Blocking synchronization device for gear-type change-speed transmissions

A blocking synchronization device for gear-type change-speed transmissions, comprising sleeve carrier means, shifting sleeve means non-rotatably but displaceably arranged on the sleeve carrier means for the connection with a gear to be engaged, two friction ring means having outer conical friction surfaces and arranged on both sides of the shifting sleeve means, spacer bolt means extending through the shifting sleeve means for holding the friction ring means at a mutual spacing and for centering the same, elastically yielding means for holding said friction ring means in a central starting position relative to the shifting sleeve means, and blocking means including inwardly directed blocking elements at the friction ring means as also blocking elements on the outside of the shifting sleeve means, characterized in that the blocking elements of the friction ring means and of the shifting sleeve means are toothed means, in that spacer bolt means engage in axial recesses of the friction ring means and in that the friction ring means are stressed axially against the spacer bolt means by drawsprings.