Symptoms of a Bad Brake Master Cylinder

When it comes to modern car components, there are many things that you should be conversant with. One of those things you ought to know is the brake master cylinder. The brake master cylinder is one of the most vital components of a modern car braking system.

It is responsible for pushing brake fluid through the brake lines to the wheels. The brake fluids cause the calipers to squeeze the pads against the rotors. This is one of the reasons why your vehicle comes to a stop whenever the brakes are depressed.

Like other car components, brake master cylinders can develop a few faults - and when it does, the overall driving experience will be bad. There are symptoms of a bad brake master cylinder that can alert the driver that such a brake master cylinder needs some help.

Symptoms of a Bad Brake Master Cylinder

The following are signs of a bad brake master cylinder:

Contaminated Brake Fluid


The function of brake fluid is not only to keep the fluid from spilling but to prevent dirt and debris from contaminating the brake fluid. If the seals are worn out, they can no longer avoid dirt and debris from mixing with the fluid - which means that the brake fluid will be contaminated.


Contaminated brake fluid will lead to low brake pressure. This would make it harder for the pedals to stop when you step on them to slow down the vehicle.

Symptoms of a Bad Brake Master Cylinder


Abnormal Brake Pedal Behavior


The most common symptom of a bad brake master cylinder is the abnormality of the brake pedals. In the braking system, it is the function of the master cylinder to generate and distribute all pressure. If it fails in this aspect, then it will affect the brake pedals. Spongy brake pedals, pedals sinking to the floor will become the resultant effects.


Warning Light


A warning light is the easiest and earliest symptom to notice. When it illuminates in the dashboard area, it is an indication that there is some kind of problem with the braking system. It may or may not be the master cylinder - and at this point, what you should do is take your car to the mechanic for inspection.


The braking systems on modern vehicles have brake fluid level and pressure sensors installed in the master cylinder. These sensors detect any problem with the vehicle's master cylinder. However, if you notice that the brake fluid pressure is dropping abnormally via these detectors, it is likely due to a faulty brake master cylinder. A warning light will still come on the screen, telling you to act as soon as possible.


Low Brake Fluid


For a vehicle to respond at the optimum, it needs a certain level of brake fluid in the master cylinder. If the brake fluid is of the required standard, it will create the necessary hydraulic pressure that will put your car to a stop when you step on the brakes.

However, if the brake fluid is leaking from the master cylinder, or if the reservoir is not secured correctly, then rest assured that you will have a master cylinder leak.


Do you know the danger of having low brake fluid? It means your car will not slow down as it should.

Spongy Brake Pedals

If your brake pedal feels spongy and soft as you place your foot on it, it is an indication that your brake master cylinder is faulty.

Your brake pedal should feel firm and strong whenever you apply the brakes. The brake pedal connects the master cylinder via a rod.

When you step on the brake pedal, it pushes this rod and the piston in the master cylinder. The master cylinder pressurizes the fluid to activate the brakes in the rear and front wheels. If you notice a spongy feel in the brake pedal, it’s a sign that you have a problem with your master cylinder brakes.


One of the primary reasons why you may have this spongy feel is the rubber seals. Rubber seals keep the brake fluid from pouring or spilling. If these rubber seals get worn out, it will lead to an internal leak. This will affect the brake pedals and would lead to a spongy feel.


Another reason is the accumulation of air in the brake lines. The air prevents the brake fluid from flowing efficiently within the brake lines, which will lead to a spongy brake pedal.


Sinking Brake Pedals


Sinking brake pedals is also another common symptom of a bad brake master cylinder. Normally, whenever you depress a pedal, it ought to return to its original position.

 However, If you notice that brake pedals don't return after you have removed your foot and it starts to sink to the floor, then it is an indication that your master cylinder is faulty.

At this point, what you need to do is fix it right away. It could be dangerous driving a vehicle with sinking brake pedals.

Brake Master Cylinder Replacement Cost

The total cost of replacing a master cylinder ranges from $350 and $500. That is if the master cylinder is very bad. The price of the replacement part itself is between $100 and $210.

However, the most significant expenses would have to be labor costs. Labor costs chunk up the majority of the total cost, with the range between $230 and $300, which is quite expensive.

To save yourself from paying this colossal labor cost, you need to learn to replace the part yourself - that is, if you are knowledgeable about braking systems. However, replacing a master cylinder requires a bit of expertise. So to avoid making things worse, take your vehicle to an experienced mechanic to fix it for you.

watch Symptoms of a Bad Brake Master Cylinder


How do you know if the master cylinder is bad?

During constant use, the seals inside the cylinder can start to wear out. When it wears out, it starts to leak inside. A bad master cylinder will result in the pedal feeling spongy when pressed.

Why does my brake pedal go all the way to the floor?

Loss of brake fluid is the common cause of brake pedals going to the floor. Also, if the master cylinder is bad, your brake pedals can go all the way to the floor. It is in the master cylinder that the brake fluid compress.

What do you do if your brake pedals sink to the floor?

Your master cylinder speaks a lot about your brake pedals. If it's defective, your pedals will sink, which will jeopardize your safety. You will notice the amount of effort that you put in to bring your car to a full stop. It is due to a bad master cylinder. What you need to do is to take your vehicle to the mechanic.

Can you bleed a master cylinder on the car?

Yes, you can. Make sure you have the required amount of fluid for your vehicle. During brake bleeding, the cap on the master cylinder should be left unscrewed, but still atop the container.

Can I drive with spongy brakes?

If your brakes feel spongy or soft, it's a sign that your master cylinder is defective. Drive to the nearest mechanic to get your car checked. Your brakes could fail at any time with soft pedals, leading to an accident.

How long does a master cylinder last?

Manufacturers build the master cylinder to last for as long as possible. However, certain factors can hinder their longevity. The seals around the cylinder can become dried, liable to break over time, and may cause the master cylinder to leak.

Why does my brake pedal go all the way to the floor?

Loss of brake fluid and a faulty master cylinder are among the common causes of your brake pedal going to the floor. If there is a drop in brake fluid pressure, you are likely going to experience your brake pedal going to the floor.

Why are my brakes still spongy after bleeding?

Bleeding is the process of pushing air out of the brake system using a fluid. If your brake pedal still feels spongy, it means that air has gotten into the brake lines. It can prevent the brake fluid from flowing properly, causing it to feel spongy.

What is a master brake cylinder?

The master brake cylinder converts the mechanical pressure in the brake pedal to hydraulic pressure by pushing the brake fluid into the brake pads and rotors.

How do I get the air out of brake lines?

You need to bleed the master cylinder to get the air out of the brake lines. Bleeding requires you to push the air out via a fluid.

Final Words

The brake master cylinder is the fulcrum of the braking system. It is vital to the operation of the brake system - and crucial to the safety of the vehicle and the driver.

A vehicle with a bad brake master cylinder is dangerous and will compromise your brake pedals and the inability to stop the vehicle. That is why this article on symptoms of a bad brake master cylinder is written.

For this reason, if you notice any of the symptoms discussed here in your vehicle’s cylinder, take your vehicle to a mechanic to access it. If the car brake needs a replacement, your mechanic will be able to tell you that. 

John D. Archer

John D. Archer is a mechanical engineer and writer based on the area of automotive accessories at, A resident expert and professional, John is passionate about all things automotive and loves to share his knowledge. He has good experience in all kind of automotive accessories. He has worked as a chief mechanical engineer in some reputed automotive garage firm.

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