use a 'listening tube' ..
a 2 foot piece of 3/8ths inch hose ..
one end searches..
the other end goes on your good ear.

you'll hear it for sure when you find it.

fwiw ...long ago I had 'lack of vacuum assist' on my first vanagon ..
like brake booster just was not seeing vacuum.

sure enough ....took a while to find the leak ...
somehow a small hole got formed on the underside of the plastic booster
vacuum hose in the engine comppartment..
like someone heated the tip of an ice pick and melted a little hole that
was not readily see-able.
Hod odd, that that was it.

also ..for internal sounds...
the hardwood listening stick is just awesome.

Scott

On 2/16/2016 10:16 AM, John Rodgers wrote:
> Have hard pedal. No brakes to speak off. Dennis Haynes said suspect a
> vacuum leak. Have just gone over as best I could the vacuum lines in the
> engine compartment. With the engine at idle I hear a very distinct sound
> like someone drawing kn a deep breath. That to me is like air being wher it
> shouldn't. The noise is in the vicinity of the thermostat housing, but I
> can't pinpoint it exactly. Is there any kind of vacuum line or device in
> that area that I might be missing? It's fairly loud.
>
> John
>