4 Bad Brake Booster Symptoms – Causes & Fixes


Symptoms of a bad brake booster are generally easy to spot.

The brake booster is an integral device that amplifies forces applied to the brake pedal. It is located within the power brake system, between the brake pedal and the master cylinder. If the booster stops working or becomes damaged, it can cause the brakes to feel hard and unresponsive. Additionally, the car may have a hard time stopping.

The most common symptom of a bad brake booster is an increased braking distance or stiffness of the brake pedal. The most common cause is a vacuum leak, either within the vacuum hose or the brake booster itself.

So, if your vehicle’s brakes no longer feel as tight or responsive as they once did, there may be a problem with the brake booster. Continue reading to learn more about how it operates and what commonly causes it to go bad.

Also, we’ll talk about how to tell whether your brake boosters need replacing. Don’t place yourself at risk when you could quickly fix the problem.

What is a Brake Booster?

Brake boosters are devices that use vacuum pressure to amplify forces applied to the brakes. The part is located between the master cylinder and the brake pedal. When a driver engages their brakes, a plunger presses into the master cylinder. This forces a diaphragm downward, pressurizing the brake fluid within the cylinder and triggering the brake system.

diagram showing how a vacuum brake booster works.

This system is also known as a power brake booster but some vehicles use a hydraulic brake booster. As the name implies, this uses hydraulic pressure to assist the master cylinder.

A hydraulic pump is connected to the brake pedal on one side and the master cylinder on the other. When a driver engages their brakes, the pump pressurizes the fluid in a similar manner to trigger the braking system.

Common Reasons Why Brake Boosters Go Bad

Brake boosters can go bad for a variety of reasons. In some cases, it may be due to a manufacturing defect that caused a flaw in the part. However, the most common reasons have to do with leaks. These can be either in the vacuum hose or in the power brake booster itself.

Power brake booster vacuum hose and check valve
Power brake booster vacuum hose and check valve

A leak in the vacuum hose will cause the brake booster to lose its vacuum pressure. This means it can no longer amplify the force applied to the brake pedal. Over time, the vacuum pressure will decrease, causing the brakes to feel stiff. In extreme cases, the power brake system may fail entirely.

A leak in the power brake booster itself is less common but can also cause the part to fail. This type of leak is usually the result of a crack in the booster, which can be caused by corrosion, an impact, or extreme temperatures. A leak in the power brake booster will also cause the brakes to feel rigid and unresponsive.

In general, though, it’s wise to check the hoses before replacing the entire part. Due to the intense temperatures generated through combustion, hoses are more prone to drying out and cracking over time, whereas the booster itself is a little more resilient to the heat of an engine.

How to Read The Symptoms Of a Bad Brake Booster

Bad brakes are inherently dangerous and put other drivers at risk of collision. To avoid a possible wreck, troubleshoot your brakes and look out for the following signs:

  • Increased Braking Distance: As fluid leaks from the booster, your vehicle will struggle to produce enough pressure to slow down your vehicle. You’ll find that your vehicle takes longer to come to a stop and you’ll have to adjust for poor braking performance.
  • Hissing Brakes: If you hear a hissing noise when you press the brakes, it may be due to a leak in the power booster.
  • Hard Brake Pedal: Without vacuum or hydraulic pressure to assist the braking action, the driver must create all of the force needed to depress the master cylinder. This causes the brakes to feel hard, stiff, and unresponsive.
  • ABS Warning Light: In some vehicles, the anti-lock braking system (ABS) warning light will come on if there is a problem with the power booster.

If you experience any of the issues while driving, consider pulling over or heading to the nearest mechanic to have your brakes checked. You can test your vehicle’s brake booster by idling the engine for a minute before shutting it off and depressing the brakes two or three times.

If the booster is properly functioning, you should feel some vacuum assistance. If not, the booster has gone bad.

How Far Can You Drive with a Bad Brake Booster?

Technically speaking, It is possible to drive with a bad brake booster but it’s inadvisable considering that it decreases the effectiveness of your vehicle’s power brake system, making it harder to slam the breaks

If the brake system completely breaks while you are driving, it could cause an accident, putting both your life and others at risk. Therefore, it’s best to repair a bad brake booster as soon as possible. 

Brake boosters provide extra power to your brakes, so without one, your braking distances will increase. This is especially dangerous at high speeds or on wet roads. If you must drive with a bad brake booster, make sure to allow extra space between your vehicle and the one in front of you.

Additionally, avoid using your brakes whenever possible. If you’re approaching a stop sign or red light, downshift to a lower gear, if possible, to help slow your vehicle’s speed. Also, use your emergency brake sparingly as it will cause your vehicle to skid if used at high speeds.

Is it Safe to Fix Your Own Brake Booster?

Some repairs are simple and can be tackled with basic household tools but, when it comes to your vehicle’s brakes, it’s best to leave the issue to a trained professional. If you are not experienced with brake repairs, attempting to fix the problem yourself could do more harm than good.

Brake boosters are located within the power brake system, which is a complex web of interconnected parts. In order to properly fix the problem, you’ll need to disassemble the power brake system, which requires special tools and expertise.

bad Brake booster location on vehicle
Brake booster location on vehicle

Additionally, the power brake system contains a number of high-pressure components that, if handled improperly, could cause serious injury. Therefore, it’s always best to consult with a certified mechanic to have the problem fixed.

How Much Does It Cost to Fix a Bad Brake Booster?

Repair costs vary depending on the severity of the problem and the make and model of your vehicle. In some cases, you may have to replace the entire power booster unit, which can cost between $663 and $820 (2024). Additionally, you may have to replace the vacuum hose, which could cost another $50-$100.

To get an estimate, take your vehicle to a qualified mechanic and have them inspect the power booster system. They should be able to give you an estimate of the cost of the repair.

The Bottom Line

A recap of bad brake booster symptoms: Your vehicle’s brake booster creates pressure that amplifies forces applied to the brake. This makes it easier to bring your vehicle to a complete stop. If the system fails, you’ll struggle to depress the brakes and notice that your vehicle takes longer to reach a complete stop. Speak with a mechanic as soon as possible to resolve the issue and prevent possible collisions.

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