Broken garage door extension spring trick

My spring failed at the last coil, a quick fix without replacing the spring. New springs may be lower quality than good old ones. This fix has been working for the past 2-3 years. My garage door is about 200cm tall 300cm wide, the spring is 4cm dia, 67cm long (no tension) and 160cm fully extended (door closed). The pulley tension cable length is 430cm, about 5mm dia.