SuperPro SPF2240HK Front Spring Shackle Upper Bush KitSuperPro SPF2240HK Front Spring Shackle Upper Bush Kit These bushings are often overlooked when upgrading the suspension of a 4WD. Leaf spring bushings stabilise the movement of the rear axle, inferior bushes in this area will cause the solid rear axle to move and impart rear end passive steer to the vehicle. It also causes the vehicle to 'wander' all over the road and be unstable under heavy braking. This can be especially noticeable carrying a load