Bad Master Cylinder Symptoms | The Definitive Guide

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rebbeca jones

This article is going to explore the subject of how to tell if the master cylinder is bad in particular detail. A deep dive into symptoms of bad master cylinder and what can be done about it alongside the replacement master cylinder cost has been discussed in depth here. 

Afraid your car is exhibiting bad master cylinder symptoms? You are in the perfect place! Read to the end to easily tackle your potential signs of a bad master cylinder.

Bad Master Cylinder Symptoms

Understanding a car’s engine can seem daunting, especially if you aren’t an automobile enthusiast. It is given that one puts a lot of trust in the vehicle they choose to drive. This makes it imperative for the driver to understand the car, at least at the primary level. This seemingly impossible task can be achieved by breaking the components down and understanding them individually.

This article will be looking at a critical component, namely the master cylinder. An in-depth look into its function and even the replacement master cylinder cost have been discussed here. 

Let us get into the main topic and other necessary particulars without further ado.

The most common master cylinder symptoms are warning light, brake fluid leak, spongy brake pedal, contaminated brake fluid, sinking brake pedal, bad brake lines, uneven brake pad wear, grinding noise, and the car pulling over to one side.

Bad Master Cylinder Symptoms: What is it?

Before diving into the actual symptoms, it is only fair to start by understanding this component in detail. So what is a master cylinder, and what defects in it lead to ‘symptoms of bad master cylinder’ that we should keep an eye out for?

Within the intricate web of components that constitute a modern disc braking system, including brake pads, calipers, and rotors, the master cylinder stands out as a remarkably essential cog in this complex mechanism.

So, how does it contribute to the braking system? As the brake pedal is depressed, the master cylinder springs into action, dispatching pressurized brake fluid to the caliper. This, in turn, compels the pads to compress against the rotor, generating friction that decelerates the wheel’s rotation.

The master cylinder’s role as the cornerstone of the braking system renders it the most vital component. Signs of a failing master cylinder should never be ignored, as it implies that the entire braking system is compromised, jeopardizing the safety of everyone on board.

 Bad Master Cylinder Symptoms: A Descriptive List

Now that we have understood the master cylinder as an extremely crucial part of the engine let us move on to the actual symptoms. 

Warning Light

One of the most common bad master cylinder symptoms is the warning light on your dashboard. If you observe a blinking light, it’s a clear sign that something is amiss. Remember that numerous master cylinder symptoms can overlap with other engine-related issues.

Pay attention to a flashing ABS light on your dashboard, as it could likely point to a problem with the brake master cylinder. This is often caused by fluid leakage, which has been discussed extensively in this context.

Brake Fluid Leak

Most master cylinder symptoms are caused due to brake fluid leaks. It should be noted that a certain level of brake fluid is ordered to create the required hydraulic pressure, which is needed to slow down the vehicle.

What happens with a leaking braking fluid which creates a bad master cylinder? Your low brake fluid level can be due to unsecured reservoirs on the master cylinder, which holds the fluid,

This, as well as other symptoms, hamper the ability of the engine actually to slow down the vehicle.

Replacement master cylinder costs vary across the states, but that is the only way to go in such a case,

Spongy Brake Pedal

A spongy brake pedal is one of the bad master cylinder symptoms that the driver can easily feel. 

While braking, the driver must put pressure on it with their foot, and if it feels spongy, there is a high chance that it is one of those flashing bad symptoms.

How is a spongy brake pedal one of the ‘symptoms of bad master cylinder’? Let us understand its mechanism in order to answer that question.

The master cylinder has a rubber seal that ensures the brake fluid is inside. This is extremely important for the smooth functioning of the braking system as a damaged, malfunctioning, or worn-out cylinder rubber seal is a major reason for internal leaks of brake fluid in the engine, which is responsible for the ‘spongy’ feeling.

Contaminated Brake Fluid

Another one of the symptoms of bad master cylinder is dirty or contaminated brake fluid in the engine. It is a major cause of worn-out or damaged rubber seals in the master cylinder.

This seal, as mentioned above, is critical as it keeps the brake fluid inside as well as ensures that there is no dirt, dust, or other debris getting mixed up with the braking fluid.

Sinking Brake Pedal

Yet another common bad master cylinder symptoms is the sinking brake pedal which can be recognized easily by the driver.

What does a sinking brake mean? If you notice that your brake pedal doesn’t return to its original position after applying pressure and appears to sink to the vehicle’s floor, be vigilant. This is among the most concerning and pressing symptoms of a faulty master cylinder. This situation presents a significant driving hazard, potentially leading to severe and even fatal accidents.

Bad Break Lines

There are generally two different circuits in the master cleaner that separate the brake fluid as required to the wheels in pairs. This is because it prevents loss of braking and further damage, even if there is a leak in one side of the braking mechanism.

These two circuits control one front wheel and the rear wheel on the opposite end. How is this connected to a bad master cylinder?

If there is a failure in one of these two circuits, you will notice that the vehicle will seem to pull to one side under the braking effect. If so, there is a clear indication that you need to get your master cylinder symptoms looked at.

Uneven Brake Pad Wear

Another common worn-out symptom of a bad master cylinder is uneven wear out of the brake pad. The reasoning for the same is quite simple. A failing circuit fundamentally causes rough brake pads within the master cylinder, preventing you from adequately applying brakes. You will notice that the left or right brake pad is worn out more.

Grinding Noise 

One of the most evident bad master cylinder symptoms is a deep grinding noise whenever the brakes are applied. Noise coming from the engine always causes concern. It should be remembered that the noise you would be hearing is not one of the direct master cylinder symptoms that indicate that it is falling apart entirely but only due to the brake material, which would have been worn out.

Another reason for the same could be unevenly more pressure on the front or rear brakes than usual, leading to premature wear and tear that will further cause the unpleasant grinding noise.

Car pulling Over To One Side

Another extremely noticeable symptom is the car pulling over to one side whenever the brakes are applied. But how so? If the car’s brakes receive uneven pressure on both sides, the brakes tend to pull the car to either side.

Master Cylinder Replacement Cost

Now that we have discussed ‘symptoms of the bad master cylinder’ in-depth, we can finally look into what can be done about it. The safest option while thinking of possible solutions is a replacement. What does the average master cylinder cost? Can one tackle this problem on one’s own?

For those skilled in using fundamental tools and possessing knowledge of the engine and braking system, handling evident malfunctioning master cylinder symptoms independently is achievable. It’s essential to remember that a vehicle’s braking system is an exceedingly sensitive and critical aspect of the engine.

Therefore, it should not be interfered with unless one has the necessary automotive expertise, as this could lead to additional damage.

Suppose you’re dealing with a defective master cylinder and wish to replace it at home. The procedure is relatively simple in that case: unbolt the master cylinder from the firewall, disconnect the brake lines, and install the new component. Subsequently, bleed the brake system, keeping a repair manual close by for reference.

By addressing the master cylinder issue yourself, you can eliminate labor costs and save a considerable sum.

To calculate the replacement cost, consider the part’s price and labor fees, which vary depending on location. The component generally costs between $100 and $200, while labor charges can easily exceed $200, sometimes nearing $300. Engaging a mechanic for this task may double the latter expense.

While the DIY approach can be cost-effective, if you’re uncertain about your abilities, it’s wise to enlist a mechanic to resolve the ongoing cylinder problem, ensuring no further harm comes to the engine.


Is it hard to change a master cylinder?

Replacing a master cylinder isn’t exactly rocket science; on the contrary, it’s a simple task for most car models. However, it’s a job here. Your hand will get dirty as it may include removing components, wires, and hoses. Little preparation is also necessary as the job involves keeping track of all the comments and respective fasteners. Lose them, you might be in trouble, and you won’t be able to assemble components properly.

How long do master cylinders last?

A master cylinder will generally last for 60,000 to 200,000 miles. Like all other mechanical components, the master cylinder will eventually wear out. How long a master cylinder will last depends on how often you use your brakes while driving. With less pressing brakes, your master cylinder will survive.

Can I drive with a bad master cylinder?

It’s unsafe to drive a bad master cylinder as it will cause the brake fluid to leak out due to internal damage, and your brake pedal could sink to the floor, which might cause the brakes to fail.

How do you test a brake master cylinder?

The quickest method to test a brake master cylinder is by using a screwdriver. Press and hold ht plunger through the screwdriver in the rear of the master cylinder. The plunger should be at least firm, if not immovable, after a few millimeters. If the plunger keeps moving in, it signifies a fault of at least one of the internal seals.


This article has deeply analyzed bad master cylinder symptoms in the hope that you understand your vehicle better. Your safety depends on this small yet important component of the vehicle, so it is crucial to keep a look out for the master cylinder and tackle them as soon as they are noticed.

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rebbeca jones

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