Help with 1975 308GT4 brakes

I am having trouble sorting out my brake system. I have rebuilt all four calipers new rotors and pads. Also had booster rebuilt and replaced check valve. Pedal is very stiff and hard to stop. Any help or suggestions would be appreciated.

 

Hi, are you getting vacuum at the brake booster? Easy way to check; with the engine off pump the brake pedal a few times, then while holding down the brake pedal, start the engine. If the pedal sinks on startup then you have vacuum at the booster. If not suggest you check the hose from the engine to the brake booster. Good luck.

 

Plenty of vacuum. No leaks from hose.

 

There should be a one way check valve for the vacuum, if that's installed backwards, you'll not get power brake. Check the valve if not, check for kink or pinch vacuum hose. Not sure where on the GT4 but, here's a pic from "ramosels" 308.
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