Bad Brake Booster Symptoms

Eagle's Garage may collect a share of sales or other compensation from the links on this page. This comes at no additional cost to you, and all the prices and availability are accurate at the time of publishing.

Brakes are some of the underappreciated safety features of a car. Most people don’t think about them until they need to use them, and by then it’s usually too late. That’s why it’s important to be aware of the signs that your brake booster may be failing. Learn what are the bad brake booster symptoms.

One of the first signs of a problem with your brake booster is a change in the way your brakes feel. If you notice that your brakes are harder to press or that they don’t seem to work as effectively as they used to, there’s a good chance that your brake booster is the culprit.

In this article, we’ll take a look at some of the other symptoms that can indicate a problem with your brake booster. We’ll also explain what a brake booster does and how it works. By the end, you should understand this vital component of your car’s braking system.

What is a Brake Booster?

ACDelco GM Original Equipment 178-0683 Power Brake Booster Assembly

Every time you hit the brakes; your brake booster helps push brake fluid through the lines to the brakes themselves. The brake booster is a vital part of your car’s braking system, and if it fails, you will definitely notice. That is because a failing brake booster will cause your brakes to feel spongy, too much force is required, or even worse, non-existent. 

The device itself is a cylinder, typically located between the master cylinder and firewall. It contains a diaphragm that is actuated by an engine vacuum. When you depress the brake pedal, it pushes against the diaphragm which in turn, activates a pushrod.

That pushrod then applies pressure to the back of the master cylinder piston, forcing fluid through the lines to your brakes. 

7 Symptoms of Bad Brake Booster

A1 Cardone Cardone 52-7370 Remanufactured Hydraulic Power Brake Booster without Master Cylinder,Black

A good brake booster will make your car’s brakes feel firm and responsive. If yours is going bad, here are some symptoms to watch out for:

1. Stiff Brake Pedal Action 

The most common symptom of brake booster failure is increased pedal firmness. If the booster is not providing enough power assist, you will have to apply more pressure to the pedal to engage the brakes. This can be dangerous if you are not expecting it, as you may not apply enough pressure in an emergency situation and cause an accident. 

2. Increased Stopping Distance 

Another symptom related to the increased pedal firmness is increased stopping distance. If it takes longer for your car to come to a stop than usual, it is likely due to a failing brake booster. Again, this can be extremely dangerous as you may not be able to stop in time for a pedestrian or another vehicle. 

3. High Brake Pedal Position

In addition to increased pedal firmness, you may also notice that the pedal sits higher than usual when not being depressed. This is due to a loss of vacuum pressure and can be extremely dangerous as it decreases the amount of time you have to react in an emergency situation. 

4. Poor Engine Function 

A less noticeable, but still important symptom of a failing brake booster is poor engine functionality. A hole in the diaphragm allows the booster to draw air into the induction system which due to the way engines work, can cause a number of problems. These include decreased power, increased fuel consumption or lean condition, and even stalling. 

5. Hissing Noise 

If you hear any strange noises coming from the area around the brake pedal, it could be a sign of a failing brake booster. You may hear hissing, moaning, or even grinding noises. These are all caused by a loss of vacuum pressure and should be checked out by a mechanic as soon as possible. 

6. Fluid Leaks 

Another symptom of a failing brake booster is fluid leaks. If you notice any brake fluid leaks, it is important to have them checked out as soon as possible. Brake fluid leaks can cause the brakes to fail completely, which can obviously be extremely dangerous. 

7. Dashboard Warning Lights 

Lastly, if your brake booster is failing, you may see a warning light on your dashboard. This can be either the ABS light or the general brake system warning light. If you see either of these lights, it is important to have your car checked out by a mechanic as soon as possible.

Related Codes

How Do You Test a Brake Booster?

Motorcraft BRB33 Power Brake Booster

There are a few ways you can test your brake booster to see if it is failing:

Check The Response of The Brake Pedal 

The first and most obvious way to test your brake booster is to simply depress the brake pedal and see how it feels. If it feels firm or spongy, it could be a sign of a problem. 

Apply Pressure While Idling 

Another way to test your brake booster is to apply pressure to the pedal while the car is idling. If the pedal sinks to the floor, it is a sign of a problem. 

Vacuum Brake Booster Replacement Cost

The average cost for a vacuum brake booster replacement is between $400 and $600. This includes the cost of the part itself as well as labor. If you need to have your entire brake system replaced, the cost will be much higher. 


A failing brake booster can be extremely dangerous and should be fixed as soon as possible but if you are vigilant and notice the most obvious symptoms such as increased pedal firmness, you should have no problem catching the problem early on.

Be sure to get your car checked out by a mechanic if you notice any of these problems and always err on the side of caution when it comes to safety. Thanks for reading!

If you liked this article about bad brake booster symptoms, consider checking out these other articles below —

Leave a Comment

Our Best Content In Your Inbox