A preliminary approach to calculate hydromount elastic shell dynamic stiffness using finite difference method is presented in the article. This approach is necessary to calculate and assess maximum shear deformations of hydromount rubber shell needed to further determine the hydromount stiffness and damping coefficients at resonance frequencies. For this reason, finite difference method is applied when assessing maximum shear deformations of hydromount rubber shell, caused by variable loads. It was found that using reduced length and reduced arc dimensions of cut-out hydromount shell segment the equivalent stiffness can be determined. The novelty of the proposed method lies in the possibility of a quick and fairly accurate numerical calculation of the rubber shell stiffness using the values of the rubber modulus of elasticity, its permissible shear stress, and the nominal load (weight). This approach can be used to determine and optimize the geometric dimensions of the mounts shells with a given stiffness.