What Is Brake Fluid and What Does It Do? Do You Need to Change Brake Fluid? Is Brake Fluid Bad? Here’s Everything You Need to Know About Brake Fluid and If It’s Time For A Change
If you’re not sure if you should change your brake fluid or not, here are four signs to watch for.
What is brake fluid?
In a vehicle, brake fluid is the hydraulic fluid used in the hydraulic brake and hydraulic clutch system.
Brake fluid is used to transfer the force being applied to the brake pedal with pedal into pressure being applied to the front and rear brakes to stop the vehicle.
Brake fluid assists in increasing the amount of braking force being applied to the brake pads because liquids are incompressible.
What Does Brake Fluid Do?
Brake fluid is important to your vehicle’s braking system—it’s a liquid chemical solution that transmits the effect of your foot pushing the brake pedal to the brakes via our hydraulic braking systems.
With the application of brakes, the pads and rotors achieve extreme temperatures through friction, thereby causing heat to develop. And as this heat develops in the brake hydraulic system, the moisture in the system gathers and condenses.
Brake fluid absorbs this moisture before it has a chance of boiling away and causing brakes to fail. Besides doing this, it also provides lubrication for the moving parts in the braking system while protecting them from rust and corrosion.
Tests and standards are made of brake fluid to conform to the use in a vehicle. To make sure that brake fluids will stay liquid at low temperatures, and resist boiling at high temperatures, brake fluid is used that is compatible with all other brake fluids and parts of the braking system, plus controlling corrosion in the brake system.
How Brake Fluid Works?
Brake fluid has a similar purpose as electrical impulses from your brain to your muscles. As a result, your foot and brake pedal send brake fluid through the brake system right from the brake pedal to the caliper and pad. A mechanic will only be able to deem that the brake fluid is low.
In pressing your brake pedal, you are forcing a piston or pistons to compress against the brake rotor, thus keeping your car from moving. While this definition means what it says, many more components to this must be addressed.
Your brake pedal does not, of itself, meet and connect to all four rotors; rather, through brake lines, you will find the single force of your foot on the brake pedal divided to all four brake system corners in our automobile. Brake lines are filled with a hydraulic fluid called brake fluid.
Why is brake fluid indicated? Because it is a non-compressible and hygroscopic liquid, no gas is released through compression when pushing down on the brake pedal by a person.
Through the hydraulic properties of brake fluid we are able to apply the brake pedal; the pressure created by this action is transferred through the hydraulic pressure of our brake lines to a pressure that compresses the brake rotors.
When the brakes are applied, the brake pistons will compress the rotors in order to create friction. When the brakes are applied, the heat from this action will add to the burning of brake fluid during hard application.
Brakes that are “boiled” or overheated will build small bubbles of air in the brake system due to their introduction. This gives a compressible gas, and the brake fluid becomes difficult to “move” the brake piston through the brake line to an application of slowing down the vehicle.
In effect, when the driver applies the brake pedal, he senses a “spongy” feeling to the brake pedal—brake pressure is being applied to the air instead of to the brake piston.
How To Check Your Brake Fluid – 4 Easy Steps
- Locate the brake master cylinder reservoir. It should be near the back of the engine bay or just next to the firewall. You should also see it directly above your brake pedal on the other side of the firewall. If you are having difficulty finding the part on an otherwise functioning vehicle, look it up in your owner’s manual.
- Check the level of brake fluid in the master cylinder reservoir.
- Newer cars: Most newer cars house their brake fluid in a plastic semi see-through reservoir. There will be a line marking the full level clearly visible through the side of the accessory. Because of this, a visual inspection is often all that is needed, and the cap need not be removed.
- Older Cars: Older cars (pre-mid-eighties) may have a metal reservoir mounted with a screw on cap secured by a spring clip. Wipe the top of the reservoir clean before inspecting, and remove the cap by applying a small screwdriver to lever off the clip. Inspect the fluid level. There should be a mark where you should fill it.
- Add brake fluid until the reservoir is filled to the indicated line (if low).
- NOTE: When your brake fluid level is low, it is an indicator that the brake pads themselves are worn and need attention. Get your auto to a brake professional ASAP.
- IMPORTANT: Never use any other type of brake fluid other than that recommended in your owner’s manual. Don’t overfill the reservoir. In the case of a double housing in your brake fluid reservoir, be certain that both are filled to the indicated levels. If your fluid reservoir is at the “absolute lowest” or lower, you may not want to take your auto on any kind of drive until the problem is resolved! Get to a professional brake technician.
- Replace the cap or other covering after inspection is completed.
6 Common Causes of Brake Fluid Leakage
Here are some of the usual culprits for brake fluid leaks, and your mechanic can spot them!
#1. Cracked Brake Master Cylinder Reservoir.
The brake master cylinder reservoir is typically plastic in construction. It becomes brittle from heating over time and cracks and allows the brake fluid to seep out the back of the engine.
#2. Piston Seal Failure.
Brake parts like the master cylinder, disc brake caliper, or drum brake wheel cylinder use Pistons for movement to push the brakes away from the wheels (among others!).
Because the Pistons are not fixed and the brake fluid is used to move the Pistons, there are seals around the Pistons, which wear out over time and can cause leaks.
#3. Worn Brake Pads and Shoes and Brake Rotors, and Drums.
The brake pads, brake shoes/rotors, brake drums/rotors, and brake drum systems break down and lose material over time.
When they do so, the brake caliper pistons and/or drum pistons may get overextended and damage the seals to leak brake fluid.
#4. Broken Brake Lines or Brake Hoses.
Brake Lines and Brake Hoses. Brake lines and brake hoses are constructed to withstand virtually all driving conditions and environmental hazards.
But over time, rust, pitting, and/or tears can develop, leading to a leak in brake fluid that comes from the brake lines, brake hoses, or brake line fittings.
#5. Loose or Damaged Bleeder Valve.
Every disc brake calliper or drum brake has a bleeder valve (or bleeder screw) attached that is used to evacuate air that is trapped in the steel brake lines.
In the event that a bleeder valve is damaged in the braking process or that a bleeder screw becomes loose, brake fluid can leak from that joint.
#6. Faulty ABS Module.
A few of the components of the brake ABS module use and store brake fluid at extremely high pressures.
Over time, the seals for the reservoir may wear and begin leaking fluid. Have the cause of a brake fluid leak located by yourself or a qualified mechanic.
How to identify a brake fluid leak?
- To identify a brake fluid leak, check for a small pool of yellowish/brownish fluid under your vehicle. You may also notice that when you press down on the brake pedal, it feels soft or spongy. This may happen if air has been introduced into the braking system through a leak.
- Leaks can come from a number of different components: master cylinder, ABS module, brake line, bleeder valve, rotor/drum, piston(s), and the rest of the braking assembly. By checking which component you see above the leak, you may be able to determine the location of the problem.
- To check for leaks, first lift your car using a jack, block the wheels, and engage the emergency brake. Next, you will want to conduct a thorough visual examination of everything under the vehicle.
- If the leak is slight or difficult to find, you can also put down newspapers under the car (this works best with the vehicle in park and the engine turned off) and then repeatedly press on the brake pedal. Through this process of pressing your brake pedal, you will force brake fluid out of any leaking areas, which then will show up in the newspapers and/or can be seen immediately upon inspection of the leaking component.
- Also, check that the lid of the reservoir is securely fastened. This, too, could potentially be a source of leakage.
Internal leaks may also occur from one part of the braking system to another without producing any external signs (eg, pools of brake fluid underneath your vehicle).
If you are filling the reservoir and the fluid level continues to decrease, and you do not see any obvious signs of leaks, you should not drive your car until you have taken it to your mechanic as quickly as possible.
How to fix a brake fluid leak?
Depending on where the leak comes from, you will either fix it yourself or have to visit a mechanic. When you are unsure which component failed, lack experience or confidence repairing cars, always seek an experienced and qualified mechanic to repair your car.
If you want to repair the car yourself, you will need the following:
- A car jacks
- Wheel blocks
- Parts (dependent on which component you are repairing)
- Car maintenance tools (noted in part-specific repair kits).
How to change brake fluid?
If you want to change the brake fluid yourself, follow these steps:
- Remove the old, dirty fluid from the master cylinder reservoir.
- Use a cheap turkey baster for this.
- Use a lint-free cloth to wipe out the reservoir.
- Do this only if you can get in there.
- Pour new brake fluid into the reservoir just until it reaches the “Full” line, replace the cap on the reservoir.
As you bleed the brakes (which you can find out how to do elsewhere on this site), the new fluid pushes the old fluid out of the system. Continue to bleed the brakes until you see clean, clear fluid exiting the bleeder screw.
How often should I change my brake fluid?
Most brands using Mineral oil-based brake fluid on cars recommend flushing and replacing the brake fluid every three years. In some cases, there is no actual factory guidance for changing brake fluid, as manufacturers say it is “lifetime” for the length of the lease or loan.
However, Haynes recommends replacing brake fluid before the two-year mark and every 30,000 miles. If you drive aggressively or tow, it is suggested that you change your brake fluid at least once per year.
Even though your brake fluid may appear fine, you should replace the fluid on a regular basis due to the moisture content that develops over time at a microscopic level.