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Thread: Pressing brake pedal increases RPM

  1. #1
    Registered User
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    Apr 2000
    Santa Monica, CA US


    Got a brake problem, probably vaccuum.

    '72 240Z
    Brakes work OK--plenty of pedal. But all braking power assist is gone. When pressing brake pedal, I notice an low hiss (like a leaking air hose) under the dash and the RPM kicks up by 1000 RPM. Opened hood and noticed liquid (brake fluid?) just below the master vac brake cylinder.

    Has anyone had this problem? Trouble shooting section of manual says nothing about the increase in RPM. I'm guessing I'll have to replace the master vac, but will await any suggestions from this illustrious group.


  2. #2
    Peon Phacade's Avatar
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    Join Date
    Apr 2000
    Tulsa, OK

    Thumbs up

    I would check the vacume line that runs from just below the master cylinder on the master vac. It runs (or at least should) to your balance tube on your intake manifold. Mine was pretty worn and needed replaced.
    Have you done any mods? Not all the balance tubes have the same diameter for this vacume tube. Check it. Fluid you say? Possible you have a bad master cylinder or master vac but I doubt it. There is the possibility that brake fluid is leaking and geting hear the carbs, which I'm told WILL increase RPM. It is, after all, a combustible substance.

    "Go into emptiness, strike voids, bypass his defences; hit him where he does not expect you" -Lao Tzu

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