If I'm thinking correctly, the brake cable splits at the control and heads back to each brake arm. Follow the cables down from the lever. Both should be hooked up there at the lever. If not, one end is likely broken. the other end at the trans is a spring. So if what you have is a spring on the loose end, it came off the back,

Thanks for your reply re: Z425:,
it is an end with the spring on it. Are you saying it hooks to the transmission?

Your mower has two separate drive units. You will likely have one cable still attached to the arm on one transmission. Look at the arm on the opposing transmission. It is most likely that the spring has broken, but at least you have 1 good side to compare to. (hopefully)