How To Bleed a Brake Booster

How To Bleed a Brake Booster


Brake boosters are the unsung hero to your vehicle’s braking systems, a component not many drivers think about, but use every single day of their vehicle’s life. It’s primary function is to assist in stopping your vehicle, by boosting the hydraulic pressure that your brake master cylinder provides. Powered by the engine’s vacuum or even hydraulics in certain vehicles, when your brake booster stops working or is malfunctioning, you can have serious issues with stopping your car.

If your brake booster is not working correctly, excessive force may be needed to bring your vehicle to a complete stop, which can be dangerous to say the least.


Because your malfunctioning brake booster can no longer operate correctly, it still may be possible to stop your car without the use of the brake booster, it won’t be an easy job. Since it’s not doing it’s job, it can take much more effort and force from your leg depressing your brake pedal in order to stop the vehicle in time.

So in this regard, we aren’t so much bleeding the brake booster, as we are troubleshooting it. You can bleed your brake system however, and that’s one option to fixing your braking issues.

When you are bleeding your braking system, you are in essence removing any and all air pockets and bubbles in your brake line, restoring hydraulic pressure. While this process does not involve the brake booster per se, it’s important to service and know how to bleed a brake booster system for any leaks or possible problems.

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In order to repair and bleed a brake booster system, you will need to diagnose where the problem is in your hydraulic setup. This may include removal of your brake master cylinder, so make sure you have the proper wrenches on hand in the event you need to do this.

Locate the problem with your brake booster


Easier said than done, the biggest step to servicing your brake booster is to locate the problem with it. This can be a difficult task to undertake, because when your booster isn’t working your brakes are inconsistent or simply won’t work.

Whenever you have a problem with your vehicle’s brakes, you should have the brake booster tested to make sure it functions adequately. The steps on how to test your Brake Booster are as follows :

  1. Turn off vehicle
  2. Depress gas pedal
  3. Start car

After you have completed this step, you should feel your brake pedal compress slightly, which should make your brake pedal sink downward. Now allow the engine to build vacuum while idling for a bit, and then turn the vehicle off.

With the vehicle turned off, depress the brake pedal slowly and firmly and repeat this process. With each and every pump of your brake pedal, you should feel your brakes stopping higher and higher at each interval. This is the sign of a properly operating brake booster, and if your pedal behaves differently you need a replacement booster or to have your brake booster serviced.

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Removing the master cylinder


To service your brake booster, you will need to remove the brake master cylinder that drives the hydraulic fluid into your brake lines and your brake calipers. This should be directly connected to your brake booster, and is attached to the brake lines.

Use a box wrench or flare wrench to properly disconnect the brake lines in question, then unbolt your master cylinder and remove.

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Once you have this master cylinder removed, it’s time to turn to the interior of your vehicle and locate the brake booster bolts that connect it to your brake pedal assembly.

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If your master cylinder reservoir is not mounted onto the brake master cylinder, you may need to disconnect and drain this container first. Take care around your paint, as brake fluid is highly corrosive and will damage your paint if left uncleaned.

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With your brake master cylinder removed, it’s a good idea to bench test your master cylinder to eliminate that as a culprit in your braking problems. Master cylinders frequently fail when owners do not keep their brake fluid clean, which can contaminate the seals inside the master cylinder. Once these seals have been compromised, the master cylinder will fail to deliver the proper hydraulic pressure your calipers are expecting.

Check our How To Bench Test your Master Cylinder Guide here.

There’s a few things to check when you are trying to learn how to bleed a brake booster, because what you are really doing is bleeding your brakes. Never attempt to work on the brake system while the engine or car is running or moving. Always disconnect the negative terminal to your battery in the case of an electrical issue, and always clean your area of brake fluid.

Brake fluid is corrosive and can irritate your eyes and skin if left untreated or uncleaned. In short, knowing how to bleed a brake booster or bleed your brakes is a vital part of your vehicle’s maintenance.  Bleed your hydraulic braking system today to ensure proper engagement and positive feedback while stopping your car.