5 MIN READ
Do it yourself: Changing motorcycle brake fluid
Replacing the brake fluid of your motorcycle is an important part of maintenance that you can do yourself. It ensures well-functioning brakes and sufficient braking power in critical situations. We'll show you how to do this!
Why should you replace brake fluid?
Brake fluid is made to withstand high temperatures during braking. Brake fluid is hygroscopic and attracts water from the air, but too much water in your brake lines lowers the boiling point. As brake fluid ages, the pressure in your brake lines decreases, resulting in reduced braking performance.
In extreme cases, the brake fluid can reach the boiling point and your brakes will fail completely. This phenomenon is called ‘vapour lock’, where vapor bubbles in the brake lines prevent the pressure from being properly transmitted from your brake lever to your brake pads. To prevent this, it is recommended to replace your brake fluid every two years.
Water in your brake lines can also cause problems, especially if you have steel brake lines. It can lead to rust and accelerated wear of your brake lines.
What should you pay attention to when replacing your brake fluid?
Brake fluid is corrosive, which means it can damage paint. Cover your motorcycle to reduce the risk of stains. Keep a bucket of water and a wet cloth at hand to immediately wipe away any drops. Wash your hands immediately if you come into contact with brake fluid.
Which brake fluid do I need?
On the lid of your motorcycle’s brake fluid reservoir, it is indicated which brake fluid is the right one for your motorcycle. You can also find this in the workshop manual of your motorcycle. You can also find your motorcycle in the Eurol Product Finder or Motul and find the right type of brake fluid there.
What is the difference between DOT 3, DOT 4, and DOT 5?
The American Department of Transportation (DOT) established the specifications for brake fluids. Each type has its own characteristics and use. DOT 3, DOT 4, and DOT 5.1 are glycol-based, this fluid cannot compress. DOT 5 is silicone-based, this fluid can compress a bit. The general rule is that DOT 4 and DOT 5.1 have higher boiling points than DOT 3. It’s important not to confuse DOT 5.1 (glycol-based) with DOT 5, this should not be mixed with other DOT fluids.
What is the difference between the dry boiling point and the wet boiling point of brake fluid?
On the packaging of brake fluid, you can read the dry boiling point and the wet boiling point. The dry boiling point is the boiling point of the brake fluid when it is new and unused. The wet boiling point is the boiling point of the brake fluid when it has been in use for a while and has absorbed water. The difference in boiling point can be 100°C.
What do you need to replace your brake fluid?
- New brake fluid, suitable for your motorcycle
- Brake cleaner
- Screwdriver to open the brake fluid reservoir
- Ring spanner that fits the bleed nipple of your brake caliper
- Transparent hose or a brake bleeder
- Collection container for the old brake fluid
- Cloths to cover your motorcycle
- Wet cloth and a bucket of water
Brake Fluid Replacement
Ensure the brake fluid can flow through
Place a cloth around the brake fluid reservoir on your handlebars to prevent brake fluid from getting onto your motorcycle. You can also cut a hole in an existing cloth and pull it over the reservoir. Loosen the lid of the reservoir and remove the rubber membrane inside. This allows the brake fluid to flow freely.
The bleed nipple is located on the brake caliper. First, place the ring spanner on the bleed nipple before connecting the transparent hose to the nipple. Guide the hose up first, then back down into the collection container for the old brake fluid. This way, you can clearly see the brake fluid flowing and you can spot air bubbles.
Build pressure to flush the brake fluid
Squeeze your brake until you feel resistance and open the bleed nipple by turning the ring spanner counterclockwise. You will feel the pressure drop at the brake lever. The brake fluid will run through the nipple into the transparent hose. Tighten the nipple before releasing the brake lever. If you release the brake lever before the nipple is closed, the brake fluid will be drawn back, which can result in sucking air into your brake calipers.
Repeat this process until the old brake fluid has completely passed through the hose. In case of heavy contamination, you can clearly see the difference between the old and new brake fluid in the transparent hose. New brake fluid is clear in color, while contaminated brake fluid is darker and brown in color.
Every time you push the old brake fluid through the lines, the brake fluid level will decrease in the reservoir. Refill the brake fluid in time to prevent air from entering the system. If you have two brake calipers on your front wheel, then repeat the above actions for the second brake caliper.
Alternative ways to replace brake fluid
Hand pump: You can use a hand pump to suck the brake fluid out of the brake caliper. Repeat this for each brake caliperor use a pump where the line is branched so that it can accommodate two brake calipers at once.
Syringe with brake fluid: You can also completely disconnect the brake line from the brake caliper to let all the brake fluid drain out of the system. When you reconnect the line, you can fill the brake lines from the bottom to the top using a syringe through the nipple on the brake caliper. This way, you directly push the air bubbles upwards while filling up from the bottom.
Clean, fill and seal
Clean the bleed nipple thoroughly with brake cleaner to avoid any residual brake fluid. Refill the reservoir up to the maximum mark, clean the lid and the rubber membrane before placing them back and securing them. Squeeze your brake lever several times until you feel the correct pressure is back.
It is possible that there are still tiny air bubbles in your lines after replacing the brake fluid. What you can do in this case is lightly squeeze the brake lever and let the motorcycle stand overnight. You can temporarily fix the lever in that position with some insulation tape or a cable tie. The pressure you create compresses the air bubbles, making them smaller and enabling them to rise to the top of the reservoir even faster.
Old brake fluid should be disposed of as chemical waste. Take this to your local recycling center to ensure it is processed correctly.
Think carefully before you start
Do not start this task if you are not confident in your own abilities. Although this is a simple task, it is always wise to seek professional help if you are in doubt of anything, especially since we are talking about your brakes.
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Nathan is our webshop employee who is ready with advice and assistance to help customers. When he is not answering customer questions, he writes helpful texts and blogs for the RAD site.