Boiling Brake Fluid and Leaking MC Cover?

Brakes for your Classic Mopar

  1. nm9stheham

    nm9stheham Well-Known Member

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    I know asking for opinions can be dangerous LOL, but what the hey...

    My son's '65 'Cuda has the 73-76 A body discs and 11x2.5" rear drums, and the stock 73-76 disc/drum MC. As the weather has warmed up, it has had a more frequent issue of the pedal going much further down than normal at random times. After one brake activation, it is restored to normal operation until the next random occurance of the same long pedal push. There also seems to be a lot more leakage from under the cover now, which did not seem to happen in cool weather. (Yeah, it is the newer stamped cover type and gasket.) and I drove a 3-4 of these cars back in the day, and never had MC leakage.

    We found that someone in the past put the distribution block (no, not a factory prop valve; that is separate) on the underside of the subframe. He routed one of the front brake lines from that block towards the header right beside it, and then turned it back to the outside. That line's loop is covered with reflective insulation but not other part of that block and lines are shielded from heat.

    We are surmising that the fluid is boiling a bit in and around the distribution block and pushing fluid back up the line on the MC. I have had that happen when racing before, but at the calipers, and had the same 'one time soft/low' pedal. I just have to wonder if this is also putting a bit of positive pressure into the MC and causing the cover leakage.

    I'd like to ask if anyone has experienced something like this, or has any other ideas on this problem. Here is a pix of the distribution block and lines; it is about 2" from the closest point of the Spitfire headers' collector.

    DSCN1927.JPG
     
  2. RustyRatRod

    RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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    First, determine the boiling point of the fluid you're using. Then get the infra red temp gun out. Verify first, or you'll be guessing.
     
  3. inertia

    inertia Well-Known Member

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    I had a disc brake vehicle have a wheel brg nut come loose, the discs kept the wheel/disc from coming off, and during long left turns would push the pistons in, and it took a pump to push them, (and the wheel I guess) back into position and get pedal.. That may also force fluid/overflow into M/C.. FWIW

    I think you can get a 90* inverted flare fitting to move that tube, or remove securing bolt. and judiciously pry some clearance there, and re-secure.
     
  4. AJ/FormS

    AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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    The zip-ties aren't melted. I would reroute that baby.

    heres the proof-test;
    Drive around for a bit with the brake pedal applied just enough to keep the C-port closed.This doesn't take much.
    With no recurrence of the symptom your theory is sound.
    If the brakes start dragging after some unspecified amount of time; the fluid may be expanding and applying the brakes for you.Stop the car, and have a helper pop the cover. Have him observe while you slowly open the Cport. A geyser would instantly prove your theory. Protect the paint!!
    With no change in normal braking, I would think the M/C is leaking internally.

    However the give-away for me is the weeping M/C cover. The fluid in there must be, being agitated. That would seem to indicate fluid returning, possibly violently, through the C-port.
    I would reroute that baby

    But I like the other solutions/diagnoses too, And while piston knock-back is often the cause of this symptom, I think because of the randomness, I would be inclined to not go there. Yet.
     
    Last edited: Jun 6, 2016
  5. inertia

    inertia Well-Known Member

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    [​IMG]

    and maybe a shield.?
     
  6. nm9stheham

    nm9stheham Well-Known Member

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    Tnx all..... the IR gun (which we do have) may be hard to focus on small parts. Fluid is just DOT3 at this point; boiling point is likely under 400 F. Good point on the zip ties though!

    At this point, I think we are just gonna move it and see what happens; IMHO it is not good to route the left caliper brake line (the shielded one) under the subframe so that will be fixed too with moving things. It is not that much work.
     
  7. TrailBeast

    TrailBeast AKA Mopars4us on Youtube

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    I'll bet you anything the fluid in that bend is getting cooked.
    That would be my first go to if I had that problem.
     
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