Brake Booster: What You Need to Know

Just as the name suggests, a brake booster exists in your car to help your brakes slow you down to a stop more quickly and efficiently. They are a part of a disc brake system and if you didn’t have a brake booster in your car, then coming to a complete stop could take quite a bit longer than it normally does.

Since the brake booster is a part of your car’s safety equipment, it’s important to make sure it’s in good running order. With that in mind, let’s check out some signs and symptoms that you have a bad brake booster, brake booster repair costs, and how to tell that you need a brake booster replacement.

What are the signs of a bad brake booster?

When your brake booster isn’t working the way it’s supposed to, there are brake booster symptoms you can be on the lookout for.

• Stopping Distance. This is one of the more noticeable and dangerous signs of a bad brake booster. The distance that it takes your car to stop from the time you put your foot on the brake is going to increase dramatically.

• Noises. The brake booster is a vacuum operated system. If the reason it’s failed is that there’s a leak in the brake booster vacuum hose somewhere, you’re going to hear hissing sounds as a result when you put your foot on the brake.

• Dashboard Lights. A faulty brake booster might trigger your ABS light to go off, or a traction control light if you have one of those on your dashboard.

• Check Engine Light. In rare cases, a bad brake booster may trip the check engine light. This is because if the vacuum fails it can throw off your fuel-to-air ratio, and you’ll start burning too much air in your engine.

• Fluid Leaks. Some brake boosters require power steering fluid to operate. They call these hydro boost brake boosters. If your brake booster is in the master cylinder, it can also end up leaking.

• Resistant Pedal. The brake booster is responsible for your power-assisted brakes functioning. If it fails, then your brake pedal is going to be very hard to push down. it’s possible that your brake pedal will just feel spongy under your foot as well. 

What happens when a brake booster goes bad?

Because a brake booster literally boosts the stopping power of your brakes, when it fails, you’ll notice it quickly. Your brakes will no longer have the booster amplifying your stopping power. That means your brakes are going to feel a lot stiffer under your foot.

 If you’re trying to stop in a hurry because maybe there’s an animal in the road ahead of you, your brakes are not going to respond quickly. You’ll need to use all your might to push down on the pedal to try to get your brakes to slow you quickly without the booster in place.

 In high-stress situations such as avoiding an accident, without a brake booster you may be unable to stop in time to prevent damage and injuries.

What does the brake booster do?

In the simplest terms, a brake booster boosts your brakes. When you apply pressure to your brake pedal, the booster increases the force relative to the force you are putting down on the pedal and applies it to the brakes.

 There was a time when the brakes of a car only responded to how hard you can put your foot on the pedal. This is before power brakes. So, if you needed to stop in a hurry, you had to have strong legs and some good downward force.

Thanks to brake boosters, when you need to react in a pinch and brake quickly, you don’t need to have the power in your legs to stop the whole car. You just need to depress the brake pedal firmly, and the brake booster will multiply that force in a way that applies to the brakes.

Can you drive without a brake booster?

It’s possible that you can drive without a brake booster in your car. The brake booster doesn’t affect your car’s engine in any way. So, if it were to fail completely, your ability to drive would not be affected.

The problem with a bad brake booster is that your ability to brake is what is going to be affected. You’ll still be able to stop your car, but it’s going to be much harder. The physical connection between your brake pedal and the brakes is independent of the booster’s ability to affect it.

What causes a brake booster to fail?

There are a few potential reasons why your brake booster might fail on you.

• Vacuum problems. The most common cause for a brake booster problem is related to a vacuum leak. If you have a hose that has come loose or develop some cracks, you’re going to lose that vacuum pressure which the brake booster system relies on.

Without a sealed vacuum, air can enter the system. You no longer have the pressure needed for the brake booster to help stop your brakes the way it’s supposed to.

• Pushrod problems. a push rod is part of your brake system that connects your brakes and your brake booster and can fall out of alignment. If you just had your master cylinder replaced or worked on and you’re finding your brakes not working properly now, the pushrod could have been misaligned during that repair job.

• Diaphragm problems. Inside your brake booster is something called a diaphragm. Over time, this can also develop leaks. It can get hard as well, which prevents it from working properly. If you live in a very cold or dry climate, this is more likely to happen.

If the diaphragm of your brake booster failed, you’ll need a brake booster replacement to fix it. Brake booster diaphragms are not typically sold on their own.

• Clogs. The brake booster has ventilation ports that allow air to enter. There is also an air filter. If any of these become clogged with dirt or debris, the functionality of the brake booster will decrease significantly.

• Valve problems. Brake booster check valves remove air from the brake booster without letting additional air in. They open and close with the assistance of springs that can wear down or break over time. When that happens, the brake booster check valve may be stuck in the open or closed position, causing your brake booster to fail.

How do you check for a brake booster leak?

If you’re hearing a hissing sound when you put your foot on the brake pedal, then you may want to check for a leak in your brake booster. The process of testing your brake booster is not too difficult.

• With your engine off, repeatedly press the brake pedal with moderate pressure. This should deplete your brake booster.  You should be able to press the brake two or three times before you notice that it gets harder to push down.

• If the brake pedal is hard to push down right away, or after only one push, then you may have a vacuum leak somewhere in the system.

• Checking the vacuum hoses from this point is the next step. If you know how to access them and what to look for, you could do this now. Otherwise, you’ll need to go to a mechanic to have the hoses inspected and use a vacuum gauge to test the system.

• If the brake booster is working normally, then when you turn the engine on and push on the brake, it should give away just a little and then become firm but not hard. 

How much does it cost to replace a brake booster?

A brake booster replacement cost may be more than you are expecting. A new brake booster from AutoZone can range from as little as $70 to as much as $500. Labour costs for your brake booster replacement are going to range from around $100 to $200. All told, you can get this job done for under $200, but in some cases, it may be as much as $700. 

The cost is very much dependent on the mechanic you take it to in order to get the job done, as well as the make and model of your vehicle. Rare cars and high-end models will typically cost more to repair then some more common vehicles.

Can you fix a brake booster?

It’s possible that you can fix a brake booster without having to replace it completely. There are brake booster repair kits available online that will cost you under $100 and can be used to repair problems with the vacuum pump. 

If you’ve never done any repairs under the hood of your car before, you may want to leave this one to professionals. However, if you’re comfortable doing some basic repair jobs on your car, then you may feel comfortable handling this on your own as well.

 The kits come with instructions and there are also videos that you can find online that will walk you through the process. If you’re looking to save yourself a few dollars and you are sure that the problem with your booster is related to the vacuum, this may be a good option.

One thing you need to be sure of is that you get the right repair kit for your make and model. Certain parts are designed to fit on certain Vehicles, so you want to make sure you have the right part, otherwise your repair kit will be useless to you.

When should I replace my brake booster?

Unlike certain parts of your car, such as a timing belt or a fuel filter, a brake booster does not have a limited lifespan. In theory, your brake booster should last the life of your vehicle. But of course, that’s not always the case.

 If your brake booster failed because of a problem with the vacuum, with the diaphragm, with the brake booster check valve or anything else, you’ll need to have it replaced. As we said earlier, if you live in a particularly dry climate, this may happen sooner than it should.

 In general, a brake booster should be able to last you at least 150,000 miles. There’s no reason that a well-maintained vehicle shouldn’t be able to get many more miles than that out of the brake booster as well.

 Once you notice an issue with your brake booster, any of the symptoms that we’ve already covered, then it’s in your best interests to head into a mechanic as soon as you can. This will be the only way to know that you need to do some work on your brake booster, either repairing or replacing it, because there is no specific lifespan for this part.

Can a bad brake booster cause rough idle?

Even though it is not the most common symptom of a bad brake booster, it’s possible that it could lead to rough idling from your engine. When it's not working the way it's supposed to it may cause vacuum issues with your engine as well. Air can bypass the diaphragm and when you apply the brakes, it will draw air from your engine. This can cause your engine to stall and also issues with rough idling. 

The bottom line

Most drivers are probably completely unaware of what a brake booster is or that their car even has one. But as we have seen, this is a crucial part of your car's braking system and an important tool for ensuring your safety and the safety of others on the road.

The brakes are one of the few systems in your vehicle that you want to ensure our working at 100% all the time. The moment you realize you have a problem with your brake system, you don’t want to let it slide and put it off until later.

 If your brake booster is not functioning the way it’s supposed to, get it to a mechanic as soon as you can to have it checked out. The longer you let something like this go, the greater the chance that you’re going to be unable to rely on your brakes in an emergency situation and put your health and safety at risk. It’s just not worth it.