Braking System

Brake Booster Symptoms-What Happens When Brake Booster Goes Bad

Mike Cross
Updated Aug 14, 2021
Male car mechanic examining brake disc with caliper in garage

Your brakes are a key part of your vehicle. Yes, the engine and being able to get going is important, but being able to stop is just as important. That is because a car is just as undriveable if it won’t stop as if it won’t start. In this article, we will look at one of the reasons why your car may have trouble stopping and that is a bad or failing brake boosters. Read on to find out what the brake booster is, how it works, and also symptoms of a failing one.

Failing Brake Booster Symptoms
Failing Brake Booster Symptoms

What is the Brake Booster?

Before getting into the signs of a failing or bad brake booster we first need to cover what it actually is. The brake booster is a part of the brake system that most people may not be familiar with. A lot of people know your brakes have rotors and pads and that when you press the brake pedal the pads grab onto the rotor slowing it down and slowing your wheel down, but the brake booster helps make this process easier.

The brake booster boost or multiples the strength that you are putting onto your brake pedal. It is a small canister and is on the driver side of the firewall inside the engine compartment. The booster is simply put together. It is divided into two chambers. A driver-side chamber and an engine side chamber.

There is a tight seal separating the two. The engine side chamber is connected to the intake manifold with a hose which creates a vacuum. Inside the cylinder is a pushrod that connects to the brake pedals on one end and the master cylinder on the other.

The master cylinder is connected to the front and middle of the brake booster. There is also a valve at the middle of the push rod that allows the vacuum to enter the rear chamber. This allows both chambers to have pressure when the pedal is at rest. Stepping on the brake pedal to slow down or stop the vehicle, causes the rear valve to open because it is connected to the push rod.  This allows atmospheric pressure to enter the rear chamber.

At the same time, the center valve closes the diaphragm valve, blocking the vacuum from entering the rear of the chamber. This allows the atmospheric pressure and vacuum to help you to push the rod against the master cylinder, which applies the hydraulic system to the brakes reducing the effort on your part.

Male car mechanic examining brake disc with caliper in garage
Male car mechanic examining brake disc with caliper in garage

So now that you know the basics of how the brake booster works and how it makes your life easier when applying your brakes we can cover the symptoms or signs of a bad or failing brake booster.

Stiff Pedal

The first and most obvious sign of a brake booster that is going out is a stiff brake pedal. That is because you now know that the job of the brake booster is to make it easier to press the brake pedal down.

If the brake booster is not working properly, then you will have to press the brake pedal much harder to get the same amount of stopping force. It can also be harder to press the brake pedal because depending on what is wrong the brake booster might be producing pressure that is counteracting you pressing the pedal. This will make the brake pedal extra stiff.

Longer Stopping Times

A harder to press brake pedal can also lead to longer stopping times. This is because you might not be able to apply enough force to the brake pedal to get the same amount of brake force on the rooters that you are used to getting.

Also, if the brake booster is going out, then it can delay how quickly the brakes engage. Even if you don’t have to press on the pedal super hard, it still may not be engaging as quickly as normal. This can obviously be dangerous because sometimes a few extra inches of stopping time can mean the difference between a wreck or not.

High Brake Pedal

The next thing that can indicate a failing brake booster is a brake pedal that is not in the normal position. The brake pedal could be higher than normal because the pressure behind it is causing it to not return to the proper position. The pressure in the brake booster could be pushing on the brake pedal causing it to be higher.

If it is higher and you forget, then you might miss it when going to hit the brake or get tangled on it which can lead to a wreck. It could also be lower though if the vacuum is bad in the brake booster and this is bad as well because you might not be able to apply enough force to the brakes to stop in time.

Engine Stalling

Tired when Engine Stalling
Tired when Engine Stalling

The last sign of a faulty brake booster is the engine stalling. Since the brake booster has a diaphragm that keeps air from passing thru, if this goes bad, then air will start getting thru. This air can get into the engine and make it seem as though it is stalling when the brakes are pressed.

This can lead to engine damage, which means if you start noticing this when you press your brakes, then you need your brake booster checked out.

Testing Brake Booster

There are a lot of ways to test your brake booster, and a whole article can write about that, but if you are having any of than signs, then you can use this simple method at home to see if your brake booster is bad. The simple test is to press the brake pedal around six times with the car off.

This will release any vacuum. Now go to turn the car on and when you do lightly apply pressure to the brake pedal. If the pedal slightly falls from your foot and is then firm, then your brake booster isn’t the issue, but if it is stiff and has trouble dropping, then you should have your brake booster looked at.


Your brake booster is a key part of your brakes and is a part that a lot of people don’t know about. After reading this though, you now know what your brake booster is and how it works.

You even know the signs of a failing brake booster which are a stiff brake pedal, longer stopping times, a high brake pedal, and a stalling engine when braking.

If you have these symptoms, then you even know a method to test your brake booster. With this method, you can determine if you need to have your brake booster looked at by a professional. Your brakes are a key part of your vehicle, and if the brake booster is going bad, you need to have it checked out to prevent from wrecking.

Luckily now you know how to catch a bad brake booster early since you know the symptoms of one before you have a wreck or more damage happen.

Mike Cross
Life is too short to drive with stock audio

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