Process and apparatus for inserting a rigid support in a contractible sleeve used to enclose a joint between a pair of electric cables. The support has an outer diameter greater than the unstretched inner diameter of the sleeve. The sleeve is enclosed in a pair of separable half-shells having radially movable pressure elements extending radially inwardly therefrom and engageable with the outer surface of the sleeve. The pressure elements are urged inwardly by compression springs, and the pressure applied to the sleeve by the pressure elements increases with radially outward movmeent thereof. One end of the support is inserted in one end of the sleeve and the support is pulled axially into the sleeve while axial movement and shortening and buckling of the sleeve is opposed by the pressure elements.