Here Is Everything You Need To Know About Air In Brake Lines

Air in brake lines: If we support one thing it is responsible and safe motoring. That is why we never condone delaying important car maintenance in order to save a few pennies here and there. The two main components where you should absolutely avoid saving money and ignoring problems are your brakes and your tires. Both need to be in perfect condition, and nothing less is acceptable. 

Today’s topic is a bit “weird”. We are going to walk you through everything you need to know about the air in your brakes. Yes, air. This simple little problem can actually be far more dangerous and unpleasant than you might imagine. You will find out how to recognize symptoms of air in brake lines, how to remove that air, and how to make sure it never returns. Let’s dive in!

What causes air in brake lines?

Generally speaking, air can get trapped in brake lines in three ways:

  1. Air can enter the brake system during repairs and if bleeding the braking system is done incorrectly.
  2. Air enters the brake system through a leak or if your brake pads are worn out. In the case of worn-out brake pads, the hydraulic pistons have to extend further to push what is left of the brake pad against the brake disc. As this happens, it creates a void in the brake system causing air to enter the system.
  3. Air can actually get into the brake system through water. Brake fluid is hygroscopic, which means it absorbs and holds water. As your brake system eventually goes through a hard braking event (driving downhill for instance), the brake fluid can actually start almost boiling. This is especially common when there is water already in the system. When the temperature rises, steam forms on top of the brake fluid container, and eventually the braking system turns this steam into water. The air that separates from the water becomes trapped in the brakes.

Is air in brake lines dangerous?

Yes, air in brake lines is very dangerous. Small air bubbles in brake lines can eventually gather and join into a big air bubble which can lead to a complete brake failure or a serious loss of pressure causing poor braking performance.

The hydraulic pressure in the brake system is supposed to compress brake fluid and force the brake pads to press against the brake discs. If there is air in the system, what gets compressed is the air and not the brake fluid. 

What are the symptoms and signs of air in brake lines?

Until you experience air in your braking system it is hard to understand the symptoms we will describe as we continue. Here are the symptoms and signs there is air in the brake system:

  • The brake pedal seems oddly soft and “mushy”
    When you normally press the brake pedal, you can feel a certain level of resistance, you feel like you are pushing something against something, you know? If there is air in the brake system, this feeling is gone. The brake pedal feels incredibly soft and mushy, which is not alright.
  • The brake pedal feels “spongy”

You are probably asking yourself how a “spongy” brake pedal is different compared to soft and “mushy”. The best way to describe this is that you actually feel the brake pedal bouncing back at you a bit. This is actually a consequence of compressed air “fighting” and expanding back.

  • Braking performance is severely impaired

Having to brake with a significant amount of air in the brakes takes a big toll on the braking distance and overall performance. You will instantly know that something is not right with your brakes. Have them inspected immediately.

Will air in brake lines go away on its own?

No, without intervention by a mechanic, air will not just escape out of brake lines. The braking system is air-tight, which means that the only way air is going to escape is through a leak or by bleeding out the entire braking system. Do not wait for these symptoms to go away on their own, because they are not going anywhere, in fact, they can only get worse and more dangerous.

Do you have air in brake lines or a bad brake master cylinder?

This is a good question, and yes both soft and spongy brake pedal feel can be a symptom and a sign of a bad brake master cylinder. However, a bad brake master cylinder will also cause the brake pedal to sink to the bottom, in more modern cars you will be alerted of a bad brake master cylinder with a warning light, and your brake pads will be unevenly worn out and your brake fluid will become contaminated.

In the end, it doesn’t matter what the problem is, whether it is air in the brake lines or a bad brake master cylinder, you should immediately visit a mechanic to diagnose the issue. If bleeding the braking system resolves the issue, there was air trapped in the brake lines. If the problem persists, your mechanic will turn to the brake master cylinder and look for faults.

How to remove it

Air can be easily removed from the braking system through a process called “bleeding”. Bleeding the brakes can be done at home but it is recommended that you allow a professional to do the bleeding if you do not have the appropriate tools and knowledge. Through bleeding, the air is pushed out of the brake lines along with a small amount of brake fluid. After the process is done, you top up the brake fluid and go for a test drive. If everything goes smoothly, the feeling of a spongy and soft brake pedal should go away. Check out the video below to see how you can bleed brakes with simple DIY equipment or bleeding kits from Amazon (much easier and cheap).

How to test

There is no particular test for determining if there’s air in your brake lines. You will need to recognize the symptoms of air in brake lines that we described above. If your brake pedal feels spongy and soft and if your braking performance is weakened, there is a high chance there is air in your brake lines. You can also bleed the brake and see if any air bubbles exit your brake lines. If there are none, you can make a further diagnosis.

How to stop getting air in your braking system

The only way to stop getting air in your brakes is by eliminating the underlying reason why there was air in the brake lines in the first place. If there is a leak in your braking system, you or your mechanic need to identify the position of the leak and seal the leak as soon as possible. If you are getting air bubbles into the brakes from water contamination, you should replace your brake fluid and check up on your brake pads. This is especially important if you do a lot of intense braking and downhill driving or towing. If you are getting air bubbles into the brake system during brake repairs, you or your mechanic needs to identify what he/you are doing wrong. It is as simple as that, air does not just magically enter the air-tight brake system.

ferrari brakes

Frequently asked questions

Can You Get Air In Brake Lines After Bleeding?

Yes, you can still get air in brake lines after bleeding the braking system if the underlying reason for air in your brakes was not determined and resolved. There is also a possibility that the bleeding process was not done correctly.

Can Air In Brake Lines Cause Calipers To Stick?

There are mixed opinions on this issue. A majority of mechanics and service technicians we talked to said no, the air in brake lines will not cause the calipers to stick. However, there is a small possibility that calipers do stick if the brake hose suffers internal damage. It is a very rare occurrence.

Can Air In Brake Lines Cause Pulsating Of The Brake Pedal?

Generally speaking, no, pulsating brakes are usually caused by warped brake discs/rotors or worn-out brake pads. Other reasons for pulsating brakes include a stuck caliper piston, stuck caliper slider or stuck brake pads.

Can Air In The Brake Line Cause The ABS Light To Come On?

Yes, whenever the ABS sensors determine there is not enough brake fluid in the brake system, an ABS warning light can come on. The same goes if there is a lot of air in the brake lines, the ABS system detects a disruption in the pressure which triggers the ABS warning light.

Can You Hear Air In your brakes?

While you cannot hear air in brake lines at any given moment, you can hear air hissing out of the brake booster, if the brake booster is leaking air. 

Can Air In the braking system Cause Brakes To Drag?

Yes, the air in brake lines can cause the brakes to drag. It is one of the common symptoms of air in brake lines.

Can There be Air In your brakes After Changing the brake Pads?

Yes, whenever there is maintenance done on the air-tight brake system, this does open a possibility for air to enter the system. A good mechanic will bleed out the brake lines after every brake-related repair.

What Will Air In Brakes Do?

Air in brake lines will lower the overall braking performance, it will cause weird sensations on the brake pedal and constantly interfere with your braking. Remove it as soon as possible.


It is astonishing to see just how much trouble can be caused by what seems like a trivial thing, just some air in your brakes. But you need to understand that modern brake systems are incredibly efficient and complex. A small disruption in the form of a few air bubbles can directly affect your braking and consequently your safety and the safety of others on the road. As we already mentioned, you should get your brake inspected at the first sign of trouble, and never take risks when it comes to braking and safety. Make sure you also check out our guide on brake pad problems!

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