Often in the study of bodies that undergo shock loading, it is desirable to measure the response of such structures with an instrumentation package. This instrumentation can be separated from the external housing by several preloaded interfaces. To better understand the effects of preload on the nonlinear dynamics introduced into the measurement, a simple preloaded interface test fixture was fabricated. Both low amplitude modal impact tests and high amplitude shock loading tests were used to analyze the effects of varying preload between the bodies on the linear and nonlinear dynamics observed in the response of the coupled bodies. The results of these measurements indicated that increases in preload reduced nonlinearity, but could amplify force transmission. Based on these results, a three degree of freedom system model was created to represent the dominant linear modes of response and the qualitative nonlinear characteristics that were observed in the high amplitude shock loading experiments.