That's the sound of atmospheric pressure providing you with 'power assisted'
braking.  The manifold vacuum on one side of the diaphragm  allows the
14.7psi on the other side to help push on the pedal.

Kind of the same way breathing works.  Drop your diaphragm and the vacuum
lets air rush in to your lungs.

Pretty cool really.

On 4/23/07, monte merrick <montemerrick@speakeasy.net> wrote:
>
> hi gang
>
> just wondering what that swuishy airy sound is that comes form the
> master cylinder area (sorry  cant pinpoint the sound any more closely
> than that) when i push on the pedal - it keeps making it for a
> lingering moment after releasing pedal -
>
>
> any thoughts?
>
> monte
>
>
> If I have unjustly wrested a plank from a drowning man, I must restore
> it to
> him though I drown myself. - henry thoreau
>

--
Jake
1984 Vanagon GL
1986 Westy Weekender "Dixie"
www.crescentbeachguitar.com