Brake fluid contamination? Or simple obfuscation?

Dear Car Talk

Dear Car Talk | Dec 01, 1990

Dear Tom and Ray:

Recently, the brakes on my 1989 Olds 88 Royale Brougham went to the floor while my wife was driving. She had to pump them to get them back. We took the car to a muffler/brake shop and were told that the brake fluid had been contaminated by something else being added to the brake fluid reservoir. We were told that an 800 dollars rebuild job was in order. We had the system drained and bled, and have had no other problems since. Another shop told me not to worry about it, and my wife later revealed that just before the brakes failed, she had driven 2-3 miles with the parking brake on. Do you think I need to spend the 800 dollars?

RAY: Probably not. I think these guys at the muffler/brake place are a bunch of myxomycetous spheroids (scientific notation for "slime balls"). There's a slim possibility that your master cylinder is faulty, but that's very unlikely on a car as young as yours.

TOM: My guess is that your wife drove for quite a while with the parking brake on. If she admits to two or three miles, we know it must have been at least 11 or 12 (I always lie when I do something stupid, too).

RAY: The friction created by driving with the parking brake on generated a tremendous amount of heat, and that heat caused the brake fluid to overheat and boil. When brake fluid boils, it doesn't work. The result is brake failure. That's why you're not supposed to ride your brakes when you're driving down Mount Rushmore.

TOM: Once the fluid cooled off and returned to normal, the brakes were fine again. So my guess is that you don't have to worry. Flushing and bleeding the system was probably the right thing to do.

RAY: Just put a little note on the dashboard that says "parking brake off, dear?" And don't be surprised when she retaliates with a note on the refrigerator that says "don't forget to defrost the TV dinner, dear."

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