A new test, involving combined pure and simple shear, that can produce failure very close to the interface between the rubber and the bonding agent in a rubber-to-metal joint, is described. The test allows changes in the position of the tip of the de-bonded region to be followed with time, enabling the failure rate to be determined. The latter can be related to the strain energy release rate so that a fracture mechanics based analysis can be applied. Failure characteristics can be correlated with features of the de-bond surface. The results suggest that even when failure is very close to the interface, the measured strength is similar to that of the rubber.