69 Barracuda 318, brake pedal sags

I just had the same thing happen after replacing all front brakes, master cylinder, along with all hard and soft lines. I just found the brake light switch bracket and bent/pushed it towards the brake pedal lever. Problem solved
Solved for now!
What happens if a brakeline bursts? and you run out of pedal before the back-up system even comes on line.
I mean think about it; peoples lives are at stake!