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  1. #1
    FEP Power Member 8384GT's Avatar
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    Jun 2009
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    Delray Bch Fl
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    1,043

    Default Brake Booster ??

    Have a 83 LDT Wagon I6 with 96k on it. Just replaced the Mater Cyc, my question is when I step on the brake I get a SSSHHHH sound, this happen before I replaced the master Cyc as well. Do I have a vacuum leak or does the booster have to be replaced? Brakes seem to work fine. Thank you in advanced
    Current Cars:
    83 GT Turbo All org w/ org paint 127k miles
    84 GT350 5.0 Period correct changes 5spd T Top 44k org miles
    83 LTD Wagon I6 65k miles
    2010 Mercury Milan AWD
    2019 Flex SEL

    Past Cars: 79 Pace Car 5.0 Auto, 80 I6 Coupe, 79 I6 Coupe, 81 4cyl Coupe, 92GT, 83 Capri RS Turbo, 82GT TTop, 83 GT 5.0, 84 GT350 5.0 Auto, 86 ASC Capri coupe #1, 78 5.0 Granada Coupe, 03 MACH 1 2013 Flex Limited

  2. #2

    Default

    either the booster or the check valve are bad
    1986 GT T Top- stock except for magnaflow cat back
    1990 LX vert- 500hp V3 and all that stuff
    2013 GT- usual bolt ons

  3. #3

    Default

    When you are applying the brakes, the SSSHHHH sound is normal, you just normally don't hear it because it's
    muffled by a cylindrical piece of foam rubber inside the booster rod bellows. The foam in yours has probably
    rotted. You can minimize the sound (and pedal travel) by optimizing the length of the master cylinder pushrod.
    You can also put some fresh foam inside the booster pedal rod boot, but that takes a bit more effort.

    At rest the brake booster diaphragm(s) have vacuum applied to both sides. When you press the brake pedal,
    a valve opens to vent the firewall side of the diaphragm(s) through the pedal pushrod hole. As the pressures
    equalize with the amount of pressure you're putting on the pedal, the vent valve closes down, to maintain the
    correct amount of brake assist.

    If the sound continues when you're just holding steady pressure on the pedal, then you may have a ruptured
    diaphragm.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  4. #4
    FEP Power Member 8384GT's Avatar
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    Jun 2009
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    Delray Bch Fl
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    Default

    JACook,
    Thank you, the sound only happens when I press the pedal, it does not continue when I hold steady pressure on the pedal. ill check the foam rubber that you are speaking of.
    Current Cars:
    83 GT Turbo All org w/ org paint 127k miles
    84 GT350 5.0 Period correct changes 5spd T Top 44k org miles
    83 LTD Wagon I6 65k miles
    2010 Mercury Milan AWD
    2019 Flex SEL

    Past Cars: 79 Pace Car 5.0 Auto, 80 I6 Coupe, 79 I6 Coupe, 81 4cyl Coupe, 92GT, 83 Capri RS Turbo, 82GT TTop, 83 GT 5.0, 84 GT350 5.0 Auto, 86 ASC Capri coupe #1, 78 5.0 Granada Coupe, 03 MACH 1 2013 Flex Limited

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