What are the Symptoms of a Bad Brake Master Cylinder

Your car’s master cylinder is one of the most important parts of its braking system.” The master cylinder converts mechanical pressure into hydraulic pressure that engages the brake calipers in the car’s wheels”. Without a functional master cylinder, the car’s braking system performs below par and can easily put you at the risk of vehicular accidents or increased car repair costs. That is why you need to be familiar with the symptoms of a bad brake master cylinder.

You must know these signs because driving with a bad master cylinder is a bad idea. Why might you ask? “A brake master cylinder serves as a valve that pushes brake fluid through the brake lines “. It does this by pushing a metal rod (which is connected to the brake pedal) through a cylinder, which forces brake fluid through brake circuits to the car wheels. It is one of the key brake system components that car owners should pay attention to.

Symptoms of a Bad Brake Master Cylinder

Interestingly, the symptoms of a bad brake booster are similar to those of a bad brake master cylinder. The same applies to symptoms of a bad clutch master cylinder. Heck, some uninitiated folks might even confuse one for the other until a diagnosis is done. That said, you want to look out for the following symptoms if you are looking to steer clear of the potential issues that come with a bad brake master cylinder.

air in master cylinder symptoms
Image Credit: Cash Cars Buyer

You Get Warning Lights

One of the more obvious bad brake master cylinder symptoms is the warning lights that come on your dashboard. Although brake warning lights applies for both bad master cylinder or brake booster, it’s a good idea to run a check on your master brake cylinder when they come on.

This warning light is often triggered by a brake fluid level sensor that is situated within the brake fluid reservoir. Barring those instances when said sensors fail, a brake warning light indicates that the brake fluid level is too low. If the lights stay on after you have topped the reservoir with brake fluid, then the chances are that there is a problem with the car’s brake master cylinder.

Brake Fluid Leak

This is one symptom that most folks overlook because it is linked to other car issues. It would be best if you were wary of brake fluid leaks because of the function of brake fluid in the braking system. The master cylinder uses brake fluid to get the car’s brake calipers or brake drums to engage.

When there is a brake fluid leak along the brake lines, the brake master cylinder won’t function as it should. You can find evidence of brake fluid leaks by looking for drops of fluid on the area directly under the brake master cylinder. Check closely for leaks at the fitting points connecting the reservoir and the brake master. Examine if there is any leak around the brake-savor. Another indication of a leak is that you have to top your brake fluid more often than not.

Read Also: No Brake Fluid Coming Out When Bleeding [Causes and Fixes]

Spongy Brake Pedals

One very obvious symptom of a bad brake cylinder is a brake pedal that feels spongy when you depress it. Functional brake pedals are firm even a tad bit hard sometimes depending on the amount of force you apply when stepping on the pedal. You get a spongy brake pedal when the master cylinder cannot create the amount of hydraulic pressure required to activate the brakes in the car’s wheels.

One reason for this situation is the ‘rubber seals’ wear and tear in the brake master cylinder. These seals are designed to keep brake fluid within the cylinder. In the event that they get worn out, a leak occurs, and that’s when you get the spongy brake pedal.

In essence, spongy brake pedals can be caused by the bad master cylinder or air in lines. The latter reason prevents the brake fluid from moving around more efficiently. Other reasons for a spongy brake pedal are damaged brake lines, rust, and leaks in the brake calipers.

Read Also: Brake Pedal hard and Brakes Lock Up [Causes and How to Fix]

Contaminated Brake Fluid

Damaged rubber seals within the brake master cylinder can contaminate the brake fluid. Openings in the damaged rubber seal let in debris and dirt that contaminates the brake fluid and lessens the hydraulic pressure.

Once the hydraulic pressure is diminished, stopping your car becomes a challenge because the braking system cannot generate enough hydraulic pressure to stop the car wheels. Stopping the car takes longer, and the risk of getting involved in an accident increases exponentially. Your best bet is to observe the fluid to check if the brake fluid color changed.

 Sinking Brake Pedal

Under normal circumstances, a depressed brake pedal returns to its standard position the moment it is released. That’s why a sinking brake pedal is a strong pointer to a bad brake master cylinder. A sinking brake pedal is one that does not return to its normal position after it has been released.

A bad brake master cylinder can cause a sinking brake pedal. The brake master cylinder is responsible for creating hydraulic pressure by compressing brake fluid, which causes the brakes to be applied to the car’s wheels. When the brake master cylinder ceases to function optimally, the result is a loss in braking power and a sinking brake pedal.

A sinking brake pedal means that the brakes are no longer function so your best bet in such a situation is to test your brake master cylinder. You might give it a try if you know how to test if the brake master cylinder is bad. If you don’t have that technical know-how then you should get professional mechanics to give your brake master cylinder a look.

Diagnosing & Replacing Master Cylinder YouTube

Frequently Asked Questions (FAQs)

Q: What Causes A Master Cylinder To Fail?

So what causes a master cylinder to fail? The truth is a range of things are responsible for a bad brake master cylinder. It is a mechanical device, so it is prone to wear and tear. The rubber seals can become worn out while its springs could go faulty at one point. Then there is the way you treat your brake fluid. Brake fluid absorbs air over time; that is why it is recommended that you replace it at stipulated intervals. When this is not done regularly, the moisture absorbed by the brake fluid can cause rust within the brake master cylinder.

Q: What Is Wrong When The Brake Pedal Goes To The Floor?

If you have experienced this recently, you might want to get your brake system checked. It is often caused by a brake fluid loss, a bad brake master cylinder, or a bad brake booster. In most cases, the brake pedal goes down to the floor when there is a loss of hydraulic pressure. Your car’s braking system utilizes compressed brake fluid that courses through the brake circuits and causes the brakes to be applied on the wheels of the car. When there is a loss of this pressure, what you get is a brake pedal that goes to the floor.

Q: What Is The Cost To Replace A Master Cylinder?

Sometimes replacing a master cylinder might be your only bet. Replacing a master cylinder is not an overly expensive affair. The bulk of this cost lies with labor costs besides several factors: the service and the make, year, and car model. The amount of repair work to be done also affects the cost of replacing a master cylinder. A host of websites can help you determine how much it costs to replace a master cylinder.

Q: How Do You Fix A Sinking Brake Pedal?

Fixing a sinking brake pedal simply requires you to address the issues that caused the situation in the first place. One of such issues is a bad master cylinder. This mechanical device has two sets of internal seals, which often become damaged after repeated use. In such situations, air might enter the braking system; brake fluid might bypass backward into the brake master’s fluid reservoir, or fluid leaks occur. Sinking brake pedals occur when there is a lack of pressure or brake fluid in the braking system. The best way to handle fluid leaks and lack of pressure is to replace the brake master cylinder.

Q: How Do I Change A Master Cylinder?

There are two ways to go about this. You either get professional help, or you go the DIY way. If you opt for the DIY, then you must have the correct toolbox with quality mechanic tools. Here are the steps you need to take to change a master cylinder:

  • Remove the Brake Master Cylinder
  • Bench Bleed the Brake Master Cylinder
  • Install the New Brake Master Cylinder

 Final Words

The brake master cylinder allows your car’s braking system to run smoothly. However, this mechanical device can go bad once in a while because of a range of reasons. When this happens, the brakes stop functioning optimally and you run the risk of getting involved in an accident. Thankfully, there are signs that accompany a bad brake master cylinder. The trick is to be able to identify the symptoms of a bad brake master cylinder. Once you are able to do that you can easily fix the root cause and save yourself the complications of an accident.

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Osuagwu Solomon

Osuagwu Solomon is a seasoned automotive technician for the past 9 years, and a technical writer. He loves writing about auto professional repair guides, DIY repair guides, and buyer’s guide. After spending six years in the automotive workshop, he decided to impact his knowledge to people aside his domain, and he has achieved this by centering his Automotive writing skills on REPAIRS.

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