Most drivers don't give much attention to their brakes until they see or, in most cases, feel a problem. That problem often comes in the form of a moderate to violent vibration as they come to a stop. No, it's not your wheel falling to pieces, but it does mean you should have your brake disc rotors looked at.
What Exactly Do Those Rotors Do?
Brake pads rely on friction in order to slow the car down, so they need a hard surface upon which the calipers can grip the pads. The source of this friction comes courtesy of your car's steel disc rotors. Since the brake pad material is softer than the steel disc, the pads wear upon the disc each time they use abrasive friction to slow the vehicle down.
The vast majority of vehicles in the U.S. will have a pair of these steel discs fitted on the front wheels, with standard brake drums at the rear. Since most of the vehicle's weight shifts forward upon braking, most automakers opt for this setup on cost and simplicity grounds. Most performance and high-end luxury vehicles feature disc brakes on all four wheels.
What Leads to Warped Brakes?
With friction comes heat, and it plays a critical role in how your brakes function. At temperatures below 400 degrees Fahrenheit, your brakes rely on abrasive friction to bring your vehicle to a safe stop. As those temperatures rise, the abrasive friction slowly transitions to adherent friction. At this point, the pads leave behind a minute amount of braking material on the rotor.
Problems can come when uneven layers of brake pad material glaze and create localized heat spots as rotor temperatures rise. These spots wear differently from the surrounding metal, creating microscopic high points in the rotor surface. That's what you'll likely feel when you press the brake pedal.
Of course, damage to the rotor itself can also cause warping, especially if the rotor remains exposed to excessively high operating temperatures for long periods.
How to Fix the Problem
Having your rotors "turned" by a trained technician is usually the quickest and most cost-effective way of dealing with warped rotors. This process involves machining the rotor surface to remove embedded brake pad material and return the surface to a uniform height.
However, rotors can only be turned so many times before the steel disc becomes too thin to safely turn. When this happens, your technician may advise you to purchase a brand-new set of rotors. Fortunately, brake rotors for most vehicles are relatively inexpensive to purchase and install.
A good way of preventing rotor warping issues in the future is by properly bedding new brake pads and rotors. This process helps prevent uneven patches of brake pad material from causing vibrations when you apply the brakes. Keep in mind that you'll need a long, uncrowded stretch of road to safely and properly bed the brakes.
Knowing the Difference between a Warped Rotor and ABS
Nearly every vehicle sold in the U.S. comes standard with an antilock brake system (ABS). This technology helps drivers prevent uncontrollable skidding upon hard braking by modulating the required amount of braking force needed to slow the vehicle without locking up the wheels. Antilock brakes help drivers reach this threshold safely in order to bring their vehicles to a safe and controlled stop.
A typical ABS adds a certain amount of pedal pulsation to let drivers know when they've activated their antilock brakes. Keep in mind that this is NOT a sign of warped rotors – the ABS pulsation is steady and it only occurs upon hard braking, when the ABS is activated.
For more information, check out the sites of local mechanics and brake shops.