What is a Bleed Block?

A bleed block, or piston spacer as it is sometimes known, is an object designed to fit snugly between the pistons of your brake calliper (once in the reset position), and its job is to prevent them from moving outwards during the bleed process.

In the picture below you will see two bleed blocks, one for Shimano brakes and one for Avid.

Avid and Shimano MTB brake bleed blocks

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.

Here is an example of a bleed block being correctly placed between the calliper pistons prior to bleeding an Avid brake system.

Avid bleed block during Elixir R bleeding

If you don't have a bleed block don't panic, follow our tutorial on how to make your own.

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