How to Bleed Brakes on Mountain Bikes: Part One

"You may have heard the mechanic at your local bike talk about bleeding brakes. What someone means when they say bleeding something when it's a hydraulic system, whether it's your suspension fork or your disc brake, is that you are getting all of the air out of the system so that all you have is fluid. Most disc brakes on the market use disc fluid, or dot fluid, which is the same fluid you use in a car or a motorcycle. Different manufactures specify different types of fluid to use to bleed things. The two disc brake manufacturers that I'm most familiar with, Hayes, who have a product that looks like this. You've got a master cylinder that comes off the handle like this, a little bit chunkier, more industrial looking. They recommend using dot 3 fluid. The other manufacturer that I ofter work with is avid. They have a little bit sleeker of a master cylinder. They like dot 3 or dot 4.1 fluid. Let me show you roughly how to bleed both of these systems, because they are a little bit different. I will start off with the Avid brakes first. Avid has their own proprietary bleed kit that comes with a bottle of fluid. It comes with some nice syringes that you fill with fluid. So you push fluid through one, and you start down here at the caliper. There's a little torx head here, a torx head screw. You unscrew that and screw in a bleed fitting, and your syringe is full of fluid. And you can see up here at the brake lever there's another one of those fittings where you screw in another syringe. The Avid brake bleed kit comes with great instructions, and they even have great instructions on their website at sram.com. You can go there and search for all the specifications, on how to do that. And the main thing to remember is to be patient. Make sure you remove anything that can be harmed by brake fluid, because brake fluid is really caustic. You probably want to wear eye protection as well as some gloves, because if you get it on your skin it kind of burns, and if you get it in your eyes, it really stings and could do a lot more damage than just sting."