A new method for determining the spring and damping constants for elastomer materials is presented. The method relies on three concepts-measurement of force and displacement or velocity across the test specimen, precise control of differential phase shift and sensitivity in transducers and electronics over the full operating frequency and amplitude range, and automatic optimal identification of K and C using analog hardware.The technique may be used in conjunction with either a resonant beam or electrohydraulic system, as demonstrated in the paper. Typical error sources are presented for both systems with indications given of their elimination by the new technique. Hardware implementing the concepts is described and calibration test results given. It is concluded that the system provides an automatic test procedure which has the potential to reduce errors and maintain consistent results for rubber properties, relatively independent of the test machines and operators.