Brake fluid is one of those mysterious things in a car that a non-car person may know is mandatory, but the purpose is vague at best.
What does it do? No idea.
Want to try driving without it? Nope.
So will a car work without brake fluid? Absolutely not! Brake fluid is the force transferring “middle man” between your brake pedal and your brakes. The pressure you apply with your pedal is carried through the fluid in the brake lines to push against the pads. Without this fluid, your brakes won’t work.
In other words, not having brake fluid is the #1 doctor not-recommended method for giving someone a heart attack when they see your car barreling towards them with no sign of stopping. Out of all the things on a car that are necessary for safety reasons, brake fluid is pretty high on the list. Don’t let this be a mystery.
How does brake fluid work?
To understand that, it helps to understand how the typical brake system works.
The brake pedal is what you press to begin the stopping process. This is the first bit of energy that sets the rest of the process in motion.
The vacuum booster (also called a brake booster) multiplies the force applied by the brake pedal. Without the vacuum booster, you’d have to use more of your own leg strength to stop your car.
The master cylinder directs this force and allows it to be applied through the brake lines.
The brake lines then direct this force to the actual brakes, which stops your car.
The brake fluid is what carries all of this applied pressure. This is the “blood” of the system. This fluid is less compressible than air and water, allowing it to transfer the force much more effectively.
If the brake fluid is absent or the levels are too low, no part of your brake system will function correctly.
Can air or water be used as a substitute?
Nope. Having any air or moisture in the brake lines is actually a concerning issue that needs to be fixed as soon as possible. The reason for this is that brake fluid is engineered to be able to carry applied force effectively and quickly. Air and water are more compressible.
This is similar to the difference between trying to squeeze a rock and trying to squeeze a sponge. The rock will keep its shape, but the sponge won’t put up as much resistance.
In a brake system, this will make the pushing of the pedal feel softer than usual. You’ll have to push farther to get your car to slow or stop, which drastically increases your reaction time and could be the difference between a close call and a fatal accident.
If air or moisture get into your braking system accidentally, you need to consider the fact that this issue will likely get worse and won’t go away on its own.
How can this fail?
- As we already noted, air and moisture cause notable issues. Bleeding the system, a solution to this, is discussed in the next section.
- A leak is an obvious and serious issue, as this will decrease the amount of fluid available for stopping your car. A leak should be resolved immediately by a mechanic, and the lost brake fluid should be replaced with the same type of brake fluid.
- As brake pads wear down over time, the caliper piston will have to push out further to move the pads to the brake rotor. This will bring the fluid levels lower.This isn’t exactly a failure (yet), but is something to be aware of. Make sure to regularly replace your brake pads and check your fluid levels at the same time.
- Rust and corrosion can potentially cause failures in any metal component of the system. This is accelerated with the introduction of moisture.
- Broken brake lines are a serious issue and may prevent part of your brake system from working. Many country require split braking systems. These divide the system into two halves, so one will still work if the other fails. But, any issues still need to be fixed immediately.
Recommended Maintenance
Know the difference between bleeding and flushing your brake fluid. Bleeding is done when air or moisture is in your brake lines, and needs to be removed. Flushing means that all of the brake fluid is being replaced with new fluid.
The recommended frequency for flushing your brake fluid may or may not have an easy answer. As always, the owner’s manual may have one for your specific car. If not, the recommended frequency for a complete flush and replacement varies widely, from 3-5 years or 25k-50k miles (48,280-80,467 kilometers).
There are some manufacturers that recommend more frequent replacements and some that don’t specify. Follow any instructions given to you for your specific model or get the fluid changed whenever you have other mandatory work being done, like changing your oil or your brake pads.
While this is something you may be able to do yourself, it’s always better to let a trained professional work on your brake systems.
Different types of brake fluid
The three typical types of brake fluid are DOT3, DOT4, and DOT5. The letters stand for “Department of Transportation” and the numbers in this case indicate relative boiling points. Higher numbers indicate higher boiling points.
DOT3 and DOT4 (glycol-based) will absorb water. DOT5 (silicon-based) does not. The boiling point of the braking fluid is extremely important and can be negatively affected by the absorption of water.
Lower boiling points make it more likely that your brake fluid will boil during prolonged periods of braking. This will make the fluid more compressible and decrease your car’s ability to stop.
This makes DOT5 seem like the ideal choice with its more stable boiling point, but any water introduced to this type of fluid will form pockets of water that increase the likelihood of corrosion. DOT5 also can’t be used in any cars that have anti-lock brakes, as this will aerate the fluid.
These brake fluids, if you have multiple types, should not be mixed. Also keep in mind that brake fluid can eat away at paint, so handle with care to avoid any visible damage to your car’s exterior.
Fortunately, the majority of modern vehicles use glycol-based fluid, specifically DOT4. This makes the choice much easier. Remember to never use brake fluid from a bottle that has been left open for a long period of time.
So… Which One?
If only it was as simple as having a monopolized brake fluid company with a standardized product for every car. Actually, we should have this for any car related product. Wouldn’t that be so much easier?
If you happen to know which brake fluid has been used in your car, that’s probably the one you should keep using – as long as it hasn’t caused you any issues.
As always, if you don’t automatically have those answers, you can always try to find them in the owner’s manual of your car. And if you don’t have that either, you can always find relevant information on official websites for your specific car model. There’s a good chance that you also have the option of downloading a PDF of the owner’s manual, if you need it.
If you forget everything else from this article, the important thing to remember is that your brakes aren’t something you want to ignore or neglect, whether you notice an issue or not. Perform your regular inspections and get any issues resolved ASAP. The rest of the world will thank you.
