My uncle and I just put a new power disk break set up on my 73 mustang. We got everything set up and in place, bled all the lines, and check for leaks and we didn’t find any. After we bled all of the breaks we had some break pressure, but it was spongy. Once i started the car and the break booster kicked in I lost all of my pressure altogether and the pedal slams to the floor. It still stops once it hits the floor but it is a sudden stop. There is no slowing down. I went from manual to power breaks so can this be because I didn’t change pedals? or Is it possible that my master cylinder or break booster is bad? or Is it something else completely? I would appreciate your help. Thanks Guys.