How Can I Tell If the Rotors Are Bad?by Jody L. Campbell
There are a couple different ways to tell if the rotors on your vehicle are bad. The first is a physical symptom known as a pulsation. This is caused by a few different reasons. The second way to tell if a rotor is bad is a physical inspection and measurement of the rotor. This requires removing the tires and brakes to do so.
Test drive the vehicle.
Accelerate to approximately 30 miles per hour on a deserted road and apply the brakes heavily without coming to a complete stop or squealing the tires. A severe warpage of the brake rotors will emit a pronounced vibration at low-speed hard braking. This vibration will be felt through the brake pedal and steering wheel for front brake rotors and through the brake pedal and undercarriage of the vehicle for rear brake rotors.
Speed up to 60 miles per hour (preferably on a deserted highway) and perform the same test as Step 2. This is to determine if the rotors have a slighter warping that can only be felt at high-speed heavy braking.
Park the vehicle on a flat hard surface and then break the wheel nuts loose with a lug nut wrench (only 1/4-turn counterclockwise).
Lift the vehicle with a vehicle jack and support it onto jack stands. Remove the wheel nuts and tires.
Visually inspect the outboard side of the rotor for rust pits, scoring or uneven surfacing. These conditions are major contributors to brake pulsations.
Remove the caliper bolts with a hand wrench. Remove the caliper from the rotor. Some vehicles employ floating calipers which leave brake pads behind in the caliper anchor. Other vehicles may feature fixed calipers with pads intact with the caliper and an integral knuckle.
Inspect the internal fins (front rotors) for thickness and durability. In extreme cases, front finned rotors can deteriorate by rust and corrosion to the point of being unsafe. This would be indicative if the rotor fins crumbled by contact.
Measure the thickness of the rotors using a rotor micrometer and then compare that measurement to the vehicle specific specifications on a rotor specifications and discard chart. Every vehicle only allows rotors to become so thin before replacement of them is required.
- In some cases, rotors can be machined to eliminate warping. However, rotors on cars today are not as thick as they used to be and or more cost effective to replace rather than machine. The measurement taken of the rotor would have to be mathematically compared to the amount of warping of the rotor (using a ball-joint gauge or other device) and determined if the rotor would still have enough safe material to be effective.
Things You'll Need
- Lug nut wrench
- Vehicle jack
- Jack stands
- Hand wrench set
- Mechanics wire
- 4- to 6-inch C-clamp or caliper reset tool
- Rotor micrometer
- Rotor specifications and discard chart
Jody L. Campbell spent over 15 years as both a manager and an under-car specialist in the automotive repair industry. Prior to that, he managed two different restaurants for over 15 years. Campbell began his professional writing career in 2004 with the publication of his first book.