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Monday, Apr 21, 2014

Modern brakes are largely unaffected by water

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Dear Tom and Ray:

I recently finished my driver’s ed class, and in it, they told us that when we drive through puddles, our brakes get wet, which is true.

Their solution to this was to lightly press the brake pedal while still holding down the accelerator.

But when I told my dad this, he said they were wrong, and that doing so would just wear out the brakes.

Which is true? — Katie

TOM: Your dad is right in this case, Katie. So give him a hug and let him revel in his correctness. I can tell you from personal experience that dads need to bask in this sort of occasional success.

RAY: Back in the old days — like, 1970s and earlier — almost all cars used drum brakes. If you went through a deep puddle with drum brakes, water could get between the brake shoes and the drums, and “lubricate” the brakes.

TOM: And like the soles of your own shoes, brakes are NOT something you ever want lubricated.

RAY: So, as a result, very wet drum brakes often would fail. Back then, the advice was to use the brakes immediately after driving through a puddle — repeatedly, if necessary, to create friction and heat them up so the water would vaporize and your brakes would work again.

TOM: But that was 40 years ago. Now, all cars use disc brakes, which are pretty much unaffected by water.

RAY: Some lower-end models still use drum brakes on the rear wheels to save money. But since the majority of the braking is done by a car’s front brakes, even those cars don’t seem to have issues with puddles anymore.

TOM: So if you have a car with drum brakes in the rear — or don’t know if you do — it’s not a bad idea to check your brakes after you drive through a particularly deep puddle, just to reassure yourself. But you do that by softly tapping on the brake pedal for half a second, with your foot off the accelerator. You should be able to confirm instantly that they’re working fine from the reaction of the car.

RAY: So you got a piece of outdated advice from that driver’s ed instructor, Katie. The victory goes to Daddio.

Wait! Don’t buy another car without the mechanic’s checklist that’s included in Tom and Ray’s pamphlet “How to Buy a Great Used Car: Secrets Only Your Mechanic Knows.” It will help you get a good used car and avoid the clunkers. Send $4.75 (check or money order) to Used Car, P.O. Box 536475, Orlando, FL 32853-6475.

You can listen to Tom and Ray Magliozzi’s “Car Talk” program at 10 a.m. Saturdays on National Public Radio station WUSF, 89.7 FM.

Got a question about cars? E-mail Click and Clack by visiting the Car Talk website at www.cartalk.com. They can’t answer your letter personally but will run the best letters in the column.

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