Why Does the Car Brake Become Hard?
2 Answers
Here are the reasons why the car brake becomes hard: 1. Vacuum booster pump leaks or malfunctions: The force applied to the brake pedal is amplified by the brake booster pump. If it fails, braking becomes difficult, meaning the vacuum force from the brake booster pump is no longer available, and you have to rely solely on your foot strength, which is easily noticeable. 2. Braking after the engine is turned off: The brake booster pump only continuously generates vacuum when the engine is running. When the engine is off, it relies on the remaining vacuum assistance, which usually disappears after a few presses. However, this condition will restore after restarting the engine and is not a malfunction. 3. If this situation occurs while driving, the first thing to do is to release the accelerator and slow down. Try pressing the brake multiple times to see if braking force can be restored. Pressing hard usually can still provide braking force. Additionally, for manual transmission cars, downshifting can also help slow down the vehicle. As a last resort, you can use speed bumps or friction to stop the car, but pulling the handbrake is not recommended unless absolutely necessary.
When I was fixing my car the other day, I encountered a hard brake pedal issue, which turned out to be mainly due to the vacuum booster pump not working. This component is connected to the engine's intake manifold and normally uses vacuum pressure to make braking easier. If the booster pump's rubber diaphragm is torn, the check valve is leaking, or the connecting hose is aged and cracked, the vacuum pressure can't be built up. Another possibility is that after turning off the engine, you pressed the brake pedal several times, depleting the stored vacuum. Using low-quality brake fluid that absorbs moisture and lowers the boiling point can also cause the pedal to harden when vapor bubbles form during continuous braking. This issue is very dangerous—if the brake pedal becomes extremely hard to press, don't force the car to move, especially on slopes where it's prone to rolling back. It's recommended to immediately check the booster system's piping and the master cylinder's sealing.
