how can i fix my simpson maxidry 450?

The spring I think you are talking about is the belt tension spring.

One end goes to the belt tension pulley, the other around the cut out switch mounted to roof or floor of dryer. If you look at switch you will see that spring tension holds it shut. If the belt comes off or breaks then there is no spring tension and contacts open shutting off power to heater or other parts.

Richard
April 2006