What Are The Symptoms of a Bad Master Cylinder? – Diagnosis Steps

The car’s braking system is one of the critical systems in your car. Without an effective braking system, braking your car can be difficult and this can result in accidents. The braking system normally has many components and one of the most important components is the brake master cylinder.

You might not notice but a lot of things happen whenever you want to slow down your car using the braking system. When you depress the brake pedal, the braking system within your cat normally uses the brake master cylinder in order to change the brake pedal pressure into both hydraulic and mechanical pressure.

Consequently, your car is able to come to a halt. Sometimes, the brake cylinder might get faulty due to one reason or another. In this article, we shall outline some of the symptoms of a faulty brake master cylinder and how you can diagnose those issues.

How Does A Brake Master Cylinder Work?

Like we stated above, the main function of the brake master cylinder is to provide the much-needed brake pedal pressure into hydraulic pressure. This usually happens because this component is able to provide the brake circuit with brake fluid.

In addition, it is able to manage the amount of brake fluid that is transferred, depending on the pressure placed on the brake pedal. This means that whether you depress the brake pedal with little force or more, the braking effect will be felt on the wheels of your car. Such is usually the case whether your car is equipped with disc brakes or drum brakes. The brake master cylinder works the same.

Generally, the law requires that all vehicles should have two different braking circuits in them. Here, the hydraulic pressure that is generated for them normally comes from tandem master cylinders. In this case, if one braking circuit stops working, the other circuit will already have the much-needed brake pressure that will enable your car to slow down.

Any time that you depress the brake pedal, the pressure piston normally receives the power pressure of your foot and consequently, pushes the piston further near the brake line. In older cars, you will note that the force of the brake generated after the pressure chamber closes from the piston collar going on top of the bore.

However, modern cars are different as they have a spring supporting the pressure piston. Therefore, when you take your foot off the brake pedal, it will resume its initial position. As a result, the brake fluid goes back into the master cylinder. The next time you press the brake pedal again, the brake pressure will increase as well and thereby aid in bringing your car to a halt soon.

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Symptoms of a Bad Master Cylinder

Although the master cylinder of your car might be working optimally for many years, there are instances when it might be faulty and thereby affect your car’s overall braking system. Here are some of the symptoms that can tell you that your master cylinder is faulty:

Symptoms of a Bad Master Cylinder

1. The Brake Warning light comes on

One of the main symptoms that your car’s master cylinder is faulty is the brake warning light. Chances are that you will see this light illuminating your car’s dashboard. The good news is that this warning light is one of the most unmistakable signs to notice and alerts you that your car has an issue with the braking system. 

It could be the brake pedals, brake pads, or the master cylinder among other components that make up the brake system of your car. Therefore, if this light pops up, you should not hesitate to take your car to a reliable mechanic for further diagnosis.

2. Brake fluid leakage

To start with, the brake master cylinder needs a certain level of brake fluid in order to maintain the hydraulic pressure. For your car to slow down hydraulic pressure is needed. Assuming the brake fluid in the master cylinder, chances are that you will experience some braking issue. 

In fact, if this happens, the brake pedal will feel soft as you lift your foot upon it. Better still, if the reservoirs are unsecured and holding too much brake fluid, your brake master cylinder might not operate more efficiently.

3. Spongy brake pedal

Sometimes, you might depress the brake pedal and all of a sudden it feels spongy. Ideally, it should not feel spongy. In fact, it should neither be too hard to press nor too spongy once depressed. If it feels spongy upon being depressed, then your brake master cylinder has issues and can be damaged over time.

Remember that the master cylinder normally contains rubber seals that help prevent brake fluid leakage. However, these rubber seals can get worn down over time and thereby lead to brake fluid leakage. An internal brake fluid leakage can make you incur huge costs in the long run when repairing the master cylinder as at some point you might have to replace it entirely.

If your car’s braking system has this problem, you might have to press down harder on the pedal in order to slow down your car and consequently, you might cause an accident whenever you want to stop immediately.

4. Sinking brake pedal

Ideally, the brake pedal should spring back up to its initial position once you have removed your foot from the brake pedal. However, this is not always the case as the brake pedal might take time before it springs back.

Other times, it might remain sunk into the floor for longer hours. If this happens, then your master cylinder has issues and should be diagnosed as soon as possible. The soft pedal can be a real hazard as you might not be able to brake your car instantly.

5. Contaminated brake fluid

Sometimes, the rubber seals on the brake master cylinder might get worn out over time. If this happens, their secure connection will be damaged and this can lead to the contamination of the brake fluid. This can make the brake fluid turn into a darker color.

If the brake fluid is contaminated, the fuel filter might get clogged as well and thereby cause issues. You will note that the seal not only keeps the brake fluid from coming out but also prevents debris, dirt and other contaminants from mixing with the brake fluid. 

If this is not checked well in good time, it might damage the master cylinder in the long run. With a contaminated brake fluid, the brake pressure of your car will not be as strong as you would wish. You might have to press the brake pedal harder for your car to slow down. If you do this over time, it might damage the master cylinder over time and you might have to replace it altogether.

6. Uneven brake pad wear

If you notice that your car has uneven braking or uneven pad wear, chances are that the brake master cylinder has issues. Here, you might experience uneven tread wear on your tires over time. For instance, the front left side and the rear left side might be worn down more than the front right and rear right wheels. 

Such issues are normally caused by a failed circuit, causing only two out of the four wheels to be able to apply brakes. One of the causes of a failed circuit is the failure of one of the pistons seals in the master cylinder. Also, a brake line leak can also lead to the same problem over time.

How to Diagnosis A Bad Master Cylinder?

Since we have looked at some of the symptoms of a faulty master cylinder, time is ripe for you to know how you can diagnose a faulty or bad master cylinder. Here, you should check the status of this component and see if there is enough brake fluid. The following are the steps that you should follow:

1. Open the brake fluid reservoir on top of the master cylinder

This is the first step whenever you want to diagnose the master cylinder. To start with, you should unscrew the cap of the little plastic bottle on top of the master cylinder. If the reservoir is metallic, you should use a screwdriver to remove the clamp off the top.

2. Inspect the lid

When the brake fluid in the master cylinder recedes, the diaphragm cups are pushed down by air that comes in through the vents in the lid. Therefore, the cups move downwards and touch the surface of the remaining fluid.

The cups basically stop the fluid from evaporating and normally keep it free from dust and other contaminants that might damage the brake fluid. Once it is back in the cylinder, the cups normally go back to their original position. If the brake fluid has contamination, you will easily be able to know by inspecting the lid.

3. Check the insider of the master cylinder

If you take a closer look inside the cylinder, you will see a line indicating ‘Full’ on the side of the cylinder. Ideally, the brake fluid should be up to that line or better still, within ½ inch of the top of each chamber. If you notice that the levels of the brake fluid are below the above-mentioned levels, you should put more brake fluid until it meets the recommended levels.

4. Close the master cylinder

Once the fluid reaches the recommended levels in both chambers, you can now close the master cylinder tightly. You should do this without allowing any contamination to take place as your braking system might be affected. By closing the master cylinder tightly, you not only reduce the chances of contamination but also reduce the chances of brake fluid leakage.

5. Check out for the stains or wetness under the vehicle

Checking the brake fluid in the master cylinder is not enough. You should also take a closer look underneath the brake master cylinder and see if there is any wetness. Besides wetness, you should be on the lookout for any form of sludge or stain marks. If you come across any of these, chances are that there is a leakage in the cylinder.

In case there is any leakage, you might be at risk whenever you are driving your car as the braking system might not be as effective as it should. Any defect on the master cylinder requires you to replace it. You can hire a professional mechanic to help you install a new master cylinder so as to avoid further damages. By doing this, you will be able to avert the problem of having a compromised braking system in your car.

Frequently Asked Questions (FAQ)

Can you drive with a bad brake master cylinder?

Not. It is not advisable to drive a car with a bad brake master cylinder. If you notice that your car’s master cylinder has issues, you should take it for auto repair. This way, you will avoid accident and further damages that are caused by a compromised braking system.

How much should it cost to replace a master cylinder?

If you want to replace your car’s master cylinder you should set a budget of between $200 and $300.However, this amount might be more, depending on the scope of the fix. For instance, if the individual wheel cylinders need to be replaced, the costs might escalate. In fact, 

How hard is it to replace a master cylinder?

Generally, it is not difficult to replace the brake master cylinder of your car. In fact, most car owners are able to do this on their own back at home. However, proper preparation is paramount. This is because you might need to remove some components, wires, hoses and many more. Therefore, you will need to keep track of where you place these components, lest they lost. If you are careful enough, you will get the job done more seamlessly.

How long does it take to replace a brake master cylinder?

To replace a brake master cylinder will take you a couple of hours and you will be good to go. However, it might take a little bit more time, if you are going to replace other aspects of the brake system.

Final Thoughts

Your car’s master cylinder plays a critical role in regulating the performance of your brakes. Therefore, you should ensure that this component is in pristine condition all the time. If you notice any of the above-mentioned symptoms, you should not hesitate to diagnose the problem.

If need be, you can replace the master cylinder and your braking system will start working more optimally. This will secure both you and your car. Consider these ideas and you will be able to enhance your safety while driving your car.