When and Why You Need to Replace Brake Fluid

| January 3, 2013

replacing brake fluidA reputable auto repair shop, like those you’ll find on the DexKnows auto repair listings site, will let you know if your brake fluid needs changing. But if you’re a do-it-yourself kind of car owner, this is a job that frequently gets overlooked. Here’s why you shouldn’t ignore it and what you can do about it.

What it takes to brake

Everyone knows brake pads and brake shoes need to be replaced periodically. (Well, hopefully you do!) Most car owners are also accustomed to being told that their brake discs need to be replaced. But brake fluid?

Here’s what brake fluid does: The brakes in your car or truck are hydraulic. That means that when you push down on the pedal, incompressible fluid transfers that force to the calipers or drums at each wheel. Each caliper fits over a disc and holds a pair of brake pads. When you press the brake, pistons in the calipers push the pads against the disc. (In drum brakes, shoes are pushed against the drum.) Friction brings the car to a halt.

Reaching your boiling point

That friction turns the kinetic energy of the car into heat; and the harder the braking, the hotter the pads and calipers get. That heat is transferred to the fluid, which can reach over 300 degrees F. But brake fluid also has to deal with extreme cold without freezing or becoming too thick. That’s a lot to ask.

Brake fluid is specified by a DOT number. This relates to the boiling point of the fluid. In times past, DOT 3, which doesn’t boil until over 400 degrees, was sufficient. Now, front-wheel-drive vehicles can generate more heat in the brakes and therefore often require DOT 4, with a boiling point above 450. A few manufacturers specify DOT 5 or 5.1, although that’s uncommon.

Why brake fluid breaks down

Over time, brake fluid absorbs water. It’s perfectly normal and there’s really no way to prevent it, but it has a very serious result: a little moisture can lower the boiling point of the fluid significantly. That means that, with repeated hard stops, there’s a real risk of it boiling. Boiling creates vapor, and when you press on the pedal, the vapor compresses rather than transmitting the pressure to the pads. In other words, the brakes won’t work!

The second problem is more insidious: It’s corrosion. Water in the brake fluid can react with the metal components of the brake system, causing corrosion. That leads to small particles in the fluid, which over time will damage the various seals in the system. When seals are damaged, they start to leak. That can let more air in, leading to a spongy pedal feel and reduced stopping power.

When to replace brake fluid

Experts recommend that brake fluid be replaced every two to four years, depending on the vehicle. If you don’t recall when yours was last done, chances are it’s time! If you like getting under the hood, take a look at the fluid in the reservoir. If it looks dark or dirty, replacement is due; but even if it seems clear, it can still be holding some moisture. A good repair shop can test it for you to determine if it needs replacing.

If you decide to change it yourself, be sure to buy a quality fluid. Motul is a well-known premium brand. Valvoline is also very good and tends to be less expensive. Alternatively, if you have no desire to tackle the job yourself, use the DexKnows local site listings to track down a good auto repair shop and ask them about replacing your brake fluid.

Tags: , , , , , , ,

Category: Auto Maintenance, Autos

About the Author ()

After twenty years in the automobile industry the craft of wordsmith called. Putting down the wrench, Nigel picked up a keyboard on which to express his passion for all things automotive.