Transients have proven to be a specially demanding operation mode for rotor cages in induction motors. The combination of thermal and mechanical stresses causes damage in weak points of the secondary circuit of these machines. A 3-D multiphysics computation may shed some light into the conditions under faults, such as broken bars developing, while taking into account phenomena as interbar currents. With the aim of reducing the computational cost involved, this paper carries out a 3-D simulation of just the rotor during the first 2.5 cycles after a direct-on-line connection, with the tangential component of the magnetic vector potential mapped on its iron surface from the results obtained by the 2-D locked rotor finite-element simulation. The results provide an insight into the skin effect and mechanical loads in the cage, a magnetic coupling between the end ring and the shaft, as well as the limitations of the weakly coupled magnetoelastic analysis.