I have a G2 93 Integra (non-ABS) that has a problem with the brake system. On
hot days, the pedal sinks to the floor, with minimal braking pressure.

Let me tell you what I have checked:
-brake lines good condition
-brake fluid less then 1 yr old
-rotors have been resurfaced/new Acura OE pads
-brake booster ok
-(I had a brake system check by Firestone and they verified above)

This does not appear to be brake fade, since the above is good, and the
pedal drops to the floor even if the car is stationary. Since the car is
high mileage (>100k) my next step is to replace the master cylinder.

Just curious if there is anything else I should check, or if anybody has
had this problem? Thanks.

 

check the master cylinder, but do the least expensive first...which is get your system bled properly! i had the same problem in my teg, and i had the brakes bled and ....viola....problem cured