Hissing when brake pedal not applied - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 10-25-2012, 12:20 PM Thread Starter
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Date registered: Aug 2012
Vehicle: 1966 200D
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Hissing when brake pedal not applied

Hey Folks. First off I have a 1966 200D. I noticed a hissing noise in my car when I have my foot off the brakes. Its a pretty quiet sound, and goes away as soon as my foot pushes on the pedal, and comes back as soon as I release it. I cant hear it under the hood, but its pretty hard to hear anything in the engine compartment with the clatter of a diesel running. Any idea if this is good, bad, or a non-issue? The car also has a problem of a surging idle and surging in first gear that I assume is a vacuum leak, but I haven't been able to figure it out yet. Could this maybe be the issue? Thanks for any info!

Last edited by 1966200; 10-25-2012 at 12:27 PM.
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post #2 of 3 (permalink) Old 10-25-2012, 06:21 PM
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The hissing is a vacuum leak.
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post #3 of 3 (permalink) Old 10-27-2012, 01:13 PM
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The hissing is probably a leak in the brake booster. This vacuum is produced by the vacuum pump.

The surging is caused by a leakage of the vacuum chamber of the governor. This vacuum is created by a venturi in the intake manifold and has nothing to do with the brake booster, they are two seperate systems.

For an explanation and troubleshooting the vacuum leakage of the governor, you can read this topic:

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