Ford 2003 Mustang Workshop Manual page 390

12. Position the correct thickness drive pinion bearing adjustment shim and the differential pinion
bearing on the drive pinion gear. Using a suitable press and the special tools, press the
differential pinion bearing until it seats firmly against the drive pinion gear.
13. Place a new collapsible spacer on the pinion shaft against the pinion stem shoulder.
14. Install the outer differential pinion bearing.
15. Install the rear axle drive pinion shaft oil slinger.