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How to Tell if Your Brake Rotors are Bad

By Mia Bevacqua, May 8, 2018

brake rotor

Signs of worn or damaged brake rotors

Your brakes are the most important safety feature on your car. If you hear or experience any of the following symptoms of brake rotor problems, get them checked out right away.

You feel a pulsation when braking: A pulsation in the brake pedal or steering wheel while braking is a common sign of warped rotors. This vibration happens because the brake pad isn’t making even contact with the rotor surface.

You hear braking noise: Rotors that suffer from excessive warping can create a clattering noise. This occurs every time the pad makes contact with the uneven rotor.

It’s harder to stop: Troublesome brake rotors can make your car take longer to stop, and even feel like it won’t stop at all. 

Rotors have excessive wear: Rotors have a “discard” thickness that is usually stamped into the them. In locations that require state safety inspections, the rotor cannot be worn beyond this point. If it is, the vehicle will fail inspection.

» MORE: Get an estimate for your brake rotor repair

What brake rotors do

Brake rotors — otherwise known as brake discs — provide a friction surface for brake pads to grab onto. The rotor is sandwiched between two brake pads. When you press the brake pedal, the pads are forced against the rotor, bringing the vehicle to a stop.

But the rotors can get worn or damaged, putting you at risk each time you get behind the wheel.

Modern cars are equipped with either two-wheel or four-wheel disc brakes. A four-wheel disc brake system has a rotor at each wheel, whereas a two-wheel system has rotors in the front, and drum brakes in the back.

Two basic types of rotors are currently in use: solid and vented. Solid rotors are one solid piece, like the name implies. This relatively inexpensive type of rotor is generally used in small cars. Vented rotors are cast with fins between the two disc faces. The fins are designed to distribute air to cool the rotors, improving braking performance.  

Get it diagnosed by a professional
 

How to fix the problem

Depending on the amount and type of wear, brake rotors can either be resurfaced or replaced. To make this distinction, several different measurements should be taken, including the following:

  • Thickness: This is the distance between the two rotor faces, as measured with a micrometer.
  • Parallelism: The amount of variation in thickness around the rotor is referred to as parallelism.
  • Run-out: Run-out is a distortion of the brake disc that causes it to wobble sideways. 

A professional mechanic can take these measurements using tools such as micrometer and a dial indicator. This should be done each time you have the brake pads replaced. If the rotor is within speciation, it can be resurfaced on a lathe. If not, it will have to be replaced. 

Brake pedal pulsation is more likely to occur with thinner rotors. If your car is prone to brake pedal pulsation issues, you may be better off replacing worn rotors than having them machined.

The rotors should be serviced in pairs — either both front rotors or both rear rotors. Whenever the rotors are resurfaced or replaced, the brake pads should be changed out as well. 

To replace the brake rotors, the mechanic will first lift the car and remove the wheels in question. The brake calipers, rotors  and pads are then removed and checked. The new pads are installed, and the rotors, calipers and wheels are replaced, if there are no further repairs needed.

Note: Removing the rotors on certain suspension types, and on some front-wheel drive or four-wheel drive vehicles, can be a significant task. For example, inboard rear discs are not inside the wheel but next to the differential under the car, and take much more time to repair. 

 

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