How to spot a bad brake booster or master cylinder?


The braking system is a very important part in your car, so you know it's time to learn about the symptoms of a bad brake booster, right?

Do you know that the brake booster is what connects the master cylinder and the brake pedal together? By the use of vacuum stored in the brake booster, the maximum fluid pressure of the brake booster is suppressed. With the help of this brake booster, the driver will not have to apply much pressure when pressing the pedal while pausing or making a slow stop of the vehicle.

On the contrary, you can find a master cylinder in modern cars today and it operates when the pedal has been pressed. It pushes the fluid from the reserving system to the braking system which puts pressures on the braking system, and after doing this, it causes the vehicle to come to a halt.

After you have been able to comprehend all these, and how the components function, we can now teach you on how to spot a bad brake booster or master cylinder.

1. Symptoms of a bad brake booster

1.1. Vehicle halts at a far distance

When you notice that you are trying to apply your brake and you notice that the stuff that makes your brake apply softly when you press is not working properly, just know that bubbles of air has gone into or entered into the brake lines through the master cylinder. After you have noticed this, you need to inspect your valve which is responsible for the elimination of air bubbles inside the system. Because if you do not do this, the issue you are facing about your vehicle pausing at a far distance after you have applied the brakes will continue to plague you.

Hard brake pedal- symptoms of a bad or failing brake

1.2. Apply reasonable amount of force on the brake pedal

The instrument used to control the pressure in the master cylinder is the check valve. If you want to know when this valve gives you problem, it makes the pedal which is soft and smooth into hard and aggressive brake pedal. So whenever you notice that it’s difficult to engage the brake pedal, it’s advisable to take your vehicle to a certified mechanic.

1.3. Stalling the engine

When you notice excess vacuum in the system of the engine, then you have to know that the diaphragm in the brake booster has failed. So as a matter of fact, when this happens and you press the brakes the engine will stall and this issue is very fatal to the vehicle.

So before you notice the failure in your brakes, it’s better to take your car to the mechanic to check it out.

2. Symptoms of a damaged master cylinder

2.1. Abnormality in the clutch pedal behavior

If you need to put more pressure on the brake, you have to know there is a possibility that there is air inside the master cylinder. And this causes fluid leakage.

If the heated fluid cannot expand, which increases the pressure on the brake line then the brake pedal is malfunctioning by depressing itself.

2.3. Expired master cylinder seals

The rubber seal that comes with the master cylinder gets spoilt with time, so when you do not replace the seals on time, the brake fluid will be contaminated thereby causing the pedal to sink itself without you touching it.


Be ware of the expired master cylinder seals!

3. Conclusion

After knowing how to spot a bad brake or a master cylinder, its is the drivers responsibility to always check the cars brake system and if you locate any of the symptoms above, will advise you to see a certified mechanic.

Meanwhile, you can check out for more tips and answers on our car maintenance section for more juicy tips!

Bello Hammed
  • Robert: On a '99 GMC Suburban 1500 when I pump the brakes I can very easily see the front of the booster moving the master cylinder in and out. Does that tell you anything?

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