brake sinks only in hot weather
 

Just recently, my 1991 Honda Accord has had brake problems. Only when
it is hot out and the car has been in the sun, the brake pedal goes
down to the floor with no appareet brake pad contact. When it cools
down outside, things are fine. I just had the brake fluid changed.
If it is a master cylinder or hose, why would it only happen when it is
hot outside, even when I only drive it for a few miles.