Car Talk

December 2008

Dear Tom and Ray:

I had new brake pads installed about three weeks ago, and when I use the brake pedal to stop, the car makes a groaning noise. The mechanic told me that it takes about a month to "break the pads in," and that after that, the noise will go away. Is that correct? -- Adrienne

RAY: It groans, huh? Well, groaning noises usually are associated with mating, Adrienne.

TOM: Just like with humans!

RAY: What's mating in your car are the new brake pads and the old disc rotors. I'm guessing that your mechanic didn't change your disc rotors, probably in an attempt to save you some money.

TOM: We don't do that anymore because when new, perfectly flat pads press against old, grooved and uneven disc rotors, they make noise. And then customers come back and complain. And then we have to get rid of them by making up some story about how it takes a month for the parts to get to know each other.

RAY: Unfortunately, this is not an entirely benign noise, Adrienne. Because your pads aren't making point-for-point contact with the surfaces of your discs, you're not getting as much braking power as you should be.

TOM: Normally, new pads will "seat" or "mate" with discs fairly quickly. In fact, we usually do it during a test drive right after we finish a brake job. And it's usually accomplished within 10-20 minutes of working the pads.

RAY: But if it's still groaning after three weeks, you probably need new discs. Or, if the discs still have plenty of life in them, they need to be resurfaced.

TOM: The reason your mechanic told you it would take a month is because he's leaving for vacation in a month. So when you go back next week, there'll be a sign on the door that says, "See you in the spring."

RAY: So I'd go back in now. Explain to him that the noise hasn't gotten any better, and ask him to take another look. My guess is that the discussion will turn to the wonderful world of new disc rotors. Good luck. Beat up old car

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