Why does the brake pedal go all the way down to the floor?
Many small problems with your car can be ignored, but braking problems should never be ignored. If the brake pedal goes all the way down to the floor while the engine is running, you should be especially careful. It can actually lead to a complete loss of braking function.
So if this happens, it is definitely not recommended to continue driving your car. But what causes it and how can you solve it? Let’s take a quick look at the possible causes.
Why does the brake pedal go down to the floor?
The most common cause of the brake pedal going down to the floor is a brake fluid leak or air in the brake system. It can also be caused by a faulty master cylinder or a faulty brake booster. Low brake fluid levels can cause air to get into the brake system.
These are the most common reasons why this problem occurs. Here is a detailed list of the most common reasons why your brake pedal gets pressed all the way to the floor when the engine is running or when starting your car:
1. Brake Fluid Leak
The most common cause is brake fluid leaking somewhere in the braking system. This is often caused by rust in the brake lines. However, it can also be due to a leaking seal problem in the brake caliper pistons.
However, brake fluid leaks are often clearly visible from the ground. So, if you find a puddle of brake fluid on your garage floor, you should definitely check for brake fluid leaks. If you press the brake pedal with a leak, brake fluid will leak out. When you release the brake pedal, air will be sucked in through the leak instead, making the brake pedal very soft.
2. Master brake cylinder failure
Another common cause of the brake pedal going all the way to the floor when the engine is running is a failed master cylinder. The master brake cylinder is located behind the brake pedal on the opposite side of the engine compartment firewall. The job of the master cylinder is to push brake fluid out to the brake caliper pistons to slow your vehicle.
The master cylinder has a seal around the pressure piston, and if that seal leaks, braking pressure will back up to the other side of the piston when you press the brake pedal. This causes a constant loss of pressure when you press the brake pedal, making the brake pedal feel spongy or sinking.
3. Brake Booster Failure
The brake booster sits between the master brake cylinder and the brake pedal. Brake boosters use vacuum to increase braking force when you press the brake pedal. If you’ve ever driven a car without a working brake booster, you know how much more pressure is needed without one.
If you experience very low brake pedal pressure, but it feels very hard when you reach the bottom, you may have a problem with your brake booster. It’s not very common for brake boosters to fail, but it does happen on some car models.
4. Air in your brake system
Have you or someone else recently replaced parts in your car’s hydraulic brake system without properly bleeding your brakes? Then this may be your problem!
Unlike brake fluid, air is compressible. Therefore, to build pressure quickly and avoid a jammed brake pedal, the brake system must be completely cleared of air. The only way to remove air from a brake fluid system is to properly bleed it. Here is a video that shows you how to bleed your brake system.
5. Low Brake Fluid Levels
If the brake fluid level warning light is on on your dashboard, it’s time to check your brake fluid levels. Low brake fluid levels can allow air to get into your brake system, especially when making tight turns. In the previous section, we discussed what happens if air gets into your brake system.
If your brake fluid level gets too low and air gets into the system, there won’t be enough fluid left to refill. The brake system must be bled again.
