(Updated on April 11, 2022)
When you step on the brake pedal, you normally don’t have to put a lot of pressure on it for the vehicle to slow down. The reason for this can be attributed to a component of the braking system called the brake booster.
The function of the brake booster is to amplify the pressure as you press down on the brake pedal. That way, you don’t have to press down too hard on the brake pedal to slow the vehicle down. This creates a much safer driving experience.
Brake Booster vs Master Cylinder
On paper, a “brake booster” and a “brake master cylinder” may sound similar. They are even located near each other in the engine bay. They serve very different purposes in the braking system, however.
A brake booster is similar to a power steering pump in the sense that it provides an assist to the driver. This assist makes it easier to operate the vehicle. The brake booster looks like a big, round drum in your engine bay. You can often find the brake booster next to the firewall on the driver’s side of the vehicle.
A brake master cylinder is the part of the hydraulic system that transfers the force from the brake pedal into each of the pistons in the four calipers. This force is transferred via hydraulic fluid (also known as brake fluid).
The brake master cylinder has a small container of brake fluid sitting on top of it called the reservoir. A bad master cylinder could leave you with no brakes at all.
Common Bad Brake Booster Symptoms
Of course, there could be situations where the brake booster will go bad. The symptoms may not seem extremely serious in the beginning, but you shouldn’t drive your vehicle anyway.
Take your vehicle to your local auto repair shop or else you may soon not be able to brake at all. Then you’ll really be in trouble.
1) Stiff Brake Pedal
Since a good brake booster will make it easier to push down on the brake pedal, a bad brake booster will do just the opposite. You will notice the brake pedal feeling very stiff and hard as you try to press down on it.
This will be the most obvious symptom of a bad brake booster, so you should get it replaced right away.
2) High Brake Pedal
Along with the stiff brake pedal, you will notice that the pedal may sit higher than it should be. This forces you to lift your foot higher just to reach the brake pedal, which is a dangerous situation to be in while driving.
If you forget about this and must brake suddenly, you could have problems. So, take your car to the shop whenever you notice a high brake pedal like this.
3) Takes Longer to Stop
Even when you press down hard on the brake pedal, it may still take longer than normal for the car to stop. With a bad brake booster, the pedal isn’t getting the power it needs to make it work quickly.
This can increase your stopping distance significantly. Obviously, this is extremely dangerous while driving because you might need to brake quickly to prevent a crash or save your life.
If there are rough weather conditions outside, then it can be even more dangerous. Therefore, get the brake booster replaced immediately before it’s too late.
4) Engine Stalls
The brake booster has a diaphragm in it which prevents air from getting through the seal. If the diaphragm becomes faulty and air gets through the seal, then your engine will appear like it’s stalling each time you press down on the brake pedal. This could lead to worse problems than just bad brakes.
You could start having engine problems too from this. That will open all new kinds of problems that you don’t want to have.
Brake Booster Replacement Cost
Before you try to replace the brake booster, check the vacuum lines (or vacuum pump) leading to the brake booster. If you simply had a hose pop off, the cost to fix the brake booster could be free (or some trivial amount for a new vacuum hose).
The average cost to replace a bad brake booster is between $290 and $720. For the parts, you can expect to pay anywhere from $160 to $550. For the labor, you can expect to pay anywhere from $130 to $170.
The actual costs really depend on the year and model of your vehicle and the labor rates of your repair shop (usually between $80-$110/hr). It is always a good idea to shop around before choosing a shop to work on your vehicle.
Can You Drive With a Bad Brake Booster?
If you didn’t have a brake booster, you could still stop the car. However, it would take significantly more pedal effort to apply a hard braking force.
Many people may struggle to apply the force needed to stop the vehicle in a reasonable amount of time, especially in an emergency situation when hard braking is required.
It is strongly recommended that you do not drive with a bad brake booster unless you are certain you can handle the excessive force required to stop the car.
Testing a Brake Booster
There is an easy way to test the brake booster at home. With the vehicle is off, press down and up on the brake pedal about 6 times. This will get rid of any vacuum that is stored in there.
Now turn on your vehicle while lightly applying pressure to the brake pedal. If the pedal slightly falls from your foot and is then firm, then your booster is fine.
If the pedal is stiff and has trouble dropping, then the booster is likely bad.