Ford 2003 Mustang Workshop Manual page 404

12. Rotate the differential assembly several times to verify that the differential bearings have seated
correctly.
13. Measure the backlash. Refer to Measuring backlash in this procedure.
Backlash not within specification
14. To increase or decrease the backlash, remove the bearing caps and install a thicker shim and
thinner shim accordingly.
If backlash is not within the specification, increase the thickness of one differential
bearing shim and decrease the thickness of the other differential bearing shim by the
same amount.
15. Install the bearing caps and the bolts.