It's very hard to predict how a justice will rule on future cases based on previous ones, which is an idea that many presidents have been burned by when trying to select a justice they agree with. This paper does some analysis of what's called ideological drift. This graph more or less summarizes that analysis. Relative to your question, you can see the bright yellow average line peaks in the early 70s before diving back down towards the liberal side. Marshall and Brennan in particular really moved in that time period, and Blackmun's transition is striking as well.

There are a myriad of reasons why this might happen and it's inherently different for every individual, and I'll leave it to others who may be more read on that specific time period than I am.