My family went on a leisurely drive to the County Fair yesterday, with my son driving our car. He didn't notice the parking brake left on for 20 miles (partly on the freeway) and because he knew it was an older car that didn't always behave as expected, he casually asked "Is the Brake Failure light just a quirk of this old car, or should I be worried?" I quickly dropped the brake lever, but he just as quickly discovered that the Parking Brake was the only brakes we had. Luckily, we were in town and nobody was going over 5-10 miles per hour due to Fair traffic. We safely made our way to parking, and I explained to my very worried wife that everything should be OK once it cooled off. I explained why the brakes were acting as they did from overheating, and indeed, when we were ready to go home, the brakes were as solid as ever, with no pulsing (I had fully expected the rotors to be warped, but we were lucky). When we got home, I took the wheels and rotors off to inspect what damage may have been done. To my surprise, the parking brake shoes still have a hair less than 1/8" on them, and a fairly frustrating internet search eventually revealed that 1/16" was the replacement threshold (why the heck is that info not in the Bentley book or the Haynes manual?), so the Parking Brake couldn't have been on very solidly. The regular brake pads look just fine.

My question: I appear to have dodged a bullet, but I assume that this all means I have excess moisture in the brake system, which means I will soon need to do a full flush & bleed on the brake system. I can handle that just fine, but I'm wondering if any other damage may have been done. I imagine steam expansion can't be good for the Master Cylinder or the caliper seals, or am I wrong and maybe it's OK as the brakes still work as well as before? Please let me know what kind of possible damage I may have to deal with.

 

Brake fluid boils at x temperature. Old brake fluid (with moisture in it) boils at lower than x temp. Good maintenance is to flush the hydraulic system every 2 years. If you are curious as to the actual moisture content - a simple tester can be had for $8 from amazon. Glad you were going slowly when the pedal went to the floor!