What Causes the Brake Pedal to Be Hard to Press When Starting the Vehicle?
4 Answers
The reasons why the brake pedal is hard to press when starting the vehicle are: 1. Vacuum booster pump leaks or malfunctions; 2. The brake was pressed again after the engine was turned off; 3. Too much impurity in the brake master cylinder, poor sealing, failure of the vacuum booster pump, dirty brake fluid, or gas resistance caused by mixing several types of brake fluid and heating, leakage in the brake master cylinder or wheel cylinder, or leakage in the air reservoir or pipeline interface. Precautions for pressing the brake while driving include: 1. When emergency braking, hold the steering wheel with both hands and avoid single-handed operation; 2. The free travel of the brake pedal directly affects braking time and distance; 3. Braking actions should be swift, and the brake pedal can be released when the vehicle skids; 4. Avoid emergency braking during high-speed turns. Braking should be appropriately done before turning, maintaining straight-line braking as much as possible to control the turning speed.
I've also encountered the issue of the brake pedal being hard to press when starting the vehicle several times. The most common reason is that you pressed the brake pedal multiple times after turning off the engine, depleting the stored vacuum in the vacuum booster. Normally, when the engine is running, it generates vacuum to assist in making the brake pedal lighter. After the engine is off, this vacuum is limited. Another possible cause could be a malfunction in the vacuum booster itself, such as a torn internal diaphragm or a leak in the connected hose, preventing it from generating the necessary assistance. If the brake pedal becomes hard shortly after turning off the engine, it's mostly a normal phenomenon. However, if the brake pedal remains hard to press even after starting the engine, you should be particularly cautious. In such cases, it's best to immediately stop attempting to start the vehicle and first contact a professional technician to inspect the vacuum pump and related piping for issues.
The inability to press the brake pedal is closely related to the vacuum booster system. When the engine is running, it provides vacuum to the vacuum booster pump through a one-way valve. After the engine is turned off, the one-way valve locks the remaining vacuum. If you repeatedly press the brake pedal after the engine is off, the vacuum will be depleted, making the pedal hard before starting the engine. Another common situation is aging, cracking, or air leakage in the vacuum hose. For example, last month, I found that a hose was chewed by a rat, making the brake pedal completely immovable upon starting. It could also be due to internal failure of the booster pump or air blockage in the brake fluid lines, leading to insufficient hydraulic pressure. If the brake pedal still can't be pressed after starting the engine, it's almost certainly a hardware failure, requiring inspection of the entire brake system. Never risk driving under such conditions.
A hard brake pedal during startup is no trivial matter. I remember one winter morning when the cold start left the brake pedal rock-hard. It turned out I had unknowingly pressed the brakes while playing with my kid in the backseat after turning off the engine, depleting the vacuum in the booster. Engine restart was needed to restore vacuum. But if the pedal remains stiff after starting, it could indicate a faulty booster pump or cracked vacuum hose. Since brakes are a safety-critical system, I recommend immediately shutting off the engine and keeping the vehicle stationary. Professional mechanics would inspect vacuum lines, booster pump integrity, brake fluid levels, and other critical components.
