Bad Brake Master Cylinder Symptoms, Causes, And How To Test It

The brake master cylinder is one of the crucial parts of your car’s braking system. If you’re encountering brake-related issues, it is possible that there is something wrong with your brake master cylinder. Learn the bad brake master cylinder symptoms, its causes, and replacement cost.

Symptoms Of Bad Brake Master Cylinder

As you press the brake pedal of your vehicle to decelerate or stop it, the braking mechanism utilizes the brake master cylinder. This component transforms the force you apply to the brake pedal into hydraulic pressure.

This transformation happens as the master cylinder supplies brake fluid into the brake circuit while you engage the pedal. This article deeply explains the bad brake master cylinder symptoms, causes, and how to test it.

What is the Function of a Brake Master Cylinder?

The brake master cylinder of a vehicle plays a pivotal role in the brake system. It converts the pressure applied to the brake pedal into hydraulic force that triggers the brake caliper.

Brake Master Cylinder

A malfunctioning brake master cylinder can significantly reduce the performance and responsiveness of the brake system, jeopardizing the safety of the vehicle occupants.

Usually situated in proximity to the brake pedal, the master cylinder is linked to the pedal via a push rod. As the driver pushes the brake pedal, the push rod propels the piston within the brake master cylinder. This action pushes brake fluid through the brake lines to the brake caliper.

These brake calipers then exert pressure on the brake pads against the brake rotor, causing the wheels to slow their motion and bringing the car to a halt.

The brake master cylinder is internally divided into two chambers—one for the rear brakes and the other for the front brakes. Upon pressing the brake pedal, both chambers receive pressure at the same time, which makes the brakes work smoothly.

Symptoms Of A Bad Brake Master Cylinder

A spongy or soft brake pedal is one of the most common symptoms of a faulty brake master cylinder. A bad brake master cylinder may also lead to a hard pedal or poor braking power.

The following are the most common symptoms of a bad brake master cylinder:

1) Spongy Or Soft Brake Pedal

Soft Brake Pedal

Much like other brake complications, a pedal that feels spongy is usually among the initial symptoms of potential issues. If you find yourself exerting increased force on the brake pedal to completely stop your vehicle, it’s possible that your brake master cylinder is damaged or leaked. 

The presence of spongy brakes is a prevalent brake-related problem, and it may stem from factors beyond the master cylinder.

For instance, it might signify the presence of air within the brake lines. In such a scenario, the remedy involves bleeding the brakes to eliminate all air and ensure optimal functionality. Spongy brakes may also result from factors like a malfunctioning brake booster, a compromised caliper, or inadequate brake fluid.

2) Hard Brake Pedal

Brake Pedal

A bad brake master cylinder may also cause a hard pedal. This occurs when the master cylinder sustains damage, potentially causing the brakes to lock up.

Nevertheless, several more prevalent issues can lead to this condition. For instance, it’s advisable to initially inspect the brake booster, along with its associated hose and check valve, when troubleshooting this problem.

3) Erratic Brake Power

When the master cylinder malfunctions, the performance of your braking system can become erratic. One moment, the brakes might operate normally, and the next, they could exhibit issues.

This condition poses a significant danger as it introduces uncertainty regarding the braking force that will be delivered.

4) Reduced Brake Power

When the master cylinder’s functionality deteriorates, you might encounter difficulties in bringing the vehicle to a timely stop. This reduced braking capability may potentially lead to accidents if caution isn’t exercised.

Once again, there exist several potential culprits for the same issue. Faulty brake lines, dirty brake fluid, or malfunctioning components may also contribute to the problem at hand.

5) Check Engine Light Illumination

Check engine light flashing

When the master cylinder in a modern vehicle becomes faulty, the check engine light starts to illuminate on the vehicle dashboard.

Modern braking system often integrates brake fluid pressure and level sensors within the master cylinder. These sensors serve the purpose of identifying any irregularities in the vehicle’s brake fluid pressure—a pressure that the master cylinder generates.

When the master cylinder sensor monitors a drop in pressure, it could indicate a potential problem with the master cylinder. Such complications could also trigger the illumination of a Brake Warning Light.

Read More: Brake Warning Light Causes

6) Brake Fluid Leaks

Brake Fluid leaks

The brake fluid of your system may also be leaked due to a damaged brake master cylinder.

Insufficient fluid levels result in decreased hydraulic pressure, consequently impairing the brake system’s proper operation. A noticeable indication is the continuous reduction of brake fluid in the reservoir, even after you’ve refilled the reservoir.

Furthermore, you might observe that the fluid within the reservoir appears dirty. Fresh brake fluid typically contains blue, clear, yellow, or red color, depending on the variant.

If your fluid looks cloudy or appears dirty, it’s advisable to perform a brake system flush. When you detect metallic particles within the fluid, it’s possible that your master cylinder is damaged internally, necessitating its replacement.

Read More: How To Change Brake Fluid?

7) Loss Of Brakes

Loss Of Brakes, Symptoms Of A Bad Brake Master Cylinder

Perhaps the most unsettling scenario is the complete failure of the brakes. Such an occurrence ranks among the most upsetting situations during driving, particularly at a higher speed.

The master cylinder of a vehicle acts as a hydraulic pump, exerting consistent pressure within the brake lines as you press the brake pedals. The improved version of the master cylinder generally prevents a total loss of brakes, but it’s possible to experience loss either in the rear or front.

The more frequent cause for the complete failure of the braking system could be a system leak resulting in the reduction of fluid. Without hydraulic fluid, your braking system can’t work efficiently.

Causes of Brake Master Cylinder Failure

The brake master cylinder of your brake system may become faulty due to one or more of the following causes:

  • Damaged master cylinder seals
  • Manufacturing faults
  • Dirty brake fluid
  • Corrosion
  • Excessive heat produced during heavy braking or due to a faulty braking system part
  • Insufficient brake fluid
  • Brake fluid leaks
  • Use of the wrong type of brake fluid
  • Normal wear and tear
  • Poor maintenance of the braking system. Regular maintenance includes checking for leaks, inspection of brake lines, and brake fluid replacement.

Brake Master Cylinder Location

The brake master cylinder is usually located beneath the brake fluid reservoir. To locate it, open your car’s hood and search on the driver’s side, typically positioned on the firewall.

Brake Master Cylinder Location

Recognizing the correct component is simple: it will feature either two or four brake lines linked to it, and it’s directly connected to the reservoir. If you encounter difficulties identifying the master cylinder, consult your service manual. This resource usually contains a brake system diagram that aids in pinpointing the parts’ locations.

Brake Master Cylinder Replacement Cost

The replacement cost of the master cylinder depends on your vehicle model, labor cost, and the brand of the part.

The average replacement cost of the brake master cylinder is between $240 to $460. In this cost, the cost of the parts is between $40 and $100, while the labor cost is $200 to $360

How Do You Test A Brake Master Cylinder?

Inspecting the condition of your brake master cylinder involves verifying the presence of adequate brake fluid. When the fluid is present, it will be pushed into the brake lines as the brake pedal is pressed. Upon releasing the brake pedal, the fluid will return to the cylinder.

Follow the following steps to test your brake master cylinder:

1) Open the Fluid Reservoir

If a plastic reservoir is positioned atop the master cylinder, unscrew the cap of the small plastic bottle. In the case of a metal reservoir, employ a screwdriver to detach the clamps. 

2) Check the External Leaks

Inspect the brake fluid level within the reservoir. Conduct a visual inspection of the master cylinder for a possible leak, including tank seals, sensors, brake line connections, and the connection to the vacuum brake booster. Examine the interior of the vacuum hose for any signs of brake fluid presence.

3) Check the Brake Pressure

Turn on the engine, press the brake pedal, and maintain the pressure for a minute. If the pedal sinks, this indicates a potential leak in your braking system.

4) Locate the Internal Leaks

While depressing the brake pedal, monitor the fluid level in the fluid reservoir. If the level increases, it suggests the chances of internal leaks within the master cylinder.

5) Checking by the method of blocking

  • Disconnect all brake hoses connected to the master cylinder
  • Let the air out of the cylinder by opening the bleed valve.
  • Put plugs into the spots where the hoses were connected.
  • Press the brake pedal down hard and check for any leaks near the plugs.
  • If the brake pedal goes down further, there might be a problem inside the cylinder.

6) Look Under Your Vehicle

Look beneath your brake master cylinder by using a flashlight for any signs of stains, sludge, or dampness. If you come across any of these indicators, it indicates that your master cylinder is leaked.

FAQ Section

What is the function of the brake master cylinder?

The main function of the brake master cylinder of a vehicle is to convert the pressure applied to the brake pedal into the hydraulic force that triggers the brake caliper.

How long can a brake master cylinder last?

The average service life of the master cylinder is at least 70,000 miles. Although it’s feasible for the master cylinder’s durability to exceed this mark, the rubber seals it contains tend to deteriorate gradually. When these seals wear down, they may lead to brake fluid leakage and diminished braking effectiveness.

Is a brake master cylinder hard to replace?

Replacing the brake master cylinder is typically not overly challenging. This cylinder is usually situated under the hood on the firewall, positioned beneath the brake fluid reservoir. The most intricate aspect is often bleeding the brakes. However, if you have the skill to perform your own brake maintenance, this step shouldn’t pose significant difficulty.

What does a bad brake master cylinder sound like?

Normally, brake master cylinder failure doesn’t produce unusual sounds. However, it leads to a range of performance problems. If you detect a hissing noise each time you apply the brakes, it’s more probable that the power vacuum booster is leaking and necessitates replacement.

Can you drive with a bad brake master cylinder?

Yes, you can drive, but it is not recommended to drive with a faulty brake master. However, it might initially cause minor braking problems; there is a potential risk of losing either rear or front brake functionality autonomously, which could lead to serious safety issues. It’s crucial to address this issue promptly.

What happens if the master cylinder runs out of brake fluid?

When your brake fluid reservoir doesn’t have brake fluid, you’ll encounter difficulties halting the vehicle while pressing the brake pedal. Furthermore, there’s a potential for harmful effects on most important parts, like the master cylinder, due to air retention within the system.

What does a bad master cylinder sound like?

Unusual brake noises are not typically linked to the master cylinder. A malfunctioning master cylinder might result in a soft or spongy brake pedal but typically doesn’t produce audible sounds. But if you notice a pronounced hissing noise upon braking, it could signify a vacuum leak within the power/vacuum brake booster.

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