I've had one come loose before too, my re-installation technique was more straight forward. 1) Align the hole in the hub with the spring hole 2) insert the spring 3) using a flat head screw driver, put it through the hub hole and insert the blade into the top of the spring 4) push hard and compress the spring so the hook end protrudes through the back plate of the brake assembly 5) turn the screw driver to engage the hook, then release the pressure and it's done.