If you ride your mountain bike regularly, you should bleed your brakes at least once a year. If you do a lot of downhill riding or if you notice that your brakes are not working as well as they used to, you may need to bleed them more often.
When bleeding your brakes, it is important to use fresh brake fluid. You will also need some tools, including a syringe or turkey baster, a small Phillips head screwdriver, and some rags. It is best to Bleed your brakes in the following order: front left, front right, rear left, rear right.
1. Start by removing the wheel from the bike. 2. Use the syringe or turkey baster to remove all of the old brake fluid from the reservoir. 3. Clean the reservoir with a rag and then fill it with fresh brake fluid. 4. Locate the bleeder screws on each caliper and loosen them with the screwdriver (you may need to use an Allen wrench). 5 Put a rag over each bleeder screw and open the bleeder until you see bubbles coming out of the fluid (this means that air is being bled from the system).