John Deere 60" mowing deck

[djta]

The tension spring keeps breaking, I have replaced it 5 times since last summer, the last one lasted about 2 hours.
Any idea why? Deck is about 20 years old on a John Deere 430 the deck serial number is M00273X576429

 

[BlazNT]

I do not know where it is breaking but i can offer a few things. First make sure both holes it is attached to are free of burs and sharp spots. Second make sure all pulleys are free turning. Spendals as well.