Power Brakes not working

[Data Plate]

I put a vacuum gauge on it today and at idle it jumps from 12 to 15 and if I give it air just a little gas goes over 20

 

[1STMP]

Thanks for all the information I really appreciate the help. Is it ok to leave the power set up in and use the car until I can figure out the pedal problem or is it dangerous to use like that

I would think that's your call. No one
here would advise driving your car
with a faulty braking system.
Also, as KD mentioned, there's too
many unknowns relating to your
braking issues.

I also suspect that the boosters
your getting are returns from
former buyers (as defective)
just judging from parts availability.
None of the retail stores have
the booster you need in stock.

How To Test a Power Brake Booster

If the brake pedal feels hard while the engine is running, the power brake booster is not operating correctly. Here's how to test it...

m.roadkillcustoms.com

 

[Data Plate]

Yes that's very possible and thanks for the testing the booster link

 

[1 Wild R/T]

FWIW most boosters officially need 14-15 in/hg but actually will work with a touch less... When I was younger & played with bigger cams I had a old 292/509 that when first installed almost ran the brakes but at idle they were a 50-50 deal.. With a little tuning mostly a little more timing the booster/brakes was fine....

The sellers 20 in/hg is BS, the stock magnum grind cam pulls 16-17 in/hg at idle...

 

[Data Plate]

I did the test wrong I didn't plug the distributor or the PCV valve or the headlight line ill do it again tomorrow

 

[Data Plate]

I got that tooll to adjust the power booster rod and put it back together and the brakes work great feel a Hugh difference with the power assist

 

[68 Sport Satellite]

so the booster rod adjustment was the only thing wrong? That's good news!

How's the pedal feel? Any spongyness at all?

 

[Kern Dog]

I have been through that as well.

That threaded nub is about 3/4" long. I've seen them threaded all the way in most of the time but a few times I've seen them with about 1/4" of the threaded shank exposed.
They can be adjusted to reduce the free play in the pedal but it can be tricky. If you adjust it to eliminate all of the slack, it may actually result on some preload. I made this mistake and it ended up putting my front brakes in a bind when the pads heated up. I had to pull the master cylinder and back that nub back in a little.