Boiling fluid and "brake fade" are totally different problems. Fade happens when the friction material of the shoes is putting more heat from friction into the cast iron drums than they can dissipate. The only cure for that problem is bigger brakes, or time for the drums to cool off. A quick stop from highway speed transfers enough kinetic energy from the vehicle to the air surrounding the brake drums to melt an average-sized cast iron skillet- - - -every time you stop. Lots of airflow over the brake drums is essential to this process. Once the drums get heat-saturated, you'll have lots of firm pedal- - - -and no stop because there's nowhere for the heat to go.
Boiiling brake fluid is caused by the "hygroscopic" property of alcohol/glycerine brake fluid- - - -it absorbs moisture and the water in the fluid boils long before the rest of the fluid does. In humid climates, a flush and change of brake fluid periodically gets rid of the moisture-contaminated fluid. That's especially important on a vented brake system like stovebolts use, not so much for master cylinders with a rubber diaphragm seal and no vent on the reservoir. DOT 4 brake fluid usually used for disc brake systems has a higher boiling point than DOT 3. DOT 5 is silicone-based, and has the highest boiling point, but it cannot be used in a system that's ever run DOT 3 or 4 fluid without a total rebuild of all the rubber parts, plus a total system flush.
Jerry
