I have a 1971 mustang coupe with front disc/rear drum brakes. The master cylinder was recently replaced to hopefully remedy a small leak in the old one. Now, the brakes are worse than ever. The pedal is very spongy, and even when pushed to the floor the car only coasts to a stop (if i'm lucky). It's nearly un-drivable in it's current state. There is also a leak between the cylinder and the firewall. But this can't be the only problem because it has always done that, even with the old cylinder in place.