Breaking in brake pads?

Dear Car Talk

Dear Car Talk | Jan 01, 2002

Dear Tom and Ray:

I am writing to ask your opinion about some advice my husband gave me. I have a 1992 Subaru Legacy with 123,000 miles. I just had the brake pads and rotors replaced. My husband insists that I have to "break them in." He told me to apply steady pressure to the pedal and stop from 40 mph. He says I need to do this several times. Since I clearly did not understand his instructions, he had to do it himself. So now this is a purely intellectual question. Is my husband correct about breaking in the brakes? I don't know whether to believe him or not, since a lot of his actions around cars have a cabalistic aspect to them. -- Alice

RAY: What a great word, Alice: cabalistic -- as if he's a member of a cabal, or secret society. I love it. And every wife in America is probably nodding her head in agreement right now.

TOM: Oh, I thought it was a reference to cabal TV.

RAY: Well, the old caballero happens to be right this time, Alice. New brakes should be broken in. Although, of course, most brakes eventually break in on their own if you just drive around long enough.

TOM: When we do a brake job on a car, we take it out and do exactly what he describes. We get it up to 40 or 45 miles per hour, and then apply steady brake pressure and bring it to a halt. Some cars are fine after the first time you do this, and some require several applications before the brakes feel good.

RAY: This "breaking in" routine also serves another important purpose: For those times my brother forgets to put the pads in or forgets to add the brake fluid, the surprise is on HIM during the "break-in" rather than on the customer when he or she leaves the shop and drives into the nearest lamppost.

TOM: What actually happens during this break-in is that the pads and the rotors are forced to "match up," or "seat," with one another. The new parts often start out either too smooth (so there's not enough friction to provide good braking) or not smooth enough (so there's not enough surface contact between them). And in either case, you can get increased stopping distances and/or brake noise.

RAY: And riding the brakes a little bit (which is essentially what you're doing when you apply constant pressure to break them in) gets the two surfaces completely in sync. Like they're members of the same cabal. Thanks for writing, Alice.

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