How to Bleed Avid Disc Brakes

Hydraulic disc brakes are very popular on mountain bikes thanks to the improved braking control and stopping power they provide. However, the liquid in the system may need to be replaced after time and this handy guide will help you to get it right without causing any damage.

• Two syringes with tubes and screw ends that fit your brakes
• Tubing clips
• A T10 and T25 torque key
• A bleeding block
• Some rubber bands and cable ties. Pedal toe straps work really well too.
• DOT fluid
• Rubber gloves or workshop gloves - brake fluid is corrosive and an irritant

If you're missing anything, you can order everything on this list from our bike maintenance and tools sections at Halfords.com

Get set up

Before you start you'll need to remove the wheel and brake pads. It's important that you don't pull the brake lever at this point, as you'll seize the pistons.

Check you've got the right brake fluid (there'll be indicator on the brakes themselves) and make sure you're using DOT fluid for SRAM brake systems. It's designed to amplify braking force, important for performance braking systems.

Now you'll need to fill your syringes with your brake fluid. Fill one syringe to one quarter full and the other to the halfway mark. Tap or flick each one to get rid of any air bubbles, as these will damage your brakes. Then, close the clamps to stop any fluid from spilling. At this point you should attach your bleed block, which will relax the pads and disc. Check the arrow is pointing the right way and push it in until your hear a click.

You'll then need to attach each syringe in place, with the half-full syringe (which we'll now call the 'caliper syringe') at the caliper bleed port and the quarter-full one (or the 'lever syringe') on the handlebars next to the brake lever that operates the brake you're working on. Make sure the tube clamps are closed so you don't spill any fluid. An easy way to keep the syringes in place is with your pedal toe straps or rubber band. Once they're in place, unscrew the bleed ports on the caliper and lever and screw in your syringes.

Start bleeding your avid or SRAM disc brakes

Now that the syringes are securely attached, you'll need to feed the new DOT brake fluid through the system. Open the tube clamps on the syringes and push the plunger to force the fluid through the system and up to the lever syringe, to the point where it's almost empty - but don't empty it! Then, close off the clamp on the lever syringe, but leave the caliper syringe open.

Now, you'll need to put a rubber band or pedal toe strap around your brake lever, making sure it's tightly on. Then, push and pull the caliper syringe to pressurise the system, slowly releasing the brake handle and keeping the plunger depressed before closing the tubing clip on the caliper syringe. Once that's done, unscrew the caliper syringe and tighten the bleed port back up, cleaning away any excess brake fluid with soapy water or an alcohol wipe.

Get rid of air bubbles and test

You'll now need to create a vacuum using the lever syringe. Open up the tube clamp, then pull and push the syringe lever to draw any air bubbles out of the system. Do this ten times, or until there aren't any further bubbles entering the top syringe. Then, unscrew the syringe while pressing the plunger and tighten the bleed port back up. Give everything another clean and dispose of excess fluid and oil safely.

Give your brakes a test by spinning the wheel and then pulling on the brake. You're looking for a firm reaction. If there are delays or braking doesn't feel firm, then repeat the process until you're happy.

If you need more information or don't feel comfortable working on your expensive Avid or SRAM brakes, then we can help out in-store. Just pop in for a chat with one of our bike experts, who can bleed them for you for a small charge.