When your car starts getting old, you might notice some of its parts breaking down. When it comes to this, it pays to know the warning signs. If you don’t, you might just end up stranded in the middle of the road not knowing what to do next. To be a responsible car owner, you need to know how to diagnose problems in major parts like the engine as well as in parts as small as the brake booster. Speaking of which, let’s talk about how to identify if you have a bad brake booster or if the problem with your car lies elsewhere.

What is a Brake Booster?

But before that, let’s first discuss what a brake booster is, since not a lot of people would know what it does and where you can find it. The brake booster’s purpose is to provide assistance to the braking system, so you won’t have to put as much force on it to make it work. This part is located between the brake pedal and the master cylinder. It uses a vacuum to overcome the fluid pressure in the braking system, which makes it easier to engage and activate.

For the brake booster to work, it needs a vacuum source, as we’ve mentioned earlier. In a gasoline-powered car, the engine is able to generate a vacuum that the brake booster can run on. However, diesel-powered engines are unable to produce such a vacuum. To compensate for this, diesel cars include a separate vacuum pump. Here, the brake pedal pushes on a rod that passes through the booster and goes into the master cylinder. In there, it activates the master cylinder piston, which is responsible for creating a partial vacuum on both sides of the brake booster’s diaphragm.

Once you step on the brakes, the rod opens a valve that allows air to enter the booster from its diaphragm. All the while, the vacuum created is being sealed off. The increase in pressure helps push the rod further, which in turn also helps push the master cylinder piston. When you let go of the brakes, outside air can no longer get in. Meanwhile, the vacuum valve is reopened, which restores the vacuum to both sides of the diaphragm.

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Car wheel brake disc

The Brake Pedal Becomes Hard to Press

Now let’s talk about the symptoms of a bad or failing brake booster. The first, and most obvious, of these symptoms is a brake pedal that’s hard to push. This may happen little by little, or all of a sudden. Aside from being difficult to press, your brake pedal will have a tendency to not return to its original position. If you notice any of these problems, stop your car immediately and park it somewhere safe and secure. Contact a professional immediately. Don’t use your car until the problem is fixed.

If your brake pedal is hard to press, your car may run at uncontrollable speeds, which may lead to accidents. On the other hand, if your car’s brake pedal doesn’t return to its original position, then unintended decelerations may occur. It may also cause your car to run slower than you’d want it to. These problems could be caused by a malfunctioning check valve. If this valve doesn’t work properly, air can’t be sucked out of the vacuum booster, which is why it’s hard to press the pedal.

A Higher Brake Pedal

Aside from the brake pedal being difficult to press on, you may also notice that it’s in a higher position than normal. Even if you can’t see the difference, you’ll surely be able to feel it once you hop into the driver’s seat. Having your feet even just a little bit higher is awkward and uncomfortable, which could prove to be a bad combination while driving. This is especially true when you need to bring your vehicle to a sudden halt due to unforeseen circumstances.

Longer Braking Distance

Another symptom of a failing brake booster is that your car takes a longer distance to stop than usual. This happens when air bubbles enter your car’s brake lines by way of the master cylinder – a part which we’ll talk more about later. These air bubbles greatly reduce the pressure you put on the brakes, causing them to apply very softly. This could be dangerous as you may underestimate how much distance you have left to put a stop to your car. If you don’t step on the brakes in time, you may crash into something.

A Stalling Engine

A problem with the power brake booster could also cause your car’s engine to stall. You may think that there is little to no connection between these two parts, aside from the fact that one makes the car go and the other makes it stop. However, when the diaphragm inside the brake booster fails, excess air from the engine may enter the brakes. This will cause the engine to stall when you press down on the brake pedal.

If you continue driving a car in such a condition, it will lead to more serious problems, which will cost a lot more of your hard-earned money to get fixed. For instance, if your car continually stalls, especially while you’re carrying multiple passengers or a heavy load, the transmission might get damaged. If this happens, you may feel a grinding or shaking sensation whenever you try to shift gears, or your car might make worrying noises such as humming or clunking. Your vehicle might not respond when it’s in gear, or worse, it may begin to leak important fluids or smell like it’s burning. Consult an expert immediately if this happens.

car brakes

How to “Bleed” Your Car’s Brakes

If this happens, the best course of action would always be to refer your car to a professional. Certified car mechanics are easy to find these days so you won’t have any problem with that. If you want to prevent these problems from getting worse, or if you want a quick fix, you need to learn how to “bleed” your car’s brakes. Remember to only do this if you’re confident in your mechanical abilities. One wrong move may end up costing you more money than you would have originally spent if you immediately brought it to a mechanic.

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Air bubbles appear in your car’s brake lines if you don’t have enough braking fluid in the master cylinder. To alleviate this problem, you’ll need to fill your cylinder back up and remove those pesky bubbles. To do this properly, you’ll need a couple of things: a brake bleeder wrench, a clean container, some brake fluid, and someone else willing to help you out. Once you’ve collected these, jack up your car then locate its brake bleeder screw. They are located behind each of your brakes. Try spraying some penetrant around the screws if they’re rusted or put on too tight.

Once you’ve located each of the brake bleeder screws, remove them. Then, attach a hose to one end of the screw. Put the other end of the hose in your container. Afterwards, fill your container with brake fluid until the end of the hose located there is submerged in it. Keep a steady hand or ask your friend to hold the bottle or jar for you to catch any brake fluid squirting out. Once you’re done with that, ask him or her to step on the brake pedal a couple of times, then to hold it in a pressed position. When you open the bleeder screw, you should see fluid coming out of the nozzle. You’ll also be able to see the air bubbles that you need to remove.

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After a few seconds, tighten the screw while your helper is still pressing down on the brake pedal. Once the screw is tightened, tell them to release the pedal. When you’re ready to bleed the brakes some more, ask them to push down the pedal again until you tell them to release it. Once the pedal is pressed down, loosen and tighten the screw to get rid of the bubbles. Proper communication is important since you should only change the position of the brake bleeder screws while the brake pedal is being pressed. Repeat this process multiple times until there are no more air bubbles left in the brake lines.

How Do I Know It’s Not a Problem with the Master Cylinder?

It’s also important to know how to differentiate problems in the brake booster with problems with the master cylinder. If your car’s master cylinder has gone awry, you may experience some abnormalities with the brake pedal. Over time, the seals inside the master cylinder will wear out, resulting in a brake pedal that feels mushy when pushed. When those all-important seals break down, they may contaminate the brake fluid, giving it a brown or black tint. Contaminated brake fluid may not work as well as a clean batch. It could also damage the components it runs through. Also, if your check engine light is always on, this might be the problem.

Now you know how to determine whether your car’s power brake booster has a problem or not. If it does, make sure to stop using it, and to bring it to a certified mechanic as soon as you possibly can.


  1. How Power Brakes Work – HowStuffWorks
  2. Symptoms of a Bad or Failing Power Brake Booster – YourMechanic