If "someone" drove 10 miles at 55mph with the parking brake on, could you damage the front brakes on the car?

Dear Car Talk

Dear Car Talk | Sep 01, 1999

Dear Tom and Ray:

I have a hypothetical question about the brakes in a car. If someone was to drive a 1991 Olds Delta 88 Royale with the parking brake on for about 10 or 12 miles before
noticing that it was on, would that also affect the front brakes of the car? In other words, would the front brakes fail, too, even through the parking brakes are part of
the rear brakes on this car? Also, I don't understand how the vehicle -- hypothetically speaking -- can even go 55 mph down an expressway with the parking brake on.
Could you answer these questions for me? -- Kevin

RAY: Kevin, you knucklehead! These aren't hypothetical questions. We know you left the parking brake on, drove halfway to your out-of-town poker game and lost
your brakes as you were stopping to pick up the cigars, right?

TOM: Hey, it's nothing to be ashamed of, Kevin. We've all done boneheaded things in our lives. Look at me. I agreed to do this newspaper column with my brother!

RAY: Here's what happened, Kevin. When you left your parking brake on, you created a tremendous amount of friction in the rear wheels. And that friction produced
heat. The heat, in turn, boiled the brake fluid, which made you lose at least half of your brakes, and with them, a significant amount of your braking power.

TOM: And on some cars (those with dual-diagonal braking systems), the brake fluid at each rear wheel is shared with one of the front wheels. So if your car has dual-
diagonal brakes (I don't have one handy today to look at), the boiling brake fluid in the rear could have caused the front brakes to fail, too.

RAY: And the reason you can drive at 55 mph with the parking brake on is that either your brakes are pretty worn out or you didn't have the parking brake fully
engaged. If the brakes were new and you had applied the parking brake forcefully, you would have had a hard time backing out of your driveway.

TOM: At this point, you should have the rear brakes inspected, because you may have toasted them. Have your mechanic check for heat cracks in the linings, and if he
sees cracking, have new linings installed. And while he's there, have him adjust everything, and make sure the parking brake is working so well that you can never make
this mistake again ... hypothetically speaking, of course.

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