As long as the sprocket on the threads are moving freely, you shouldn't really need it. You rotate the outer sprocket through the slot on the backing plate (right below the yellow arrow) and with the pressure of the spring on the pads and the slotted ends of the cylinder somewhat pre-adjusted by hand, the cap stayed in place pretty well for me. I then cut the zip-ties (rear cylinder) or rubber bands (front cylinder) holding the cylinder together and pulled out the strands. I didn't spread the pads too far, otherwise getting the brake drum back on is difficult.
