4 Symptoms of A Bad Brake Master Cylinder

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The brake master cylinder plays an important role in your braking system. If you don’t resolve this issue, it can result in serious damage, and your car can become dangerous to drive.

Unfortunately, identifying an issue with your brake master cylinder is challenging. The symptoms can often get confused with other issues or overlooked until the issue gets worse.

Don’t worry; I’m here to help. In this post, I will go over five symptoms you can use to help you identify a bad brake master cylinder.

1. Leaking Master cylinder

One of the most common signs of a bad master cylinder is brake fluid leaking.

You can look for leaking brake fluid on the brake boost or the firewall.

When a master cylinder starts to fail, the master cylinder will start externally linking out into the brake boost or down the firewall.

Other common areas you can look at are around the gaskets or bolts of your brake master cylinder.

Internally the master cylinder can leak when rubber seals internally wear out. This can reduce the amount of fluid pressure into the brake lines.

Low brake fluid will allow air into the brake system giving your brakes a spongy soft feeling to. The only way to get air out of your braking system is to bleed the brakes.

Adding brake fluid to your master cylinder in some cases can give the driver a better brake pedal feel until the brake fluid reduces again.

If your master cylinder is leaking internally, adding brake fluid will not help your brake pedal feel.

2. Contaminated Brake Fluid

Two things can contaminate your brake fluid. 

  1. Moisture 
  2. Small particles 

One of the most common reasons that master brake cylinders cause leaks is wear and tear. Wear and tear will allow for air and moisture to enter the brake fluid. 

Any moisture and particles that get inside your brake fluid will reduce its effectiveness. 

One of the most common reasons that brake fluid becomes contaminated is when the seal on the back of the master cylinder goes bad. 

Dirt, water, debris, and air can enter your brake fluid, contaminating the brake fluid. The contaminated brake fluid affects the hydraulic pressure making it harder to slow down your vehicle. 

Warning signs your brake fluid could be contaminated include:

  1. The brake pedal is less responsive.
  2. Increase stopping distance
  3. The ABS warning light comes on 
  4. Brake malfunction causing the brakes to lock up under normal braking situations. 
  5. Your brakes stop working. 

Flushing the braking system and bleeding the brake will help in some situations. At this point, it’s wise to replace your master cylinder to prevent future damage to your brake system. 

3. The Brake Warning Light Turns On

brake warning light

One of the easiest ways to determine if you have issues with your brakes, including your master cylinder, is when your brake warning light turns on.

Some cars have different lights depending on the issues, while others don’t.

To help you determine the reason that your brake light turns on, you can use an OBD scanner to help narrow down some of the potential issues.

You can also have a mechanic inspect your brakes for any potential issues.

Below you will find some common brake light dashboard lights. This will help you differentiate different brake warning lights on your car.

4. Soft Or Sinking Brake Pedal

After stepping on the brake pedal, you notice that the brake pedal did not return to the original position.

A soft brake pedal or sinking brake pedal are signs your master cylinder is going bad.

Low brake fluid will allow air into the brake system giving your brakes a spongy soft, or sinking brake pedal.

This can be dangerous because the brake pedal could completely compress into the floorboard, eliminating your braking capabilities.

You suspect an issue with your brake pedal getting very soft or sinking into the floorboard. Replace your master cylinder or have a trained mechanic complete the replacement.

What Is A Master Cylinder?

The master cylinder distributes the brake fluid to your brake lines and brake calipers.

When you apply pressure to your brake pedal, this signals your master cylinder to release brake fluid. The master cylinder will determine the amount of brake fluid to release based on the pressure you applied.

Without a properly functioning master cylinder, your brakes won’t receive brake fluid. Without brake fluid, your brakes may not function properly.

A faulty master cylinder can result in loss of braking power as well as damage to your braking system.

How Does A Brake Master Cylinder Work?

The brake master cylinders function starts when you apply pressure to your brake pedal.

The pressure on your brake pedal is converted to hydraulic pressure.

When your press your brake pedal, it compresses the pushrod inside the master cylinder.

Once you compress the pushrod, it allows the primary and secondary reservoir to release brake fluid into the brake line. The brake fluid will allow your brake calipers to close, which will slow down your vehicle.

As you continue pressing your brake pedal, it will release brake fluid into your brake line to facilitate the braking process.

Break Master Cylinder Replacement Cost

The average cost to replace a master cylinder ranges from $350-$530, including parts and labor.

The parts of the master cylinder will cost between $130 and $250. The brand, make, and model of your vehicle will determine the overall cost. Typically, higher-end vehicles will require a more expensive master cylinder while older vehicles are typically cheaper.

The labor to replace the master cylinder cost between $200 and $300. It typically takes several hours to complete this task. Although it’s not a complicated job, it typically involves inspecting the other components of your brakes.

If your bad master cylinder caused damage to other parts of your brakes, such as the brake pads or calipers, this would increase the repair cost.

Sample Master Cylinder Replacement Cost

Since the cost to repair a master cylinder can vary depending on the make, model, and year you can compare the replacement cost to a car of similar value and style.

Typically newer vehicles or luxury vehicles will be more expensive.

Ford Explorer Master Cylinder Replacement Cost

A 2008 ford explorer master cylinder replacement cost will range from $ 230- $300, including parts and labor.

Ford Explorers are common and inexpensive SUVs. This makes replacing a bad master cylinder inexpensive because parts are readily available.

The parts for a Ford Explorer brake master cylinder cost between $65 and $130.

Labor will cost between $150 – $230. Since this is a common car that is easy to work on, labor cost is relatively low.

Honda Civic Master Cylinder Replacement Cost

A Honda Civic master cylinder replacement will cost between $350 and $430.

The parts will cost between $175 and $250, and labor will cost another $100 to $150.

These prices are similar for other Honda vehicles and similar brands such as Toyota, Hyundai, and Nissan.

Jaguar Vanden Master Cylinder Replacement Cost

The master cylinder replacement for a Jaguar typically costs between $350 and $650.

Parts for the Jaguar are typically expensive because they are harder to find and not as common as other vehicles such as Hondas.

You can expect to pay between $250 and $400. Labor can also be on the higher end because some dealers won’t work on Jaguars.

Labor will typically cost between $150 and $300.

Jaguars are a good comparison for other luxury vehicles such as BMW, Mercedes-Benz, Rolls-Royce, and Porsche.

You can expect brands such as BMW, Mercedez-Benz, Porsche, and Rolls-Royce to be on the higher end of the scale and even more expensive than Jaguars. On the other hand, brands such as Toyota, Lexus, Fiat, and Chrysler will be less expensive.

How hard is it to replace a master cylinder?

Replacing the master cylinder would be considered a moderate to difficult repair job. Although the overall replacement is not as difficult as other replacement jobs, multiple steps need to be taken to complete the replacement.

Two main steps you need to be comfortable with are removing the brake lines and bleeding the brakes. If you are not prepared or don’t have the right equipment to complete these tasks, you should not replace your master cylinder.

If you are familiar with cars and have done other repairs on your vehicle, you can consider replacing your master cylinder. Replacing your master cylinder is definitely for those who are mechanically inclined.

Do I Have a Bad Master Cylinder Or Air In Brake Lines?

A bad master cylinder and air in your brake lines cause the same issues. The main symptom of both is a sinking brake or a soft feeling brake. If you experience these issues, it can be hard to differentiate the issue.

Fortunately, there is an easy way to help you differentiate them. One easy step you can take is to drain your brake lines.

After draining your brakes, the sinking brake or soft brake feeling should go away. If this feeling doesn’t go away, then it’s likely you have a bad master cylinder. If the feeling goes away, then the issue was air in your brake lines.

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