Why did the brake disc turn black?
2 Answers
The blackening of the brake disc indicates severe oxidation, and it needs to be replaced promptly. More knowledge about brake discs is as follows: 1. Overview: The brake disc is a round disc that rotates as the vehicle moves. The brake caliper clamps the brake disc to generate braking force. When the brake is applied, it clamps the brake disc to slow down or stop the vehicle. Brake discs offer excellent braking performance and are easier to maintain than drum brakes. 2. Features: Brakes include disc brakes, drum brakes, and air brakes. Older vehicles often have disc brakes in the front and drum brakes in the rear, while many newer vehicles have disc brakes on both front and rear wheels. Disc brakes dissipate heat better than drum brakes, making them less prone to thermal fade during high-speed braking, thus providing superior high-speed braking performance. However, their braking effectiveness is inferior to drum brakes during low-speed cold braking.
Last time I washed my car, I also noticed the brake discs were covered in black grime, so I asked my cousin who runs an auto repair shop. He said this is extremely common—it's mainly metal dust from brake pad friction sticking to the discs. Especially for speed enthusiasts like me who brake hard frequently, more iron particles accumulate. Even new cars experience this because brake pads have a break-in period. As long as there's no metal scraping noise when braking and the steering wheel doesn’t vibrate, it’s fine. However, if the discs turn black again just a couple days after washing, it’s best to visit the shop to check the brake pad thickness and clean the wheel hubs—that black dust is a nightmare to wash off.
