Brake Booster Sound

[-009-]

Likely an easy answer I am overlooking. When the brakes are applied while the car is running there woosh like sound from the brake booster. The brake pedal is soft and does not seem to build pressure while running. With the engine off there is no sound to be heard and the pedal is hard to push. Currently, there is snow and ice on the ground so I am unable to take it for a test drive to see how well they work.

Any ideas what might be the cause?

-70 Cuda
-Front disc/power brake conversion
-New Master cylinder
-Correct proportioning valve installed

Thanks for your time.

[Chryco Psycho]

is the booster holding vacuum ? you can tell by twisting the valve that the hose connects to , it should hold vacuum , if not the booster or check valve is bad

[-009-]

is the booster holding vacuum ? you can tell by twisting the valve that the hose connects to , it should hold vacuum , if not the booster or check valve is bad

Just to clarify with this test I will want to have the engine running then break the seal where the check valve goes into the booster? I would then hear a hissing noise if its holding vacuum?

I pulled off the check valve and it has tested good.

[Chryco Psycho]

You can run it & shut it off & check right away within a minute or 2 & make sure there is vacuum

[Bullitt-]

This sounds very much like what I experienced after a complete brake system rebuild.
  My issue was the rear drums were not adjusted properly, after revisiting the self adjuster setup & correcting the lever to adjuster screw setup, which allowed the drums to adjust themselves tighter by running the car in reverse & pumping brakes, the brakes behaved as they should.   

[greentween]

On the brake pedal side of the booster there is a felt type packing which acts like a muffler. Its under the rubber dust cover. Its going to be hard to check with booster still in the car though.

[-009-]

You can run it & shut it off & check right away within a minute or 2 & make sure there is vacuum

Just ran that test, I had the check valve halfway installed to make it easier to break the seal. After the car ran for a few minutes I pulled back on the check valve and you can hear hissing from the booster. With the car running at an idle, there is 17 inches of vacuum at the booster check valve.

[-009-]

This sounds very much like what I experienced after a complete brake system rebuild.
  My issue was the rear drums were not adjusted properly, after revisiting the self adjuster setup & correcting the lever to adjuster screw setup, which allowed the drums to adjust themselves tighter by running the car in reverse & pumping brakes, the brakes behaved as they should.   

@Bullitt- For some reason, I can't wrap my head around how that would fix the problem. I understand if the rear shoes are out of adjustment would allow for a longer pedal travel. How would that cause the brake booster to make the woosh sound when the pedal is depressed?

[Bullitt-]

This sounds very much like what I experienced after a complete brake system rebuild.
  My issue was the rear drums were not adjusted properly, after revisiting the self adjuster setup & correcting the lever to adjuster screw setup, which allowed the drums to adjust themselves tighter by running the car in reverse & pumping brakes, the brakes behaved as they should.   

@Bullitt- For some reason, I can't wrap my head around how that would fix the problem. I understand if the rear shoes are out of adjustment would allow for a longer pedal travel. How would that cause the brake booster to make the woosh sound when the pedal is depressed?

I can't explain why it would make the sound but I'm thinking the rear shoes having a lot of travel allowed the master cylinder to have more travel.. I could pump & pump and never get a solid pedal which went to the floor & I remember the WHOOSH each time the pedal was pressed.  I just know it went away after correcting my error with the adjuster, tightening the rear shoes which in turn gave me a solid brake pedal. I had manually adjusted the rear brakes but obviously they needed more. 

[-009-]

@Bullitt- Well that was interesting, it appears that the rear brake shoes were way out of adjustment. I tightened the adjusters, bleed the rear brakes then ran the car while pumping the brakes with no improvement. Starting to think the booster is bad.

Sound the brake booster is making.
https://www.youtube.com/watch?v=7ctt3TVpb44

[Bullitt-]

@Bullitt- Well that was interesting, it appears that the rear brake shoes were way out of adjustment. I tightened the adjusters, bleed the rear brakes then ran the car while pumping the brakes with no improvement. Starting to think the booster is bad.

Sound the brake booster is making.
https://www.youtube.com/watch?v=7ctt3TVpb44

   Your whoosh does seem to me magnitudes louder than what I recall and mine occurred lower in the pedal travel .... For the self adjuster to work the car must be run in reverse as the brakes are pumped.   

[-009-]

Well it looks like it was the brake booster after all. Spent the morning rebleeding the master cylinder and the brakes with no improvement. Finally went ahead and pulled the booster and discovered the foam silencer had disintegrated, brake fluid inside it and worn seals.

Thank you for your help.

The photos show the pushrods bad seal, the other the lack of a foam silencer and a little rust.

[Chryco Psycho]

That doesn/t look good 

[RUNCHARGER]

Only 50 years? Stuff just doesn't last.