Run to fast variable speed. Find a socket the correct length to wedge in the lower spread apart sheaves. loosen main and traction drive idler, remove AC comp belt, and while having a gorrila buddy you trust holding up main idler or otherwise taking off spring and snubber and hyd hose, roll off old main drive belt under traction drive belt and roll new belt back on. This is in lieu of unscrewing and removing outter sheave in VS units. On hydros use a come-long to raise hydro idler. If you mean main drive to be traction drive belt, follow step to space lower sheaves apart and remove hose then take off sheave end nut by unscrewing and remove sheave, then belt. Adjust new belt to have 1_8" clearance between lower sheaves at slowest speed. Check Torque sensing drive by having someone hold the brake and momentaraly slip the clutch while you watch as the inner pulley will move out to auto tighten the belt. If it don't you got problems.