converting power brakes

What is the difference from manual brakes master cylinder and power brakes master cylinder. Im trying to convert my manual to power brakes. I have bendrix power booster from 70 mustang. After installing everything and bleeding the brakes lines, now I having an issues with engine is running. The brake pedal has no resistance with engine running. I mean I can press the pedal too easily to floor but when the engine is off, the resistance will build back up and the brake pedal feels firms like it should. is it where the MC connects to the booster... any help be appreciated


also does anyone have a lower ac box for 69/70 i could have or purchase, i ran over mine[/font]

I bought a power brake booster/master cylinder assembly from Master Power Brakes. While I understand you are using available hardware, I want to point you to their web-site for technical support. They have a really good FAQ/Tech support section:

Master Power Brakes - Reference/FAQs

From their section on Power boosters:

How do I check to see if my booster is operating properly?
Shut off the engine. Depress the brake pedal a few times to evacuate the booster. Apply a steady pressure to the pedal and start the engine. The pedal should fall slightly.

Robert