Today: When to Replace Brake Rotors

Dear Car Talk

Dear Car Talk | Jul 06, 2012

Dear Tom and Ray:

This morning at the gym an acquaintance (Fred) told me that he took his car to a mechanic for some brake work, and the mechanic replaced the pads and rotors. Fred said that he wanted the mechanic to replace the pads but not the rotors. I asked him if the mechanic explained why he replaced the rotors too, and Fred said no. This led to a discussion. How do you know when the pads are all that need to be replaced versus when you need to buff or replace the rotors, too? What symptoms should we typical folks look for?

Thanks. -- Ed

TOM: Well, the classic symptom of warped rotors is a pulsing in the brake pedal when stopping from high speeds. Sometimes that's accompanied by a simultaneous wobbling of the steering wheel.

RAY: But that only tells you when your rotors are warped, not when they're simply worn out. And my guess is that your friend Fred's were worn out.

TOM: Brake pads used to be relatively soft. They were made of asbestos. And they would wear out quickly. But the hard, metal rotors would last through several sets of pads. That's all changed.

RAY: When we got rid of asbestos, brake pads began to be manufactured out of much harder materials -- namely, metal. So now, the metal pads grind against the metal rotors, and they wear out at almost the same rate.

TOM: So these days, 99 cars out of a hundred need to have their rotors replaced when the pads are swapped out.

RAY: We almost always replace the rotors now rather than machine (resurface) them. When you machine a rotor, whether it's on or off the car, you have to do at least two passes to do it right, and that takes a good half-hour of labor. You add the cost of using the machine, and you have to charge 60 bucks a rotor. And you can BUY some brand-new rotors now for 30 bucks! So machining them rarely makes sense.

TOM: There are exceptions. Some rotors won't come off without breaking the wheel bearing, and we'll machine those rotors right on the car if there's enough metal left. But the vast majority of cars that come in for brake jobs these days get new pads and new rotors.

RAY: And for those of you concerned about the environmental impact, don't worry. Once a week, a guy named Stumpy comes in and collects all the used rotors for recycling -- where they're shipped over to China and come back as fireplace implements.

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