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The Ultimate Brake Fluid Change Guide for Harleys

There aren't many aspects of motorcycle maintenance you can put off, but some are absolutely critical to your safety. If you don't have your oil changed on schedule, that means more wear and tear on your engine and reduced efficiency and longevity. It's a big deal, but it probably won't get you killed.

But if you don't take care of your brakes, it puts you at greater risk of brake failure that leads to an accident. Let's talk about what brake fluid does, how often you need to change it and the best way to get it taken care of this month.

What Does Brake Fluid Do For Your Harley®?

The braking system on your Harley® is a pretty sophisticated collection of levers, pistons and fluid that supplies stopping force to the front and rear brakes. When you apply pressure to the pedal or lever, pistons in your brakes turn the mechanical force applied by your hand or foot into hydraulic pressure. Your brake fluid is what transfers that force and allows you to stop by converting kinetic energy into heat energy. 

What Happens If You Don't Change Your Motorcycle Brake Fluid?

When it's new, brake fluid has an extremely high boiling point. For example, DOT 4 has a boiling point around 140 degrees Celsius, 311 Fahrenheit. That helps it transmit pressure evenly to your brakes.

But brake fluid contains glycol, a substance that absorbs moisture from the air.  The second you or the service tech you hire opens the bottle of brake fluid, that fluid starts absorbing moisture. Even though it travels through a closed system, it still comes into contact with water as it passes through hoses and seals. Over time it absorbs more and more moisture, and water boils at a much lower temperature. 

It's never okay for motorcycle brakes to fail, and waiting to change the brake fluid becomes a game of Russian Roulette. The longer you put it off, the more water your brake fluid absorbs and the less effective it will be, especially in demanding situations and on long rides. 

Bubbles of water vapor form as heat rises. Eventually, the fluid becomes unable to transmit the pressure you need for stopping force. You don’t want to find out your brakes aren’t effective when you’re cruising down a twisty mountain road or you need to make a sudden stop in heavy Dallas traffic.

Why Are There Different DOT Classifications for Brake Fluid?

Different brake fluid types have different boiling points. Brand new brake fluid that hasn’t absorbed any water is described in terms of its dry boiling point. Once it has absorbed 3.7 percent water by volume, it’s measured in terms of its wet boiling point. After it absorbs enough moisture to have 8 percent water content, the boiling point drops to that of water, around 100 degrees Celsius/212 Farenheit. The Department of Transportation (DOT) classifies brake fluid as follows:

  • DOT 3: Wet boiling point – 140 degrees Celsius/284 Fahrenheit
  • DOT4 – 160 degrees Celsius/311 Fahrenheit
  • DOT5 – 180 Celsius/356 Fahrenheit
  • DOT 5.1 – 190 degrees Celsius/374 Fahrenheit

Always use the recommended grade fluid for your Harley® or go with a higher grade.

Can You Mix Brake Fluid Types?

You can’t mix DOT 5 with anything because it’s silicone-based, not glycol-based. The other types you can mix, but your boiling point won’t be as high as the higher grade.

How Often Should You Change the Brake Fluid for Harley®?

Glycol-based brake fluid needs changing at regular intervals as recommended by Harley® for your bike. For most riders, that’s every 1-2 years. If you use DOT 5 you can go longer between changes.

You can tell it’s time with a tester or by checking the color of what’s currently in your system. New brake fluid is clear with a yellowish tint. Brake fluid in need of changing is dark, gritty brown. 

Is Changing Brake Fluid a DIY Job?

Changing brake fluid isn’t hard, but for most bikes, getting to it is complicated. If you have a lot of patience, good basic mechanical knowledge and a Saturday afternoon to spend, you can do it yourself. It’s complex enough most people just turn it over to a professional. There are a lot of easier aspects of motorcycle maintenance you can DIY.

Part of the issue is, brake fluid is toxic and flammable. Plus, if it gets on your paint job, it can ruin it. Bleeding the brakes often causes air to flow through the lines and fluid to splatter out of the top of the reservoir. If your bike isn’t protected, it might get on chrome and paint.

Because it’s toxic waste, you can’t just throw your old brake fluid in the trash can. You’ll have to follow regulations that vary by state and city.

Our mechanics use a brake flushing machine to completely remove all the old brake fluid before replacing it with new. We know all the ins and outs of handling brake fluid properly and safely so your brakes work like new and you quickly get back on the road.

Local Harley® Shop for Brake Fluid Changes

Take advantage of our Brake Fluid Awareness Month special, now through the end of August. When you bring in your bike for any front and rear brake flush and bleed service, we'll give you 50 percent off labor. Schedule your service today.