Does replacing the brake master cylinder and ABS pump require bleeding?

[JourneyFitz]

Replacing the brake master cylinder and ABS pump requires bleeding. Working principle of ABS: During braking, the ABS quickly determines the wheel lock-up state based on the speed signals from each wheel speed sensor, closing the normally open input solenoid valve of the wheel that is starting to lock up to maintain the braking force. If the wheel continues to lock up, the normally closed output solenoid valve is opened, causing the braking pressure on that wheel to rapidly decrease due to the direct connection to the brake fluid reservoir, preventing the wheel from completely locking up due to excessive braking force. This keeps the braking state at the optimal point (slip ratio S of 20%), achieving the best braking effect and maximum driving safety. Classification of ABS: ABS is mainly classified based on channels. In ABS, the brake pipelines that can independently adjust the braking pressure are called control channels. ABS control channels are divided into four-channel, three-channel, two-channel, and one-channel types. One-channel ABS: Also known as single-channel ABS, it has a brake pressure regulator installed in the rear wheel brake master cylinder and a wheel speed sensor mounted on the rear axle differential (sometimes one on each rear wheel). Two-channel ABS: This type of ABS struggles to balance directional stability, steering control, and braking efficiency, and is rarely used today. Three-channel ABS: It independently controls the two front wheels, while the two rear wheels are controlled together based on the low-select principle (i.e., both wheels are controlled by one channel, ensuring the wheel with less traction does not lock up), also known as hybrid control. Four-channel ABS: It has four wheel speed sensors, with a brake pressure regulator installed in the pipeline leading to each wheel brake cylinder, enabling independent control and forming a four-channel control system.