Brake pedel is hard to push, car hard to stop

[raventech]

I have a 68 Camaro with new 10" dual PB, 4 wheel disc, new master and valve. Vac is at 18 with engine at 900. Went through all the test in the trouble shooting pamplet for "hard pedals" Everything checks out. Bleed master and brake lines. Hooked a external vac pump to the master at 25", but pedal still hard? Any ideas?

[Mario]

Do you hear any hissing noises coming from the booster?

[raventech]

Do you hear any hissing noises coming from the booster?

No noises and no hissing Unit hold air and bleeds off by pushing pedal when engine is turned off.u