Wes, it could just be the o-ring between the master cylinder and the
booster.  I have had customers come in and we check it out and that
o-ring has just disintegrated.  Of course it could also bee the booster
itself.  You really aren't going to know for sure until you pull the
master cylinder off to check the o-ring.  Let me know if I can help you
further.

Ken Wilford
John 3:16
www.vanagain.com

On 10/30/2011 11:42 PM, pickle vanagon wrote:
> I've noticed that with hard brake application, I slight hissing sound can
> be heard coming from under the dash in our 83 westy.  I fear it's the brake
> booster?
>
> You don't need to be moving to hear it.  When idling, if I push in the
> brake medium-far, I hear nothing, but pushing down *hard*, I hear the
> hiss.   It seems like the noise is on or off, and doesn't vary continuously
> with depth.
>
> There is no fluid leak....
>
> Is this a problem?  I don't usually push down the brakes hard, so I'm
> wondering if its down this for a while without me noticing.
>
> I'm afraid to ask the next one...
> do I need to remove the dash to replace the booster?
>
> Thanks!
> Wes
>