Diagnosis And Testing - Brake Rotor Lot Rot

If the vehicle has been parked for an extended period of time, the rotors may have a condition commonly referred to as lot rot. There may be a visible brake pad imprint on the friction surface, signs of corrosion, or both. This can lead to vibration or pulsation (judder) while braking. The amount of time required to cause this varies and some vehicles are more sensitive than others. It is not always possible to tell visually if the vehicle exhibits lot rot, in part because the inboard rotor surface is hidden. It is best to perform a test drive, per the following procedure:

1. Apply the brakes several times from 80-48 km/h (50-30 mph), to clean off the rotors.
2. Take the vehicle on a smooth highway, and at 97 km/h (60 mph) apply the brake lightly such as when slowing down to exit the highway. Do this several times noting any vibration, either felt through the seat/body, or through the steering wheel.
3. If steering wheel oscillation exists, that indicates the front rotors are likely the issue. If vibration is only felt through the seat/body, the rear rotors are likely the issue and less likely the front. A combination might indicate both front and rear rotors are an issue. Smooth braking indicates no issue.
4. Resurface or replace front or rear rotors as necessary, per test drive, to resolve the vibration/pulsation (judder) issue.