Usually it breaks one spring and we drive it forever until it breaks the other. I noticed on mine when I installed the Jake and had to add an extra spring, I was already missing one!!!! If you get it from Cummins it's a lot cheaper, or you could just use a throttle spring from the local hardware. That's what I used as an additional spring and it has lasted over 200K so far.
Also, the book shows a real good view, there is a third spring on the linkage further back. Make sure you have that one too.