Thats easy, if your shackles are too short like stock they are a limiting factor in the amount of compression and droop. For instance my 84 had stock shackles on it when I got it. They were too short, the springs had rubbed a groove in the bottom of the frame from riding on it for who knows how long. It rode like crap and had O flex. I put 2" longer shackles on it wow what a difference! After that the springs were allowed to compress instead of just hitting the frame, also it could droop more because of the added length of the shackle just added to the distance from the frame to the tire. See you do gain flex with shackles, if you didnt gain anything then why would basically ALL vehicles that run leaf springs offroad use an extended shackle of some sort??
WT
