According to The New York Times archives the Teamsters supported Reagan in both 1980 and in 1984.
http://www.nytimes.com/1983/09/26/us/teamster-says-union-prefers-reagan-to-mondale.html
From the article: The teamsters’ union will support President Reagan in 1984 if he is running against Walter F. Mondale, the union’s president, Jackie Presser, said in an interview today.
(Snip)
The teamsters’ union, which does not belong to the A.F.L.-C.I.O., was one of the few labor groups to support Mr. Reagan in 1980, and Mr. Presser said the union, which claims a membership of 1.8 million, remains committed to the President. Mr. Presser said he and other teamster leaders believe the President deserves praise for lowering interest rates and for other economic improvements, and he said the President’s next responsibility must be to reduce unemployment.
I do remember that McGovern was so bad, the Teamster's actually came out early for Nixon. Even more surprising was the AFL-CIO refused to make an endorsement at all. I was too young to vote at the time (by just a few years) but very active politically. I also remember some reporter asking George Meany (then AFL-CIO boss) why he didn't run for president and he replied tersely "I don't care to step down!" He was an arrogant bustard, but he did have a small sense of humor.