If you find that you have warped rotors or drums, there is a low-cost alternative to replacement. Machining your drums or rotors can bring back a warped part and extend its service life. To do this, you need a piece of equipment called a brake lathe.
You can mount your warped rotors or drums to this machine and it will actually cut a new surface into the drum or rotor. These machines aren't normally available to the DIYer, but your local auto parts store might have one. If they do, you can remove the rotors or drums from your vehicle and take it to them in to have them machined. They usually charge a flat fee for this. Once your rotors or drums have been machined, you can reinstall them on your vehicle with new friction material and be on your way, vibration-free.
It might not be possible to machine your rotors or drums, however. Sometimes there's not enough metal remaining in the part to perform a machining. To make this determination, the person doing the machining needs to measure the thickness of the metal remaining on your drum or brake disc. If it falls below or close to the minimum, they cannot machine the part. These measurements are often stamped on the outside of the part and are considered the minimum thickness allowable by the manufacturer. Here's a video that explains this in a little more detail.
One last note on machining. It’s a little known fact that you should machine new rotors or drums before installing them on your vehicle. Check with any rotor or drum manufacture and they recommend this practice. So don’t think that installing new rotors or drums will solve a vibration problem, sometimes it doesn’t. Manufacturers cover their collective butts by stating that you should machine rotors or drums before installation for best results.