Basics: My brake pedal is vibrating/pulsing. What's up?

So you're driving down the freeway and hit the brakes to slow for an exit, and the brake pedal and/or steering wheel vibrates. What's going on? This is a pretty common problem on cars, and it's usually referred to as a "warped rotor." That's kind of a misnomer, so let me explain a bit. If you already know how disc brakes work, skip the next paragraph and I'll discuss the issue at hand.

The image to the left represents a typical disc brake setup. The pads are held by the "caliper," which is grey and on the left part of the disc. To the right, you can see a picture of the pads. Most modern cars have these disc brakes. Basically, a metal disc (called a rotor) rotates with the wheel when the car is moving. When you step on the brakes, hydraulic pressure forces two pads against the metal discs, creating friction, heat, and stopping power. The pad material wears down over time, causing brake dust and eventually requiring replacement. The rotor also wears down over time but more slowly than pads.

So, what's a "warped rotor?" From the name, you'd assume the rotor became warped and caused the pulsing. In my experience, usually this is NOT the case. It's usually caused by an uneven depositing of the brake material onto the rotor as you wear it down. That is, as you use the brakes, hot spots form for one reason or another on the brakes and cause extra pad material to fuse onto it. When it cools, it gets really hard, and causes unevenness on the rotors that leads to vibration.

What can you do about it? Probably the best thing to do would be to take your car into your trusted mechanic and have him or her check the brakes out. The usual course of action is to "turn" the rotors - that is, to take them off the car and sand them down so you have a clean new surface. Then the mechanic will clean the brake pads and inspect them, and either reinstall or replace them.

The most important thing is what happens next. Some pads need to be "bedded in," which means that you'd go through a short series of prescribed stopping maneuvers to wear off any hot-spot areas. This will prevent the brakes from having depositing issues in the future. I would ask your mechanic if this needs to be done, and have the mechanic do this. It's easy to do it wrong, and requires some hard, fast braking, so it's best to leave it to a professional.

If you want to know more about brake pads or how to bed them in, feel free to email me. My email is in my Blogger profile.