When's the last time you had your brake fluid changed? If you can't remember or haven't had it changed since you've bought your car, you're not alone. Despite brake fluid playing an essential role in your braking system, it also tends to be one of the most neglected fluids in the entire vehicle. For example, Audi recommends that you have an Audi service center change your brake fluid every two years regardless of mileage.

So what happens when you skip out on a brake fluid change? The following offers some insight and a cautionary tale about neglecting your brake fluid.

Moisture Contamination

There's a good reason why your mechanic tells you not to open your brake fluid reservoir unless it's absolutely necessary. That's because the fluid itself is hydroscopic in nature, meaning it'll readily absorb any moisture that's present. That explains why your brake fluid is designed to operate in a sealed environment where it's well-protected against moisture and air intrusion.

Even in a sealed system, minor moisture contamination is inevitable due to minute amounts of moisture within the hydraulic brake system being absorbed by the fluid as it ages. Being careless with how long you take to top off your brake fluid can also expose it to excess moisture.

Moisture contamination can lower your brake fluid's boiling point, making it more likely to overheat and lose its effectiveness. To make matters worse, excess moisture can also cause vapor pockets to form within the fluid. When compressible vapor displaces uncompressible liquid, it could cause your brake pedal to sink to the floor once depressed without actually applying the brakes.

Debris Buildup

As your brake fluid ages, it's also bound to be contaminated with debris. The various seals and hoses that make up your brake system can shed tiny amounts of rubber as they age. Moisture-laden brake fluid can also cause metal components to rust and corrode, resulting in rust particles finding themselves in your brake fluid. Improperly closing your brake fluid reservoir cap can also allow dirt, grime and other debris to make its way through the brake system.

Although you can find the bulk of this debris suspended inside your brake fluid reservoir, some of it is bound to find its way into the antilock brake system (ABS) unit. This debris can build up inside the tiny passageways of the hydraulic unit, eventually plugging them closed. Of course, this could render your ABS system nonfunctional and have dangerous implications for your car's braking performance.

Poor Braking Performance

When you don't change your brake fluid, your car's braking capabilities suffer greatly for it. In most cases, you can tell simply by pressing the brake pedal—if it feels incredibly spongy, then there's a good chance your brake fluid has nearly given up the ghost. You might notice that it takes more effort and longer to bring your vehicle to a stop. In some cases, you may even have to pump your brakes just to build up enough pressure for a safe stop.

There's also the dangerous possibility that your brakes could fail altogether—an unsettling prospect if you're traveling at any speed. This can happen if the brake fluid manages to reach its boiling point under operation, especially if that boiling point was artificially lowered through moisture contamination.

Needless to say, having your brake fluid changed at the proper intervals is absolutely important if you want to keep yourself and others safe on the open road. When it comes to your brakes, ignoring your mechanic's recommendations could be a recipe for eventual disaster. If you feel that something's amiss with your brakes, don't hesitate to have them checked out as soon as possible.