COXY!!
I JUST BUILT MY YOKOMO 1/12TH SCALE ITS PRACTICALLY LIKE THE ASSOCIATED CAR..
I HAD A PROBLEM WITH MY DIFF.. UNABLE TO ADJUST.. AND REAL GRITTY, THE CONE WASHER FOR ADJUSTMENT BOTTOMED OUT AGAINST THE BEARING.. I INSTALLED 2 WASHER TO FIT ONLY ON THE INNER RACE OF THE BEARING.. THIS MADE THE DIFF TOTALLY COME TO LIFE.
MAKE SURE THE WASHER AND/OR SHIM DOESNT TOUCH THE OUTER BEARING AND YOU SHOULD BE OK.