This is the part of the brake system that actually stops the car. They are usually made of solid cast iron and can be ventilated (depending on vehicle weight and power). The action of stopping is caused by the friction of the brake pads pressing down hard on the brake discs. Brake discs are subjected to very extreme temperatures and conditions. Over time, the discs can become worn and develop hotspots which will cause the wheels to wobble (vibration in the steering wheel).
Brake Disc Skimming
Skimming the discs so that they perfectly match the drive flange again will eliminate issues and prevent the need for replacement.
Skimming is necessary when: