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The master cylinder is one of the most important parts of a vehicle’s braking system. It converts mechanical pressure into hydraulic pressure to engage the brake calipers in the wheels. Unfortunately, the brake master cylinder can also fail. Here are some of the most common symptoms of a failing brake master cylinder you need to know.

Brake Warning Light Turns On

When you step on the brake pedal, it pushes a rod in the brake master cylinder. This also pushes the pistons that are present in the cylinder bore. The pushing displaces brake fluid and directs the fluid through the different brake circuits. The fluid then goes through the brake lines and to the individual brake components in the wheel.

One of the earliest indicators of a failing brake master cylinder is the illumination of the Brake warning on your dashboard. It is also one of the easiest ways to tell if you have issues in your braking system. It indicates a reduction in brake fluid pressure. Unfortunately, a bad brake master cylinder is not the only reason the warning light will turn on.

At the bottom of the brake fluid reservoir is a brake fluid level sensor. It communicates with the car’s computer to tell it if the reservoir contains the right amount of fluid or not. The sensor can also fail. It can send the wrong information to the computer. This can turn on the Brake Warning light.

A low level of brake fluid can also illuminate the warning indicator. If you notice that you are topping off your brake fluid more often than necessary, then it is possible that you have a problem with the brake master cylinder. It can also signify that you have a leak somewhere in the brake circuit.

One way you can isolate the problem is by filling the reservoir with brake fluid. This should make the symptom go away. If it comes back, then there is a potential problem with your brake master cylinder or there could be leaks somewhere along the brake lines.

Brake Fluid Leak

The master cylinder contains the brake fluid that you put in the reservoir. It uses this fluid to activate the different brake systems in the individual wheels. It pushes the fluid so that the brake calipers or the brake drums will engage.

The brake master cylinder sits under the brake fluid reservoir. You should be able to check if there is a leak in the proportioning valves or the fluid control valves. The former connects to the different brake circuits of your car. The latter receives and conveys fluid from the reservoir and into the master cylinder.

You can also try checking under the car. Look at the position of the master cylinder relative to other parts of the car in the engine bay. Check also the area on the ground directly under the master cylinder. See if there is any indication of a leak coming from this part of the brake system.

Spongy Feel of the Brake Pedal

Another telltale sign of a failing brake master cylinder is a spongy response of the brake pedal. Under normal circumstances, the brake pedal should feel firm whenever you apply the brakes. This is proportional to the amount of force that you apply to the brake pedal.

As mentioned, the brake pedal connects to the master cylinder via a push rod. The master cylinder generates the right level of hydraulic pressure to activate the brakes in the front and rear wheels. If there is a problem with the master cylinder, you may notice a very spongy response in the brake pedal.

One of the most common reasons why you may have a master cylinder-related spongy brake pedal is worn-out rubber seals. These are important parts of the brake master cylinder that serve to keep the fluid within the cylinder. If the rubber seals get damaged or are worn out, then it can result in an internal leak. This can cause the brake pedal to feel spongy and soft.

There are other causes of a spongy feel of the brake pedal, however. The most common is the presence of air in the car’s brake lines. This prevents the brake fluid from flowing in a more efficient manner. Damage to the brake lines can also give you a soft feel on the brake pedal. Rust can degrade the brake lines and cause leaks. Leaks in the brake calipers can also create a spongy feel.

Contaminated Brake Fluid

We mentioned that the brake master cylinder contains rubber seals. In addition to a spongy feel on the brake pedal, damaged rubber seals can also lead to contamination of the brake fluid. Dirt, debris, and other particles can enter through the small opening of the damaged rubber seal. These particles can mix with the brake fluid and reduce the hydraulic pressure.

If this happens, you may find it more difficult to stop your car. The hydraulic pressure may not be enough to apply the brakes on the wheels. It may take the car a much longer time to slow down. This can have significant implications when driving. If the vehicle in front of you makes a sudden stop, you might hit its rear because of the reduced stopping distance of your car.

Sinking Brake Pedal

One of the surest signs of a brake master cylinder failure is a sinking brake pedal. When you depress the brake pedal, it should return to its normal position the moment you release it. What happens in a sinking pedal is that it no longer returns to its original position. It stays close to the floor. In some cases, it may still go back up. However, it may take a while before it reaches its starting position.

This is dangerous. You should never drive your car if you have a sinking brake pedal. It is important to have the brake master cylinder checked. Depending on the damage, a mechanic can fix the problem or replace the cylinder altogether.

Any issue with the brake master cylinder can make driving unsafe. If you notice any of these symptoms in your car, you should have a mechanic check it at once.

Related Post: Best Brake Bleeder Kits, Best Car Brakes and Best Car Brake Pads

Sources:

  1. Symptoms of a Bad or Failing Brake Master Cylinder – Your Mechanic
  2. What are the signs of a bad brake master cylinder? – Quora

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