What is brake fluid?
Your brake pedal is connected to something called a master cylinder, which is filled with brake fluid. When you push on your brake pedal, the master cylinder pushes brake fluid through your brake lines to the wheels.
At each wheel, your vehicle has a brake caliper or wheel cylinder that squeezes your brake pads or shoes, in order to provide the friction that slows the wheel. Basically, your brake fluid connects your brake pedal to the wheels via hydraulic force.
Why does brake fluid need to be changed?
Your brake fluid needs to be replaced periodically for a number of reasons. The main reason is that most brake fluids are hygroscopic, which means that they absorb water from the air and materials around them. As the fluid’s water content increases over time, its boiling point drops.
Traditional DOT 3 brake fluid has a “dry” (new) boiling point of 205°C. Once the fluid has reached 3% moisture, this boiling point has fallen to 140°C! This is referred to as the “wet” boiling point, as around 3% water is considered the safe limit for brake fluid, and it should be replaced if the water content gets any higher. If the boiling point of the fluid becomes too low, it may boil inside your brake calipers under hard braking. This is potentially unsafe, because boiling fluid releases air, and air in a hydraulic system causes a loss of pressure – or a brake pedal that falls to the floor.
Brake fluid also contains additives that only last for so long, like corrosion inhibitors to protect the metal parts of your brake system from deteriorating.
How often should brake fluid be changed?
Most car manufacturers recommend replacing the brake fluid in their vehicles every 2-3 years. Recommendations vary a bit from car to car, but you should be able to find this information in your owner’s manual – or we can look it up for you!
While our complimentary brake fluid testing can help determine when it’s time for a change, it’s important to remember that some things like the fluid’s corrosion inhibitors cannot be tested, so the fluid should be replaced from time to time, regardless what its boiling point has become.
Different types of brake fluid:
Brake fluid is not universal; there are actually several different types produced and used today. These fluids are classified by their boiling point; viscosity (or “thickness”); and additive content.
Most vehicles built prior to 2005 use a DOT 3 fluid with a dry boiling point of 205°C and a viscosity of 1500 mm²/s. Most 2006 and newer vehicles use DOT 4 fluid, with a dry boiling point of 230°C and viscosity of 1800 mm²/s. Some off-road or racing vehicles use a purple-coloured DOT 5 brake fluid that is silicone-based. While this fluid has a very high boiling point of 260°C and does a great job maintaining a constant viscosity over a wide range of temperatures, it should not be used in street vehicles as it’s not compatible with ABS systems. Fairly recently, some manufacturers have started using new DOT 5.1; a conventional glycol ether fluid that offers most of the performance benefits of DOT 5 fluid, but is compatible with newer vehicle brake systems.
These different fluid types should not be mixed. When we’re maintaining your brake system, you can be confident that our expert technicians will always use the correct fluid for your vehicle.
Don’t top up brake fluid.
Brake fluid should never need “topping up” under normal conditions, and a very low fluid level usually indicates a problem. Brake fluid normally only becomes low for one of two reasons:
- There is a leak in the system. Brake fluid leaks are potentially very dangerous, since a loss of fluid can also result in a loss of brake pedal pressure (and your ability to stop).
- The brake pads or shoes are worn. As the pads and shoes get thinner, your calipers or wheel cylinders must extend further to make up for this wear. As more brake fluid moves into your calipers, the level in your brake fluid reservoir drops. The brake fluid reservoir contains enough extra fluid to account for this – but a fluid level near the “low” point may indicate your brakes need to be replaced soon.
If your brake fluid is low, we recommend having us perform a quick inspection of your brake system to determine why.
What happens if I add something other than brake fluid?
About once a year, we’ll hear from a customer who has accidentally added a different automotive fluid (such as power steering fluid) to their brake fluid reservoir. Unfortunately, this often turns into a very expensive mistake. Because oils and most other automotive fluids are mineral-based, they are not compatible with the seals used throughout your brake system.
These oils swell up and rupture the seals inside your master cylinder; ABS hydraulic control unit; brake calipers and more. This can result in a total loss of pressure inside the system, and a brake pedal that goes to the floor. If the contaminated fluid has made its way into the brake lines, sometimes every major part in the brake system must be replaced in order for the brakes to function normally again.
This can cost thousands of dollars, so it’s important to be careful you’re putting the right fluids in the right places. If you’re not sure, ask someone who knows! We are always happy to help.
Replacing brake fluid in Airdrie:
The process of replacing brake fluid is often called a brake fluid flush. As the name suggests, this procedure involves not only replacing the fluid in your reservoir, but also flushing out all of the fluid that you can’t see, in your brake lines and other system parts. We accomplish this by connecting to bleeder screws on your calipers and other moving parts in the system: old fluid is drawn out the end of the system, while new fluid is being added at the beginning.
We’ve heard of folks replacing just the easy-to-reach fluid in their brake reservoir. Unfortunately, that basically accomplishes nothing, since it is the fluid inside your calipers, wheel cylinders and lines that are subject to the most heat, and does most of the work.
For a great quality brake fluid flush in Airdrie, look no further! If you’d like to make an appointment for this service, or even if you just have a question, please get in touch with us!