brake booster symptoms

Bad Brake Booster Symptoms, Causes & Replacement Cost

In Brakes by Magnus Sellén2 Comments

brake booster symptoms

A brake booster can be found in most modern vehicles.

When you depress the brake pedal, you do not have to apply too much pressure to brake the vehicle. This is due to the brake booster, which amplifies the pressure you apply and helps to stop the car comfortably.

Brake boosters are also called “servos”, and they not only increase the safety of the car, but also help to improve performance. Like any other component in a car, the brake servo can become damaged after a while, which can cause problems when stopping the car.

In this article we will discuss the most common symptoms you will experience with a defective brake booster and how you can replace it.

Purpose of the Brake Booster

In the past, vehicles were equipped with drum brakes that used their own power assistance. After that they were replaced by disc brakes, but the drivers still had some difficulties to apply enough pressure to stop the car. Therefore the modern vehicles were equipped with a brake booster.

The main task of the brake booster is to reduce the effort of the driver when braking. The brake booster, which is located between the brake pedal and the master cylinder, uses a vacuum to overcome the fluid pressure in the brake system.

Symptoms of a Bad Brake Booster

Below are the most important symptoms you should notice if your brake booster is threatening to fail or has failed.

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Difficulty in Pushing Brake Pedal

The most common and first symptom you will notice is that the brake pedal is difficult to operate. In addition, sometimes the brake pedal does not even return to its original position and may stick to the ground. If you notice something like this, it means that something is wrong with the brake servo. Because it is not safe to drive with defective brakes, we recommend that you have the brake booster replaced as soon as possible.

Brake Pedals Gets Higher than Usual

In addition, the brake pedal might be stiffer than average, so if you notice that it is slightly higher than usual, it means there is a problem with the brake booster. Such a situation can be dangerous and should be corrected immediately to avoid an accident.

Car Takes Longer to Stop

If the brake booster is defective, the pedal does not receive enough force to stop the car immediately. So if your brake booster starts to fail, it will take longer for the car to stop. In slippery weather this can be dangerous, so we recommend that you take your car to a professional mechanic and have the brake system checked.

Engine Stalling

A failed or defective brake booster draws additional vacuum from the engine. This happens when the diaphragm in the brake booster fails, allowing air to escape through the seal. As a result, every time the brake pedal is depressed, the engine stalls a little. This problem can even damage your engine and lead to more expensive repairs.

Hissing Sound Heard Under the Dash

A failed brake booster sometimes produces a hissing sound that can be heard under the dashboard. The noise is caused by the escaping vacuum, and this vacuum loss can also lead to performance problems. To avoid further damage to the brakes or the engine, it is recommended that the booster be repaired quickly.

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How to Test the Brake Booster?

brake pedalBefore you go to a mechanic to replace the brake booster, it is advisable to check it yourself using the following procedure.

Step 1: Start the Engine

Start by sitting in the car and putting the gear in neutral in a manual car or in park in an automatic car. Start the engine with the handbrake on, let it idle for a while, and then switch it off.

Step 2: Press the Brake

Start pumping the brake pedal, generally about four times, and keep the pedal depressed with light pressure.

Step 3: Start the Engine

Start the engine with your foot on the pedal and you will notice that the brake pedal moves down slightly. If this is not the case, then the brake booster probably lacks a sufficient vacuum.

Step 4: Turn off the Engine

Carefully lift your foot off the brake and turn off the ignition.

Step 5: Press the Brake Pedal Again

Pump your foot on the brake pedal about four times. If you feel the pedal lift after the second or third time you press it, it is possible that the brake servo is retaining a vacuum, or there is a vacuum leak in the brake booster. You can use a vacuum gauge or vacuum pump to know exactly where the problem is being caused.

Step 6: Hold the Pedal

Start the engine, then depress the brake pedal and turn the key to stop the engine. Keep the pedal depressed for 30 seconds after turning off the engine and check if the pedal remains in that position after releasing it. If it does not remain in this position, there may be a leak in either the brake booster, the vacuum hose or the engine vacuum.

Here is a video of the whole process:

Brake Booster Replacement Cost

The average cost of replacing a car’s brake booster is between $300 and $750. The parts themselves cost about $160 to $550, while labor costs range from $140 to $170. Depending on the mechanic, additional fees may also be charged.

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However, the cost of replacement usually depends on the model and make of your car. New vehicles with an advanced braking system are difficult to diagnose, and replacement costs can be higher for such vehicles. It is recommended that you do some market research and contact a few different mechanics before you decide on the right vehicle.

Leave a comment below if you have further questions about brake boosters!

Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.

2 thoughts on “ Bad Brake Booster Symptoms, Causes & Replacement Cost ”

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  1. On drive, when I press my brakes, the rpm drop to about 500rpm, then I get a soft vibration. Please help. I have recently clean the throttle, I notice it a day after the cleaning

  2. Can a faulty brake booster and vacuum booster cause a car to break down and not be able to start?

  3. Due to a very high demand and high ammount of comments, you have to wait for some time for your car questions to get answered. If you want to get fast answers from a certified master technician you can ask your questions here:
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