my murray lawn mower won't go?

I was riding along and I heard something pop. My engine kept running, but mower would not move.I see a spring that is broke (on one end), the other end is hooked to a pulley@ the rear near back wheels(drive shaft???).My blades engage. The mower just won't move forward or backward.I believe this spring engages the pulley system that turns the belt with the drive shaft of back wheels.What do I need to fix problem? Is there some sort of diagram I could use TO SEE WHAT KIND OF SPRING I NEED AND WHERE I SHOULD HOOK IT?(serial#- 40702x92e date of manufacture-2774.