Brake Pedal Goes to Floor (Pedal Hard When Car Is Off, Then Soft When the Car Is On)

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Brakes are one of the most crucial components of a car. If your car’s brake pedal is hard when the car is off and goes to the floor when the engine is on, you definitely have a significant problem that can impact your ability to stop the car; thus, you should not drive until the issue is fixed. In this article, I have explained what causes this issue and how to fix it; make sure you do not miss anything. 


What Are the Causes?

  1. Loss of brake fluid
  2. Air in the brake lines
  3. Malfunctioning master cylinder
  4. Malfunctioning brake booster
  5. Malfunctioning wheel cylinder
  6. Malfunctioning brake caliper system


How Do We Diagnose the Problem?

Diagnosing the issue can be as simple as inspecting a brake fluid leak or something complicated like replacing a faulty part like a master cylinder, which requires skills. Below, I have explained all the solutions to fix the issue; most people can perform the first two methods by just following the basic instructions, and the rest require some skills.

1) Check the Brake Fluid Level

Brake fluid plays a vital role in the braking system. Its main role is to transmit force using hydraulic pressure in the brake lines. When the pedal is depressed, the force makes the calipers or wheel cylinder press against the brake rotors or drums, resulting in friction that ultimately brings the vehicle to a stop. 

Make sure the fluid level is not below the ”Min” mark mentioned on the brake fluid reservoir. Also, inspect the brake fluid reservoir and brake lines for potential leaks. If you find any leaks, get them fixed and refill the brake fluid. Doing this will fix the issue of the pedal going soft when the engine is off. 

2) Bleed Brake Lines

If the car’s brake lines have air deposits, the air will prevent brake fluid from flowing properly, resulting in insufficient hydraulic pressure that causes the brake pedal to go soft and touch the floor. The air pockets in the brake lines are usually formed when you make any changes in the brake system and do not bleed the brake lines; for example, if you install new brake calipers, you will have to bleed the brake lines to remove the air deposits. 

How to Bleed Brake Lines?

Brakes can be bled using a brake bleeding machine, but if you do not have access to a bleeding machine, you can easily bleed brakes without it as well. Below are the instructions to bleed brakes without using a bleeding machine. Keep in mind this is a two-person job. You would need someone to help you.

Before we dive into the instructions, make sure you have a bleeder bottle and a wrench for the bleeder valve. If you do not have a bleeder bottle, you can easily make one using a regular water bottle and a pipe. 

Read: How to make a bleeder bottle at home

Watch Video: How to make a bleeder bottle at home

  1. Depress the brake pedal
  2. Open the bleeder valve (counter-clockwise) using the wrench (The valve is located at the top of the caliper, and usually, it’s covered with a rubber cap.)
  3. Close the bleeder valve and release the brake pedal.
  4. Depress the brake pedal again and open the bleeder valve again

Note: Repeat these steps until all the air is out of the system; make sure you do this with all the wheels; in case your car only has disc brakes in front, then bleed both of them; else you have to bleed all four.

3) Replace the Brake Master Cylinder

The brake master cylinder plays an important role in braking. It converts the force the driver applies on the brake pedal into hydraulic pressure that pushes brake fluid and transfers the force to the brake assemblies at each wheel to stop the car. 

Over time, the seals and pistons of the master cylinder can wear out, resulting in a bad brake master cylinder that cannot keep enough pressure to apply the brake and stop the car. Brake fluid contamination can also damage the master cylinder since it can lead to corrosion. And there are other causes that can damage the master cylinder such as overheating.

Steps to replace the brake master cylinder:

  • Drain the brake fluid
  • Remove brake lines
  • Remove the old master cylinder
  • Install the new master cylinder
  • Refill brake fluid
  • Bleed the brakes
  • Check for leaks and test brakes

4) Replace brake booster

The brake booster helps increase the force applied to the brake pedal so the driver can smoothly engage the brakes. A brake booster can cause the brake pedal to go soft if it malfunctions or leaks. 

Watch the video to figure out how to replace the brake booster:

5) Replace wheel cylinder

The wheel cylinder has an important role in the drum brake system of a car; a malfunctioning wheel cylinder can cause the pedal to sink to the floor. The video below has detailed instructions about how to replace it: 

6) Check the brake caliper system

The brake caliper system is one of the most important components of a vehicle’s braking system. Get it checked because, in some cases, it can be responsible for the issue. 



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