How To Test A Brake Booster Off The Car


When your brake booster stops working, it is important to determine whether that is due to poor performance or complete failure of the device. If you feel like the brakes are not bringing your vehicle to a stop as quickly as before, then this could be because the booster has failed completely.

A bad brake booster will no longer increase braking force when engaged. It may also make applying pressure to the wheel brake discs difficult, if not impossible. A good way to test this is by pulling over next to another car or somewhere safe where you can check for a handbrake.

By checking both feet off the floor, there is no chance of success using the handbrake. You can either use the normal brake pedal to apply pressure, or use the back up brake which does not require a pedal. Only do this in very close quarters though, we cannot stress enough!

When performing these tests, make sure nothing is blocking access to the foot pedals, and remember, only perform this if the vehicle comes with one! Also, turn off all engines and tools such as drills etc so they do not interfere.

What should you look out for?

You should be able to pull the handle down without any resistance. If you can’t get it going down, then the brake booster has failed.

Use a clamp and some electrical tape

how to test a brake booster off the car

In addition to using your hands, you can also use an adjustable clamp or tool to test your car’s brake booster. An easy way to do this is by using a small piece of electrical tape as glue and then attaching the pin onto the booster housing.

Now push down hard with the screw driver on both sides of the pin and see if it moves in or out.

Use a hammer and some pebbles

how to test a brake booster off the car

In fact, one of our favorite easy brake booster tests is to try to see if your car will shut down when you use the engine as a motor to push down on the pedal. This is called coasting or rolling up the wheels and there are two ways to do it.

The first way is to use your own power source (your muscles) and pull out of a parking spot using your momentum. The other way is to have an external force work for you. A tool that can be used to test this is a metal sledgehammer.

We recommend hitting the front brakes with the hammer just as the vehicle comes to a stop and then seeing if the brake lights go off. If they do not, the brake booster may be malfunctioning.

Connect a hose to the booster

While it is not necessary to test your car’s brake boosters in any official way, you can do so by connecting a hoses to the back of the booster.

Most cars have at least one white pipe coming out of the back of the master cylinder that goes into the front of the booster. This is the fluid line for the brakes! You should be able to find this part easily if you look under the hood.

If you are able to connect a clear plastic or copper tube to this port, then the brake booster is working and being filled with hydraulic fluid. If the tube gets hot when you use the brakes, then the brake booster may no longer work properly. Make sure to check your brake booster before bringing it up for sale or donating.

You could also check whether the pump is functioning correctly by looking underneath the vehicle at the shape of the pistons.

Blow into the booster

how to test a brake booster off the car

While testing your brake booster, you will need to make sure it does not resist when pressed. If it does, then something is wrong with the sensor or the booster itself!

By using a mouth piece, you can easily blow air into the booster to see if it resists being pushed in. By doing this, you can also test whether the fluid in the booster has dried out and lost its effectiveness.

If it does not, then there may be some squeaking or grinding sounds that require investigation. Make sure to check both the front and back of the booster, as well as both sides of the master cylinder!

Test each part separately so you do not get confused.

Let the car sit for a while

how to test a brake booster off the car

One of the most important things when testing your brake booster is having a good starting point. You cannot determine if it is working properly unless you have a baseline level!

A lot of people test by pressing down hard on the pedal with no vehicle movement. This may work in some cases, but not all vehicles are designed to take full braking power at rest. Some cars will actually feel like they need more pressure before they respond!

So instead, we recommend letting the vehicle sit for a few minutes and seeing what kind of response you get. Most manufacturers suggest waiting five minutes after rolling up an engine block before checking the brakes!

Some experts even say that you should leave the brake booster alone and see how much force you must apply onto the pedal before it activates! This is because as the brake pads wear out or the booster gets old, then it might require more effort to activate it.

Check the brake pedal

how to test a brake booster off the car

The first thing you should do if your car does not feel or seem to be working properly is check the brake pedal. If it takes a long time for the vehicle to stop, this can indicate something is wrong.

A soft brake could be due to a weak brake booster, but more likely there are fluid issues such as moisture or salt that have affected performance. Make sure your wheels get enough friction when braking so they will slow down correctly and the master cylinder has adequate hydraulic fluid.

By checking the brakes before trying to push hard on the accelerator, you save yourself from having an accident. You also avoid wasting money buying new brake parts because of poor maintenance.

Testing the firmness of the pedal is another way to determine whether the brake system is functioning normally. If it feels very light and flimsy, then try rubbing your hands over it to see how much pressure it takes to make a difference. A normal amount of pressure should take at least some degree of effort to apply.

Look at the brake lines

how to test a brake booster off the car

It is important to check your car’s front brakes before testing your booster. Make sure there are not only ample amounts of brake fluid in the wheel cylinders, but that it is fresh and has been mixed thoroughly with benspeed.

If you do find dry brake lines, make sure they are completely filled so that enough liquid exists for good friction between the line and the cylinder wall. If they are still very thick and don’t seem to be going anywhere, try rubbing them with your fingers or using a tool like a flat head screw driver to see if they go down slightly in thickness.

That would indicate the line needs to be replaced, which isn’t too expensive unless you accidentally bought one new already!

Also, look out for bubbles coming from under the calipers where the master piston goes back into its housing. This could mean something got wet, such as brake fluid leaking out, or the seal around the piston breaking down and letting air get inside.

Both of those things can cause the pistons to lose pressure, which will prevent the boosters from working properly.

Practice emergency braking

how to test a brake booster off the car

In addition to practicing how to quickly apply your brakes in normal conditions, it is important to practice this technique while there’s no car next to you.

Practice stopping as if someone was chasing you or trying to run you down. These scenarios can be more frightening than doing so from inside your vehicle, where you’ll at least know what’s going on ahead of time!

Fortunately, you don’t have to train for an actual situation, unless you are actually being chased or confronted with another driver that isn’t behaving logically (or safely). But still, practicing for those situations is helpful because it will make you feel more prepared.

And hopefully, you never need to use these practices, but they should at least give you some degree of comfort when needed.

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