Why do rotors need turning when brake pads get replaced?

Dear Car Talk

Dear Car Talk | Oct 01, 2003

Dear Tom and Ray:

In your column about breaking in brake pads, you said that the pads need to be broken in so that they match the "grooves and ridges from the previous, say, 30,000 miles of stopping." That makes perfect sense to me. So why does my brake shop tell me it has to turn my rotors to eliminate all those "grooves and ridges from the previous 30,000 miles of stopping"? As I see it, unless the rotors are badly warped, the shop is just making extra money off me by turning my rotors, isn't it? -- Joe

RAY: Well, of course it is, Joe. They've got kids to send to college, too.

TOM: Actually, what it's doing is keeping you from coming back and complaining about noisy brakes. While new brake pads will eventually seat to old rotors, they're likely to make noise when you stop. And our customers really hate brake noise.

RAY: So actually, on lots of the brake jobs we do, we just go ahead and replace the rotors. Like a lot of other shops, we've discovered some excellent, less-expensive alternatives to factory rotors. For example, we found some Taiwanese rotors that perform beautifully on Honda Civics and Toyota Corollas. And they cost about 20 bucks each. At that price, it doesn't make sense NOT to replace them.

TOM: Sometimes we have extremely frugal (i.e., cheap) customers who are willing to put up with the noise. For those customers, assuming the rotors are safe, we'll just put on new pads without turning or replacing the rotors. But we specify on the repair slip that stopping distances might be longer until the brakes "seat." And even after that, the customers might experience squealing brakes.

RAY: We make them acknowledge our warning by signing the repair order, so when they come back a few weeks later with their hands over their ears, wailing "I can't take it anymore!" at least our backsides are covered.

Get the Car Talk Newsletter

Got a question about your car?

Ask Someone Who Owns One