4 Reasons Why Your Brake Pedal Goes to the Floor
Few vehicle problems are as frightening as your brake pedal bottoming out without even pressing it. Not only is it a frightening thought, it’s also a real danger.
We’ll explain the most common and specific reasons why your brake pedal bottoms out to the floor with little resistance and how to fix it. We’ll also detail what to do if this happens to you while driving.
Why Your Brake Pedal Bottoms Out
Your car’s brake pedal can bottom out for a variety of reasons, each one just as concerning as the last. Understanding each of these possible causes can help you diagnose the problem and get you back on the road in a timely manner.
Below are some of the most common reasons why your car’s brake pedal is pressed to the floor:
1) Poor Brake Bleeding
One of the most common causes of spongy brakes or a brake pedal that is pressed to the floor is insufficient bleeding after a previous brake system repair. You may hear a “whooshing” sound next to a spongy brake pedal.
This is because air is compressible, but fluid is not. After properly bleeding your brakes, you should restore the functionality of your braking system.
2) Significant Fluid Loss
A significant loss of brake fluid can also cause your car’s brake pedal to drop to the floor. This is because the rapid loss of fluid means that the vehicle’s brake calipers and wheel cylinders can no longer exert hydraulic force.
Over time, a significant loss of fluid results in a loss of overall braking functionality. In most cases, this type of problem is accompanied by the brake warning light appearing on the dashboard of your car.
3) Faulty Master Cylinder
The master cylinder of your brake system can fail and become internally diverted, which in most cases also causes your vehicle’s brake pedal to drop straight to the floor.
4) Brake Booster Issues
If you have noticed that your car’s brake pedal feels strange only when the engine is running, your car’s brake booster could be the culprit. When your vehicle’s brake booster works as designed, it provides the necessary assistance to allow for effortless braking. However, problems with this component can cause a number of anomalies in the braking system itself.
How Car Brakes Work
Before we can determine the root cause of a brake system failure, we must first understand the basic principles of how car brakes work overall. These principles are explained below in their most basic form:
1. Mechanical Input: The braking process begins when the vehicle driver depresses the brake pedal, which activates an attached push rod. This generates a mechanical force that is transferred to the push rod itself.
2. Force Augmentation: This push rod acts on the vehicle’s vacuum-assisted brake booster, which increases the initial mechanical force applied by the vehicle driver.
3. Mechanical-Hydraulic Transmission: The mechanical force generated in steps 1 and 2 is converted into hydraulic force when further movement of the push rod acts on the inner piston of the vehicle’s master cylinder. Hydraulic fluid (brake fluid) is then forced out of the vehicle’s master cylinder through a series of brake lines.
4. Wheel-end application: This hydraulic fluid transmitted power travels to each wheel end and exerts a similar force on the vehicle’s brake calipers/wheel cylinders.
5. Hardware Actuation: Force applied to the vehicle’s brake caliper/wheel cylinder is transferred to the brake pads and shoes on the end of the corresponding wheel. This causes the vehicle’s brake pads to grip their respective rotors.
The vehicle’s brake shoes are also forced outward to contact their corresponding brake drums. Each of these actions creates the friction needed to stop the vehicle.