This Thesis of Master of Science Degree in Automotive Engineering attained at “Politecnico di Torino” is carried out in collaboration with Silatech S.r.l. Company, based in Orbassano (TO), inside the Innovation Department (R&D). The argument of my MSc Thesis is the mechanical design, precisely the study and development of an ‘Automatic Mode Engagement’ (actuator) for shift-by-wire and shift-by-cable automatic transmissions, starting from a set of specifications and rules provided by the customer. Benchmarking procedures are applied during the study, in particular the kinematics of the spring retention system, nevertheless each component is verified and dimensioned and in some cases solutions to increase the performance and reliability of the components are provided.