If you’ve ever stepped on your automotive brake pedal and felt it flutter beneath your foot, or if the steering wheel vibrates slightly when you apply the brakes, the problem could be warped brake rotors. To understand how this condition develops, and how to fix it, we need to take a quick look at how rotors work.
The concept of braking is quite different in a bicycle or a go-cart, for instance, than it is for a vehicle. If you want to stop a bike, you simply apply a hand brake or a pedal brake, and the pressure applied by your hands or feet is enough to bring the two-wheeler to a full stop within a short distance.
To stop something that typically weighs more than 2,000 pounds, however, you’ll need a system that’s a little more sophisticated. In a car, a chain reaction takes place in a moment when hydraulic pressure transfers from your foot to the car’s brakes through the master cylinder.
Brake fluid is the hydraulic conduit that transfers energy from this cylinder to brake calipers at each wheel. The calipers then squeeze brake pads into the rotors, and the large surface area of these metal discs slow the wheels down based on how much pressure is applied.
If you overwork the brake rotors on each front wheel, either because of repeated hard stops or because of a few sudden full stops while traveling at high speed, they heat up. Sometimes, they’ll even get hot enough to turn red from the excessive heat. Racecar fans have probably seen this a few times, when broadcast cameras mounted behind the tires clearly show the reaction when drivers brake at high speed into turns.
In a passenger car, this type of use can be hazardous to a brake rotor’s health, sometimes even fatal. What happens is that excessive heat and friction can build up between the brake pads that causes the metal on disc rotor discs to warp. Many cars still use drum brakes in the rear wheels, and since front-wheel drive vehicles are common, front brakes tend to wear out more quickly.
Rotors can also be damaged by worn brake pads. If a driver allows pads to wear down to the point that the backing metal plate beyond the semi-metallic layer begins to make contact with the rotor, it can easily scratch or “glaze” the rotor surface when the metal begins to crystallize under stress. In extreme cases, brakes can fail completely under these conditions.
Something as simple as a hard stop applied while driving through a puddle of water can cause rotors to warp. Towing a heavy payload, driving down steep or long hills on a road trip, faulty pistons in the calipers – over time, these individual events accumulate to break down or compromise the integrity of a single rotor.
So, how do we avoid these conditions, or put another way, how can we keep brake rotors healthy? Have authorized mechanics check your brakes whenever the braking action causes an unusual response, like a steering wheel shimmy, a “soft” pedal, a pull to one side, or an audible squeal or scraping noise.
This sound is a signal that worn brake components or metal wear indicators on brake pads indicate unsafe conditions, and brakes need mechanical attention as soon as possible. If the rotors are truly warped or worn down, they can sometimes be “trued” or “machined” to re-create a smooth surface for safe braking, using a special grinder in a machine shop.
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