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Sunday 19 January 2020

Bike brake piston expander

When bleeding Shimano and other makes of bike disc brakes it is necessary to fit a bleed block.
This is nothing more than a 10mm thick spacer that prevents the pistons closing during the bleed process. It avoids overfilling the system with too much hydraulic fluid.

It is common for the pistons to be slightly too close together to fit the bleed block. Most people use a screwdriver or similar handy tool. This is fiddly and risks damaging the pistons.

There are specialist brake piston presses available, which are like a thin spatula. These only press on one side at a time. These serve multiple purposes but they can still be fiddly when trying to open to the full 10mm width.

I've come up with a simple design that can be quickly pressed between the pistons to separate them by the required amount.

It's not an essential tool by any means, often a chamfer on the bleed block is all that is needed. The  tool I have designed is just a little time saver.


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