Avid hydraulic brakes require DOT 4 or DOT 5.1 brake fluid so DO NOT USE MINERAL OIL.
The Avid brake bleed kit comes with two syringes, one to catch discarded fluid and one to push clean fluid through. For both syringes, you’ll need to perform the same procedure. One will be half full while the other (the catch syringe) will have only a quarter filled with fluid. There are clamps on the tubing that leads from the syringe and the ends are specially threaded to properly attach to the bleed ports.
With the syringe pointing upwards, tap the body to make all the air bubbles rise to the syringe nozzle. With a rag, cover the nozzle as you push the air out. Then, clamp the tube and pull on the plunger to create a vacuum. Air bubble will start to form so tap the syringe to make them rise. Keep repeating until no more bubbles form. Then open the clamp and with your rag, cover the tip to push out the air again. Repeat this process until you’ve eliminated all the bubbles. Make sure there are no air gaps in the tube itself.
Remove your wheels and get on your gloves. Make sure your bike is set up so that it’s an upward bleed, from the caliper up to the lever. Loosen the screws on your levers, enough so that you can swivel them with ease but not so much that they swing.
Remove the brake pads and insert the caliper shim. If you want to be extra careful, put a rag around the lever, just in case any fluid comes out. The fluid can take the paint off your bike so be very careful that it doesn’t get on your frame or your components.
Using a Torx screw, remove the bleed port plugs from both the caliper and the reservoir by the lever. Screw in the half full syringe into the caliper. Up top, where the lever is, attach the quarter-filled syringe.
Now, while holding both syringes upright (you may want to get someone to help you out), depress the plunger at the caliper while pulling at the plunger connected to the lever. You’ll see bubbles and discolored fluid up top. Keep doing this slowly, until the caliper syringe is a quarter full and the lever syringe is half full.
Clamp the lever syringe and then with a rubber band or a strap, keep the brake lever squeezed all the way down to the handlebar. Pressurize the system by pulling on the plunger on the caliper syringe and then pushing it back in again. Keep doing this until large bubbles stop appearing.
Once done, you can take off the rubber bands from the lever but you’ll want to keep it held down on the handlebar. Push down on the plunger at the caliper and slowly release the lever. Then you can remove your caliper syringe and replace the bleed port screw. Remember to keep the syringe upright when removing because if you turn it on its side, air bubbles might just wander back into the system. Clean off the caliper with a clean rag and alcohol.
Up top, do the same thing: open the clamp and pull on the plunger. Then, push down to create pressure. Squeeze on the lever 10 times to make absolute sure that the master cylinder has no air bubbles in it. Once that’s done, while keeping the syringe upright and the bleed port is pointing as upward as it possibly can, remove the lever syringe and put in the cap. If you want to be super meticulous, you can put in one or two drops of brake fluid into the port before closing it up. Once closed, make sure you wipe down and clean with a rag and alcohol.