Why does the brake feel soft and ineffective after replacing the brake pads?

[StGarrett]

After replacing the brake pads, the brake feeling soft and ineffective is mainly due to the following two reasons: 1. The surface of the brake pads is relatively flat. 2. The contact area with the brake disc is small, resulting in lower braking force. New brake pads require a break-in period, typically around 200 kilometers. Only after this break-in period can the optimal braking performance be achieved. Different issues have different solutions: 1. Severe wear of the brake pads. Some cars are equipped with a brake pad wear warning function. Once the brake pads wear close to the critical value, a warning light will appear on the dashboard. Even without this function, there are raised indicators on both sides of the brake pads, which represent the wear critical value. When the brake pads wear down to these raised indicators, they will contact the brake disc and produce abnormal noises. At this point, the brake pads should be inspected and replaced promptly. 2. Leakage between the master cylinder and the wheel cylinder. The master cylinder internally uses the brake pedal to pressurize the brake fluid, which then transmits the pressure to the wheel cylinders, pushing the brake pads to frictionally engage the brake disc and generate braking force. If there is internal leakage between the master cylinder and the wheel cylinders, the pressure will dissipate internally, causing the brake to feel soft. To resolve this, the internal air should be bled, and the brake lines should be inspected and replaced promptly.