them laying around bling factor) I was thinking of IS mount and an adapter with a full length mount bracket for more rigidity vs two posts. Either put a brace between the two posts or something like the HJ high low disc brake mount.
    Dont make me go all Jonathan Winters on this gas station.

  9. #9
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    Quote Originally Posted by azimiut View Post
    would you suggest TIG over Braze for the caliper mount?
    As long as you're solid with either technique, I don't think it much matters.

    Quote Originally Posted by azimiut View Post
    Either put a brace between the two posts or something like the HJ high low disc brake mount.
    There are 1 piece post mounts available, too

    Adding disc to a older frame question-e44.jpg

    I've never used that one, just an option I noticed.

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