6 Symptoms of a Bad Brake Master Cylinder (& Replacement Cost)

Have you noticed your car’s brakes feeling spongy or unresponsive? It could be a sign of a faulty master cylinder. This small yet important component is essentially the heart of your vehicle’s braking system and vital to reliable braking operation. Any problem with the master cylinder should be addressed immediately.

This article discusses the most common symptoms of a bad brake master cylinder, how much it could cost to replace it, and important steps to take before it’s too late and put you in a dangerous situation.

6 Bad Master Cylinder Symptoms

The most common symptom of a bad master cylinder is abnormal brake pedal behavior, such as the brake pedal feeling spongy, soft, or keep sinking toward the floor. This issue should promptly be addressed, and ignoring it can cause inconsistent braking, reduced braking ability, and, worst case, even brake failure.

Here’s a closer look at the most common bad master cylinder symptoms:

1. Spongy, Soft, or Abnormal Brake Pedal

One of the most common and first symptoms of a bad brake master cylinder is abnormal brake pedal behavior. So if you’re having trouble with your brake pedal, it might be time to check out that trusty old brake master cylinder. 

It’s the brain of the braking system, responsible for generating all the pressure that makes your car stop on a dime. When it starts malfunctioning, you might notice the brake pedal behaving strangely. 

It might feel spongy, soft, or mushy underfoot, and ignoring a faulty brake master cylinder can be a recipe for disaster. It’ll wear out faster, start leaking all over the place and might even take the rest of your brake system down with it

2. Dashboard Warning Lights

Another common symptom that indicates a bad brake master cylinder is the check engine light or brake warning light popping up on your dashboard, especially in newer vehicles. 

Many newer vehicles have sensors installed in the master cylinder designed to detect brake fluid pressure problems. A fault code is stored in the vehicle’s OBD (on-board diagnostic) system if these sensors detect a pressure drop.

The good news is that a code reader will allow you to pull the codes and read them off easily.

3. Contaminated Brake Fluid

If the brake master cylinder is faulty, there’s a possibility that the master cylinder is letting moisture into the system, but more likely, that wear from rubber seals or metal shavings contaminates the fluid from an internal piston tear or even failure.

The brake fluid in good condition should be lightly golden and clear in color. If the color gets darker, the fluid becomes dirtier and more contaminated. 

4. Brake Pedal Sinks to the Floor

Another possible bad master cylinder symptom is if the brake pedal is sinking closer to the floor than usual when you press it. Normally, there should be a firm resistance in the brake pedal as the master cylinder creates pressure in this closed system, forcing your brakes together to slow down your vehicle.

So if the brake pedals sink to the floor, it either means the master cylinder is faulty and struggles to provide the pressure needed, or the system isn’t as closed as it used to be. In other terms, there’s a leak.

5. Leaking Brake Fluid

A master cylinder is responsible for transferring the force from the brake pedal to the brakes with the help of hydraulic fluid. So if you see a puddle under the front of your car, it could indicate that your brake master cylinder is faulty.

If this is the case, you’ll likely notice the brake fluid level in the reservoir is low or empty.

This is something you should address as soon as possible. And even if topping it off helps for a short time, it shouldn’t be considered a long-term solution. 

Losing your braking pressure and performance is a scary situation you don’t want to find yourself in.

6. Grinding Noise When Brakes Are Applied

It’s never a good sign when you hear a grinding noise while applying your brakes. But while this noise usually indicates excessively worn brake pads, the brake master cylinder can actually be at fault here.

A bad cylinder can be the culprit by applying more pressure than normal to the front or rear brakes, prematurely wearing out the brake pads. This, in turn, causes the grinding noise.

So if you noticed your brake pads wearing faster than normal, don’t wait to get this checked out. It’s better to be safe than sorry when it comes to your brakes.

What Causes a Brake Master Cylinder to Fail?

There are several causes of a bad brake master cylinder. But apart from normal aging, wear and tear, here are the most common causes of a brake master cylinder failure:

  • Worn or damaged seals
  • Contamination in the brake fluid
  • Corrosion or rust in the brake system

The most common cause is worn or damaged seals. These seals are responsible for keeping the brake fluid within the system, so if they become damaged, leaks can occur, leading to a loss of brake fluid and reduced braking ability.

Another potential cause is contamination in the brake fluid. Over time, brake fluid can become contaminated with dirt, debris, and other contaminants, which can cause issues with the master cylinder and other brake system components.

Finally, corrosion and rust are other potential causes of brake master cylinder failure. When moisture enters the brake system, it can cause the lines and other components to rust from the inside, preventing the master cylinder from functioning properly. This can lead to reduced braking ability and potentially dangerous situations on the road.

How to Diagnose a Bad Master Cylinder

If you suspect that your brake master cylinder may be causing issues with your vehicle’s braking system, there are three different steps to diagnose the problem. First, it’s a good idea to start with a visual inspection

1. Make a Visual Inspection

Look for any leaks or damage around the master cylinder. If there is wetness or clearly a fluid leaking from the master cylinder, it needs to be replaced. However, if there’s a puddle of fluid near your wheels or fluid leaking far away from the master cylinder, it’s likely not coming from the master cylinder itself. Instead, you need to determine where the leak is coming from.

2. Perform a Pressure Test

Next up is testing the brake master cylinder. So grab a friend, family member, or neighbor and have them sit inside the car and apply and hold pressure to the brake pedal as you observe the fluid level in the brake fluid reservoir. If you notice bubbles forming or that the fluid level rises as they press the brake pedal, it’s a clear sign that your master cylinder is not working as it should and will most likely need to be replaced.

3. Check For Trouble Codes

Finally, you can use a diagnostic tool to check for fault codes that might indicate an issue with the brake master cylinder. As mentioned earlier, in newer vehicles, a faulty code will often be stored as your car senses the fluid pressure or level is different than expected.

How to Fix a Bad Brake Master Cylinder

If you determine that the brake master cylinder is faulty, you want to take your car to a mechanic immediately or tackle the issue by replacing it yourself. Either way, it has to be fixed as soon as possible.

Replacing the master cylinder is typically not a difficult procedure, and it should only take a couple of hours if you decide to do it yourself. However, with many newer models, it’s much less accessible, which could make the procedure harder. 

Here’s normally the procedure of replacing a master cylinder usually includes these steps:

  1. Set the parking brake and put the transmission in park.
  2. Suck the remaining fluid out of the reservoir and use a wrench to loosen the brake lines.
  3. Remove all the mounting bolts, sensor connectors, brake lines, and any other parts connected to the master cylinder.
  4. Unclip the piston rod from the brake booster.
  5. Install the new brake master cylinder.
  6. Fill the master cylinder with the correct brake fluid (as specified in your owner’s manual).
  7. Bleed the air from the brakes at each wheel, making sure the reservoir never empties.

If you feel the job is above your head and you feel uncomfortable doing it, it’s best to have a mechanic handle the repair. 

How Much Does a Brake Master Cylinder Replacement Cost?

The cost of replacing a brake master cylinder can vary significantly depending on your vehicle’s make and model, the specific parts and labor needed, as well as the location of the shop. But on average, you can expect to pay between $250 and $400 for this repair. Diagnosis fee, labor, and parts included.

It’s important to keep in mind that this is just a rough estimate, and the actual cost may be higher or lower.

Typically, the labor cost for this repair will make up most of the total cost. Depending on your location and the mechanic you choose, you can expect to pay anywhere from $100 to $200 or more for labor. 

The cost of the actual brake master cylinder part will vary as well, but you can expect to pay anywhere from $50 to $150 or more, depending on the specific part needed for your vehicle.

When replacing a brake master cylinder, you have two options: replacing it with a new one or repairing the existing one. While repairing a brake master cylinder can often be less expensive in the short term, we always recommend replacing the brake master cylinder with a new one to ensure the best performance and reliability

What Happens If a Brake Master Cylinder Fails?

If a brake master cylinder fails, the brakes will either not work at all or will not work as effectively as they should. This can be dangerous and potentially lead to accidents if the vehicle is not able to stop properly. You may experience inconsistent braking, reduced braking ability, or no brakes at all.

1. Inconsistent Braking

Inconsistent braking refers to a situation where the brakes on a vehicle do not consistently provide the same level of braking force or stopping power. One second the brakes might work fine, and the next second you might not be able to stop at all.

2. Reduced Braking Ability

If a master cylinder begins to fail, it might not be able to provide the necessary pressure required, and if this happens, it’s common to lose brakes in either the front or back – significantly reducing the braking ability.

3. No Brakes

In the worst-case scenario, you could find yourself in a situation with a brake master cylinder that can’t create any pressure at all, which means no brakes at all. However, this doesn’t happen very often, but it’s still a possibility worth mentioning.

Frequently Asked Questions

1. How Long Does a Master Cylinder Usually Last?

A brake master cylinder is built to last as long as the car does. However, depending on use, most times, a typical master cylinder doesn’t make it that far and usually lasts between 60,000 to 200,000 miles. As with all mechanical and hydraulic devices, it can fail to wear and tear.

2. Can You Drive With a Bad Master Cylinder?

Even if you can drive with a bad master cylinder, you shouldn’t. A faulty master cylinder puts your whole braking system at risk, and ignoring it could potentially put you, passengers, and other road users in danger. Instead, let a professional take a look to find out whether or not a replacement is required.

3. Can Master Brake Cylinder be Repaired?

Many times it’s possible to repair a leaking brake master cylinder if the cause is worn-out seals. However, since your brakes are such a vital part of your car’s safety, it is recommended to replace the master cylinder with a new one, especially if the master cylinder is broken or faulty. 


In conclusion, the brake master cylinder is vital to your vehicle’s braking system. If you notice any of the symptoms of a bad brake master cylinder, it’s important to address them as soon as possible. 

Regular maintenance and inspection of your braking system can help to prevent issues with the master cylinder and keep your brakes in good working order.

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Rickard Cefalk

Rickard is the owner of Caraspect.com and a dedicated and avid do-it-yourselfer who has always enjoyed working on his own vehicles since childhood. He now devotes his time to sharing his expert knowledge of car maintenance and other car-related information through his website.

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