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    #1

    brake booster?

    Hi!

    Just a couple weeks ago, I was in a bad mood and decided to exert some extra force with my leg just as one might clench a fist. I heard a nice hissssssss, the brake pedal goes down further; I push further, and hissssss and the brake pedal goes down further.

    Now, this could be business as usual for all I know: is the booster designed to relieve pressure if one is pushing too hard on the brakes?
    And the car stops just fine, it's only if I push extra hard, such as I'd only do when I'm already at a stop (or god forbid, avoiding an imminent accident-- haven't tried slamming on the brakes while still in motion though!) that it does this; wouldn't manifest under normal braking.

    Or should I worry in the least?
    I'm also curious: hydraulic fluid is noncompressible, right? So in fact, when you push on the brakes, it should stop when the pads are on the rotors and go no further? Oh wait... but there's a lot more travel in the drums in the rear, so perhaps that's what let's the pedal go down further still...?

    I did do two other tests: if I hold the brakes, turn off the car, and leave my foot on the pedal it does not rise against me (so it should be holding vacuum?), although, if I take my foot off just once, the brake pedal becomes immediately hard (whereas I know some cars require 2-3 pumps), so vacuum assist goes away immediately.

    Well, car does stop quite adequately-- but I'd like to know irregardless! Trying to keep this antiquity in perfect shape one bit at a time.
    Tags: None
    #2
    If it doesn't hold vacuum after you shut the car off, you have a bad check valve more than likely. That's on the side of the booster. Get a new valve. You can pull it out and check to see if it works by putting your mouth to it, blow into it in one direction, and then go to the other opening and blow into that too. If it's working, it'll only allow movement in one direction.

    The brake booster is designed to amplify the force exerted on the brake pedal. It uses engine vacuum to do so. When the brakes are not applied, the booster is in vacuum suspension. This means the diaphragm inside of the booster has vacuum on both sides of it. When the brakes are applied, a hiss is heard, this is due to the vacuum on the side of the diaphragm closest to the driver is released into the atmosphere, via an internal valve. The side with vacuum pulls the diaphragm which pushes on a piston in the master cylinder for brake action.
    Last edited by 86VickyLX; 12-27-2010, 02:47 PM.

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      #3
      Leaks around the rubber grommet will do this too. I had both problems on my car. Rubber grommet I couldn't get, but some RTV fixed it up.
      86 Lincoln Town Car (Galactica).
      5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

      91 Lincoln Mark VII LSC grandpa spec white and cranberry

      1984 Lincoln Continental TurboDiesel - rolls coal

      Originally posted by phayzer5
      I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

      Comment

        #4
        Originally posted by gadget73 View Post
        Leaks around the rubber grommet will do this too. I had both problems on my car. Rubber grommet I couldn't get, but some RTV fixed it up.
        huh really? I thought that grommet was used throughout the years? The check valve is basically the same.

        Comment

          #5
          this is the same place that could get me a trans mount for 80-85 and 87-90, but not the 86. Don't ask me.
          86 Lincoln Town Car (Galactica).
          5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

          91 Lincoln Mark VII LSC grandpa spec white and cranberry

          1984 Lincoln Continental TurboDiesel - rolls coal

          Originally posted by phayzer5
          I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

          Comment

            #6
            Originally posted by gadget73 View Post
            this is the same place that could get me a trans mount for 80-85 and 87-90, but not the 86. Don't ask me.
            Haha!
            Have you checked the check valve's operation yet mang?

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