The first step in finding a solution for a steering wheel that vibrates during braking is to determine the cause of the shaking. As we mentioned, this is almost always caused by a problem with the rotors. Other causes of a vibrating steering system would generally cause shaking all the time, not just when braking. With that in mind, we'll focus this section on the most common rotor problems and their solutions.
One possible cause of vibrations in a car's wheel is an uneven tightening of the rotors. In that case, you should get yourself to a mechanic who knows how to tighten in a star pattern [source: Distad]. This is an elementary concept that any mechanic worth his or her salt should know. Most will also have a torque stick to measure the tightness of the seal. Keep in mind that every car has its own standard torque specifications, which are generally printed on the rotor itself.
More often, a steering wheel that shakes when braking is caused by warped rotors, which your mechanic may be able to diagnose with a simple test -- that is, by spinning the rotors by hand to feel for imperfections. A rotor in good working order should move freely and make a complete revolution without any bumps or signs of resistance areas. If you or your mechanic does notice these issues, you've probably got yourself a rotor problem.
For a more definitive diagnosis, your mechanic will need to remove the rotors and measure them with a micrometer. Rough spots or areas that are more worn than others may be re-machined with a lathe. This is called "turning" the rotors, and it shaves off a very thin layer of metal until the surface is smooth again [source: Distad]. However, this tactic may not be your best bet. With less metal, the rotor is more susceptible to re-warping, which would likely occur again very soon [source: 2CarPros]. In most cases, you'll need to have them replaced.
If your car has received a diagnosis of bad rotors, you might be wondering how urgent a problem this is. It depends on a few factors, which we'll address in the next section.