How to Tell if Brake Booster or Master Cylinder is Bad?

Are you facing a problem with the car brakes and finding it difficult, how to tell if brake booster or master cylinder is bad? Then, without wasting much time, look for the following symptoms in the brake system and follow the immediate maintenance tips for the respective part, which is running badly.

Symptoms: How to tell if Brake Booster or Master Cylinder is Bad

A brake booster connecting the brake pedal and the master cylinder is known to suppress the high fluid pressure by the use of a vacuum stored in it. The purpose of the brake booster is to decrease the force needed when pressing down on the brake pedal. In fact, with this booster, the driver doesn’t have to exert extra pressure on the pedal, while stopping or reducing the speed of the vehicle.

Contrarily, the master cylinder found in every modern car today begins to operate when the brake pedal is pressed. It pushes the fluid from the reservoirs to the lines in the braking system, which exerts pressure on the brakes. Finally, this pressure slows down the car or causes it to halt.

Now, after comprehending the basic meaning and functioning of these components, let’s learn how to tell if brake booster or master cylinder is bad?

Symptoms of a faulty brake booster

1. Vehicle stops at a longer distance

When the air bubbles enter the brake lines via the master cylinder, it reduces the pressure that causes the brake to apply very softly. This situation immediately calls for the inspection of the valve (responsible for removing the excess air bubbles inside the system). Or else, the problem of vehicle stopping at a longer distance, after the brake is applied, would continue.

Read more:

2. Needs to apply more force on the brake pedal

The check valve is responsible for controlling the pressure inside the master cylinder. If this valve starts creating a problem then, it turns the soft and smooth pedal into the aggressive and hard brake pedal. So, whenever it gets difficult to engage the brake pedal, seek its inspection from a certified mechanic.

Tips to know about how to tell if brake booster or master cylinder is bad
Look for how to tell if the brake booster or master cylinder is bad. (Photo: Youtube)

3. Stalling the engine

When the diaphragm inside the brake booster fails, it allows the excess vacuum to enter the system from the engine. As a result, when the brake is pressed, the engine stalls or has a rough idle which can later cause issues that are more serious.

Therefore, before you encounter any event of a brake failure, it is better to take your vehicle to the nearest trained professional.

4. Check engine light on

A dysfunctional brake booster can have a vacuum leak allowing unmetered air to enter the engine. This causes more air than fuel in the combustion process also known as a lean mixture. At this time, the misfire will happen in the engine and the check engine light will show off on your dashboard. 

5. Strange noise

If you hear a constant sound like a hissing noise when you press down on the brake pedal. This can be a symptom telling that the brake booster has trouble. When the diaphragm inside the brake booster is torn allowing air to pass through. However, if you hear a hissy sound without pressing down the pedal then you might have a faulty brake booster plunger seal.

Watch this video to know how to test the the brake booster:

Symptoms of a bad master cylinder

 1. Abnormal clutch pedal behavior

Under normal circumstances, a functioning brake pedal should feel firm when depressed. However, if you notice the brake pedal starts to feel spongy when pressing, it will be an automatic sign that your brake master cylinder may be having an issue. At that time, it indicates the presence of air in the hydraulic brake system.

If you have to exert extra pressure on the brake pedal then, there are chances that the master cylinder has the air inside it, which is further causing leakage of fluid.

Or, if the brake pedal is depressing itself then, this means that the heated brake fluid is not able to expand. Because of this, it causes extra pressure on the brake lines.

2. Worn-out master cylinder seals

How to tell if brake booster or master cylinder is bad from different ways
Search how to tell if the brake booster or master cylinder is bad. (Photo: Rio International)

The rubber seals used in the hydraulic system not only help keep the brake fluid from coming out but they also prevent dirt and debris from mixing with the brake fluid. The rubber seal on the master cylinder wears out with time. And, if these seals are not replaced timely, they may contaminate the brake fluid. Thus, causing the pedal to get soft and doughy or slowly sinking to the floor.

3. Brake fluid leak

An external leak can come from the grommets between the reservoir and the body or from the seal inside the master cylinder that’s closed to the brake booster. Internal leaks could also occur if the seals are torn preventing the brake cylinder from holding the pressure when pressing the brake pedal.

In addition, if you notice that the fluid is darker or brown than normal, it’s also a sign of a bad brake master cylinder. It could be the moisture debris that enters through leaks on the seal because the master cylinder uses rubber seals that can break down over time.

Final Thoughts

After knowing how to tell if brake booster or master cylinder is bad, it is the responsibility of the driver to keep a check on the brake system of the car. And in case you locate any of the above symptoms with your car, it’s better to take it to the expert mechanic.