Quadrasteer was developed by Delphi by the old Saginaw Steering Gear division. It was only developed on the big Dana 60 rear axle used in 3/4 ton trucks. It used an electric motor powered steering rack bolted to the axle cover. The whole thing was massively heavy and caused the rear of 1/2 ton trucks to ride pretty badly. They steered great, especially with a trailer. It was, as @wolyrobb said, very expensive. $4500 when first offered, if I remember correctly. Dropped to $2500 to increase sales. I’d guess quite a few ended up in the boneyard if they broke swapped out with a standard axle because of the cost and difficulty of repair.