A car’s brakes are essential to safety and drivability. They are the only thing standing between you and a potentially deadly collision. Today’s brake systems are highly advanced, and have evolved a lot even in just the past few years. Most cars today use a combination of disc brakes on the front and drums on the rear, although four-wheel disc brakes are becoming more and more common. Most cars today also have ABS systems, and as advanced driver assistance systems become more widely utilized, additional technology becomes involved.

Despite all those advances, our brake systems have not changed in a few ways. The most important is that they are still fluid-driven. Brake fluid is placed under high pressure and sent through a series of brake lines to the calipers and drums, where that pressure is used to press the pads against the inside and outside of the rotor, or press shoes against the interior surface of a drum.

Because fluid is at the heart of your brake system, a brake fluid leak can be disastrous. Over time, even a very minor leak could allow most of the fluid to leak out, leaving you with no way to stop your car. Obviously, if you suspect a leak, you need to be able to locate it, and then repair it. What should you do?

Check the Reservoir

First things first – you’ll want to check your brake fluid reservoir to see if the fluid is at or below the correct level. If it is low, you might have a leak. However, the most common cause of low brake fluid is pad wear. It has nothing to do with a leak, and everything to do with the fact that as the pads thin, more fluid must be maintained in the system (and out of the reservoir) to operate your brakes.

So, if you do notice that your fluid is low, check your brake pad level. In many cases, you can use a flashlight to get a look at the edge of the pad through the wheel of your car without having to remove it, but in some instances, you may need to pull the wheel to see the pads. If they are thin, then chances are good that you do not have a leak and the level will return to normal when you replace your pads.

However, if the pad level is good (say 75% or more remaining of the pad), and your fluid is below the full line, then there is likely a problem and you’ll need to dig deeper.

Check the Master Cylinder

Perhaps the single most common place for a leak to develop is at the master cylinder. The good news is that if you are looking at the reservoir, you’re already in the neighborhood. The master cylinder is the large metal drum that supports the reservoir and attaches to the firewall between the engine compartment and the dash of the car. The master cylinder’s job is to help build pressure in the system as you press the brake pedal. As such, there are quite a few seals that can and will fail over time. These can allow air into the system, but they can also allow brake fluid to escape. To tell if your master cylinder is leaking, use a flashlight and look at the bottom of the metal drum, where it attaches to the firewall. If you see any moisture running down from the bottom of the drum, you’ve found your leak. To fix this, you’ll need to replace the master cylinder.

Check the Brake Lines

If there is no leak from the master cylinder, you’ll need to go further. This is where things begin to get tricky, because you will need to get under the car. First, though, check the lines where they attach to the master cylinder/reservoir assembly. If you notice signs of wetness here, you likely don’t need to dig any further. However, chances are good that the leak is actually farther down under the car.

Find a way to put your car in the air. This is easiest done on a vehicle lift, such as at a mechanic shop. However, you can do it on your own with a pair of jack stands. Just be very careful putting it in the air and ensuring that it is stable before you slide under it.

Once under the car, you’ll need to trace the brake lines. They will be solid metal as they run from the master cylinder down toward the wheels. These can develop pinhole leaks over time, sometimes due to friction as other metal components rub on them, but also due to corrosion from road salt or exposure to environmental salt (living near the coast, for example). If you spot a pinhole leak, you will need to replace the entire line from the master cylinder to the wheel cylinder.

If you don’t find a leak here, don’t fret. The metal lines will transition to either rubber brake fluid lines, or braided steel lines. Rubber brake lines are subject to a lot of wear and tear, and are also a common source of lost brake fluid. Braided steel lines won’t leak unless they corrode and deteriorate. If you notice a leak here, you’ll need to replace the rubber/braided steel line section.

Check the Wheel Cylinders

As a final note, you should check your wheel cylinders if you are unable to spot a leak anywhere else. You may notice brake fluid on the inside surface of your wheel – this is a sign that fluid is dripping from the cylinder. However, you may also be able to see moisture around the area, or feel it with your hand. The cylinder will need to be replaced in this case.

Never take chances with a brake fluid leak. If you are not 100% sure you can handle the repair on your own, take your car to a shop.

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