So on my 1980 2 door sedan, I'm having an issue with the brakes. 95% of the time they work fine. About once per trip, when I apply the brakes, the pedal goes lower than normal (not to the floor) and isn't as firm. If I let off the pedal and apply the brakes again, they act normal. Been doing it for awhile. I had the brakes bled, and it still does it. Does this sound like a problem with the master cylinder? Thanks in advance.
Sounds like the master to me, might also be a leaky caliper or wheel cylinder.
Defiantly do a visual check for fluid leaks at each wheel and the distribution block. If there is no sign of a leak then it is likely to be the master cylinder.