My vehicle has a freshly rebuilt 350sbc with a carb.
I have a vacuum line feeding off the carb heading straight to the brake booster and another feeding the vacuum advance on the distributor. These are the only vacuum lines that are hooked up in the vehicle. The lines are good and have no leaks, there are also no hissing noises in the engine bay.
The brake pedal is hard to press at all times, with the engine on or off, or with any attempted actuation of the brake pedal. With the healthy 350 in drive, I can just barely get enough braking power to stop the car from moving at idle (and this is pushing quite hard on the pedal ). I am used to driving race cars with no power brakes equipped, but this is ridiculous.
The brake booster has a one way valve inline between the booster and the vacuum source. I suspected that the brake booster was no longer good and I replaced it with a used brake booster that was bench tested to be "good", the symptoms did not change. I have not replaced any other component upstream or downstream in the braking system other than front brake pads. I know that one piston, out of the four in each caliper, on the left front is stuck, but not dragging. The vehicle does also have a proportioning valve just after the master cylinder.
What should I be doing to determine the fault in this braking system?