Maintenance Tips for Motorcycle Brakes (Part 1): Brake Fluid

We wrote about how hydraulic disc brakes work in the last article; it is now time to look at a few maintenance aspects.

Read How It Works: Hydraulic Disc Brakes.


The brakes on any vehicle is one of the most neglected components, unfortunately, despite being the most important, due to how reliable modern brakes are. However, you will soon discover how a little TLC will have your brakes performing at their optimum level.

Let us start with the brake fluid.

Next to having sufficient brake pad thickness, the brake fluid is the most important factor to safe braking.

First and foremost, it needs replacing every two years, irrespective of the mileage the motorcycle has covered or how it looks. Certain motorcycle manufacturers may specify 20,000 to 30,000 km or two years, whichever comes first, but the two-year period still applies.

Virtually all vehicles use glycol-based brake fluids. Glycol-based fluids are hydrophilic, meaning they attract moisture from the air.

Brake fluids have boiling temperatures higher than water—water boils at 100oCelsius. When the water boils, it creates air bubbles, leading to “brake fade”. Brake fade means losing braking power and the tell-tale sign is when the brake lever feels “spongy” or it moves all the way back to the handlebar grip. It usually strikes when you apply the brakes for a longer duration (slowing from high speeds or down a mountainside) or with lots of pressure (for example, in emergencies), exactly when optimal braking power is needed most!

Here is a table specified by the American Department of Transport (DOT), showing each grade’s “dry” and “wet” boiling points. “Dry” boiling point stands for fresh fluid, which is completely free of moisture and, conversely, “wet” means the fluid contains 3.7% of moisture. Do take note that just 3.7% of moisture renders the brake fluid dangerous and needs to be replaced immediately.

Brake fluid grade Dry boiling point (o C) (0% moisture) Wet boiling point (o C) (3.7% moisture)
Dot 3 205 140
Dot 4 230 155
Dot 5 260 180
Dot 5.1 260 180

As you can see, just 3.7% moisture reduces your DOT 4 brake fluid’s boiling point to a (very) low 155oC. It does not take much braking effort for your brakes to hit that temperature!

Also, old brake fluid may start to gel and form flakes. These flakes could go on to cause brake failure or ABS failure in extreme cases.

Replacing the brake fluid is even more important in hot and humid countries where there is always high moisture content in the air.

So, remember to completely flush your brake system and replace it with fresh fluid from an unopened bottle. You may refer to the DIY video on how to do it or send your motorcycle to a reputable workshop.


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