Brake Fluid Basics

To most drivers, brake fluid is just another one of those mysterious liquids that lives inside the engine compartment of your car. Ideally, it stays there and never shows up on the driveway or garage floor to let you know there’s a problem. Today I’m going to explain the basics of brake fluid and how it serves two very important purposes within your vehicle’s braking system.

The first, and most important, job of your brake fluid is to serve as the mechanical link between your brake pedal and your vehicle’s brakes. All modern vehicles are equipped with hydraulic power brakes. In a hydraulic brake system, pushing down on the brake pedal forces fluid through the brake lines and applies pressure to the brake caliper pistons on all four wheels. The caliper pistons apply pressure to the brake pads and clamp onto the brake discs(or rotor), providing the mechanical force that slows down the vehicle. The pressure that you apply to the brake pedal is amplified by the brake booster, creating the “power” braking system. The antilock brake system in your vehicle uses a combination of pumps and valves to apply and relieve pressure to each wheel as needed to maintain traction. A leak in any one of these components can cause loss of pressure in the brake system, and prevent your brakes from applying when you press on the pedal. If your vehicle leaks brake fluid, you need to have it repaired immediately to avoid dangerous brake failures. If you see the red “BRAKE” light, like the one below, your vehicle may have a brake fluid leak.

The second, and less known, function that brake fluid serves is to trap and disburse moisture within the brake hydraulic system. The hydraulic system that controls your brakes is made up of several expensive hydraulic components, and all of them can be damaged by moisture in the system. To prevent the buildup of moisture from condensation, engineers specify brake fluids that are hygroscopic - meaning they can trap and absorb water molecules. That’s right, the fluid in your brake system is capable of trapping and holding water like a sponge. Instead of droplets of water pooling together in your hydraulic system where they can cause untold damage from rust and corrosion, the brake fluid traps the water and holds it, preventing rust damage. Unfortunately, no matter how great the fluid is, it can only hold a limited amount of water. The fluid can become saturated, like a sponge that wont absorb another drop. At that point, there is nothing to prevent water from building up in your brake system and wreaking havoc on expensive hydraulic components like your master cylinder or antilock brake module.

That potential for saturation is why many manufacturers recommend replacing your brake fluid based on a time interval, no matter how much you drive. BMW, for instance, recommends replacing brake fluid every two years.

At Red Dirt Euro and EV, we test the moisture content of your brake fluid every time you stop by for service. If your fluid becomes saturated with moisture, we’ll recommend a brake system flush that replaces 100% of your fluid with brand new, ultra-dry DOT 4 brake fluid. This extends the life of your brake system components and saves you money on expensive repairs down the road.

If you’re interested in having your brake fluid checked or replaced, give us a call at 405-338-7267 or click the “Schedule Service” button at the top right of this page.

Thanks for reading, and happy driving!