This leaf-spring swap took about two hours with the right tools. The CJ already had aftermarket shackles in the front and rear, and they play an important role in suspension performance because they can either stiffen or soften the spring rate. Shackles also reduce leaf-spring stress and increase spring durability. Also a taller shackle will increase the vehicle's ride height. Most Jeep shackles are mounted up front, but shackle-reversal kits are available which help smooth the ride of the Jeep when it hits a bump.