How To Change the Hydraulic Brake Pads on Your Bicycle (and properly bleed the lines)

This procedure is pretty generic and should work with most hydraulic brakes. One of the goals of this post was to use as few photos as possible.

It’s important that you don’t skip any steps here.  Skipping a step or not following the directions exactly may result in spilling hydraulic fluid, dropping the hydraulic reservoir by accident and splashing it on your friend’s shoes, or worse, getting hydraulic fluid on your pads.

There are two reasons you might want to change your pads:

  1. They got contaminated with oil of some type. You will know they got contaminated because they will make a very loud SQUAWK when you use them
  2. They are worn out.  You will know they are beginning to be too thin because they will start to make an unpleasant sound when you brake or may begin to vibrate. New pads are 8-12 mm thick. You’ll want to check with the manufacturer to see when you should replace them.

What you need:

  1. Either a really robust set of Allen and Torx wrenches, or one of the kits they sell for bikes.  These will usually have everything you need
  2. A small glass or a large shot glass, something you can place the reservoir into and is a tight enough fit to keep it from falling over.
  3. Some sort of container, like a shampoo bottle or something (cleaned) that you can use to dispose the fluid.  If you don’t have a clumsy friend around to accidentally spill your fluid on the ground, here is a discussion of several interesting methods of disposal/recycling. I prefer the recycling approach.
  4. A SPRAY bottle of 95% Isopropyl alcohol – they sell them at Walgreens in the first aid area.
  5. A roll of paper towels
  6. A small pair of flat ended pliers. A set like this will serve you well for many years.


  1. Remove both wheels and support the bike somehow. I used a large plastic bin and a friend to support the front fork and keep the bike from falling on my head.  We supported the bike at the center with an old paint can. The plastic bin also makes a convenient bench.  Find the smallest chair you can, or a log, or maybe your spouse’s favorite footstool, so you have something to sit on.
  2. Make certain you read through this procedure ENTIRELY and check as you read that you have a tool that will fit each bolt head.
  3. Buy one of these.  It comes with more than enough oil for the job for two brakes, even if you accidentally spill the entire reservoir on your friend because you have butter fingers.
  4. To avoid contaminating the brake pads, first we are going to completely drain the fluid from the system.
    1. The brake assembly down by the disk, located usually on the left side of the fork a the center of the wheel, is called the “caliper” and it comes apart into two pieces.  Observe how the hydraulic line from the lever housing goes into only one side of the caliper. This will be the “inside” caliper.  I will call the other one the “outside caliper.”
    2. On the bottom of the outside brake caliper, locate a small, plastic cap.  Pop the cap off, holding it securely.  There should be a little ring holding it to the bleed valve nipple, but they do break sometimes.  You don’t want to lose this because dirt can get compacted in the nipple and, if you perform this procedure in the future after having lost that cap, you will surely clog your lines.
    3. In the kit you bought, locate the flat, elliptical tool that has notches in both ends. The tool is a flat piece of plastic, shaped roughly like an American football. Clip it to the end of the clear tube. One of the notches may fit your nipple better than the other. Use the end that fits most snugly.
    4. Test that you can seat it all the way down onto the nipple. This is super important. It must be ALL THE WAY SEATED. Just leave it there like that. It should stay, all on its own.  If it doesn’t, you screwed up.  Try again with the other side or get some help because you might not have the chops to do this.
    5. Using your pinky and thumb, attach one of the knobby things with the flanged nipples to the syringe.  It’s plastic, so be careful not to cross thread! The rule of thumb with plastic parts is don’t go past pinky tight!

  1. Fully depress the syringe plunger
    1. Attach the syringe to the tube. 
    2. On the outside caliper, above the nipple, is a screw.  Loosen it two or three turns
    3. On the brake lever housing you will see a circular, flat, screw head. It receives one of the smaller Allen wrenches. Completely remove it and put it in a bowl that you borrow from your wife’s pantry without telling her.
    4. Pull the plunger, drawing all of the fluid into it.  If there is no fluid and it is hard to pull, then the valve didn’t open.  Maybe you turned the wrong screw.
    5. Once you have successfully drawn out all the fluid, tighten the valve screw and, while pulling gently on the plunger, remove the hose from the nipple and dispose of the fluid into the shampoo bottle. Thoroughly clean the syringe and hose using the isopropyl alcohol. Place the tip of the spray bottle of isopropyl directly up to the end of the hose and flush the tube.

Congrats! You have successfully drained the system for the front brakes.

Replacing the brake pads

What you will need:

  1. You need to have first drained the system. If you skipped the first half of this checklist, go back and do it. Seriously. It is important that you drain the system or you will almost certainly contaminate the pads and make a fucking mess.
  2. A pair of helping hands OR some rubber bands

The Procedure

  1. The pads are held in by the geometry of the calipers and also a cotter pin, or maybe a regular bolt. Remove the cotter pin (or the single bolt). If it is a cotter pin, bend the end straight with a mini pair of flat nosed pliers.
  2. The caliper is held together by two bolts.  They will likely be Torx. Remove them both and place them in the bowl. The assembly should fall apart in your hand. Note that hydraulic fluid does not leak out all over the place. This is because you were smart, and drained it all.
  3. There may be some small tiny amount of leakage. wipe down the area, as follows: Spray a towel with isopropyl alcohol and clean the entire area thoroughly.  If the pads were contaminated, take a family member’s toothbrush (clean it thoroughly with hot water and then alcohol) and spray the pads and get them nice and soaked.  Brush them vigorously with the brush. Wipe with the towel.  Do this until the towel comes away clean.
  4. Place the new pads into the caliper in such a way as to match the geometry therein. The metal clip AND the two calipers should be securable with the cotter pin.  
  5. Have a friend hold the caliper together while you insert the pin. Once the pin is in, and through all three parts (the two pads and the metal brace), screw them together.
  6. There is a flat, plastic, thin block. This is a spacer that is slightly thicker than the disk. Insert it between the pads.Use a rubber band to hold it in place if needed.
  7. Attach the reservoir to the hydraulic chamber on the top of the brake lever body. Thread it carefully, pinky tight. Ensure the stopper is inserted.
  8. Fill the reservoir as high as you can. 
  9. Insert the tip of the syringe into the reservoir and draw as much fluid into it as you can
  10. Connect the hose to the nipple on the outside caliper, ensuring a snug fit.
  11. Connect the other end to the syringe.
  12. Open the bleed valve a couple turns.
  13. Ask your friend to pour just a quarter inch or a centimeter or so of hydraulic fluid into the reservoir.  This will keep it from sputtering and spraying in his face when you press the syringe in the next steps. It will also allow him to redeem himself in the event he dropped it on you before.
  14. Have your friend remove the stopper and place it in the bowl.
  15. Depress the plunger, holding it higher than the caliper and pointing toward the ground
  16. Have your friend tell you when it stops bubbling. 
  17. Repeat the drawing and pushing of all of the fluid, without ever fully emptying the reservoir, two or three times or until all air is out of the tube between the syringe and the caliper, and there are no more bubbles. Go slowly! Wait a few moments between draws to give bubbles a chance to work their way out. The pulling and drawing of the plunger should work to purge the air completely.
  18. When completed, reinsert the stopper.
  19. Close the bleed valve tightly. 
  20. Remove the reservoir, dumping the excess into the recycling. It may have little bits in it from the system, so don’t reuse it. Place the reservoir into the shot or juice glass to hold it because you will need to use it again to do the rear brakes.
  21. Insert and tighten the brake lever housing hydraulic cap screw
  22. Remove the yellow spacer
  23. Repeat the entire procedure on the rear brakes. They will be very similar.
  24. Ensure the brake disks are clean – use the alcohol and towels to ensure their cleanliness.
  25. Reattach your wheels. Brake check by walking the bike and depressing the brake lever. Next, test by riding slowly.  If you hear a squawk, stop and immediately remove the wheel.
  26. Spray the pads with the alcohol. Using a folded paper towel, gently drag it through the opening until you are sure it is clean. 
  27. If you still hear squawking, repeat the entire process.  Practice makes perfect!

You are awesome! You have successfully replaced your brake pads and bled your brake lines!