Audible lining wear indicator

In a friction disc for use in a frictional engagement device including reaction members operating in a fluid environment the improvement comprising:

• a core plate having obverse and reverse faces and a plurality of apertures passing therethrough including a central aperture and apertures spaced inwardly of the outer periphery of the core plate;
• a primary frictional material of microporous material in a configuration of an annular ring having a plurality of apertures therethrough, having its static coefficient of friction substantially similar to its dynamic coefficient, bonded to each face of the core plate with the apertures of the primary frictional material annular ring aligned with the apertures of the core plate which are spaced inwardly of said outer periphery;
• slugs of secondary frictional material occupying the outer periphery core plate apertures, the slugs being slightly longer than the length of the outer periphery core plate apertures and freely slidable therein where the slugs are of such material as to produce an audible signal upon contact with cooperating reaction members to indicate wear of the primary frictional material.