Pulsing Brakes

Nov 01, 2014

RAY: This comes from someone named Brad Hamill. This fellow takes his Volvo to the shop. Now, it could be any car. And he complains of a strong pulsing in his brake pedal when he applies the brakes. The mechanic looks over the car and finds that, sure enough, the front disc brake rotors are warped. He installs new ones and sends the fellow off on his way. Five thousand miles later, the same car owner comes back to the shop and complains that the pulsing is back.

TOM: Oh!

RAY: Suspicious and yet confident that his work was perfect, the mechanic asks the owner a few questions. "Do you ride the brake? Have you tightened your lug nuts with a high-powered air wrench, or has anyone done that?" "Have you bought new tires?" The owner answers no to all questions. In fact, he answers no all the time to everything. The mechanic is at a loss and replaces the warped rotors.

A thousand miles later, the guy comes back, and guess what? He has an oil leak this time. But a thousand miles after that, he comes back with the same problem. This time, the mechanic asks straight up what the heck he's doing to the car that could be causing this problem, knowing that there's nothing wrong with the parts and nothing wrong with the installation.

The fellow says, "I don't know." He says, "I go on a lot of long car trips, and it's always the day after I arrive home from these trips that I start feeling the pulsing, but never during the trip."

TOM: This is great!

RAY: The mechanic asks him one question, and he knows the answer to the puzzle. What question did he ask him?
RAY: The question he asks him is, "Do you wash the car immediately after returning from these long trips?" And the fellow says, "As a matter of fact, as soon as I pull into the driveway, before I even loosen my tie, I've got the hose out, and I'm hosing the dirt off the car, and in doing so..."

TOM: "Ach! I'm warping the disc rotors!"

RAY: Right, because he's hitting just the wheel side of the disc rotor. When you go through a puddle, you're immersing the whole disc rotor in the water and so you tend to equalize the forces. But when the thing is red hot, because you've been driving like crazy to get home to your sweetie, and you put that ice-cold water on that red-hot disc brake, on one side of it, zzzzzzt! It's warped! And who's our winner this week?

TOM: The winner is Jessie Dornstreich from Philadelphia, PA. Congratulations!

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