Brakes Master Cylinder Symptoms and How to Fix it

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So, you’ve been driving for a while now, and you’re getting an inadequate response from your brakes. You do the usual. You change your brake-pads, check for leakages and top up the brake fluid. But the problem persists. Then one of your pals tells you it could be brakes master cylinder symptoms of malfunction. Now you’re stuck there wondering how he knew that.

Today, we’ll take a closer look at the brake master cylinder. We’ll see what part it plays in the whole braking system and issues related to it. We’ll look at how to diagnose it and identify the specific fault it got. We will then check out how to fix the problem and what it will cost you. And finally, see when to attempt a fix and when it’s time to replace the master cylinder.

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How does a Brake Master Cylinder Work?

brakes master cylinder schematic
Master cylinder schematic

All braking systems require a master cylinder to operate. It operates on the principles of fluid dynamics and incompressible fluids. It converts the force you apply to the brake pedal into hydraulic pressure. It transfers the brake fluid into the brake line and multiplies the force that eventually pushes the brake pads onto the brake disks. This is what causes the car to slow down and finally stop.

It is located under the hood close to the main cabin. For visual reference, it is the whole mechanism connected to the brake fluid revisor. Whenever you top up your brake fluid, it is a metal component that recesses into the main cabin with the reservoir located on top of it.

Symptoms of a Bad Master Cylinder

Loss of braking power can’t always be linked to the master cylinder. Sometimes, the problem exists elsewhere in the whole braking system. However, some signs show a clear indication that the problem is rooted in the master cylinder. These are the Brakes Master Cylinder symptoms to watch out for.

Soft and Spongy Feeling When You Push on the Brake Pedal

The most notable indicator is having the brake pedal feel spongy when pressed. The cause of this is mostly an internal fluid leak. Once it gets really bad, the brake pedal might stick to the floor and not return to its normal position once you lift your foot.

Uneven Brake Pad Fading

Depending on how your brakes are biased, the braking force on the right tires should be equal to the left. If you replace the brake pads and notice the pads are worn out unevenly, this is an indicator that there could be a malfunction with the master cylinder.

Warning Light on the Dashboard

Most cars have sensors placed within the master cylinder and have been programmed to display the brake (parking brake) warning light. Depending on the make of the vehicle, the check engine light may come on too. When this warning light comes on while the car is running, it could indicate a problem with the master cylinder.

Leakages on the Master Cylinder

A brakes master cylinder
Leakages are one of the symptoms of a bad master cylinder

Another indicator is when you pop up the hood on your car and notice a lot of oil leakage and build-up on the brakes master cylinder. This is a sure sign that the master cylinder has some issues. The problems could be because of a crack or loose-fitting.

Contaminated Brake Fluid

You go top up your brake fluid, but you notice the brake fluid is contaminated as soon as you open the lid. The brake fluid could contain particles or water. Water contamination is the most dangerous as once the brakes heat up, it might cause the water to change into a vapor. Gas is compressible, and having it in your system might cause the brakes to fail completely.

Particles that might be due to dust cause blockages in your system. The blockages might cause the brake pressure to be unevenly distributed, making the car pull to a side when the brakes are applied.

How to Know The State of The Brake Master Cylinder

The most common way of checking brakes master cylinder symptoms of failure involves starting the car. First, make sure the car is on level ground, and the parking brake has been engaged. Check the state of the brake booster and ensure the hoses are in good condition.

After ignition, let the car idle for around 5 minutes. If it is a vacuum leak in the system, the hoses and fittings will be leaking out air. Pump the brakes until they become stiff. Turn off the engine and push down on the brakes. With the brakes pressed down, turn on the car. The brake pedal should sink a bit. If this does not happen, it’s a clear indicator that the master cylinder is a malfunction and about to fail.

How to Fix a Bad Master Cylinder

Now that you’re sure that the brakes master cylinder symptoms indicate that it’s faulty, these are the fixes you should consider;

Replace the Rubber Seals

To keep the oil pressure constant within the master cylinder, the rubber seals should be changed periodically. It is a simple fix which most of us can attempt. Depending on the usage of the car, the life span of the rubber seals might vary.

Check the Oil Pressure in the Master Cylinder

Make sure your brake fluid oil pressure is always to the manufacture’s specifications. Some cars come with a pressure gauge, but most new ones do not. If you’re not sure of the pressure, you could use a diagnostic tool to give you the exact readings. You can then change the parameters until they fit the manufactures’ specifications. This is done by pumping the brakes and then bleeding the braking system at all wheels.

Add More Brake Fluid

As simple as it sounds, this might fix your issues. If the brake fluid runs low, then the brakes master cylinder has a tough time trying to transfer the braking pressure to the calipers. Without brake fluid, the whole system is rendered useless. You should periodically check the brake fluid level in your reservoir and ensure it never falls below the minimum mark.

Check the Master Cylinder’s Plumbing

The brake fluid in the master cylinder has to maintain a certain pressure. Leakages cause the pressure to drop. Leakages may come from the connection of the reservoir to the main metal master cylinder. Pipes to and from the master cylinder should also be appropriately fastened to avoid leaks. The master cylinder grommets that allow the brake fluid’s regular movements should also be checked to ensure they are not damaged.

How Much does it Cost to Replace a Brake Master Cylinder?

Some issues like leakages and loss of pressure are an easy fix. All it will take to replace broken O-ring seals is just a couple of standard wrenches and a few minutes of your time. Bleeding the brakes might require another person to pump the brakes as you release the air pressure. But it’s easy and doable in around 10 minutes.

Serious problems, like cracks on the main metal body of the master cylinder, must be replaced. You could attempt to fix the crack yourself, but this offers no guarantee that the pressure inside is maintained. Considering the importance of the brake systems, this should be replaced immediately the problem is noticed.

Depending on your car’s make, replacing the master cylinder could cost you about $300 to $600. Labor cost for replacement and installation could also cost you a pretty penny, depending on the mechanics/technician’s company. They might charge you around $200 to $400, depending on the complexity of the car. The labor cost also depends on the type of fix. It will definitely be lower for replacing rubber rings than complete replacement and bleeding of the system.


All automotive machines require a way to be slowed or stopped. Systems to achieve this are engineered into the machines. We started with how it works, then covered the brakes master cylinder symptoms and related issues and how they can be solved. It goes without saying that the best way to avoid master cylinder problems is constant check-ups and proper maintenance.

If you ever experience problems with your master cylinder, you now know what to do. Always try and run a diagnostic of your braking system when issues arise. Then, you can judge if to fix the problem yourself or call a mechanic if you are not adequately equipped for the fix.

What other brakes master cylinder fixes do you know? Have you ever attempted a fix? How did the process go?

Read more: 7 Signs of Automatic Transmission Problems

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