FORD 2013 F-550 v.1 - Manual (Page 311)

TRANSFER CASE FLUID CHECK (IF EQUIPPED)
1. Clean the filler plug.
2. Remove the filler plug and
inspect the fluid level.
3. Add only enough fluid
through the filler opening so
that the fluid level is at the
bottom of the opening.
Use only fluid that meets Ford specifications. Refer to the Capacities
and Specifications section .
310 Maintenance
2013 F-250/350/450/550 (f23)
Owners Guide gf, 1st Printing
USA (fus)