Jmackin

1940 Plymouth with a 440 and mid 70s Monte Carlo brakes. The problem I’m having is my engine is pulling 10-12 in of vacuum. With my brake booster getting vacuum from my engine I have easy to press brakes. They just do not do much to stop the car. I put a vacuum pump on the car that was pulling around 20 and will shut off at 23. With that hooked up to the brake booster the brakes are rock hard. Does anybody know what the issue could be?