Our Add-a-Pack rear springs are a proprietary design built for us by Deaver Spring MFG. The lower overload leaf is removed and replaced with thinner gauge leaves. The O.E.M. load capacity is maintained while improved ride is achieved.

If Pairing to 4.5″ System: Super Duties equipped with a 2″ tall block from the factory will require the factory 3-5/8″ tall Block to achieve a leveled stance to a 4.5″ kit with the Add-a-Pack.
Factory Block Part Number: 7C3Z-5598-HB, 7C3Z-5598-JB

If Pairing to 2.5″ System: Super Duties equipped with a 3-5/8″ tall block from the factory will require the factory 2″ tall Block to achieve a leveled stance to a 2.5″ kit with the Add-a-Pack.
Factory Block Part Number: 7C3Z-5598-L, 7C3Z-5598-K

These packs are designed to eliminate the incredibly harsh rebound of the factory overload spring they replace, helping to tame medium to large bumps when paired with a Carli Suspension System. The Progressive add-a-pack replaces the lower overload springs on the factory pack — the 1″ thick leaf that doesn’t follow the contour of the rest of the pack. In removing this spring “wall” and replacing it with a mini progressive leaf pack, the capacity of the truck remains unchanged, as it’s determined by the factory springs, while the progression of the rear spring rate becomes substantially more predictable. The engagement and disengagement of the spring becomes smoother, increasing both ride quality and traction. As the “wall” was removed, the rear may sit lower with a heavy load BUT it will ride better loaded.