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What Is The Brake Fluid Reservoir? (Problems, Fixes, FAQs)

April 21, 2021

The brake fluid reservoir is the part of your brake system that stores your car’s brake fluid

And while it’s rare for things to go wrong with it, when problems do arise, they need to be addressed ASAP.  

But what can go wrong with the brake fluid reservoir? 

And more importantly, what can you do about it?

We’ll cover the different types of reservoir failures, what happens when something is wrong, the easiest way to get your brake fluid reservoir fixed, and 7 brake fluid reservoir FAQs.

This Article Contains

Let’s begin.

What Is The Brake Fluid Reservoir?

The brake fluid reservoir is a canister connected to your brake master cylinder.

It stores your vehicle’s brake fluid and protects it from dirt and moisture contamination, helping your car’s brakes function at optimal levels.

Brake fluid reservoirs are usually made of polymer plastics and are typically separable from the master cylinder body. 

The reservoir cap is vented and has a diaphragm that expands and contracts to maintain normal pressure inside. There’s also a fluid level sensor that alerts you when brake fluid levels are low. 

Now that we’ve got the basics out of the way, what can go wrong with your brake fluid reservoir?

3 Common Brake Fluid Reservoir Problems:

Here are 3 common fluid reservoir problems:

1. Damage To The Plastic Reservoir

The plastic reservoir body can become cracked and brittle over time. When this happens, brake fluid will seep out. 

Reduced brake fluid levels will, in turn, compromise the braking performance of your vehicle. 

These cracks will also allow moisture to enter and contaminate the brake fluid — accelerating brake fluid degradation.

2. Fluid Level Sensor Malfunction

If the fluid level sensor fails, you won’t be alerted when the brake fluid level drops below the minimum threshold. 

Not knowing when your brake fluid levels are low (and when you need to add brake fluid) will increase your chances of total brake system failure and compromise your vehicle safety.

3. Worn Reservoir Cap Diaphragm

When the reservoir cap diaphragm is fine, it keeps moisture out while allowing the brake fluid level to drop naturally as your brake pads wear down. 

A worn diaphragm, however, can leak, letting moisture and air into the brake fluid and ultimately into the brake lines. 

While moisture contaminates the brake fluid, air can also create air bubbles in the brake line, reducing hydraulic pressure and brake performance.

Now that you know what can go wrong with your reservoir, how do you spot these problems before it’s too late? 

3 Symptoms Of A Faulty Brake Fluid Reservoir

These symptoms usually accompany a failing brake reservoir:

This brings us on to the next question:

What’s the best way to get your brake fluid reservoir fixed?

The Simplest Way To Get Your Brake Fluid Reservoir Fixed

Replacing the brake fluid reservoir doesn’t just involve popping the container off the master cylinder. You’ll need to get the correct fluid reservoir for your car, install it properly, possibly bleed the car’s brakes, and so on. 

As there are so many steps involved, it’s best to find a qualified mechanic to do it for you.

And whenever you’re looking to get your brake fluid reservoir fixed, opt for a mechanic who: 

Fortunately, RepairSmith meets all those requirements.

What’s RepairSmith?

RepairSmith is a convenient mobile vehicle maintenance and repair solution that offers you these benefits:

How much can you expect to spend?

The cost will depend on what repairs are needed, your location, and the make and model of your vehicle. For a more accurate estimate of the costs involved, simply fill out this online form.

Now that you know what the brake fluid reservoir is and what can go wrong with it, let’s go over some fluid reservoir FAQs.

7 Brake Fluid Reservoir FAQs

Here are some answers to a few questions you may have about brake fluid reservoirs:

1. What Does Brake Fluid Do?

Brake fluid is the hydraulic fluid that acts as a conduit for hydraulic pressure in your brake line. 

When you depress the brake pedal, that force is amplified through a brake booster to the brake master cylinder. 

The brake master cylinder then pumps the hydraulic fluid from the brake fluid reservoir into the brake line, converting the pedal force into hydraulic pressure, engaging the brake calipers

Each caliper then clamps your brake pads onto your brake rotors, stopping your wheels. 

2. What Are The Signs Of Low Brake Fluid Levels?

Here are a few signs that you have low brake fluid:

3. How Can I Check The Brake Fluid Level?

It’s best to let a mechanic handle this. 

However, if you really need to check the fluid level, here’s how to do it:

1. Position the car. Make sure the vehicle is parked on a level surface, then pop the engine hood.

2. Locate the brake fluid reservoir. It’s usually mounted near the firewall at the rear of the engine compartment, close to the brake pedal.

3. Check reservoir type. Newer vehicles may have a translucent brake reservoir, so there’s no need to open the cap. If the reservoir is opaque, clean the top to prevent dirt from falling in before opening the lid to look inside.

4. Check the fluid level. The brake fluid level should lie between the MIN and MAX marks. 

5. Check brake fluid color. Fresh brake fluid is clear and typically an amber color. Old brake fluid is a muddy brown or black color, like old engine oil, due to the gunk and debris that contaminates it.

6. Fix the cap back on if you removed it. Don’t leave the brake fluid reservoir open too long as brake fluid will start to degrade.

Some IMPORTANT notes :

4. Can I Add More Brake Fluid If The Levels Are Low?

Yes, you can add brake fluid if you’ve found that you’re running low. 

However, ensure that it’s from a new container and is the correct brake fluid DOT type as different brake fluids can’t mix. Additionally, remember that brake fluid is toxic and corrosive, so handle it carefully.

If the brake fluid reservoir is empty, the brakes will also need to be bled of air. And if the vehicle’s brake fluid lies above the MAX mark, it may have water in it.  

Under these circumstances, it’s better to get a mechanic to help you resolve the problem.

5. How Often Should I Change The Brake Fluid?

You should get a brake fluid change every two years, or according to the brake fluid manufacturer’s recommendations. 

Sticking to a brake fluid change schedule protects your hydraulic system from internal corrosion and reduces the risk of premature failure of the braking system.

6. Can I Change The Brake Fluid Myself?

While you can change it yourself, it’s recommended that you let a professional mechanic do it for you.

Changing the brake fluid can require many different tools, some of which are specific to the process.

While you may be able to remove some of the old fluid from the brake fluid reservoir using a turkey baster, you’d still have to replace the old brake fluid with fresh fluid correctly and bleed the brakes to prevent air bubbles.

7. What Does Flushing The Brake System Mean?

Flushing the brake system refers to the process of removing old brake fluid from your brake lines and replacing it with new fluid. This fresh brake fluid will improve the performance of your vehicle braking system.

Final Thoughts

The brake fluid reservoir serves a simple yet important function. 

If you notice any issues with it, consider getting it inspected immediately.
Fortunately, for a convenient solution to your braking system issues, rely on RepairSmith. Contact them, and ASE-certified technicians will be at your doorstep, ready to fix your car issues!