In hot weather the drum brakes on my 1962 PV 544 tend to lock up. When I restored the car I replaced the master cylinder. I've also replaced all wheel cylinders and the rubber final flex hoses to the wheel cylinders.
Seems that the heat, either engine or ambient 80's, causes the brake fluid to expand and not release when I take my foot off the brake?? Is there something in the master cylinder that would cause this? I put in a new one. I also made sure that the small hole in the fluid container was open and not plugged. But interestingly, there is a small amount of fluid that pushes out of this hole when it happens.