Using a methodology based on the crude adiabatic approximation, we study the complete linear and quadratic vibronic coupling in the ground state of SCH3 radical. In order to build the representation of the hamiltonian, we evaluated 30 integrals intervening in the formulation of the vibronic coupling. Diagonalization of this representation gives the vibronic levels. For the lowest vibronic states, the implied modes are Q1 (symmetric C-S stretching) and Q4 (CH3 rocking). Energy gaps A1-A2 and A2-ε resulting from the splitting due to the Jahn-Teller coupling E e = A1 + A2+ ε are evaluated to 250 and 169 cm-1, respectively. Essential coupling parameters are surrounded to simplify the study of highly vibronic states.