What are brake rotors?
The braking systems on modern automobiles involve many components we’ve all heard of, such as: brake pads, brake rotors, master cylinders, hydraulic hoses, and brake fluid. Understanding what a brake rotor is and how it relates to the other components in the system is crucial when faced with replacement of brake components on your vehicle.
At the most basic level, a brake rotor is a round metallic component with a machined surface that is attached to the wheel hub on the vehicle. If you have ever looked through the spokes of your wheel and seen a shiny metal disc, that is your brake rotor. They are almost always found on the front axle of modern vehicles, and increasingly found on the rear axle as well.
During operation, brake pads with friction material are pressed against the brake rotor by a brake caliper, using hydraulic pressure generated by the master cylinder and transferred to the caliper via rubber hoses and metal lines. The friction caused by pressing the brake pad against the rotor generates heat energy. This heat energy is absorbed, and then dissipated by the brake rotor. This happens every time you push on your brake pedal in your vehicle to slow or stop the car.
Essentially, the job of the brake rotor is to absorb, and dissipate heat energy every time you use the brakes on your vehicle.
Why are they important?
Having functioning brakes on your vehicle is paramount to safely driving on all types of roads, and in all traffic conditions.
What can go wrong?
The most common reason a brake rotor is no longer usable is simply wear and tear. Brake rotors are subject to wear every time the brakes are applied while driving your vehicle. Over time and repeated application, the brake rotor material is gradually worn away. Most European vehicle manufacturers recommend replacement of the Brake Rotors with any brake pad replacement, while Asian and Domestic manufacturers generally allow the brake rotors to be resurfaced if it meets the minimum thickness specification — if below the specified minimum thickness, it requires replacement as well.
Other reasons for brake rotor replacement include being warped beyond the ability to resurface from repeated heavy usage. When any metal is constantly heated beyond its tolerance and then rapidly cooled, the surface becomes warped over time. This can happen on your vehicle at high brake demand instances, such as when driving in hills or mountains, towing a boat or trailer, or when your vehicle is carrying additional cargo.
Rarely, brake rotors can develop cracks in the machined surface. Whenever a crack is present in a brake rotor, replacement is required to safely correct the issue and ensure proper braking performance.
How to tell when they need to be replaced?
If a brake pad replacement procedure is being performed on your vehicle, the brake rotors will either need to be replaced, or resurfaced to ensure proper braking on your vehicle. If the brake rotor measures above the minimum thickness specified by most Asian and Domestic manufacturers, it can be resurfaced and reused. After machining the brake rotor, an automotive technician must verify the rotor is still above the minimum thickness specification by measuring the brake rotor with a micrometer.
On most European vehicles, replacement of the brake rotor is called for when the brake pads are replaced. Resurfacing and reusing the brake rotor is generally not recommended in the repair manuals of these vehicles. By always using a new brake rotor, the manufacturer is ensuring that your new brake rotor can absorb and dissipate the most possible amount of heat, which is its primary responsibility.
Additionally, if you press on your brake pedal during normal driving and feel a pulsation in the pedal, this could be a sign that the brake rotor is starting to warp and requires attention. It may also need inspection if you are hearing any abnormal squeaking from the brakes when they are applied.
How much do they cost, and why?
When brake rotors are replaced as part of a routine brake job on a vehicle, the automotive technician will generally need about one and a half to two labor hours per axle to complete the operation. Brake rotors can cost as little as $25 dollars for a generic brand brake rotor, up to several hundred dollars for a premium brake rotor using advanced metallurgical compounds; each vehicle manufacturer uses slightly different brake rotors for their vehicles, but generally this is a normal price range.
How long do they take to replace?
Brake rotors are commonly replaced in as little as two hours. Based on the workload of the auto repair facility, brake rotors are almost always replaced on the same day the vehicle is brought to the shop.
Is there any way to reduce the cost?
There are many different manufacturers of brake rotors. It is always worthwhile to comparison shop for different options for your vehicle. There are generally several options readily available for most vehicles.
What other work might be associated?
We have learned that the brake rotor operates as a part of the braking system on the vehicle, and as such it is common to replace or resurface a brake rotor with other brake components. The most common other item seen during replacement of the brake rotor is the vehicle’s brake pads. If replacing any of the rubber brake hoses or metal brake lines at the same time, a brake fluid exchange is also needed to clear the air from the lines.
Does the type of vehicle matter?
There are a few applications that this article doesn’t totally account for, such as when electronic parking brakes/sensors are present, exotic and performance vehicles using high performance compound brake rotors, or on a Mercedes-Benz SBC brake system. While additional labor charges and material charges are common on these applications, the basic principles are still the same.
Our recommendation
Whenever servicing the brakes on your vehicle, be sure to give the brake rotor the attention it needs in order to ensure safe braking for many miles. Whether it needs replacement or resurfacing, it is essential to properly maintaining your vehicle’s brake system.