Brake Pedal Goes to Floor When Car is Running

But if the car is shut off it has perfect and firm brake pedal.:wack:
The car had the Master Cylinder and booster assembly taken off when we had gotten the Valiant but rest of the system was there.
I replaced the Front Calipers and Master Cylinder with 10 yr old reman units as well as putting brand spanking new Rubber lines and Front pads.
Didn't replace the rear shoes or wheel cylinders as they looked really good when I inspected and cleaned out the insides of the drum assembly with an air gun to remove years of brake dust build up.

I am at a total loss as to what would cause the pedal to do this when you fire the car up. It causes the brakes to engage and car wont move even when you hit the loud pedal some.:banghead:

I researched for a few hours last night but nothing I found said the same thing was the problem or had the solution to the problem.

So if any of you know why this is happening or have experienced this before I would love to get some help here.
Right now it is the only thing keeping this bad boy off the road and being driven a ton.