ford f1 brake booster issues

[Becky Stump]

Installed a brake booster on 1952 F1 pickup. Brake pedal is now hard. Bled the lines and it worked like it was supposed to for only a few minutes now they stay hard. Got great vacuum can find no leaks in the hoses. Worked on it yesterday for 8 hours. Ready to sell the truck! What could be causing this issue? Can't get it inspected and really can't drive it. Unit is 6 years old, replaced the front brake pads also. NEED HELP!:mad:
These are drum brakes.

[CPPAaron]

Sounds like a vacuum source issue, I would check at the manifold and at the end of the hose to see if you have a min of 18" at idle. This is the min requirement for power boosters.