Updated at: 03-08-2023 - By: Lucas

How much do you trust the brakes on your car? When you’re driving your 2-ton car down the highway, you should be sure that your brakes are in good shape. But, let’s be honest, brakes aren’t something that most people think about when they take their car in for service. Most of it is about taking care of the engine.

In this post, we’ll talk about the signs that your brake master cylinder is going bad. If you think your car is having trouble stopping, it’s a good idea to go through this list.

Symptoms of failing Master Cylinder

1) Brake Fluid Leaking

Brake Fluid Leaking

Do you see brake fluid dripping from your car? Or is your brake fluid level keeps getting low? If you answered “yes” to any of these questions, your master cylinder might be leaking. Over time, the rubber seals in the master cylinder wear down and might break.

When you don’t change the brake fluid as often, the seals get worse. Every two years, brake fluid should be flushed out. Using brake fluid that doesn’t work with the car could also damage the seals. So, make sure that you use the right kind of brake fluid. DOT 4 brake fluid is recommended for most new cars.

Before blaming the master cylinder, it’s important to make sure that the brake fluid line doesn’t have a hole or a loose connection. Repairing the master cylinder is much harder than fixing the brake lines.

2) Spongy Brake Pedal Feel

When there is air in the hydraulic brake system, the brakes will feel soft. When a car is well taken care of, air doesn’t get stuck in the brake lines, and the brake pedal feels hard when you step on it. This will make it easy for the car to stop because pedal force can be transferred to the callipers well.

If there is a leak in the system or air is stuck, the brakes will feel like they are springy or spongy. When you step on the brake pedal, it will go down much further with very little resistance.

We can feel this effect because it is easier to squeeze air than it is to squeeze oil. This is what makes it possible for the brake calliper to clamp down on the rotors.

If the master cylinder is leaking, the brake line is cracked or not securely connected, the brake fluid level is too low, or the brake fluid hasn’t been changed in a long time, air can get stuck in the system.

3) Sinking Brake Pedal

Sinking Brake Pedal

If the master cylinder leak is too bad, the brake pedal would just go all the way down when you step on it. When you push down on the brake pedal, you are pushing brake fluid out of the leak.

A loose brake line bolt or a cracked brake line can also cause a leak. But most of the time, it’s because the master cylinder or brake calliper seals have failed.

4) Brake fluid level low

Even though service technicians do check the level of brake fluid every time they do a service. But even then, they don’t usually have to add more. If the brakes are working well, you shouldn’t have to add more brake fluid even after a year or two.

So, if you see that the brake fluid level is dropping every month, that means there’s a leak in the braking system.

5) Dirty Brake Fluid

Dirty Brake Fluid

When the seal on the master cylinder or the seal on the calliper piston breaks, brake fluid can leak out and dirt and debris can get into the brake system.

This would make the brake fluid look darker, and in some cases it might even look brown. Most of the time, brake fluid is clear or has a slight honey colour to it.

6) Uneven brake pad wear

Most cars have two separate brake lines coming out of the master cylinder. The brakes on two wheels are controlled by each circuit. So if one circuit has a leak or blockage, it will have less stopping power than the other circuits.

This will lead to uneven wear on the brake pads. If a circuit is broken, the brake pads will wear out less quickly.

If you drive around the city every day, you might not notice weak brakes. But if you need to stop quickly and hard, the car will pull to one side.

Brake Master Cylinder Replacement Cost

Bad Brake Master Cylinder-2

Depending on your car, the total cost to replace the brake master cylinder will be between $300 and $580. This includes both the cost of labour and the cost of parts. Most of the time, this job takes about 2 hours to finish. Check Amazon for the price of a master cylinder rebuild kit

You can save $200 to $300 on labour costs if you do it yourself. Cost of labour is a big part of this, so you need a skilled mechanic.

You can do this yourself if you are good with wrenches and know how to work on cars. If you want to fix your car yourself, it’s a good idea to buy a workshop manual for it.

If you’re not sure, it’s worth it to pay for the labour since good braking should be your top priority when it comes to safety. Don’t forget to tell the mechanic to check the brake hoses and connectors as well if they are getting worn. Since now is a good time to replace it too, why not?

After a new master cylinder is put in, the brake system will need to be bled again (the process of removing air from the brake lines). Keep in mind that to bleed the brakes on some European cars, a computer had to be plugged into an OBD diagnostics port.

How does Brake master cylinder work?

Both disc brakes and drum brakes use a master cylinder to hold the rotors or drums in place.

When you push down on the brake pedal, you are basically pushing down on the piston in the master cylinder to pump up the hydraulic system. When the piston in the master cylinder is pushed down, it fills the pistons in the brake callipers, which squeezes the rotors.

Brake lines connect the callipers on all four wheels to the master cylinder.

Master cylinders can be either single channel or dual channel.

The brakes on all four wheels are fed by a single-channel master cylinder, which has one reservoir and one output.

A master cylinder with two fluid reservoirs and two outputs that each control two wheels is called a dual-channel master cylinder.

As you might have guessed, a master cylinder with two channels is safer. Even if one channel leaks or gets blocked, the other channel can still control the brakes on the other two wheels.

How to prevent early failure of the master cylinder?

When you brake quickly and hard, a lot of pressure builds up in the hydraulic system. On a racetrack, if you drive fast for a long time, the brake fluid can get very hot.

This not only adds pressure to the hydraulic system, but it could also cause the brake fluid to break down and turn into a gas. The piston seals will try to get past this vapour.

But driving on public roads doesn’t usually heat up the brakes too much. So, for most drivers, the best way to keep their brakes from giving out is to change the brake fluid every so often.

There are many things in new brake fluid that keep the seals in good shape. Over time, the brake fluid will lose its pack of additives and also get dirty. This old fluid can be hard on the seals and wear them out faster.