One of the most vital components of your vehicle's braking system is its rotors. When you apply the brake pedal, you effectively engage a hydraulic system that compresses the vehicle's brake pads against the moving rotor. The resulting pressure and friction help slow the momentum of the vehicle. Of course, this friction creates a great deal of heat. It is this extreme heat and wear that have the potential to warp the brake rotors. If you fear your brake rotors are warped, check them immediately and replace them if needed.
Take the vehicle for a short drive and apply the brakes. If you notice that the brake pedal pulsates or vibrates, you should check the rotors immediately, as this is a sign that the rotors may be warped.
Park your vehicle on flat ground or in a garage and set the emergency brake. Turn the vehicle off and retrieve your car jack and lug wrench. You must check both the driver and passenger sides in order to ensure the rotors are in good shape. If you have four-wheel disc brakes, check the rotors in the rear as well.
Use the lug wrench to loosen the wheel's lug nuts on the side you have chosen. Only break the nuts loose; don't remove them entirely.
Situate the jack under the car or truck and lift it so that the tire is an inch or so off the ground. Then adjust your jack stand and place it under the frame or axle of the vehicle.
Unscrew the lug nuts completely and remove the tire. If the rotor is extremely dusty or dirty, spray it down with brake cleaner.
Hold the straight edge of your ruler lengthwise against the surface of the brake rotor. Look between the rotor and the ruler. If you see a gap between the two, it's a good sign the rotor has been warped. A warped rotor must be replaced with a new one. It cannot be turned or resurfaced. If the rotor isn't warped, be sure to check the brake rotor on the other side as well.
You can also check for a warped rotor by using a dial indicator. If you happen to possess a dial indicator and the expertise to use it, simply attach it to the rotor and spin the rotor several times. If you see the dial move drastically to the left or right, or the indicator shows a difference greater than .003, then your rotor is warped.