Something I think is interesting: we often say that Minnesota was once a fully entrenched helmet and after "a long time" they lost it. But "a long time" doesn't really mean anything without a point of comparison. Absent cataclysm, the length of time it took for a school like Minnesota to lose its status is a flash in the pan compared to what it'll take for a modern helmet to lose its status now.
As a starting point, we don't even really know when Minnesota ceased to be viewed as a "helmet".
First off:
I've seen a lot of people cite 1967 as "the end" because that was Minnesota's last conference title. Also, I think these people assume that Minnesota's 1960 NC needs to be included. However, as I noted above, Minnesota's 1960 NC Claim is particularly weak: They lost to a mediocre Purdue team, finished as BigTen co-Champ (with Iowa), went to the RoseBowl, and lost to Washington. In 1960 Minnesota did beat co-champ Iowa but they didn't play the next two best teams (4-2 tOSU and 3-2 MSU). Further, Minnesota's OOC was terrible. They beat Nebraska who sucked that year and Kansas State who sucked worse.
Minnesota's 1967 BigTen Championship is another co-championship. It was a weird year. Indiana, Minnesota, and Purdue all finished 6-1. Ohio State finished 5-2 and the rest of the BigTen all finished below .500. Purdue was almost certainly the best team in the league that year. The Boilermakers curb-stomped both Minnesota and Ohio State and lost a close game in Bloomington. Minnesota curb-stomped Indiana and didn't have to play tOSU. Indiana also avoided Ohio State.
I would submit that by the time Minnesota won their last two conference titles in 1960 and 1967 they were already a non-helmet. Those wins were basically just flash-in-the-pan successes that many non-helmets experience once in a while.
What is surprising is how abrupt Minnesota's fall was. I already mentioned Minnesota's back-to-back undefeated and untied conference and national championship seasons in 1940 and 1941. Additionally, they had:
- 39: off year
- 38: conference title
- 37: conference title
- 36: tied with tOSU for second behind NU, won NC
- 35: conference and national titles
- 34: conference and national titles
- 33: conference title
- 30-32: off years
- 29: tied with NU for third behind PU and IL
- 28: third behind IL and UW
- 27: conference title
As of 1941 the Gophers had six NC's. Michigan had seven. Neither Ohio State nor Nebraska had won one yet. Illinois had four.
As of 1941 the Gophers had 16 league titles. Michigan had 15. Illinois had eight. Ohio State and Wisconsin had five each. Iowa had three.
My point is that Minnesota's success in 40-41 was not a flash-in-the-pan thing. They were a consistently powerful team basically from the formation of the conference up until the beginning of WWII.
The war years are a confusing mess. With draftees leaving and trainees arriving it wasn't unusual for teams to be great one year and terrible the next. For example, Ohio State went 5-1 in conference and 9-1 overall in winning their first NC in 1942 then went 1-4/3-5 in 1943. During the war league titles were won by 42: tOSU, 43: PU and M, 44: tOSU, 45: IU.
After the war Michigan quickly resumed being a consistent power (for a short time) but Minnesota simply never came back. The Wolverines had back-to-back undefeated seasons and conference and national titles in 47-48. Then they won the next two BigTen titles as well (one shared with tOSU). Over those same four years Minnesota, who had been every bit of Michigan's equal in the 30's went 3-3, 5-2, 4-2, 1-4-1.
Here is the thing that I find interesting. Michigan had their own fall from grace. From 1951-1968 the Wolverines only won one conference title and no NC's. BigTen titles over those 18 years:
- 5: Ohio State
- 3: Wisconsin
- 3: Iowa
- 3: MSU
- 3: Illinois
- 2: Minnesota
- 2: Purdue
- 1: Indiana
- 1: Michigan
Michigan obviously recovered strongly with the hiring of Bo in 1969 and his immediate success. Within a few years Michigan was known as one half of the "BigTwo" while Minnesota was one eighth of the "LittleEight". Why did Michigan recover while Minnesota did not? Also note that Michigan's fall from grace and recovery both occurred prior to your 1970 date of helmets being fixed.