Shift cable end

Hi all,
I've recently had the shift cable end pull out of the splitter  under my
 tandem's bottom tube a couple of times. https://ritcheylogic.com/bike/accessories/bab-cables-disconnectors?srsltid=AfmBOorh2jimj_mZVmrUvtHd0Eqi0YXAmUdIp2Ttxewb0wVsCGzGTDdV
I've tried increasing the force I apply to the set screw, and just seem to
 get broken/breaking strands.  Is there anything I can do to improve this
 (e.g., treating the cable end with something before inserting it into the
 splitter)?
--
Ted H <theise@panix.com>