Some of the jarring ride of the Super Duty rear can be attributed to the factory vulcanized bushings in the leaf spring pack and shackle. The factory shackle is very strong, BUT the design is not conducive to a smooth ride. This is no surprise as a Super Duty isn’t made to ride well; it’s made to tow. The factory leaf springs are high-spring-rate and short-travel, so why would Ford design a shackle that rides well and is capable of extended suspension travel?
Vulcanized bushings are a press-fit bushing often utilized by OEMs in which the bushing material is adhered on both points of contact. In this case, the black bushing material you see above (installed into the factory shackle) is adhered to both the shackle itself and the crush sleeve the bolt goes through. The crush sleeve (silver sleeve that runs the length of the bushing) is very thick, making the actual bushing very thin. When your bushing is designed to only move as much as it can deflect and the deflection is minimal, the ride will suffer.
We, at Carli, do everything in our power to milk these trucks for as much ride quality as we can. The vulcanized bushings may not seem like a big deal until you consider that there are 6 total bushings fighting suspension movement in the factory configuration – front leaf spring pivot, rear leaf spring pivot, and shackle pivot.
Replacing the factory springs with Carli-spec Deavers replaces 4 of these (front and rear leaf-spring pivot) with free-moving, serviceable bushings; this shackle replaces the final 2.
In contrast to the factory bushing, the Carli Bushing assembly utilizes more bushing material and a thinner sleeve to prioritize ride damping. Further, our bushings are serviceable. Droop the rear end and grease them through the protected zerk fitting. You’ll note in the high-res pictures, there are channels for the grease from the zerk. The grease travels through these channels, around the crush sleeve, and to the bushing face for optimal grease migration and bushing life. If you do manage to wear out the Carli Shackle bushings, you can purchase new ones and swap them in; reuse the crush sleeve. The factory shackle requires replacement in its entirety when the bushings crack/rot.
In short, the factory shackle is beefy BUT utilizes a press-fit vulcanized bushing designed to bind and resist movement. This makes for a poor ride, no serviceability, and no rebuildability. The Carli shackle costs less than a pair of American-Made sneakers and works wonders to free up the rear end of your Super Duty (even fits factory leaf springs) while offering BOTH serviceability and rebuildability.
