We already talked about visually inspecting the brakes for wear. Your hands and feet can feel wear from the inside of the car too. If you feel grinding when you push the brake pedal, either your pads are worn out or you have a foreign object like a rock or piece of debris lodged between the pad and rotor. In both cases, you need to inspect the pads and rotors immediately. If the steering wheel shakes when you apply the brakes, you probably have a warped rotor or two.
Usually, when you've worn the pad down to the metal, the rotor is damaged and must be either machined or replaced. Run your fingernail across the rotor. It should be smooth like glass. If you feel grooves, it needs to be machined. If you replace the pads but leave the grooved rotors, the pads will wear unevenly from the beginning. To optimize performance of your braking system, the brake pad should be mated to the metal surface as much as possible. These grooves take away from that process. The same is true with warped rotors. Warped rotors will wear the brake pads unevenly.
If you've ever experienced a severe pull to one side during braking, chances are you have a problem with the hydraulics in the braking system. You could have a clogged brake line or a leaky caliper piston. As a result, you're going to have some uneven brake wear here too if you let the problem linger [source: 2carpros]. This is a dangerous condition you must attend to at first notice. Once you've figured out the problem, inspect the pads for uneven wear and replace them when necessary.
Each vehicle wears out the front and rear brakes at a different rate. The heavier the front of the vehicle is, the faster the front brakes will wear out. Consider this when inspecting and changing your brakes. Don't inspect the rear brakes and assume that because they look like they have plenty of mileage left, the front brakes are good too.
You can read more about brakes and related automotive articles in the next section.