Ford 2003 Mustang Workshop Manual page 468

23. NOTE: Apply pressure toward the left side to fully seat the differential bearing cup.
Install progressively larger differential bearing shims on the RH side until the largest differential
bearing shim selected can be assembled with a slight drag feel.
24. Install the RH differential bearing cap.
Tighten both bearing caps to specification.
25. Rotate the differential assembly to make sure it turns freely.