Ratios for the SM420; 1rst-7.05:1, 2nd-3.58:1, 3rd-1.71:1, 4th-1:1. Reverse-6.78:1.
For comparison; SM318: 1rst-2.94:1, 2nd-1.68:1, 3rd-1:1, Reverse-2.94:1, Overdrive (if equipped) .70:1.
HD 3 speed (Borg-Warner) 1rst-3.17:1, 2nd-1.75:1, 3rd-1:1, Reverse-3.76:1
