I was replacing a chain and managed to cut the chain too short. Is it possible to make the chain longer using a simple chain breaker? If so, how?
First off, hope that you properly removed the links before so you can just snap the links back into place, that is easiest.
Any breaker that is designed properly will push the pin just to the point where you can snap the links out leaving the pin still attached.
Snap the removed links back onto the chain and place the chain back onto the breaker with the pin facing into the breaker like this:
Carefully push the pin back into the link making sure the breaker pin and the roller pin are aligned. Misalignment can cause damage to the chain and breaker. Only push the pin through until it is extended past the link as far as the pins in the rest of the chain:
Now the link will be too tight to bend easily, this is fixed by placing the chain in the middle jig and pushing the pin slightly, just enough to free the link up.
Test the link to be sure it bends easily. Now go back and remove the proper number of links, making sure the male/female links match up when the chain is looped with or without a master-link, your preference.
Some narrower chains for 10 or 11 speed systems have pins that are designed for a single use only, and have a part designed to be broken off after insertion.
If you have a chain like that, you can't just push an old pin back in, but mostly you can.