How do You Know if Brake Rotors are Warped

Review common symptoms reported from drivers when brake rotors are warped. Discover how this condition can complicate a simple brake job. Learn about the only true way to know if brake rotors are warped to the point action is required. Having the right information and asking the correct questions can help stop a simple brake job from ballooning into a major punch in the wallet.

Rotors are a Problem

The construction of modern-day rotors has changed drastically from the parts that were used on cars from the 70s and 80s. A brake rotor from those days was a thick heavy disk that could be resurfaced several times before replacement was needed. Vehicle manufacturers are now forced to reduce weight to help them meet ever tightening regulations on corporate average fuel economy. Car makers look to the brake rotor identifying this component as low hanging fruit to lighten the vehicle and reduce manufacturing costs. Rotors are now made from a composite material that is lighter than those in the past. The thickness has also been greatly reduced in an effort to shed pounds from the vehicle. The unfortunate side effect is that a thinner and lighter rotor is more susceptible to warping.

Why Rotors Warp

Although this components ability to ventilate heat buildup has improved with the installation of more efficient cooling fins and body designs that assure a fresh flow of cool outside air across the rotor surface, warping from rapid heating and cooling can still be an issue on vehicles that are piloted by aggressive drivers. Interesting enough driving the family sedan like it’s an F1 race car is not the leading cause of problems.One of the most common causes of warping is improper lug nut tightening procedures. Thanks to the thin face around the mounting hub on these modern style composite rotors, how tight each lug nut is, becomes very important to the longevity and performance of the component. Even more important is that each lug nut be tightened to the same torque specification. Wheel nuts with uneven torque will push and distort the rotor. This really doesn’t become a factor until maximum temperatures are reached. At this point during the naturally occurring heating and cooling process these improperly tightened nuts will do the most damage.

Warped Rotor Symptoms

When the warping becomes severe enough to cause noticeable symptoms drivers should share this information with mechanics performing a safety inspection. Brake noise is not usually associated with warping, in fact technicians refer to the most common symptom as a brake pulsation. This is basically a surge when the brakes are applied. This surging and pulsing will increase in severity as speed increases. Often the pulse can be felt in the steering wheel in the form of a vibration and in the brake pedal as a push back against the driver’s foot. Again these conditions become more violent as vehicle speed increases and will disappear completely when the brakes are released.When you get down to it there is only one way to determine the severity of the warp and this is to measure it. This can be done in a couple of different ways but a quick and popular method with mechanics is to mount a dial indicator against the rotor surface and then rotate the assembly one full revolution, measuring the high and low points on the dial indicator. This can be compared to manufacturer specifications to determine a course of action. The other method is to use a micrometer to measure the overall thickness in several places. The minimum thickness is stamped on the inside hub of most factory installed rotors.

How to Handle Rotor Problems

In the old days rotors were so substantial, heavy and thick that a course of action was simple. You could cut or re-surface the rotor using a brake lathe several times before being forced to discard it. Composite rotors are much more difficult to resurface because of the materials they are made from and their total thickness. This does not mean that they need to be thrown away automatically. A well-equipped shop will have accessories to aid in resurfacing composite rotors. This is why a conversation with your mechanic is recommended.As a rule of thumb if you feel a heavy pulsation when braking at Highway speeds, the warp is probably severe enough to warrant replacement. Another thing to consider is the replacement cost of new parts against the cost of reconditioning old parts. As time goes on these numbers are becoming closer together. If new parts are only a few dollars more than replacement would make sense and free you from relying on the accuracy, skill or a shop’s ability to resurface the original rotors correctly. As a special note, be wary of shops that use ABS systems as a selling tool. On Modern cars there is no difference between the rotor used on an anti lock brake system and one used on one without.