Ford 2003 Mustang Workshop Manual page 417

3. Position the differential side gear and thrust washer assemblies in the differential case.
4. Engage the differential pinion gears with the differential side gears and rotate the pinion gears
to align with the differential pinion shaft bore.
5. Insert the differential pinion shaft.
Align the hole in the differential pinion shaft with the hole in the differential case.
6. Install a new bolt finger-tight.