The braking system of a vehicle has one important purpose; to slow down (and stop) your vehicle. The brake pedal is what you use to communicate to the car that you want it to slow down and it should always function the same.
When you push down on the brake pedal a little, you’re telling your car to slow down a bit. When you apply maximum force to the brake pedal, you’re telling your car you want to slow down very quickly. But even with stomping on the gas pedal, it should not go all the way down to the floor.
So what happens if you push down on the brake pedal and it does goes all the way to the floor when the engine is running? If the pedal sinks to the floor, there is certainly an issue in your braking system.
Reasons Your Brake Pedal Goes to the Floor
Technically, there are two main causes that would make the brake pedal sink all the way to the floor.
1) Leak from Brake Line or Brake Caliper
One of the reasons is, the brake system loses pressure from an external brake fluid leak. The leak may coming from a brake line or one of the brake calipers on your vehicle. Finding and fixing this leak should be your top priority.
2) Bad (or Leaking) Master Cylinder
Another reason is a bad brake master cylinder allowing fluid to bypass seals internally. This master cylinder is where the action of increasing the brake fluid pressure occurs. If this cylinder is not working properly, there are two possibilities: the brake system won’t be as powerful as it usually is or the brakes won’t work at all.
Diagnosing and Fixing the Problem
The good thing about noticing when the brake pedal goes down to the floor is that it’s usually very easy to diagnose, as there aren’t many possibilities as to why it’s happening.
Even better is that you can actually diagnose the issue yourself even with limited mechanical experience. In case the brake pedal goes to the floor, there are several actions to be taken in order to fix the issue.
1) Check Brake Lines and Brake Calipers (or Wheel Cylinders)
The first action you can take is to check the level of the brake fluid. If the fluid is full, it means that there is no leak. If some fluid is missing or it is empty, it means that you have a leak somewhere.
In case there is a leak, you must check all brake lines from all four wheels, to see if the brake lines are leaking. In case the brake lines are dry, it means that the issue is not there. If you see that there is a leak on one of the four wheels, it means you found the issue.
In order to fix it, you need to remove the wheel, find the source of the leak, and replace the part if necessary. Often the culprit is a leaking caliper or wheel cylinder seal.
2) Check the Brake Master Cylinder
The second action you can take is to check the brake master cylinder, as it has two sets of seals which can wear in time and cause leaks. If this is indeed the issue, the brake master cylinder must be replaced with a new one.
Pay attention, it is recommended to be replaced with a brand new unit, not with a rebuilt one because they don’t last long or sometimes don’t even work from the beginning. As with many other objects, when a second-hand unit is used, it is not as effective as a brand new one.
It is very important to mention that if you notice there are leaking signs, do not try to drive your vehicle, as the brake system will not work properly and is unsafe. Instead, try to fix the issue and if you cannot manage it by yourself, have your vehicle transported to the nearest trusted service, where trusted professionals are able to solve your issue.