Daystar's front or rear original equipment leaf shackle employees bushings crafted with shock absorbing rubber to mount springs to framework. Although this provides superior shock absorption, rubber wears quickly, requiring regular replacement. When the rubber is worn down from normal use, dirt and grime picked up from the road and off road adventures, the leaf spring loses its ability to spring back, forcing the shock and jolts into the frame and causing one bumpy ride. That's why Daystar uses high quality polyurethane, making the most durable and comfortable leaf shackle bushings. Replace all four uv and wear resistant bushings at the same time to maintain a comfortable ride.