How to bleed the brakes or flush the brake fluid on the Yamaha R3:
I wanted to separate this information into a new post because sometimes you just need to bleed the brakes or flush the brake fluid without changing brake lines or pads or anything. I also prefer to use pressure from the brake lever instead of vacuum from a pump to bleed or flush the lines with new fluid. This post will cover bleeding the front brakes and flushing the fluid through the front brake line, but bleeding and flushing the rear brakes uses exactly the same process, you just press the rear brake lever instead of the front brake lever, duh.
fresh bottle of brake fluid, I use Motul RBF600 racing brake fluid:
Step 1: Set the bike on the kick stand instead of a rear stand. Turn the bars all the way to the left, and unbolt the brake lever so you can tilt the reservoir as upright and flat as possible, then clamp the lever again so it doesn’t move when you squeeze it. Remove the cover, plastic insert, and rubber boot from the reservoir.
Step 2: Pry off the cover for the bleed nipple and connect a drain line to the bleed nipple at the caliper, I use the line on my vacuum pump.
Step 3: Fill the fluid reservoir with fresh brake fluid as high as you can without spilling. Brake fluid gets crusty after sitting open on a shelf for too long, so always use fresh brake fluid, or at least check your fluid before pouring it into the reservoir and making a crusty mess.
Step 4: Squeeze the brake lever to apply pressure to the line, then while squeezing it, crack the bleed nipple open just far enough so that fluid starts to flow and you feel the lever move. Squeeze the lever to force fluid into the line. Close the nipple again before the lever bottoms out and stops moving. Pump the lever a few times until you feel pressure in the line again, then repeat step 4 until all air has been forced out of the bleed nipple, or until you see the new fluid coming out of the bleed nipple (it’s generally a different color than the old fluid). Here’s a video to more clearly illustrate this process:
Step 5: There seems to be a spot at the top near the master cylinder where one last air bubble likes to get stuck. To make sure you get it out, carefully tilt the bike even farther over to the left, you may want to have a buddy help you to be sure you don’t drop the bike, and be careful not to spill brake fluid from the reservoir. Tap the brake line up and down the line with a wrench or screwdriver and also gently tap the side of the master cylinder. This will help any additional tiny bubbles or any bubbles stuck at the top by the master cylinder come out of the top into the reservoir. Then set the bike back upright. Thanks to Stirz from R3-forums.com for figuring out that little trick.
Step 6: Make sure the reservoir is filled to the mark in the inside of the reservoir with fluid (add more, or suck some out with the vacuum pump or a turkey baster), then place the rubber boot in, then the plastic piece, then the cap, and screw the cap back on. Readjust your brake lever wherever you like it, push the cover back onto the bleed nipple, and you’re all done!