BD Diesel Shift Kit - Chevy Allison 1000 2006-2008 6spdIncludes our exclusive Smart Trim Clutch Control valve assemblies and items to modify the C2 clutch piston for increased capacity and more durability. The C2 clutch is the weakest part of the early 5 Speed Allison Includes our exclusive Smart Trim Clutch Control valve assemblies and items to modify the C2 clutch piston for increased capacity and more durability. The C2 clutch is the weakest part of the early 5 Speed Allison Smart Clutch Control Valves