A highly versatile damper-weight system enables the installation of adjustable swing-weight in a vibration-damped manner inside a golf club shaft. A plug assembly of selectable weight is inserted through a circular opening in the golf grip cap with a special tool, moved to any desired location within the shaft and securely fastened in place in a vibration-damped manner by radial expandable of a cylindrical resilient expandable element. A weight rod, made available in different materials, lengths and weights, is spaced from the shaft by one or more resilient damper sleeves to minimize shaft vibration. The expandable element is secured by a machine screw threaded into the upper end of the weight rod, and is dimensioned (unexpanded) to enable easy insertion and location adjustment of said plug assembly. The tool provides dual functions: as a screw head driver to expand/contract the expandable element radially by axial pressure/release as required, and as a removable coupler capable of pulling the plug assembly (with the expandable element unexpanded) upwardly, as well as pressing it downwardly within the shaft for adjustment to any desired location.