Pretty heavy in the weight department. My Vermeer baler has a slip clutch that uses diaphram springs instead of coils. It's heavy too,maybe there is a really small one somewhere. I'm not sure how this kind of slip clutch would work to allow the difference in wheel speeds in turning. They are used in ag equipment to prevent catastrophic distruction when your mower or baler eats a tree limb or breaks a chain. When Murph built his 2 wheel drive he used a semi-viscous clutch from an awd auto. They are small and probably lighter than the spring clutches.