Will be very happy if it’s a simple adjustment! I’ll keep you posted

Measured the distance between the push rod and master. It was opposite of what I was hoping.. It’s actually .030 heavy..

I would adj it so there is .020" clearance & an engine 5/16 pushrod makes a good measureing tool to stick into the MC piston "thimble" to get it dead on.

The 'woosh' you here is the entire booster vacuum 'dumping' rapidly, because the pedal went to the floor. With no air in lines, adjustments OK, a pedal should NEVER go to the floor regardless if booster working or not. With no leaks anywhere & bled properly; only way is if m/c seals allowing fluid to leak past seals.

I think You are correct. I am thinking master cylinder is toast or not bench bled well enough. We are getter a new master today and seeing if that’s the issue. We started the car last night and split the booster and master apart and watched the booster functioning,it appears to be working correctly! Thanks guys and I’ll update tonight when new one is on.

when you pickup a MC you might grab those MC port brass plugs & see if your current MC hold pressure (light pedal pressure & stomp it) & if it ain't the current MC then you can return the new/rebuilt one & while you are there likely they will let you use the MC in the box to get the correct fittings (1/2-18 or 1/2-20 or 9/16-18 or 9/16-20 iirc).

Will do.

mymcodebee, what you posted before is fine for bench bleeding.
in the old days when these were 500 dollar cars, I used to bleed them on the car with just my fingers over the ports.
worked just find back in the day when you didn't care how much brake fluid ate the fender paint.

I am assuming your car, you wouldn't do that to a customers car would you?

When I mentioned my buddy using his thumbs earlier and deleted it, it was due to the statement sounding confusing. My buddy could bleed the master by pushing the master with his thumbs instead of using a large screw driver etc.. Sorry for confusion.

Ok here is where were at. I diagnosed into the late hours last night. A new master and booster will show up today in case we need either.

Master on the car removed last night to check to see if it was bench bled correctly. It appears to be bled correctly. Plugged both ports with fittings, put in the vice and can easily push the cylinder in and out with a screw driver and see steady line of fluid pushing up into the port of front and back.
Also removed the ports and got solid streams of fluid shooting out of both ports.

While master was off started the car and pressed the pedal to check booster with pressure applied to the rod. It appears to function as it was intended by still has a very loud whooosing sound under the dash. This sound is literally louder in the car then in the engine bay.

adjusted the road to within .20" and put everything back together. When master was removed I plugged off lines with rubber plugs to limit air intake when rebleeding.
Bled lines again and did have a little air which was expected from taking it apart. Solid, very solid fluid at all four bleeders. Pedal feels hard at this point when not running but fire it up and a loud very easy pedel pressure to within a 1/2 of the floor,(or about 10% of the pedal throw) and it does actually hold brakes at that point. That's what I have and I have no idea why its doing it... Stumped and never run into this issue. So at this point I have one more night to try a few things and then we leave in the AM as is. So if you see this Cuda rolling in you may want to step back.... LOL. Thanks for all the help!

You might want to double check your brake adjustment.

I don't think this is correct.
Plugged both ports with fittings, put in the vice and can easily push the cylinder in and out with a screw driver and see steady line of fluid pushing up into the port of front and back.

if you plugged the ports and you had it bled correctly you should not be able to push the rod in at all. It should be hydro locked.

as to stumpy's comment, if you can pump the brakes and the pedal comes up, that would indicate adjustment issues, but it never hurts to check. It might also resolve the low pedal issue you see.

but I am with a bad master, even if it holds right now.

I used to have one that the rubber cup had a weak spot and it would fold sometimes allowing the pedal to go to the floor. But if I hit the brakes just right it would hold for a bit.

This is correct.
Once the rod moves forward it closes off the ports to the bore itself.

Last three posts are 100% correct. The master was leaking slightly out of one of my plugs which is why I could still push the cylinder when in the vise. The poster that mentioned the brake adjustment has nailed it. When the drums were pulled on the rear a short while ago I noticed my buddy using a rubber hammer to get them off... I instantly thought, wow those are a little tight and just assumed they are were very close. My buddy sent out many of the suspension parts to be powder coated years ago when powder coating was the rage. He would not do it now as it is a pita to deal with.. To wrap this story up quickly the hubs were sticking on the studs due to powder coating. I pulled them off the studs and it had a ton of play in the shoes! It made all the difference in the world! Can not believe it was something simply we overlooked but got to get out and load the car. Thanks for the help and advice and helping us get this car headed to Carlisle!

That is beautiful, can't wait to see it.

Sometimes it's the simple stuff.

Glad you got it solved. Pretty unusual solution. Had EXACT same issue on daughters 69 Charger RT with power drums. Bench bled MC a couple times, seemed fine. Replaced booster. Pedal would still go to floor at startup. Replaced MC...all good since. They can be fickle.

glad you got it working.