This article discusses If your brake pedal suddenly sinks to the floor but first, below you need to know how the car’s brake system work.
How Does Your Car’s Braking System work?
To understand what causes a soft brake pedal, here’s a quick reminder about your car’s braking system. The most common braking system is the hydraulic system.
To put it simply, when you press the brake pedal it will drive the amplifier which will itself drive pistons supplied with the brake fluid.
The brake fluid will then act on the wheels of your car via the disc brakes or the drum brakes and therefore cause the braking action.
Brake fluid is therefore at the heart of your braking system, so you will understand that you must regularly check its condition because it is often the cause of poor braking. To be effective, the liquid must be able to maintain its content and consistency regardless of temperature changes.
What Is A Soft Brake Pedal?
Your brake pedal feels sluggish if you feel it sinking deeper and deeper when you brake and almost touch the floor. If so, you will also notice that the braking distances are much longer than usual and sometimes you will even have trouble stopping your car.
How To Fix A Soft Brake Pedal?
Pump the brake system
All you have to do is press your pedal several times, the problem will then be solved, but only temporarily. In any case, you will need to purge the fluid if you want to solve the problem of the sluggish pedal in the long term.
Bleed the brake fluid
The solution to permanently removing air bubbles from brake fluid is to bleed your fluid. Here are the steps to be followed to bleed the brake fluid effectively.
Access the bleed screws located behind the wheels
You can access it either by completely removing the wheel to access the brake calipers and therefore the bleed screws or by turning the wheels to the maximum and sliding under the car to directly access the screws.
Prepare your car for bleeding
Start by finding the brake fluid reservoir, it is usually placed on the driver’s side. The brake fluid reservoir must be filled before bleeding. If your brake fluid is too old, replace it with new brake fluid.
Remember to always use the brake fluid recommended by your manufacturer.
Choose the order in which you want to bleed your wheels
There are several diagrams for this, the most common is the Z diagram (right rear wheel – left rear wheel – right front wheel – left front wheel), but you can also choose another order if you wish.
Again, your vehicle’s maintenance booklet can give you more specific information about what the manufacturer recommends for your car.
Bleed your wheels
o do this, first install the bleeder pipe, then you will need a container with some brake fluid at the bottom. Then remove the screw cover and insert the bleed pipe into it, the other side of the pipe should land in the container.
To perform the purge you will need a friend to help you. He will need to get into your car and press the brake pedal until it gets hard, once the pedal is hard, open the bleeder screw to let the fluid flow into the container. Your friend will then need to press the pedal several times before holding it down.
Your purge will be complete when you no longer see any air bubbles coming out of the hose. At this time you can remove the pipe, empty it, tighten the screw and then reassemble the wheel if you had removed it.
Check that the purge has been effective
To do this, press the pedal several times to check that it is no longer soft. Be careful, remember to throw the brake fluid at the recycling center because it is a very toxic and polluting fluid.
Causes Of The Brake Pedal On The Ground When The Engine Is Running Or Starting
these causes are the most common causes that this problem can occur. Here is a more detailed list of common causes of the brake pedal going to the ground when the engine is running or when starting the car.
Brake fluid leak
The most common reason for this to happen is that you have a brake fluid leak somewhere on the brake system. This is often due to a rusty brake line, but it can also be problems with leaking seals from the caliper pistons.
Brake fluid leaks are often very noticeable on the floor, however, if you’ve seen a puddle of fluid on the garage floor, it is time to check for brake fluid leaks.
When you press the brake pedal with fluid leaking, the brake fluid will flow out. When the brake pedal goes up, it will instead suck air through the leak, making your brake pedal very boggy.
Brake master cylinder defective
Another common reason why your brake pedal goes to the ground when the engine is running is caused by a bad brake master cylinder. The brake master cylinder is located behind the brake pedal on the other side of the firewall from the engine compartment.
The purpose of the brake master cylinder is to push brake fluid to the caliper pistons to reduce vehicle speed.
The brake master cylinder has a seal around the push piston, and if that seal starts to leak, brake pressure will return to the other side of the piston when you press the brake pedal.
This will cause your brake pedal to lose pressure constantly when you press it, which will look like a boggy or sinking brake pedal.
Defective brake booster
Between the brake master cylinder and the brake pedal, you will find the brake booster. The brake booster uses a vacuum to increase brake power when you touch the brake pedal.
If you’ve ever driven a car without a working brake booster, you know how much pressure it takes without it.
If your brake pedal starts to build up very low pressure, but feels very stiff once it gets near the bottom, you probably have a problem with your brake booster. It is not very common for the brake booster to fail, but it does happen on some car models.
Air in the brake system
Have you or someone else recently replaced something in the car’s hydraulic brake system without properly bleeding the brakes afterward? Then this might be your problem!
Air is compressible, unlike brake fluid. Therefore, the brake system should be completely free of air for rapid build-up pressure, not for a boggy brake pedal.
Low brake fluid level
If you have a brake fluid level warning light on your dashboard, it is time to check the brake fluid level.
If the brake fluid level is low, air can get into the brake system when performing sharp turns, for instance. What happens with your brake system when you have air in it, we talked about in the previous section.
If your brake fluid was so low that air is getting into the system, it wouldn’t be enough to fill it up. You have to bleed the brake system over.
How To Fix The Brake Pedal That Goes To The Ground When The Engine Is Running?
Now that you know the common reasons your brake pedal may fall to the ground, you probably want to know how to diagnose and fix this problem. So let’s get started.
Check anywhere under your car for any signs of brake fluid leaks. Check brake lines, hoses, and brake calipers. The most common leak is from rusted brake lines but can be from bad rubber seals in the caliper pistons. Replace the leaking part.
Brake fluid level
Check the brake fluid level in the engine compartment reservoir and top it up to MAX if necessary. If the fluid level was really low, there is a risk of air in the brake system, which means you need to bleed it.
Bleed Brake System
The next step is to bleed the brake system to get all the air out. You can find it in this video to experience the complete process of bleeding the brake system at home.
Disconnect the suction hose from the brake booster
Disconnect the power hose from the brake booster and try to press the brake pedal over. If the problem persists, you probably have a faulty brake master cylinder.
Replace the Brake Master Cylinder
Remove and inspect the brake master cylinder for any signs of seal damage. For most brake master cylinders, you cannot purchase the gasket on its own – so you have to replace the brake cylinder.
Inspect or Replace the Brake Booster
The last step is to inspect and replace the brake booster if you see anything suspicious with it. However, if everything else seems fine and is 100% sure that there is no more air in the brake system, there is a great chance that the brake booster is the faulty part.
Brake Pedals Faq
Why does the brake pedal fall to the ground when starting my car?
The most common reasons your brake pedal falls to the ground when you start your car are a brake fluid leak, a bad brake master cylinder, or a bad brake booster.
How do you know if the master cylinder is bad?
The easiest way to determine if the brake master cylinder is defective is to remove the vacuum hose from the brake booster. If the pedal is still depressing, it is most likely due to a fluid leak, the air in the system, or a faulty brake master cylinder.
The only way to know for sure is to visually inspect the gasket inside of it.
How do know if the brake booster or master cylinder is defective?
Disconnect the suction hose from the brake booster. If the problem is gone when you press your brake pedal very hard, you probably have a faulty brake booster. If the problem persists, you probably have a bad brake master cylinder.
Why does the brake pedal go to the ground after a bleed?
There are times when you have not performed the procedure correctly. You must close the air bleed screws before releasing the brake pedal; otherwise, air will be drawn into the system before you close the purge valve.