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February 25, 2011

Car Talk

Hitting brake and gas is bad move

Syndicated columnists

Dear Tom & Ray:

I can recall quizzing my dad about car stuff and asking a question that has remained unanswered for 35 years now: What happens if you press the brake and the accelerator at the same time? When I asked him, he said, "Well, it wouldn't be good, I can tell you that," and wouldn't elaborate. Would you please tell me what would happen if I stepped on the gas and brake simultaneously?
-- Anthea Miller

Tom: Well, it wouldn't be good, I can tell you that!

Ray: Actually, we do it all the time in the garage. If you plant your foot on the brake hard enough and then step on the gas, you are mimicking a situation in which there's a load on the engine. Now, when we step on the gas and brake simultaneously, we do it for only a few seconds.

Tom: But if you do it for a much longer time, you might damage the automatic transmission's torque converter.

Ray: Right. When you're at idle, the torque converter spins slowly in transmission fluid. But if you make it spin quickly, without allowing the fluid to transmit power to the wheels, you could damage the torque converter. Or, at the very least, you'll overheat and degrade the transmission fluid, which will shorten the life of the transmission.

Tom: And that wouldn't be good.

Ray: What if you let up on the brake a bit, and allow the car to move while stepping on both pedals? Or engage the brake when you're already moving and stepping on the gas? Then you risk overheating your brakes

Tom: When brakes overheat, the brake fluid can boil. And boiling brake fluid doesn't work, so you'd have no way of stopping the car. And what can we say about that?

Ray: All together now: It wouldn't be good.

(Car Talk is a nationally syndicated column by automotive experts (and brothers) Tom and Ray Magliozzi. Write to them at the Car Talk website.)

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