maintenance September 01, 2017

411 on your vehicle’s brake rotors

All vehicles have brake rotors - usually four of them. Brake rotors, sometimes called discs, are the part of the braking system that gets clamped down on by the brake pads, stopping the wheel from spinning. Rotors wear every time the brakes are applied. The rate at which rotors wear depends on several things:

  • Type of brake pads on the vehicle

  • Hardness and quality of the castings

  • How efficiently the rotors cool themselves

  • How the vehicle is driven

  • Braking style of the driver (aggressive or easy)

  • Exposure to moisture and/or road salt

Rotors can sometimes be resurfaced, depending on the amount of wear. When rotors are resurfaced, a mechanic grinds down the surface of the rotors and makes them smooth and flat again. This will only work if the rotors are not warped or cracked. Here are some other factors considered when deciding to resurface, rather than replace rotors:

Rotor Thickness - Original equipment rotors used to be made with enough thickness to go two or more brake pad replacements. However, some cars being made now use thinner rotors to save weight and cost. Consequently, the rotors may be worn down to minimum thickness specifications (which is usually marked on the casting itself) by the time the first set of brake pads need to be replaced.

The minimum thickness specification is an important factor because it is the minimum thickness that provides safe braking. As a rotor wears and becomes thinner, it has less mass. This reduces the rotor’s ability to absorb and dissipate heat. It also reduces the strength of the rotor, increasing the risk of cracking or even breaking (rotor failure).

Corrosion - If a car is parked and not driven for a period of time (a week or more) the rotors will start to rust. Rust is bad because it weakens rotors over time, and makes the brakes noisy when the vehicle is first driven after being parked. Rusty rotors also increase brake pad wear.

Heat effects - Aggressive driving, pulling a trailer, hauling heavy loads or mountain driving all can cause brake temperatures to rise. Over time, this will increase both pad and rotor wear, requiring the brakes to be serviced sooner than would be necessary with more normal or light-use highway driving. The pads and rotors on vehicles that spend most of their time driving in stop-and-go city traffic will always wear out much sooner than vehicles which are driven mostly on the highway or in light city traffic.

Rotor Inspection - When brake pads are replaced, the rotors should be measured to see if they still have enough metal left for safe braking. If the rotor is worn down to an unsafe thickness or cannot be resurfaced without exceeding a safe specification, the rotors must be replaced.

Like brake pads, brake rotors don’t last forever; they usually last anywhere from 30,000 to 70,000 miles. Rotors in good condition have plenty of metal and show no evidence of hard spots, cracks, severe grooving or rusting and no complaints about pedal pulsations. If you are due to have your brake pads replaced, it may be cost effective to have your vehicle’s rotors replaced or resurfaced at the same time. We welcome you to talk with your trusted Wiygul Automotive Clinic technician at your next appointment.

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