Why Do You Need to Press the Clutch When Braking?
3 Answers
If you brake without pressing the clutch, the wheels are forced to stop rotating, and the resistance is transmitted to the engine through the drivetrain. The engine cannot overcome such a large resistance and will stop working, i.e., stall. Below are the functions of the clutch: 1. Facilitates car starting: Before the car starts, it is stationary. Since the engine and transmission are rigidly connected, once a gear is engaged, the car will suddenly surge forward due to the abrupt connection of power. This not only causes damage to mechanical components but also makes the driving force insufficient to overcome the huge inertia generated by the sudden forward movement, causing the engine speed to drop sharply and stall. 2. Reduces torsional vibration impact: The output torque of a car engine is usually unstable. During the operating stroke, the inertia of the engine's rotating system can reduce torsional vibration, but the remaining impact still adversely affects the subsequent transmission and driveshaft. The damping springs in the clutch can significantly reduce the torsional vibration impact from the engine, extending the lifespan of the transmission gears. 3. Prevents excessive pressure on the drivetrain from causing damage: During emergency braking, the wheels suddenly decelerate sharply, while the drivetrain connected to the engine maintains its original speed due to rotational inertia. This often generates an inertia torque in the drivetrain far greater than the engine torque, making the drivetrain components prone to damage.
This issue was repeatedly emphasized by the driving instructor during driving school. When braking in a manual transmission car, you must press the clutch primarily to prevent the engine from stalling. When the vehicle speed drops very low, the engine RPM will also decrease. If the clutch remains engaged at this point, the engine will be dragged down by the wheels to below idle speed. I’ve forgotten to press the clutch a few times, and the result was the car stalling before coming to a complete stop. The brake assist instantly disappeared, and the pedal became extremely heavy, nearly causing a rear-end collision. Additionally, when queuing at traffic lights in the city, braking without pressing the clutch can cause the car to jerk, making passengers nauseous—I once had a friend in the passenger seat who vomited. However, during emergency braking on the highway, you should first press the brake to reduce speed before pressing the clutch, as the inertia is too great otherwise. Ultimately, this practice is to protect the powertrain and ensure smooth driving.
As a veteran driver with over a decade of experience, I've long developed the habit of letting my feet follow my instincts when driving a manual transmission car. When braking, my left foot naturally steps on the clutch without even thinking about it. Not doing so would definitely cause the car to shake and stall, and more importantly, it becomes particularly troublesome in stop-and-go traffic. Once, while stuck in traffic on an elevated road, I braked without pressing the clutch, and every time I slowed down, the car lurched forward like a jumping frog, stalling three times in less than five minutes. Later, my instructor told me that this also accelerates clutch plate wear due to prolonged semi-engaged states. Now, when teaching my child to drive, I repeatedly emphasize this key point, especially since the steering wheel becomes heavier after stalling, which can be dangerous in sudden situations.
