How to Make a Bleed Block

How to Make a Bleed Block

Posted by Alex Mansell
How to Make a Bleed Block

What is a bleed block?

A bleed block, or piston spacer as it is sometimes known, is a plastic object designed to fit snugly between the pistons of your brake calliper, and its job is to prevent them from moving outwards during the bleed process. Today we're going to show you how you can make your own using the Epic Bleed Solutions' preferred method.

There are certain criteria a bleed block has to meet in order for it to work. It must:

  • fit snugly between the pistons of your brake calliper;
  • be made of a non-compressible material (wood, thick plastic);
  • be a non-marring material - not metal, as this will cause damage to the surface of your pistons.

Why would the pistons move anyway?

During the bleed process it is necessary to operate the brake lever for the purpose of dislodging trapped air, or to flush brake fluid through the system. Any lever movement following brake pad removal will cause the pistons to advance, this is bad for two reasons:

  • It can stop you from refitting the brake pads, wheel and brake rotor;
  • It causes accidental over-filling of the system with brake fluid.

Can't I just leave the pads in?

By bleeding your brakes with the pads in place you're running the risk of contaminating them with brake fluid, especially if it's your first time, and this will render them useless. Also if your pads are partly worn you will overfill the brake system with fluid making it difficult to replace the pads when the time comes.

Convinced yet?

Things you'll need

  • 3-5 old credit/store cards (or alternatively our Bleed Block Kit)
  • Superglue
  • Scissors
  • Elastic band
  • Pad separator or flat blade screwdriver
Tools needed to make your own bleed block/pad spacer

Step 1

Start by removing the front or rear wheel to access your brake calliper. For the purpose of this guide our brake is not attached to a bike but the steps in this guide will be the same.

Step 2

With the brake pads in place, use a pad separator or a flat blade screwdriver between the pads and twist to separate them. This will push back the pistons to where we need them to be. Be careful not to damage the surface of your brake pads.

Separating Shimano brake pads with a flat blade screwdriver

Step 3

Remove the brake pad retaining pin and then remove the pads from the calliper. Set them aside somewhere safe.

Removing the Shimano brake pad retaining pin from the calliper
Removing the brake pads from the Shimano calliper

Step 4

Once the pads are out make sure that the pistons are pushed as far back as they will go. The face of the piston should be flush with the inside of the calliper.

Shimano pistons fully reset and pushed back into the calliper

If your pistons will not push all the way back it may mean that the system has previously been overfilled with brake fluid.
If you suspect you may have too much fluid in your brake, with your bike the correct way up, remove the master cylinder bleed port screw or reservoir cap. Push the pistons back now. Get ready to catch any brake fluid with a paper towel and then re-tighten the bleed port screw or refit the reservoir cap. This will remove any excess fluid from the brake system.

Step 5

Take your old credit/store cards, or if you've bought our Bleed Block Kit now is the time to open it. Start by cutting 3-4 cards into quarters. You should end up with something like this:

Cutting up a blank plastic credit card with scissors
Blank credit cards cut into quarters

If you've got the patience, measure the width and length of each card and cut into equal pieces. This way your bleed block should fit perfectly inside your calliper.

Step 6

Now stack small pieces together and try them between the pistons of your brake calliper. Add or take away pieces until you find the correct amount of cards you need to make it a snug fit.

Epic Bleed Solutions bleed block method

Step 7

Next, add a small drop of superglue to each piece and stick the lot together. Allow time for the glue to set before proceeding.

Gluing plastic pieces together

Super glue is a strong adhesive and it bonds quickly. Take care that it does not come into contact with your skin, eyes, clothes or work surfaces and ALWAYS keep out of reach of children. Read more on removing super glue.

Step 8

Now you're ready to bleed your brakes. Use the rubber band to secure the bleed block in place during the bleed procedure.

Elastic band holding the Epic Bleed Solutions bleed block in the brake calliper
Elastic band holding the Epic Bleed Solutions bleed block in the brake calliper

Now it's your turn!

Have you tried this technique with success? Maybe you use something else as a bleed bock? Post your comment below.

Alex Mansell is the founder of Epic Bleed Solutions, blogger and mountain bike enthusiast. His blog focuses primarily on providing guidance to fellow MTB enthusiasts during brake bleeding. Follow Alex on Google+, Twitter and Facebook.

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