Allison C-2 Clutch Hub. TCS has addressed the early failure of the C-2 clutch hub in high torque/horsepower applications with this new billet steel clutch hub. Made from 4140 HTSR billet steel. Spline is lengthened .125″ for more contact, plus a spline boss diameter increase of .100″ for added strength. No weight penalty for strength. The TCS hub is only 2.8oz. heavier than the O.E.M. part. Comes with a modified thrust washer. NOTE: Machining modification to P1 Sun Gear Required.