My brakes on my older Chevy seem to work fine, but several times lately
when I've had to brake fast, the brake light comes on. On normal
braking it does not come on. The master cylinder fluid is full, and
there are no leaks in the lines that can be seen. The car has a
proportioning valve, and I assume that valve is not getting even
pressure to cause the light to come on. The question is why? Could the
master cylinder be bad, yet still stop the car properly? This has me
puzzled.