Disc Brake Conversion question

Discussion in 'Technical' started by MikeG747, Oct 28, 2009.

  1. MikeG747

    MikeG747 Member

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    Guys I converted my 73 Grabber to front Disc this year. I retained the drum Master Cylinder & Proportioning Valve. They stopped pretty well but did not have a great pedal. The Master Cylinder started leaking around the cap right after the conversion. I replaced the cap gasket but it still leaked. Next I replaced the Master Cylinder with a Disc Master. The cap fits extermly tight. Still leaks but I have a great pedal now. Can it be the drum Proportioning Vavle making it leak? Any input will be appreciated. (y)
     
    MikeG747, Oct 28, 2009
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  2. mike75mav

    mike75mav Member

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    The proportioning value will stop the leak. I would return the master cylinder and get another one. The one you bought is bad.
     
    mike75mav, Oct 28, 2009
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  3. mean_maverick

    mean_maverick Senior Member

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    i have the same problem on my '71 and was just thinking about it today. i was thinking i just had a weak m/c clip and/or bad gasket but maybe i need to look into swapping the prop valve :huh:

    btw, my m/c is new as well (purchased March '08)
     
    mean_maverick, Oct 28, 2009
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  4. Joe Dirt

    Joe Dirt BBF life

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    Prop valve will not make the master cyl leak.
     
    Joe Dirt, Oct 28, 2009
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  5. mean_maverick

    mean_maverick Senior Member

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    maybe if the drum prop valve was causing enough back pressure... :huh:
     
    mean_maverick, Oct 28, 2009
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  6. Joe Dirt

    Joe Dirt BBF life

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    only if it was completly blocked and the cup seals in the master cyl were very worn. But its a very unlikly senario meaning he would have had total brake failure =no brake pressure/bypass condition. a leak at the cap will be due to either a faulty gasket on the lid,hold down clamp,or warped sealing surface or bent lid.
     
    Last edited: Oct 28, 2009
    Joe Dirt, Oct 28, 2009
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  7. Jamie Miles

    Jamie Miles the road warrior

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    I've been running the drum master cylinder and prop valve with my discs for nearly 3 years now with no problems.
     
    Jamie Miles, Oct 28, 2009
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  8. ford84stepside

    ford84stepside Lone Wolf

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    There was mention of this in a thread the other day....seems some masters aren't machined flat on the gasket surface, causing them to leak. I'd just about bet it was an imported rebuild or new master. They don't seem to take as much care with them as US makers did....
     
    ford84stepside, Oct 28, 2009
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  9. Mavman72

    Mavman72 Gone backwards but lookin' forward

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    Replace the MC, its no good...Prop valve has nothing to do with an MC leak.
     
    Mavman72, Oct 28, 2009
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  10. CornedBeef4.6L

    CornedBeef4.6L no longer here

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    Are you topping off the master cylinder? it needs room to expand....you should leave about 1/4 inch down....otherwise it could leak around the cap gasket.
     
    CornedBeef4.6L, Oct 29, 2009
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  11. cdeal28078

    cdeal28078 Member

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    Why would it make the cap leak? Too much pressure building up inside the master cylinder?
    Not a Maverick but the new rebuilt Master cylinder on my F100 leaked out of the cap. I put a machinist straight edge across the top in several places and it was lousy. I pulled the gasket out of the top and placed some soft gasket making rubber under it and put the original gasket back in. Sealed tight for a couple of years now.
    clint
     
    cdeal28078, Oct 29, 2009
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  12. mike75mav

    mike75mav Member

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    Boy is my face red. I met to say the proportioning value will not stop the leak. Just replace the master cylinder for a disc brakes. Sorry guy on the type-o.
     
    mike75mav, Oct 29, 2009
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