Why do the brakes not work when the engine is switched off? What should I do if the engine dies off while driving?

        
Some people are unaware that the brakes may not move when the vehicle is turned off, because they have never stepped on the brakes after the car is turned off. Occasionally, if they step on the brakes a few times at once, they believe it is a malfunction. The inability to apply the brake when the engine is turned off is a normal phenomenon and is easy to understand because of the loss of assistance. The reason why stepping on a fire is relatively light is because it has assistance, which means that other forces are helping us when we step on it. Because the brake pads require a lot of clamping force to hold the brake disc, relying solely on our foot force is not enough, so assistance is necessary, so that the driver can step on them more easily. This power comes from a component called a vacuum booster package, whose name indicates that in order to have assistance, there must be a vacuum, which is generated by the operation of the engine. If the engine stops running, there will naturally be no vacuum and no assistance, and stepping on it must be very hard.
        
How does vacuum assist? There are two cavities inside this booster bag, separated by a diaphragm in the middle. When we step on the brake, the front chamber is in a vacuum state, while the rear chamber is opened and connected to the atmosphere. This creates a pressure difference between the front and rear chambers, which, under the action of atmospheric pressure, pushes the middle isolation diaphragm forward. This force also acts on the brake master cylinder piston, which, combined with the force of the human foot, drives the brake master cylinder piston to move.
        
It is common for vehicles to stall due to malfunctions or other reasons during driving, so some people are concerned about the danger of not being able to apply the brakes after stalling. Actually, there is no need to worry at all. Even if the engine is turned off, the first two brakes are not affected, and there is still assistance, the car can still be stopped normally. This is because the vacuum booster pack can store vacuum, and the vacuum will not disappear immediately after the car is turned off, and can still provide maximum assistance. If the brake is not pressed, the vacuum of the booster pack can be stored for a long time. The car has been parked with the engine off for a few days, and before starting again, the brake is still soft, indicating that there is still assistance. When one foot is released and the second foot is pressed, it will feel that it cannot be stepped on, and at this point, there is no assistance.

        
Therefore, if the vehicle suddenly stalls while driving and the brakes start to apply, it is best not to release them again. Depending on the road conditions at the time, gradually increase the braking force until the brakes come to a stop. You cannot step on it repeatedly, as each step will consume a certain amount of vacuum. Generally, both feet will be exhausted and there will be no further assistance. However, even without vacuum assistance, braking is still useful. It only requires a lot of effort to apply it, and the braking distance will also increase. It can still be applied, so don't feel like you can't step on it and give up.
       
    The brakes will be affected after stalling, mainly for automatic transmission vehicles, because when an automatic transmission vehicle stalls, the engine will immediately stop running. As the vehicle continues to move forward, even if the gear is still in D gear, the wheels will not drive the engine to rotate. If the engine does not rotate, there will be no vacuum and no assistance. However, cars with manual transmission are different. After the engine is turned off, as long as the gear is not in neutral, the wheels can still drag the engine to rotate, and as long as the engine rotates, it can continue to generate vacuum, so braking still has assistance. So when manually blocking the car and driving with the engine turned off, do not shift to neutral. You should continue to maintain the original gear and take braking measures. In gear, the engine can also have a reverse braking force, making parking faster.

From: WONDEE Autoparts 2023-8-18