What is brake fluid and when does it need to be replaced?

If you’re like me and your car is braking as it’s supposed to, you don’t give it another thought, right? Our cars’ braking systems are something we should be mindful of though, especially when it comes to towing or more to the point, stopping when you can be literally pulling a ton or more of weight behind you.

How does brake fluid work?

This hydraulic fluid works by activating the car’s master cylinder when you plant your foot on the brake, essentially stopping your car when you expect it to. The brake fluid travels through the brake lines under pressure and makes its way to the calipers which transfer pressure to the disc brake rotors.

The fluid also lubricates all of the moving parts in the braking system, and protects against rust. It basically ensures the whole system stays operational, cool and does what we expect when needed.

If it’s a closed system, why does it need replacing?

As with a lot of things with cars, age, wear and tear can take their toll on seals and hoses, which in turn allows moisture to creep in. When moisture mixes with the brake fluid it increases the water content and as a result, reduces the effectiveness of the brake fluid.

Over time, the integrity of the fluid can be compromised, reducing its ability to protect against corrosion. The added moisture can also bring down the brake fluid boiling point, further reducing performance.

How often should it be replaced?

You might notice your car isn’t braking as it should be, in which case, it’s most likely time to replace your brake fluid. To be safe, take a look at your car’s service manual where you’ll find an accurate guide.

Chatting to a mechanic is the most reliable route to take. Failing that, ask a service centre or brake specialist to check out your vehicle. They’ll be able to analyse the fluid electronically or with a strip test.

What’s the difference with brake fluids?

If it turns out that your brake fluid does need replacing, the technician will be able to recommend the most suitable brake fluid according to your manufacturer’s specifications. Believe it or not, there are many different brake fluid types on the market, and each includes a DOT number reference. A what reference? Stay with me here – all will become clear soon.

What the DOT?

DOT refers to the Department of Transport, and the numbers on the brake fluid containers are set according to acceptable safety regulations. These ratings are given to brake fluids based on wet and dry boiling points.

For the layperson, generally the higher the DOT rating the higher the boiling point and longevity of the fluid. Naturally, that would have you thinking that you’d always go for the highest rating, right? This isn’t necessarily the case, because not all brake fluids are compatible with all brake lines and systems.

So which brake fluid should I be using?

Some brake fluids are more commonly used for cars, trucks, buses and motorcycles than others. Bendix DOT 3 and DOT 4 brake fluids are widely used because they provide optimal performance for vehicles whether they have ABS or non-ABS disc and drum systems.

These brake fluids are suitable for both hydraulic and conventional systems and meet the stringent Australian and U.S. specifications.