7 Symptoms of a Bad Brake Booster

Knowing the symptoms of a bad brake booster can save you from vehicular accidents or costly car repairs. Brake boosters are an essential part of your car’s braking system, but what’s the big deal about them?

Brake boosters reduce the effort you put into applying the brakes by applying force to the master cylinders, which dispenses the pressurized fluid that activates the brakes. So you don’t want to drive around with a bad brake booster. Besides the damage to your car, it is very unsafe for you and other folks on the roads.

That is why the question “can I drive with a bad brake booster?” should never come up. Experts believe that paying attention to certain signs will save you from many issues that might arise from having a bad brake booster. That said, once you notice any of the following signs, you most likely have a bad brake booster.

symptoms of bad brake booster check valve

What Are The Symptoms Of A Bad Brake Booster?

Here are the symptoms that suggest that you have a bad brake booster:

1. A Rock Hard Brake Pedal

One of the more common signs of a bad brake booster is a rock-hard brake pedal that is difficult to press down.

Get your braking system checked out when you observe that your brake pedal becomes rock hard and difficult to engage. It is not a great idea to drive a car with a rock-hard brake pedal because it becomes difficult to manage it. You are only putting yourself at risk of being involved in an accident. You shouldn’t drive the car until you have fixed the problem.

2. Your Car Takes Longer To Stop

This is one of the frequent symptoms of a bad brake master cylinder that arise when there is a bad brake booster. When you notice that your car takes much longer to come to a complete stop while the brake pedal is still firm, then the chances are that there is an issue with the brake booster. The reason why this happens is the presence of air or there’s any air leak. Try checking if the booster hose is leaking or the clamp is not well-tightened.

This is a dangerous situation to be in when driving in snail-like traffic. The risks of vehicular accidents are high, so you want to find out how to test a brake booster once you observe this symptom.

3. The Brake Pedal Is A Bit Higher Than Usual

Many folks might miss out on this, especially when they are not looking out for it. As long as the brake pedal responds appropriately, most people are good to go. However, you should be able to detect if the brake pedal is a bit stronger than normal. The first sign is that it will feel weird at your feet. If you are super observant, you might discover that your pedal is a bit stronger than it used to be whenever you step on the brakes.

If you find yourself in this situation, then your best bet is to check your brake booster.

 4. A Constantly Stalling Engine

Does your engine stall whenever you hit the brakes? You might not easily attribute this occurrence to a bad brake booster because a constantly stalling engine is a symptom of many things that could be wrong with your car. Here is why your car stalls whenever you hit the brakes.

Brake boosters have diaphragms that can fail at any time. When this happens, excess air enters the brakes from the engine and bypasses the seal. This causes your car to stall once you hit the brake pedal.

You should check your car once you notice this because the issue might easily degenerate into serious problems for your car. Beyond the possibility of brake failure, you might damage your transmission if you continue driving the car without resolving the issue.

5. Hissing Sound

One of the symptoms of a bad brake booster is a hissing sound under the dashboard or the brake pedal. The reason for the hissing sound is the vacuum starts to escape. So whenever you press down the brake pedal and noise comes from the brake, the odds are that your brake booster is already bad or about to be. Kindly note that this noise I likely to be a symptom of a bad brake booster if the noise comes from your engine bay or from the brake pedal areas.

6. Fluid Leaks

This is also one of the symptoms of a bad brake booster check valve. When you observe that your braking system has developed a leak, especially around the brake pedal, your brake booster might be bad. This is because hydro-boost brake boosters use power steering fluid, and when it develops a leak, some of the fluid that makes it function effectively gets lost in the process.

7. Warning Lights

Your brake boosters can trigger warning lights when they go bad. These lights come on when certain sensors in your braking system detect that something is not right. So when you see that the brake warning light is triggered, it is a sign that something is wrong with your brake. Low fluid level, bad master cylinder, and other things can cause these lights to turn up.

bad master cylinder or brake booster

Frequently Asked Questions (FAQs)

How Do You Test A Brake Booster?

Knowing how to test a brake booster is a great thing to do if you want to ascertain your car has a bad brake booster. Here are some methods that you could use to test your brake booster:

Check The Response Of The Brake Pedal

Here is where you run your car engine for a bit before switching it off. The next step is to depress the pedal a few times. Your brake booster is fine if the depressed pedal gets to a point where you can’t press it any further, not too hard but firm. Your brake booster is likely to be bad when the brake pedal does not move this way.

Apply Pressure While Idling

With this method, you first press the brake pedal with the ignition switched off. You then let the engine idle before pressing the pedal a few times. If you notice that the pedal does not drop while doing this, or it’s very hard to move, your brake booster is likely bad.

How Does A Brake Booster Work?

A brake booster uses atmospheric pressure to assist the pushing of the master cylinder piston. That means it needs a vacuum to function. That’s why your car’s brake booster has a hose that is connected to the manifold of the engine, which provides the vacuum. When you press the brake pedal down, the booster’s valve is opened, allowing atmospheric pressure that causes the diaphragm in the booster to thrust on the master cylinder piston via a plastic hub. It is this pressure that provides the boost for the master cylinder piston.

Why Does It Sound Like Air When I Press The Brake Pedal?

It sounds like air because some air is leaving the braking system. This occurs when air gets forced out of the bellows-shaped seal on the rod from your brake pedal into the booster. That is why you hear that sound, which often indicates a bad brake booster vacuum leak.

Can A Brake Booster Cause A Soft Pedal?

The common symptom of a bad brake booster is a strong pedal. Air bubbles that find their way into the brake lines cause a reduction of pressure that causes your brakes not to engage. They become unresponsive.

Can the Brake Booster Be Repaired?

Yes, but you are better off letting professionals handle it. It often requires checking and replacing the bad brake booster. However, if you choose to go the DIY route, here are the things you will need in your suitable tools box:


The brake booster is an essential aspect of your car’s brake system that is why you must know the symptoms of a bad brake booster. This is because early detection of a bad brake booster will save you the possibility of an accident due to car brake failure. You also get to save your car from developing much more complicated issues when you detect and fix bad booster problems early. Now that you can recognize the symptoms of a bad brake booster, you can save yourself a whole lot of complications and problems. However, you might want to get professional help if you replaced your brake booster but found out that your new brake booster is not working.

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Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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