Strong “stroke” while turning and narrow slow curves

Hello guys, I’m new here at Subaru forum, and wanted to ask you something, what I couldn’t find in the SuFu: With my Subaru Legacy from 1991 ( Limo ) it starts to hit through the whole car, if I turn at a crossroads or drive very narrow curves very slowly. Is that because now a wheel turns off when turning through the four-wheel drive? Can you fix that somehow or is there bigger behind? would be very happy about an answer. 🙂