In the engineering world, academia certainly leans to the left, decisively but not overwhelmingly (somewhere between 60-40 and 70-30 I'd guess). Most of the conservative engineers tend to go into industry, and since there are far, far more engineers in industry than academia, those with any engineering degree are overall a Republican demographic.
The most liberal field is probably gender studies, which I suspect votes about 100-0.
I think that might be the main reason why academia leans to the left. Left-wingers tend to stay in after graduating while more conservatives and Republicans go into an industry, whether it is in their field of study or not.