Here’s How To Bleed a Brake Master Cylinder

Let's bleed'em until they stop again.

Time Needed: 1-2 hours, Difficulty: Medium, Cost: ~$30

*TV Infomercial voice*

“Is your brake spongy? Have you found yourself without adequate brake feel or pressure? Have you recently introduced the front of your vehicle to that tree over there through less than amorous conditions? Well, fine people of Car Bibles, have we got the right fix for you! It’s known as bleeding your brake master cylinder!”

Our dad jokes aside, air trapped in your brake master cylinder is no laughing matter. It means less braking force, more braking distance, and a far more likely chance of you ending up in a ditch or connecting with the Prius in front of you. Bleeding your brakes and brake master cylinder of trapped air is a high priority when it occurs, so let Car Bibles’ editors show you the way to do it right!

Let’s begin.

A Brake Master Cylinder and how it works.
A Brake Master Cylinder and how it works. Depositphotos

What Is a Brake Master Cylinder?

A brake master cylinder is a primary mechanism that pushes brake fluid to and from your brake system. Essentially, it ensures you come to a safe and complete stop when you hit the brake pedal.

How Does a Brake Master Cylinder Work?

The cylinder is filled with brake fluid that, when actuated through the brake pedal, is pushed through the cylinder by a piston and to the brakes.

Do You Need to Bleed Your Brake Master Cylinder?

When air enters the cylinder, it provides less braking force and requires longer stopping distances. That’s unsafe and could lead to an accident, so yes, you do need to bleed your brake master cylinder.

The Safety Brief

We want for you to exit the garage with all the fingers you went in with. There’s no need for safety to come third, make it first.

To ensure your skin stays unblemished and your bones intact, you’ll want to first and foremost wear some clothes you don’t mind getting dirty. Second, grab a pair of mechanic’s gloves. And lastly, make sure you’ve let the car cool before you work underneath the hood.

Refilling a brake master cylinder.
Refilling a brake master cylinder. Depositphotos

The Tools & Parts You Need

A trip to the auto parts store can be a time-suck. Don’t spend the day twiddling your thumbs waiting for a package or driving to and from the store.

Get everything the first time, such as: a brake bleeding kit, a length of clear plastic tubing sized to your bleeder valve, a container, a selection of wrenches and screwdrivers, and new brake fluid.

You’ll also need a friend, partner, child helper, or very well-trained dog.

The Job: How To Bleed a Brake Master Cylinder

Let’s get after it.

Pop the Hood

Locate the brake master cylinder. It should be near the firewall on the driver’s side of the car.

Remove the Brake Master Cylinder Cap

Remove the brake master cylinder cap and pour in new brake fluid. You’ll want to make sure it’s topped off so that no air returns into the cylinder during the bleeding process.

Find the Bleeder Valve

Find the bleeder valve on the master cylinder and attach your clear plastic tubing or the bleeder kit as directed.

Have Your Assistant Hop Into the Car

With your assistant in the driver’s seat, have them press the brake pedal three to five times then press and hold the brake pedal all the way down.

Open the Bleeder Valve

Open the bleeder valve and allow the fluid to flow through. If there’s air in the master cylinder, it’ll start coming through as bubbles in the tubing. Close the valve and repeat until no more air bubbles come through.

The Questionnaire

Car Bibles answers all your burning questions!

Q: Do I Have to Bench Bleed My Brake Master Cylinder?

A: You don’t. Though many will argue it’s more thorough, bleeding it while the master cylinder is still in the car will work.

Q. Do You Have to Leave the Master Cylinder Cap Off During Bleeding?

A: Yes.

Q. Why Are My Brakes Spongy After Bleeding?

A: It could be a few things, but the most likely reason why your brakes are still spongy is that there’s still air in the lines. The second most likely reason is that you forgot to close the bleeder valve/reconnect the master cylinder cap.

The Brake Master Cylinder Video Tutorial on Bleeding Your Brake Master Cylinder

Car Bibles’ editors understand that not everyone is a text-based learner. For those kinesthetic people out there, we have your back with a video showing you exactly how to bleed your brake master cylinder. We pulled it from one of our favorite, and most trusted, sources and it’s a great additional resource.

Car Bibles’ Favored Brake Tools

You can buy tools to work on your brake system at almost every auto parts and home improvement store. As well as online stores like Amazon. You have a sea of options to select from. Why even deal with all that uncertainty when you can just listen to us? Such as these bench vises, new brake pads, or brake rotors.

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Jonathon Klein

Jonathon KleinJonathon has jumped Aston Martins for Automobile Magazine, clocked 200 mph in a McLaren 720S for Playboy, and sampled his best life behind the wheel of a Ferrari Dino Evo for Road & Track. He’s hopelessly addicted to the strongest coffee he can brew. Please send him more. Contact the author here.