A compound turbocharger is provided, including at least one housing. A first turbocharger having an outer shaft is disposed within the housing, and a second turbocharger is provided having an inner shaft co-axial with and extending within the outer shaft. At least one displacement limiter is disposed at a selected position along the length of the outer shaft. A method of reducing vibrational amplitude in an inner shaft of a coaxial shaft assembly is further provided, including the step of operably positioning at least one displacement limiter at a selected position along a length of the outer shaft.