What causes a car's brakes to feel hard and fail to stop the vehicle?

[StCora]

Reasons for hard and unresponsive brakes: 1. Braking before engine shutdown: The car's braking system operates at maximum efficiency when the engine is running, with the brake booster being the key component that amplifies the force applied to the brake pedal. When the engine is off, the brake booster stops functioning, and typically, the remaining vacuum force is depleted after pressing the brake pedal about three times. Thus, the hard brake feel is due to the lack of assistance from the brake booster. Solution: In this case, simply restart the engine and firmly press the brake pedal again. Once the engine is running, the brake booster will resume operation, and the brake pedal will return to normal. 2. Brake booster malfunction: If the car's brake booster is leaking or malfunctioning, and you haven't pressed the brake pedal after turning off the engine, or if you notice the brake pedal is hard to press while driving, it's likely due to a faulty brake booster, a leaking vacuum tube, or a blockage. Solution: If you notice this issue before driving, it's safest to avoid driving and have the car inspected at a repair shop immediately. If the issue arises while driving, stay calm, reduce speed gradually, and try pressing the pedal multiple times to see if braking can be restored. Applying strong pressure can often engage the brakes.