Your Mustang Rear Differential Cross Pin is considered a wear part & will eventually need replacing. From stock replacement to notched for lower gears we have all varieties of Mustang Cross Pins for both 28 spline & 31 spline Differentials. Dont forget a new Mustang Cross Pin Bolt while you're there! Also, once you start making power & applying it to the ground with Slicks, you very well may spit out a set of Spider Gears. We have you covered there too with replacement Mustang Spider Gear Sets for both 28 spline & 31 Spline Carriers.