Zeolites are versatile materials widely used in various aspects of modern society and are some of the most relevant industrial catalysts. Regardless of such ubiquity, the conventional hydrothermal synthesis of zeolite materials with predetermined properties is challenging and in some instances not feasible, motivating a constant search for new synthesis avenues to expand their application potential. Here, thermally controlled mechanochemistry results in rapid, controllable, and energy-efficient organic structures directing agent-free (OSDA-free) interzeolite conversions. Milling under elevated temperatures yielded pure solid phases distinct from the parent commercial zeolite Y. In situ synchrotron X-ray diffraction monitoring revealed a strong effect of the composition of the reaction mixture on the reaction pathways and interconversion outcome. The properties of the formed material arise as an outcome of the subtle interplay of the kinetic and thermodynamic factors. The findings reported here afford directions for broader zeolite mechanosynthesis.