6 Bad Brake Booster Symptoms and Causes

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bad brake booster symptoms

A brake booster is an important part of a car’s braking system. It helps to apply the brakes evenly and with more force. A faulty brake booster can cause all sorts of problems with your car.

The most common symptom of a bad brake booster is the stiff feel of the brake pedal. Other symptoms may include warning lights, brake fluid leaks, increased braking distance, and a hissing noise when you press the brake pedal.

In this article, we will discuss the symptoms and causes of bad brake boosters, as well as their location and function. Let’s get started.

What is a Brake Booster?

A brake booster is a device that helps increase a vehicle’s braking force. It is usually located between the master cylinder and the brake pedal and uses vacuum or hydraulic pressure to assist in applying the brakes. Many types of braking systems including an anti-lock braking system include this safety feature.

Brake boosters are an important safety feature and can be found on both cars and trucks. They help ensure that the brakes are applied evenly and with enough force to stop the vehicle safely.

How Does a Brake Booster Work?

The working of brake boosters is based upon simple principles of vacuum pressure. Let us dig deeper to break down what goes inside the brake booster.

Pressing the brake pedal pushes a plunger in the master cylinder, which forces hydraulic fluid through the system of hoses and pipes to the brakes at each wheel. The fluid pressure activates the master cylinder piston in each of the brake calipers and clamps the brake pads against the rotor or drum, creating friction that slows down or stops your vehicle.

The pressure you exert on the pedal determines how much braking force is generated. If you push hard on the pedal, more fluid is forced through the system, and more braking force is generated. The brake booster helps you exert more pressure on the pedal with less effort by amplifying the pressure you generate.

It does this by using vacuum pressure from the engine to assist the pressure you create when you press on the pedal. The brake booster check valve opens and air enters through it.

The brake booster is divided into two working chambers with the help of a rubber diaphragm. When the engine is running, a vacuum pump creates a partial vacuum in the booster, which increases the pressure in one chamber and decreases the pressure in the other.

This pressure difference creates a force that amplifies the hydraulic pressure generated by your foot on the pedal. This is because the plunger of the master cylinder passes through the diaphragm, which gets pushed outward.

The diaphragm, in turn, pushes on the hydraulic fluid in the other chamber, amplifying the pressure.

Where is Vacuum Brake Booster Located?

The vacuum brake booster is located on your vehicle’s right side’s firewall adjacent to the master cylinder. You will have to look through the engine compartment to spot it.

It is a black, cylindrical component that has a large vacuum hose connected to its side. The other end of the booster is attached to the master cylinder’s pushrod.

Bad Brake Booster Symptoms

Now that we know what a brake booster is and does let’s take a look at some of the symptoms of a bad brake booster.

  1. Braking System Warning Lights
  2. Stiff Brake Pedal
  3. Brake Fluid Leaks
  4. Increased Braking Distance
  5. Hissing Noise
  6. Engine Stalls

Let’s try and understand each of these symptoms in a better way:

1. Braking System Warning Lights:

One of the first signs that something is wrong with your brake booster is when the braking system warning light comes on. This could indicate a problem with the diaphragm for brake boosters or the master cylinder.

While most new vehicles have a dedicated warning light for the brakes, some older models may have a general “check engine” light that could indicate a problem with the brake booster.

2. Brake Fluid Leaks:

Brake Fluid

In a hydraulic brake booster system, the master cylinder and the brake booster are connected by a pushrod. If there is a leak in this connection, it can cause brake fluid to leak from the system.

This will not only reduce the level of brake fluid in your vehicle but can also lead to air getting into the system, which will further reduce braking performance.

3. Increased Braking Distance:

This is probably the most obvious sign that something is wrong with your brake booster. If you notice that it takes longer to stop your vehicle than it used to, it is a good idea to get the brake booster checked out.

This happens because the booster helps to create vacuum pressure in the brake system, which helps to push the brake pads against the rotors. Without this pressure, the brakes will not work as effectively, and you may have to pump the brakes more often or apply more pressure to stop.

4. Stiff Brake Pedal:

If you notice a stiff brake pedal action or hard brake pedal than usual, it could be a sign of brake booster failure. This can happen if there is a leak in the vacuum hose or the diaphragm has developed a hole. You may also notice a high brake pedal position.

In some cases, this may also be an indication of air in the braking system. While this is not necessarily a problem with the brake booster, it can lead to reduced braking performance and should be fixed as soon as possible.

In some cases, the brake pedal might also go down to the floor.

5. Hissing Noise:

If you hear a hissing noise when you press the brake pedal, it is a good indication of a problem with the brake booster.

This noise is usually caused by a vacuum leak, which can happen if there is a hole in the diaphragm or the vacuum hose is not properly connected.

6. Engine Stalls:

In some cases, a problem with the brake booster can cause the engine to stall. This happens because the brake booster is connected to the intake manifold, and if there is a leak in the booster, it can cause vacuum pressure to drop in the engine.

This can lead to a loss of power and eventually cause the engine to stall. If you notice this happening, it is important to get the problem fixed as soon as possible.

What Causes a Faulty Brake Booster?

There are many reasons why your brake booster might fail. The most common cause is a leak in the diaphragm. This can be caused by wear and tear, as well as dirt, moisture, or other contaminants that get into the system.

Another common cause of failure is a loss of vacuum pressure due to a vacuum leak. This can be caused by a problem with the engine, such as a vacuum leak or an intake manifold leak. It can also be caused by a problem with the booster itself, such as a bad check valve or gasket.

The booster can also fail if the plunger in the master cylinder sticks or if there is too much fluid in the system. This can be caused by a leak in the master cylinder, a problem with the brake lines, or a problem with the calipers.

Brake Booster Replacement Costs

If your brake booster has failed, it will need to be replaced. This can be a costly repair, as brake boosters are not cheap to replace.

The average cost of a new brake booster is between $200 and $400, with labor costs adding $100 to $200 onto the total bill.

However, if your booster is failing due to a problem with another component of the system, such as a leak in the master cylinder, you may need to replace the other component as well.

Additionally, if your vehicle is older and has high mileage, you may need to replace other components of the braking system at the same time. This can add to the overall cost of the repair.


If you are experiencing any of the above symptoms, it is important to have your vehicle inspected by a qualified mechanic as soon as possible.

While some of these symptoms can be caused by other problems, such as low brake fluid or dirty brakes, they can also indicate a problem with the brake booster.

If the booster is not working properly, it can lead to increased braking distance, resulting in an accident. Therefore, it is important to have the problem diagnosed and repaired as soon as possible.

This concludes our article on diagnosing bad brake booster symptoms. We hope you found this information helpful. If you have any further questions, please feel free to contact us. Thank you for reading!

Frequently Asked Questions

What happens when the brake booster goes bad?

When the brake booster goes bad, it can cause several problems. The most common problem is increased braking distance. This can be caused by a loss of vacuum pressure or a problem with the plunger in the master cylinder.

Additionally, the brake pedal may feel spongy or stiff, and there may be a hissing noise when the brakes are applied.

Why do brake boosters come in different sizes?

Different vehicles require different-sized brake boosters to function properly. The size of the brake booster is determined by the amount of vacuum required to operate the brakes.

A larger booster will require more vacuum, while a smaller booster will require less. Depending on the size and power of the engine, a different-sized booster may be necessary for your car.

Additionally, the weight of the vehicle and the type of brakes (disc or drum) will also affect the size of the booster required. Ultimately, it is important to consult with a professional to determine which size brake booster is right for your vehicle.

Is it safe to drive with bad brake booster symptoms?

If your brake booster is not working properly, it can put you and your passengers at risk. A bad brake booster can cause your brakes to feel spongy or unresponsive, making it hard to stop your car in an emergency situation.

If you think your brake booster might be failing, take your car to a mechanic for inspection as soon as possible. Driving with a bad brake booster is not safe and could lead to an accident.

What is the average lifespan of bad brake boosters?

Brake boosters typically last between 50,000 and 100,000 miles. However, if they are not properly maintained or constantly used in stop-and-go traffic, they can fail sooner.

How to prevent brake boosters from going bad?

There are several ways to prevent brake boosters from going bad.

  1. Check your brake fluid level regularly. If it’s low, top it off.
  2. Bleed your brakes regularly. This gets rid of any air that may have gotten into the system.
  3. Inspect your brake pads and discs/rotors for wear. If they’re worn out, replace them.
  4. Get your brakes serviced regularly. This helps to catch any problems early on.
  5. Drive safely and avoid sudden braking whenever possible.
  6. Upgrade to better quality brake components if possible. This can help to extend the life of your brakes overall.
  7. Follow the manufacturer’s recommended maintenance schedule for your vehicle.

Can you drive without brake boosters?

Although it is not impossible to drive without brake boosters, it is not advisable. Brake boosters are an important safety feature. Without a functioning brake booster, stopping your car would be much more difficult. It may also lead to brake failure.

You would have to use considerably more force on the brake pedal to get the same amount of braking power. This could be dangerous in an emergency situation, as it would take longer to stop the car and avoid an accident.

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