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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 of the 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

Brake Booster connecting the brake pedal and the master cylinder, is known to suppress the high fluid pressure by the use of vacuum stored in it. 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. And 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?

1. Symptoms of a Faulty Brake Booster

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.

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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 the certified mechanic.

Tips to know about how to tell if brake booster or master cylinder is bad
Look for how to tell if brake booster or master cylinder is bad. Source: Youtube 

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, 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.

2. Symptoms of a Bad Master Cylinder

Abnormal Clutch Pedal Behavior

If you have to exert extra pressure on the brake pedal then, there are chances that the master cylinder has the air inside them, 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 which, it causes extra pressure on the brake lines.

Worn Out Master Cylinder Seals

The rubber seal on the master cylinder wears out with the 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.

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

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 mechanics.

  1. Firewood Alfred says

    I drive a Toyota double cabin D4D. It’s not smoking, but can not start until I push for close to 40 meters to start the engine. the battery is good. Could it be due to worn out rings or what? I checked both heater plugs and nozzles but they are ok. What is wrong?

  2. kaci grieger says

    I didn’t have ANY ISSUES with my breaks, in fact my regular mechanic told me I had aprox 10,000 miles before my pads would need to be replaced. 3,000 miles later I brought my car in for a General inspection as I was going to be taking my three children on a road trip with me. The Machanic on staff that day said I needed new break pads immediately, so I had them replaced. We made it from Florida to Louisiana with no problems the dayb before we were to leave to come home, We got in the car to go to the playground and my break light was on and petal was going to the floor! I checked the break fluid and it was VERY LOW! I added aprox 16 ounces of fluid the strange sound stopped and the Break light went off but the petal still had to be compressed to the FLOOR before the vehicle would stop! I made it safely back to Florida and returned to the Machanic who is telling me that the master cylinder and booster are “NOW SHOT” this isn’t the first time I have brought my car in for General maintenance and had it returned with BIGGER ISSUES! Is it possible that the Machanic did something wrong or didn’t do something correctly that would have caused this MESS??? They’re taking no responsibility and wanting to charge me almost $3000 to fix an issue that didn’t exist prior ??‍♀️ Any advise you can give would be greatly appreciated Thanks in advance!

    1. Zee says

      So, when changing the brake pads, a mechanic will not need to do anything to the hydronic system of the vehicle meaning all he does is depress the caliper pistons using a clamp to slide the brake pads in. With that being said, it is unlikely the mechanic was at fault. If you had a caliper replaced, then the tech would of had to bleed the braking system to rid it of air.
      More than likely a seal wore out on the MC or BB. It’s hard to say with out knowing the year make and model. Another option would be you had a leak in a brake line. I strongly recommend in the future to get second opinions. $3000 is entirely too much to charge for such a simple job. I’d have it all set in 4 hrs.

    2. Brett says

      Brakes….. not breaks. My god.

  3. neilmaclean says

    my brakes come on after a short drive pedal gets hard and brakes come on. changed all parts acept booster and maqster cylinder. any info on what is gone!

  4. neilmaclean says

    its a kia rio5 2007

  5. Wanda Moss says

    my 2003 4 runner brake pedal without warning or lights, would not stop and i had to use the emergency brake…like nothing there. repair shop states my truck will not communicate with the diagnostic leaks, no bad cylinders…but i have no brakes. new pads, rotors, the works less than a year ago.

  6. Dr Jimmy says

    Would like to understand how drive 2 in automatic cars work

  7. Atul says

    When I pressed my brake pedal it pull to left side, my caliper brake house pipe are all good and working properly and refaced rotor and install new brake pads tyre pressure and leaf spring is maintained but still the issue remains same plz help..

  8. Kit hannigan says

    Thanks for pointing out how a hard and aggressive brake pedal can point to a problem with your brake booster. My son frequently goes on interstate drives to meet up with his clients. Naturally, he relies a lot on his car for his business. I wouldn’t want him to get any car trouble while on the road, so I will be sure to advise him to get his car into a car shop immediately should he find any abnormalities with his brake pedal.

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