Brake Fluid Change and Brake Bleeding

It is recommended to change the brake fluid in a motorcycle's brake system every two years.

The type of brake fluid to use is indicated on the reservoir cap and on the brake hoses. As a rule, modern motorcycles use DOT 4 brake fluid (see photo). To change the brake fluid and bleed the brake system you need a hose, preferably transparent so you can see air bubbles (sold in any auto parts store), an 8 mm open-end wrench or a special tool, a screwdriver, a transparent container for the used fluid, new brake fluid (half a liter is enough) and a helper (you can't bleed the brakes alone).

Brake fluid is very corrosive and can damage paint. Wear gloves and wipe up drips immediately.

Changing the brake fluid

• Drain the old fluid from the reservoir into a container, but not completely: the bottom must stay covered. To do this you can unscrew the reservoir and tilt it, or suck the fluid out with a syringe or a bulb. Keep a constant eye on the level during the process and don't let the reservoir outlet become exposed, otherwise a lot of air will get into the system and it will take a long time to bleed.
• Put the hose on the bleed nipple of the slave cylinder (caliper): the old fluid is drained through it. It is advisable to spread the pads in the caliper, for example with a screwdriver.
• Press the brake and open the bleed nipple (loosening it slightly is enough).
• Once the fluid has come out and the brake has gone down, close the nipple, then release the brake.
• Monitor the fluid level in the reservoir. If the level drops to the bottom and the master cylinder draws in air, the system will need bleeding.
• Do this several times until fresh fluid comes out.

For the front brake system, if two calipers are used, do the same for each caliper. With this kind of fluid change the system doesn't strictly need bleeding, but we recommend bleeding it: it doesn't take long and guarantees there is no air in the system. Although, if you did everything correctly, didn't let the reservoir level drop and your system was bled before the fluid change, bleeding is optional.

Bleeding a motorcycle brake system

Bleeding the brake system starts with bleeding the master cylinder. On some motorcycles the front brake master cylinder can't be bled. In our case the master cylinder has an air bleed nipple, so it needs bleeding. On all motorcycles the rear brake master cylinders aren't bled: they automatically purge air into the reservoir when the brake lever is pressed.

• Pour brake fluid into the reservoir.
• If the master cylinder has an air bleed nipple, bleeding starts with it, then the slave cylinder is bled. Otherwise only the slave cylinder is bled.
• Put the hose on the nipple. Put the free end of the hose into the container.
• Pump the brake lever several times (press sharply, release slowly), then squeeze the lever and hold it under pressure. The nipple is closed.
• Open the nipple. The brake lever «goes down», and fluid comes out of the hose. Check the fluid coming out for air bubbles. Close the nipple. If there are bubbles, repeat steps 4 and 5 until the bubbles disappear. Don't forget to watch the fluid level in the reservoir and top it up as it drops.
• Top up the reservoir to the maximum level. Not to the brim, but to the maximum mark shown on the reservoir (see photo). Close the reservoir. The system is bled.

So for the rear brake system only the slave cylinder needs bleeding. For the front: the master cylinder (if needed) and two slave cylinders.

For stunt riders:

When bleeding the handbrake master cylinder (the rear brake on the handlebar), if you use a right-hand master cylinder (from a front brake), bleed it with the air bleed nipple on top. To do this, remove the master cylinder and turn it over to the standard position. Questions and comments in the comments!