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brake disc refurb

This is a discussion on brake disc refurb within the Technical forums, part of the Caferacer.net Forums category; thought id have a play around with my old disc and see if its poss to make it presentable, the disc was in pretty bad ...

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  1. #1
    Official Site Vendor ukTony's Avatar
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    brake disc refurb

    thought id have a play around with my old disc and see if its poss to make it presentable, the disc was in pretty bad shape, i used my air palm sander on it with 180 grit pads then 400 grit, it looks pretty good considering ive only spent half hour on it.
    before..


    after..
    'old hooligan...

  2. #2
    Senior Member Geeto67's Avatar
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    um...yeah...make sure you take the disc to a machine shop and have them check it on a lathe....hopefully you didn't introduce any high or low spots on the disc or warping from the sander.
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.
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  3. #3
    Official Site Vendor ukTony's Avatar
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    no i was pretty carefull mate, if i can sand a flat peice of soft alloy without introducing high spots then stainless shouldnt be a prob, im gonna fit it to my bike and see how it faires under braking.
    'old hooligan...

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  5. #4
    Senior Member Geeto67's Avatar
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    quote:Originally posted by RetroTony

    no i was pretty carefull mate, if i can sand a flat peice of soft alloy without introducing high spots then stainless shouldnt be a prob, im gonna fit it to my bike and see how it faires under braking.
    high spots in discs come from localized heat not from the actual sanding discs. If you focused the sander on one spot more than the others sufficient to build heat in that area then the disc could warp. I would still check it on a lathe or a brake cutter.
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.
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  6. #5
    Moderator joe c's Avatar
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    or sand it on a flat table.

    i cant see that using a palm sander is really going to damage it.



    not a pretty boy honda rider... i\'m fag on a TTR

  7. #6
    Senior Member HackAsaw's Avatar
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    quote:Originally posted by Geeto67

    quote:Originally posted by RetroTony

    no i was pretty carefull mate, if i can sand a flat peice of soft alloy without introducing high spots then stainless shouldnt be a prob, im gonna fit it to my bike and see how it faires under braking.
    I would still check it on a lathe or a brake cutter.

    The spec for parallelism is pretty much accepted to be 0.0001". Please enlighten me why any form of lathe would be required or preferred to check this geometric constraint. I actually know how to check it and the correct simple tool one would use.


    Now had you stated a turning device should have been used to simultaneously grind both sides to assure near absolute parallelism... I'd not have an issue with such an assertion. Do you know what symptom an out of parallel disc will manifest?
    Accidental inventor of the worlds fastest wearing rocker arms and other edible engine parts! Try my yummy blue cheese camshafts!

  8. #7
    Senior Member HackAsaw's Avatar
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    now see.. I'd buy this if you were talking about the disc being warped or made out of parallel from use and you were chastising him for claiming to have fixed it by hand

    yet even then.... a lathe would only be useful for checking to see if it were 'unwarped'..... still pretty much useles for confirming parallelism

    now I agree one could actually high or low spot a brake disc....0.0001" doesn't require too much effort to move... no significant... perhaps not any heat would be required or resulting

    however.... to change the crystaline structure as you are implying.... man that thing would have to get hotter than you obviously realize and would be much more likely to happen on the bike than off it and being barbarically stroked with hand tools


    I certainly did not see any signs of such overheating in the before (which would be where you'd see them unless Tony tried to nuke them) or after pix



    [quote]quote:Originally posted by Geeto67


    high spots in discs come from localized heat not from the actual sanding discs. If you focused the sander on one spot more than the others sufficient to build heat in that area then the disc could warp. I would still check it on a lathe or a brake cutter.
    Accidental inventor of the worlds fastest wearing rocker arms and other edible engine parts! Try my yummy blue cheese camshafts!

  9. #8
    Senior Member crazypj's Avatar
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    Surface plate and height gauge off mounting flange, you can check both sides without flipping it over. Micrometer will only tell you if its same thickness all round.
    Lathe would rely on bearing tolerance so not really accurate enough IMO

    PJ
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  10. #9
    Senior Member parks61's Avatar
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    car rotors usually develop their warps due to hard braking down to a stop, and then the (hot) brake pads continuing to be pressed onto that one spot on the rotor. then you get the "thump thump thump" brake feel. even after a careful skimming on a lathe, the rotors re-warp shortly after the brake "service" is done. if hack man doesn't see tell tale signs of the dreaded local cook, then your rotor is prob. o.k. but can't you find a new one? i've been doing work with my hands most of my life and have a pretty good feel for "flat". but .0001" accuracy would have me a bit intimidated even with 400 grit on a palm sander.
    -parks
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  11. #10
    Senior Member HackAsaw's Avatar
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    since I'm sure this is one of those times somebody almost knows what they are geeting about.....

    I'll go ahead and lay it out

    parallelism is simply measured with a micrometer


    it does not take much to cause problems


    and the initial symptom is not shaking or pulsing...

    but a low brake pedal or lever that is most noticeable after an extended run without using the brakes..... yet it will pump up firmly and stop well

    may not even be noticeable around town....

    seen it kick many allegedly 'ace mechanics' keyboard asses

    cpj... the precision/omg$$$ taper bearings in my harrison knock off do not have enough play anywhere that I can measure it


    I do not really have any opinion about the pictured refurb job other than I'd have deglazed it while on the bike if I thought it may be junk

    If not and pricey/rare... it would have been set up and both sides properly machined or ground at the same time

    otherwise I wouldn't have bothered
    Accidental inventor of the worlds fastest wearing rocker arms and other edible engine parts! Try my yummy blue cheese camshafts!

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