In a standard TH400, when the unit shifts from 1st to 2nd to 3rd, the direct drum and internal components are spinning up backwards, completely stopping and then re-accelerating to input RPM. At racing RPMs this takes a huge amount of energy and puts a lot of strain on the transmission, which is why parts fail when they hit their limit. The traditional method of installing lighter components to improve performance won’t overcome this basic inefficiency of the TH400.

Sonnax re-engineered the entire forward/direct drum system so only a few parts counter-rotate instead of the entire direct drum: the inner sprag shaft, aluminum clutch hub and friction plates. Weighing 3.3 lbs less than an aluminum drum, with weight concentrated at the center, the Smart-Tech drum module's direct clutch components take 53% less energy to start/stop/re-start than an aftermarket aluminum drum. This is a HUGE advantage no matter vehicle power level or what type of racing you’re looking to do. Plus, direct drums that explode due to overspeeding are simply no longer a threat thanks to the module’s unique design.