Have you ever thought of how your vehicle stops with the least force applied on the brake pedal? In fact, this is the brake booster that delivers that additional force to the braking system which makes your vehicle easily stop. Driving a vehicle without a brake booster is just like riding a horse without a bridle that puts your safety at risk and increases the chances of collision especially when you need emergency stop.

And without brake booster, applying the brake on your vehicle would be very disgusting as it would require tremendous force to be exerted on the brake pedal which is not possible for everyone.

Let’s take this component very seriously and keep an eye on the symptoms that indicate us of its failing. But before we go deep into the symptoms let’s first understand its working mechanism.

What Does a Brake Booster Do?

The basic function of the brake booster is to multiply the force you apply on the brake pedal so that you have to apply minimum pressure on the brake pedal for stopping the vehicle. The brake booster is placed right between the brake pedal and the master cylinder.

When you apply pressure on the brake pedal to stop the vehicle, the shaft attached to the brake pedal moves towards the brake booster. This shaft opens the atmospheric valve that allows the fresh air to enter the booster.

This air is further separated into two sections via a diaphragm. The air enters the air side of the booster causes the primary shaft to push the diaphragm to the master cylinder due to the pressure difference between the airside and the vacuum side of the booster.

The vacuum valve attached to the engine suction valve maintains the vacuum during its suction stroke. This negative pressure helps the diaphragm to move and multiplies the pressure applied by you. When the diaphragm moves, the secondary shaft also moves towards the master cylinder’s piston which causes the vehicle to stop.

Signs and Symptom of Bad Brake Booster

1. Brake Pedal Becomes Difficult to Press

The first and the most common symptom of a failing brake booster is that the brake booster becomes very hard to press. And when you press the pedal, it does return to its original position.

If you notice something like this, it means the brake booster has some fault with it. In such a condition, you should not drive the vehicle at all until the issue is resolved.

2. A Higher Position of Brake Pedal

Apart from the brake pedal being stiffer, you may also notice that the brake pedal is slightly higher than normal. However, you will not see the difference while looking at the brake pedal but when you place your feet on the brake pedal, you will feel the change in its position. And a driving vehicle with this condition could be very dangerous. Therefore, you should immediately get it repaired to save yourself from any catastrophic situation.

3. Longer Braking Distance

Another alarming sign of a bad brake booster is that you may notice a sudden increase in the time it takes to stop the vehicle. In such a condition, when you press on the brake pedal, it does not stop the vehicle immediately instead it takes a little longer that makes your vehicle’s braking system unpredictable. Due to this fault, you may not have the exact idea when you have to press the brake pedal that can lead to a crash. Therefore, you should strictly avoid driving the vehicle until the braking system is repaired.

4. Engine Stalling

When there is a problem with the brake booster, you may experience a little stall in the engine. It happens when a faulty brake booster draws an additional vacuum from the engine and the defective diaphragm inside the brake booster allows air to escape through the seal. In such a condition, when you press the brake pedal, you feel like the engine is stalling. If you keep driving the vehicle with this condition, it can cause serious damage to the engine that leads to expensive repair.

What Happens When You Have a Bad Brake Booster

The key role of brake boosters is to multiply the power applied on the brake pedal. If you drive a vehicle without or a faulty brake booster you have to apply a great amount of strength of your muscles to stop the vehicle.

But thanks to the brake booster that does not only make the braking of the vehicle easier but also makes your drive safer.

When your vehicle has a bad brake booster, you have to deal with several issues including hard pressing brake pedal, longer braking distance, unpredictable braking system, and engine stalling. Aside from these issues, your vehicle may have grinding or humming sound while shifting the gears or your vehicle may stop responding when it is in gear.

Can a Bad Brake Booster Affect Engine Performance

However, it seems like there is no connection between the brake booster and the engine but when there is some fault with the brake booster, it affects the performance of the engine too. A defected brake booster may cause the engine to stall. However, it happens especially when the diaphragm of the brake booster fails, it allows excess air from the engine to enter the brakes that cause engine stalling when you apply force on the brake pedal to stop the vehicle.

If you experience frequent engine stalling and you still continue driving the vehicle, it may lead to serious damage to the engine.

How to Check for a Bad Brake Booster

If you’re not sure whether the brake booster is affecting the performance of the braking system, you can test the brake booster at home without needing any tool. The simple way to test the brake booster is by pressing the brake pedal in different conditions. Let’s begin the test.

Power Brake Booster Test 1

Start the engine, let it idle for a couple of minutes, and then shut it off. Now, pump the brake pedal and hold the pressure on the pedal while you again start the engine. On starting the engine, the pedal should drop by half an inch or less. If this happens, it means the booster is working perfectly.

Power Brake Booster Test 2

With the engine off, press the brake pedal several times using normal foot pressure. if you notice the brake pedal is becoming firmer while pressing the pedal second or third time, this means the brake booster is in the absolute right condition with sufficient vacuum in it.

Power Brake Booster Test 3

Start the engine and let it idle for a few minutes. Now, press the brake pedal and shut off the engine but still keep the pedal pressed. Keep the pedal pressed for a couple of seconds even after shutting off the engine. If the pedal does not go out of its actual position after maintaining the pressure on the brake pedal, it means the brake pedal is in good working condition. But if it goes out of its position, it means either there is a leak in the brake booster or the vacuum hose.

During the test, if you have received all the results that point to a defected brake booster but you still want to confirm that brake booster is faulty, you can test the brake booster using a hand-held vacuum pump.

For this test, start the engine; let it idle for 15 to 20 minutes and shut it off. Now disconnect the vacuum hose from the check valve and place the vacuum pump at its place and plug it into the check valve. Now, apply vacuum to the brake booster. And then press the brake pedal. If you notice the vacuum drops by a little margin, it means the booster is in good condition. But if the vacuum remains stable or directly drops to zero, it means the brake booster requires replacement.

Can You Drive with a Bad Brake Booster

Certainly, you can drive the vehicle with a faulty brake booster but it is not recommended. If your vehicle has a bad brake booster, the braking system of the vehicle would not work properly. You would have to press the brake pedal down very hard each time you want to give a complete stop to the vehicle. And sometimes, you would not be able to fight with the inertia of the heavy vehicle despite applying the full strength of your muscle. And if you’re not able to put the brake in the right time that can lead to a crash.

Brake Booster Replacement Cost

First of all, you should consult an expert mechanic who can guide you the right way whether you need the entire brake booster replacement or a little repair and maintenance. When it comes to the replacement cost, it largely depends on the make and model of the vehicle but on average the cost ranges between $300 and $700 where labor cost can go up to $100 to $180 and car parts costs range from $200 to $500. The tax percentage in your country also affects the cost to some extent.

If you want to save on replacement cost, you should do a comparison between prices from different mechanics, it will help you to cut the cost by a few bucks.


While you know, with a faulty brake booster you can drive your vehicle as the brake will not go completely out of order, it will become much harder to apply the brake to stop the vehicle. But once it is confirmed the brake booster is defective, you should not drive your vehicle as it poses safety risk especially when you need emergency stop.

So if you notice that the brake pedal is becoming hard to press or taking longer to stop the vehicle while applying the brake, you should immediately approach a certified mechanic to avoid potential accidents and damage to the vehicle.