9 inch diff oil capacity

Typical capacity (Ford 9-inch differential): about 2.4–2.8 litres, depending on the housing and gearset.

The proper method is to fill with GL-5 gear oil (75W-90 or 80W-90) until the level just reaches the bottom of the fill hole with the car sitting level—because gravity is still undefeated. If it’s a clutch-type LSD, add the recommended friction modifier; chattering on tight turns means you need more. After a rebuild or a decent run, let it cool and re-check the level. Consult official documentation for exact figures.