Having issues with some of your brake pistons not moving properly? If so, you're leaving brake performance on the table.

Sorting a sticky 2 piston brake is a fairly simple job, just constrain (carefully) the freely moving piston with a plastic tyre lever and pull the brake lever. 4 piston brakes are a bit of a different story, you would need an extra pair of hands...

Here's a tool that can be used on 4 piston brakes to constrain 3 pistons so you can get the stuck piston moving with ease. Just drop the tool into your brake, pull the brake lever and hey presto, the stuck piston will move. Clean the piston with a cotton bud and gently press the piston back into the brake caliper with your tyre lever. If you want to clean them all, push them all back with your tyre lever and do them one at a time. 

The tool looks a bit odd but between rotating and flipping the tool you can extend any brake piston. It also has a chamfer on the leading edges to make it slightly easier to install the tool.

We promise that the tool doesn't look nearly as bad as the product image, we just have been without photography resources recently and wanted to list it anyway.

Cleaning procedure:

1. Carefully all pistons back into the caliper using a tyre lever. 
2. Insert this tool. Put the retaining pin through the tool and caliper to keep it in
3. Pump the brake and watch that the piston on the side of the tool with the cutout extends
4. Stop once the piston hits the tool - feel free to grab it a few times
5. Remove the tool
6. Clean the sides of the piston - we use isopropyl alcohol and cotton swabs
7. Push the piston back into the caliper with your tyre lever
8. Repeat with other pistons
   
9. Optional - apply a droplet of brake oil to the piston surface before pushing it back in. Only do this if you are going to douse the caliper with alcohol to clean it after the procedure, you don't want any rogue fluid hanging around!
   

Here's roughly what the tool will look like when being used: 

Park tool has this video available which explains the process without using this tool on 2 piston brakes. It's the same procedure for 4 piston brakes, just use this tool.