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How to Spot a Bad Master Cylinder on Your Vehicle

Newton’s first law of motion tells us that an object will remain in motion unless acted upon by an outside force. You may not realize it, but your vehicle’s master cylinder plays a big role in your brakes, acting as an external force to slow or stop your car. 

Today, we’ll help you learn how to spot a bad master cylinder on your vehicle to keep you and your loved ones safe while traveling. Let’s get started.

What Is a Master Cylinder?

A master cylinder is a crucial component of a vehicle’s braking system. The entire braking system relies on it to do its job. If not, the brakes won’t function, and it will cause a dangerous situation. Your master cylinder must work correctly, and you should have it checked out at the first signs of any issues with your braking system.

Pro Tip: Find out How Do You Check RV Brakes? to keep yourself safe on the road.

What Does Master Cylinder Do? 

The master cylinder is a hydraulic pump for a vehicle’s brake system. After a driver presses on the brake pedal, the master cylinder sends hydraulic fluid through the brake lines. This increased pressure activates the second cylinder in the wheel’s braking mechanism, which drives the caliper piston to employ the brakes.

If your master cylinder works properly, it will evenly apply pressure to slow down the vehicle. You can watch for some things to know if you need to have your master cylinder or brake system checked out by a professional.

Close up of master cylinder
Your master cylinder is a crucial component of your vehicle’s braking system.

How Do You Know if Master Cylinder Is Bad?

First, if you ever experience issues with your brakes, get it to a professional immediately. One of the first signs that your master cylinder is beginning to fail is unusual behavior from your brake pedal. You may notice that the brakes are less responsive or that the pedal doesn’t return in place when you remove your foot from it.

Another major sign is noticing uneven brake pad wear. This means one set of brake pads will wear down faster than the other. When applying your brakes, you’ll feel the car weaving to one side. You may also notice leaking brake fluid pooling under your car. This could result from a seal leaking in your master cylinder and cause a lack of performance.

How Do I Change a Master Cylinder?

First, you must know what you’re doing if attempting to change a master cylinder yourself. Making a mistake when working with the brakes on your vehicle can be extremely dangerous. Familiarize yourself with the process, gather the necessary tools, and take your time to do it right. If you can’t, you should hire a professional.

Locate and Remove the Master Cylinder

To get started, chock the wheels of your vehicle to prevent the car from moving. Open your hood and disconnect the negative battery terminal. 

Next, release the vacuum pressure from the system by pumping the brake pedal a few times until the pedal is firm. You can now locate the master cylinder on your vehicle and remove the connection leading to the brake fluid reservoir. 

Disconnect the Brake Lines

Next, unscrew the mounting nuts and disconnect the brake lines from the brake fluid reservoir. Avoid getting brake fluid on anything as it’s highly corrosive and can cause damage to your vehicle’s paint. 

Then pull the master cylinder out and place it in a drain pan to catch any remaining fluid. Vehicles with anti-lock brakes will also need to disconnect the brake lines from the hydraulic control unit. 

While doing this, inspect the lines’ seals. Damaged seals can cause leaks, which will prevent the master cylinder from performing.

Close up of vehicle brake system with master cylinder.
Stay safe while on the road by continuously monitoring your master cylinder.

Prepare to Install the New Cylinder

Clean the mounting surface of the new master cylinder before bench bleeding it. You’ll need to mount the cylinder in a vice and plug in the cylinder’s outlet ports. Then place a drain pan under the cylinder and fill the reservoir with new brake fluid. You’ll start to see fluid drip from the outlet ports, so you’ll need to install the threaded plugs. 

Next, you’ll need a blunt tool to compress the master cylinder’s piston in three-quarters to one-inch strokes every 10 to 15 seconds. You should continue this cycle until you can no longer depress the piston more than an eighth of an inch, and you don’t see any air bubbles in the reservoir.

Reconnect Brake Lines and Mount the Cylinder

You can now install the brake lines from the old master cylinder onto the hydraulic control unit and new master cylinder. Now, mount the new master cylinder, tighten it, and reconnect the vacuum hose, hydraulic control unit, and brake lines. 

Finish up by reconnecting the electrical connector leading to the brake fluid reservoir, reconnecting the battery terminal, and bleeding the brake system.

Test the System

Once everything is back to normal, start the engine and test the brake pedal pressure. Test the brakes several times in your driveway before hitting the road. If all goes as planned, you’ve just changed the master cylinder, and you’re ready to drive.

Pro Tip: We uncovered Is It OK To Tow A Camper Without Trailer Brakes? to ensure your safety on the road!

Master cylinder product
While it’s not difficult to replace a master cylinder, if you have no previous experience, it is best to hire a professional.

How Long Does It Take to Replace a Master Cylinder? 

A professional can change a master cylinder in about an hour and a half. However, if you want to do this yourself, plan for it to take twice as long. Take your time not to feel rushed to avoid making a mistake.

How Much Is a Master Cylinder?

A master cylinder typically costs between $250 and $350, depending on your vehicle. If you don’t repair it yourself, you can likely expect to pay an additional $120 to $190 in labor. The total replacement will typically come to $370 to $550, but it depends on your car and service location.

Is Replacing Master Cylinder Hard?

It is not difficult to replace the master cylinder, but it does take some technical skills and knowledge of a vehicle’s components. It will not be easy if you’re not comfortable working on cars or don’t have the tools or space for the job. Because your brakes are an essential safety component of your vehicle, it might be best to leave this repair to the pros.

Have you ever had a master cylinder go bad? Drop a comment below!

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