Do You Have To Bleed Brakes After Changing Pads

Do you have to bleed your brakes after changing the pads? You might have heard it from someone or your mechanic. This post is for you if you are unsure about it.

Bleeding your brakes is not always necessary after changing the brake pads. It depends on whether other brake system components are replaced, which is not always the case.

You only need to bleed the brakes if the brake line was disconnected or the brake fluid reservoir was opened for a considerable time.

Read on for more information about bleeding the brakes, including the various methods and steps to perform it yourself.

What Does it Mean to Bleed Brakes?

Bleeding brakes refer to removing air bubbles from the brake line. The air bubbles get into your brake system if the brake lines are disconnected or the brake reservoir is opened for a long time.

To understand how air bubbles affect the brake system performance, we should recap how it works. This system consists mainly of the brake pedal, brake lines, brake pads, brake fluid, and brake fluid reservoir.

When you step on the brake pedal and apply pressure, it is resisted through the brake fluid in the lines. Brake fluid transmits this pressure equally to all four wheels and amplifies it.

The hydraulic pressure transmitted to the brake pads presses them against the brake rotors. That resists the wheel’s rotation, thereby stopping the car.

One of the main properties of brake fluid is that it is incompressible. That allows it to generate uniform hydraulic pressure to stop the car.

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If the air bubbles get into the brake line, it compromises the property of the brake fluid. Air is compressible. That means the brakes may fail to stop the car when needed. In some cases, the vehicle may take longer to halt.

The brakes will feel spongy when depressed if air bubbles are trapped in the brake lines. This is why you need to bleed the brakes.

Do You Have to Bleed the Brakes After Changing the Brake Pads?

Working on the brake system requires expertise because you trust the brakes with your life. One of the most common tasks is changing brake pads. So, do you have to bleed brakes replacing them?

Whether or not you should bleed the brakes after changing the brake pads depends on how it is done. As mentioned, it is only necessary when the brake lines are disconnected. Or, the reservoir is opened.

Opening the brake lines allows air into the system, which should be removed. On the other hand, opening the brake fluid reservoir allows the brake fluid to absorb moisture from the air.

Water has a low boiling point. So, the moisture absorbed by the brake fluids will form bubbles when the temperature rises. This situation will make the brakes feel spongy.

However, you may need to bleed the brakes after replacing brake pads if other system components were also replaced. Let’s find out more in the next section.

When to Bleed Brakes

Drum Brake Cylinder Replacement or Disc Brake Caliper

Your car can have either a drum brake cylinder or a disc brake cylinder, but all-wheel drive vehicles mostly have disc brake calipers. Regardless, replacing these components necessitates brake bleeding.

Removing and replacing the drum brake cylinder and/or disc brake caliper requires disconnection of the brake line, which allows air into the system. That is why brake bleeding should be done in this case.

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Piston Caliper Compression

You or your mechanic may need to release the exhaust valve while changing the brake pads. This compresses the piston, which might allow air to get into the brake lines.

A brake caliper is a stationary assembly you see over the rotors. It houses brake pads, which move when you depress the brake pedal to decelerate or stop your car.

Other Brake System Components Replacement

Any brake system component that requires the brake lines to be disconnected or the brake fluid reservoir to be opened requires you to bleed the brakes. Removing them will allow air to get into the system.

Also, failure of these system components may allow air into the brake lines. For example, any repair in the master cylinder necessitates brake bleeding.   

How Long Does It Take to Bleed Brakes?

You can bleed your brakes in 30-40 minutes for the four wheels depending on the method. You may also need someone to depress the brake pedal to make the process faster.

However, do not attempt it if you are unsure of your DIY skills. Working on the brake system requires confidence because it is a life-saving system in your car.

Common Ways of Bleeding Brake Fluid

These methods can help you bleed your brakes. The one you choose depends on the tools you have, and the time it takes varies from one to the next.

Gravity Method

The gravity method is the easiest but not the most effective or efficient. It involves opening the brake bleed screws and letting the brake fluid flow out of the system by gravity. As the fluid drains, the trapped air bubbles also get out.

Manual Method

As the name implies, you manually remove brake fluid and air bubbles from the brake line. Open the brake bleed screw and place a container below it to catch the draining fluid.

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Finally, slowly depress and release the brake pedals to push brake fluid and air bubbles down the line. Be gentle here to avoid the formation of more air bubbles.

Pressure Method

This is the fastest and best method if you don’t have someone to help you. It involves attaching a pressure pump to the master cylinder to increase the system’s pressure, after which you unscrew the brake bleed screw.  

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Vacuum Method

This is the reverse of the pressure method. It is also fast and reliable. To perform this, you need a vacuum pump, which you attach to the bleeder valve once opened. The vacuum pump is opened to suck out all the fluid and air bubbles in the system.

How to Bleed Brakes: Tools Needed and Step-by-Step

You can bleed your brakes using any method from the list. We will describe the manual technique here because you may not have the equipment for other brake bleeding techniques. So, it is best to find a second person to help you.

To bleed your brakes, gather the following:

  • Brake cleaner
  • Box-end wrench for opening the bleeder screws
  • Additional brake fluid
  • A disposable container for holding the waste fluid
  • A helper (can be a family member or a friend)

Proceed as follows if you have everything ready:

  1. Create a small hole for fitting the silicone pipe on the top of the disposable container. You can also use a caliper bleed nipple if you have it but not necessarily.
  2. Park the car on flat ground and use a jack to raise it up. This will create enough space to access each brake, and you may need to remove the wheel.
  3. Ask your helper to get into the driver’s seat and be ready to depress the brakes on command.
  4. Use the wrench to unscrew the bleeder valve and place the bleeder container to catch any draining fluid without causing spillages. Ensure the container is stable.
  5. Ask the person in the car to slowly depress the brake pedal and open the bleeder valve. Close the valve as soon as the brake pedal goes down to the carpet.
  6. Repeat the above steps on other wheels until the brake fluid that comes out is clearer.
  7. Test the brake system for any air bubbles. You should repeat the steps if it feels spongy.

FAQs

Do you have to bleed four brakes?

Yes. It is highly recommended to bleed all four brakes, even if you only opened one brake line when working on the brake system. It should take you about half an hour to complete the process.

How long does it take to bleed brakes?

The time it takes to bleed the brakes depends on the method used. But generally, it should take only 30-40 minutes to do it on all four tires.

Can I bleed brakes with tires on?

Yes. You can bleed your brakes with tires on if you can access the bleeder valve and have no problem fastening and loosening it. But removing the wheels will give you more space.

Do I need to bleed the brake after changing the caliper?

Yes. Changing the caliper requires the disconnection of brake lines, which allows air to get into the system. Bleed the brakes to remove the air bubbles after replacing the caliper.

How much do mechanics charge to bleed brakes?

It will depend on the car brand and model and where you take your vehicle for this service. Mechanics typically charge anywhere between $20 and $200 to bleed brakes.

Why are my brakes still spongy after bleeding?

Your brakes feel spongy because there are air bubbles trapped inside. That might happen if you miss a step when doing it. So, you should repeat the process to ensure all air bubbles are expelled from the brake system.

What is the difference between bleeding and flushing your brakes?

By definition, flushing brakes means removing all the old brake fluids from the brake system and replacing them with new ones. On the other hand, bleeding brakes involve removing enough fluid to expel any trapped air bubbles.

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Final Remarks

Bleeding brakes after changing brake pads depend on other factors. You may or may not do it. You should do it if the baking line is disconnected or the brake fluid reservoir is opened.

Situations that require brake bleeding include replacing the disc brake caliper or drum brake cylinder. You should also bleed the brakes if the caliper piston was compressed when changing pads.

Bleeding brakes remove air bubbles that make the brakes feel spongy and fail to stop the car when needed. You should, therefore, never skip it when it should be done.

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