Since you're going back 40 years I would say Bill Hess was number 1. In that 40 year time period, Solich has won the most games. Grobe brought the program back from the depths of despair.
So last 40 years, 1975-2015. This catches coach Hess' final three seasons; 1975-1977. During these three seasons coach Hess was 13-19-1 and 9-13-1 in the MAC. Those were different times, losing 0-20 to William & Mary, beating NIU 63-15, beating Marshall 49-27. What the heck happened in 1977, his final season, 1-10, 0-8 in the MAC? Hess deserves high ranking, he won four MACC in 19 seasons, but, what happened in 1977?