Don't Forget the Splines

Because the rear ends in dirt cars often see extreme articulation, many racers use Bert's ball-spline tailhousing. This innovation allows the tailhousing shaft to extend several inches without allowing dirt and sand to invade the housing when the shaft slides back into place. Cook recommends disassembling and cleaning the ball-spline shaft and housing after every two to four races.

SOURCE
Bert Transmission
St. Constant, Canada  PQ, J5A 2E
Jim Cook Racing