[ImperialCrown]

A 'whoosh' while holding the pedal down would be a vacuum leak from a torn internal diaphragm. The booster would need replacement.
If the master cylinder is leaking brake fluid out the rear cup into the booster, the cylinder would be needing replacement as well.
The 'wiper bucket' can be removed to open up a whole lot more room to get at things in the engine compartment.

 

[valiant67]

I concur, and IC is right about the master cylinder leak possibly being the cause of the booster failure.

 

[bguy]

If your booster is holding vacuum you should have a "regular" brake feel for at least one brake application with the motor off. In other words if you were rolling down your driveway before you start the engine it should feel normal as you depress the brake. A second or more pump would deliver that stiff unassisted feel. Not holding vacuum would indicate a leaking diaphragm or a faulty check valve. The other possibility if the booster is good is a weak vacuum signal from the manifold. It may be related to the drivability symptom in your other thread.

 

[wambus]

Outstanding response time!

I replaced the master cylinder last year trying to firm up the brake pedal. The original cylinder was not leaking.


There is one vacum line to the booster, yes? Is there a way to check the fitting and line for being sealed? A new booster is only $73.00, but hey - that's $73.00 I could spend on some other broken stuff....

 

[chuzz]

I've always used the pedal to check. If you put your foot on the brake pedal and start the van, what happens? If it moves slowly towards the floor when you start the van, that's normal. If it feels hard or doesn't move, the booster is probably bad.

 

[A.j. Schreiber]

I've always used the pedal to check. If you put your foot on the brake pedal and start the van, what happens? If it moves slowly towards the floor when you start the van, that's normal. If it feels hard or doesn't move, the booster is probably bad.

+1 I'd try that