Hissing brake pedal when cold...problem? - JeepForum.com
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post #1 of 5 Old 03-23-2006, 03:03 PM Thread Starter
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Hissing brake pedal when cold...problem?

I have a 99 WJ, and after I press the brake pedal and release, it hisses at me. After a while (couple minutes), it goes away. If I push the brake pedal down even slightly, the hiss goes away. It brakes just fine, whether hissing or not. Any ideas?

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post #2 of 5 Old 03-23-2006, 06:49 PM
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Have you checked under the dash to see if you have a snake hiding under there?

Anyways, it sounds as though your vacuum booster may have a slight leak in it. Maybe another WJ owner can verify if this is normal or something to investigate.

One slightly modified '96 ZJ

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post #3 of 5 Old 03-23-2006, 09:59 PM
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The booster draws in the air under the dash when you apply the brakes. There's supposed to be a foam silencer in the end of the booster to silence the hiss, over time the silencer deteriates and disappears. This is probably what's causing the hissing. It causes no problems except for some irritating noises.
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post #4 of 5 Old 03-24-2006, 01:04 AM Thread Starter
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Thank you, that is a relief.
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post #5 of 5 Old 03-24-2006, 12:50 PM
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The foam filter quites the booster as you apply it. So when you press the pedal down the filter quites it. If it hisses after you relase the pedal, or hisses without you touching the pedal the booster is bad.

Vanco Power Brake Supply
9738 Atlantic Ave
South Gate, Ca 90280
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