You Should Know All: Bad Master Cylinder Symptoms [+Solutions] In 2023

Pedal going straight to the floor? That’s one of the most common bad master cylinder symptoms you’ll run into.

Generally speaking, you might experience several other symptoms when there’s something wrong with the master cylinder, not just one.

In this guide, we’ll explain how you can track down these issues and fix them independently.

Diagnosing some of these problems can be challenging, but getting stranded in the middle of nowhere is worse than that.

That said, here’s everything you need to know about the master cylinder:


What Is a Master Cylinder?

The master cylinder is a vital part of your vehicle. This little part of your car has a simple job: to supply brake fluid to your vehicle’s four wheels through the brake lines.

The master cylinder has a reservoir tank mounted on top, where all the brake fluid is stored.

But if the brake lines got damaged, all that fluid coming from the reservoir tank will come out as it’s flowing through the hoses. As a result, the pedal will sink to the floor.

8 Signs Something Is Wrong With the Master Cylinder

Unlike other mechanical issues, a bad master cylinder usually makes it very clear when it’s no longer working.

The problem will persist until it gets addressed. It’s not just a one-time thing. That said, here is how to find the root of the problem and fix it:

1. Master Brake Cylinder Brake Fluid

Does your pedal have zero resistance, and it feels like it goes to the floor as soon as you step on it? Well, there’s a high chance you got a broken brake line.

In fact, if you look underneath the car, you will find a massive puddle of brake fluid.

Alternatively, check the brake fluid. If the level is not the same as before and it’s significantly lower, you’re losing fluid somewhere.

To make sure the brake line is indeed the problems follow these steps:

  • Start at the master and then follow the lines throughout your vehicle. Follow all those lines all the way to the four wheels.
  • For this, you might have to lift the vehicle as following the brake lines without jacking it up can be difficult. Also, if you jack it up, don’t forget to use jack stands.
  • With the suspension unloaded, move the wheel around and carefully look at the brake hose to find out if it’s leaking.

Some broken lines are hard to find if you don’t know where to look. So, you might spend a lot of time before you can find the culprit.

Once you’ve found the broken line, replace it, and the problem will be gone.

2. Master Cylinder Leaking Inside Itself

Similar to the first problem we covered above, the brake pedal sinks in your car as you step on it. Most of the time, this issue is related to the brake lines.

But if you couldn’t find any brake fluid and they all seem to be dry, then perhaps the brake master is leaking inside itself.

This usually means that air got inside the system. And when this happens, it can ruin the master cylinder seals.

Unfortunately, the only way to fix this problem is to replace the unit itself.

Since you have to get a new one, we wholeheartedly suggest getting a brand-new master cylinder. Do not get a cheap rebuilt one.

Usually, they take shortcuts when making them, so they won’t last as long as a brand new one.

What’s more, sometimes they don’t work out properly. It’s pretty much gambling.

3. Brake Light Going On And Off

Brake lights going on and off are among the most common symptoms you’ll get if the master cylinder is acting up.

There’s a little switch built into the system. When there’s something wrong with the system, the sensor will let the driver know by triggering the brake light on and off.

Usually, it could mean several things. But for the most part, it is related to the air inside the lines. That said, consider the following symptoms to rule this out:

  • If the pedal is sinking to the bottom as you press it down, you might have air inside the lines.
  • If the brake pedal is unresponsive, there’s a high chance you need to bleed the air out of the system.

If you’ve run into any of these symptoms, do not put them off. If you’re not fond of doing repairs on your own, take it to a professional.

Either way, this is a cheap and straightforward fix. So, you can probably pull it off if you’re willing to spend some time.

If that’s the case, we suggest watching this video. This guy goes through all the steps required for this job.

What’s more, he’ll walk you through two common ways to bleed the air out of the system:

4. Dirty Brake Fluid

Did you by any chance put oil in the brake system? Well, you might have to replace everything that has rubber.

If oil gets inside the brake system, it’ll contaminate everything, making all the rubber in the brake system go bad.

This is pretty common and can be very expensive to fix.

You have to replace all the rubber parts in the vehicle, including the rubber brake hoses, the brake master cylinder, the calipers, and the ABS module it has a few rubber seals.

What’s more, you’ll have to clean the system out using some type of brake clean and then flush it. In total, you might spend $4,000-$5,000 to fix your vehicle.

5. Brakes Lock Up

Were you going down the road only to realize that the front brakes locked up? Well, you’ve run into one of the most common bad master cylinder symptoms.

If you recently installed a master cylinder, perhaps you used a rebuilt-one. Those types of master cylinders are not reliable, and they only do more harm than good.

If that’s not the case, consider loosening the mounting nuts on the master cylinder. After that, gently pull it towards you. In theory, this should release the brakes.

There’s also another reason why the brakes might lock up. For example, you might need to bleed the brakes as you might have air in the lines. Moreover, the brake fluid could be too old.

The latter is usually caused by water getting inside the master cylinder since it destroys the hydraulic pressure you’re supposed to get.

6. Overheating Brakes

If you’ve recently installed aftermarket rotors and pads and noticed that they are overheating as you drive, perhaps the master cylinder got damaged.

Even though it might seem like this problem is related to the new rotors and pads, consider troubleshooting the master cylinder before getting OEM rotors and pads.

Usually, when the rotors and pads are overheating but the brakes are not locked, it means the master cylinder must be replaced as it failed.

Here is how to determine that culprit is indeed the master cylinder and not the new rotors and pads:

  • Drive around without using the brakes. If that does not overheat the brakes, it’s safe to assume the problem lies within the master cylinder.

So, it comes down to replacing the master cylinder. Replacing it will fix this issue.

7. Worn Brake Pads

Uneven pad wear will drastically reduce the longevity of a vehicle’s pads. When this happens, the braking performance will also be reduced.

Now, there are plenty of reasons why your pads might be wearing out evenly, including stuck pins

But there’s also a high chance the seals on the master cylinder are coming to an end.

When these seals are disintegrating, they’ll cause uneven brake pad wear. The solution to this problem is to replace the damaged brake pad.

8. Damaged Sensor

Diagnosing a bad master cylinder can be as easy as hooking up a multimeter to your vehicle.

The whole idea behind using a multimeter is to determine whether the sensor built into the master cylinder is still in great shape as it might not be working correctly.

When this happens, it will trigger the brake light even though there’s nothing wrong with the master cylinder. To test the state of the master cylinder, follow these steps:

  • Get a multimeter, as you’ll test for continuity. If you’re running low on fluid, the light will illuminate on the dashboard. That said, unplug the harness connector from the master cylinder.
  • Now set the multimeter to the “CAP” option and then press the mode button until you find the WIFI hot-spot symbol. Next up, take the lead from the multimeter and hook it up to the connector where the harness plug goes.
  • If you don’t hear any noise as you connect the multimeter, then it means there’s no continuity and that the fluid is at the proper level. But If you hear a beeping sound, then it means you’re running low on brake fluid.
  • Now drain the brake fluid to ensure the sensor is in great shape. If you hear the beeping sound, it’s safe to assume that the sensor is working as intended.

How Much Does It Cost to Replace a Bad Master Cylinder?

The average cost to replace a master cylinder can go anywhere from $300 all the way up to $500.

The new master cylinder usually costs between $150-$250, while the labor is priced at $300.

However, if the dealer has determined that the master cylinder is in great shape, expect to pay anywhere from $70-$100.

If you take the vehicle to a mechanic, make sure you take it to a certified mechanic. The master cylinder is the last part of your car.

You’d want somebody who doesn’t know what they’re doing to work on.

Furthermore, this issue should be addressed immediately. This is not something drivers should cheap out on.

Frequently Asked Questions

Have any questions about the master cylinder? Below, you’ll find the most common questions about it:

Does a bad master cylinder make noise?

Generally speaking, a bad master cylinder does not make noise. When it goes bad, it’ll go straight to the floor when you press it down, but that’s about it.

Instead, it could be the booster. When it fails, it’ll make some hissing noise.

Is a bad master cylinder dangerous?

No, it is not safe to drive with a bad master cylinder. Since the pedals do not work correctly, you’ll have a hard time stepping on the pedal.

As a result, you could get into a terrible accident. Instead, call a professional to diagnose your vehicle.

How do you troubleshoot a master cylinder?

The easiest way to find out if something wrong with the master cylinder is crawling under the vehicle to inspect the brake lines.

If they are leaking, you must replace them. After that, the pedal should work like before.

What happens if you get air in your master cylinder?

When the air gets inside the lines, the pedal will sink to the floor.

But when air gets inside the master cylinder, it’ll make the pedal creep towards the bottom. After a while, the pedal will work like it always does.


The pedal hitting the floor is one of the most common bad master cylinder symptoms.

A damaged master cylinder will change the way the pedal feels. Hence it sinks to the bottom the moment you press it down.

But as you know by now, other signs suggest there’s something wrong with the master cylinder—for example, broken brake lines.

These are generally easy to spot as you only need to follow them throughout the car.

That said, if the master cylinder went bad, refrain yourself from driving. The vehicle is unsafe as of now. is a participant of the Amazon Affiliate program. We may earn a small commission if you purchase through our recommended links. More details.

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