FORD 2003 F-550 v.2 - Manual (Page 246)

Checking and adding transfer case fluid (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 Lubricant
Specifications in this chapter.
DRIVELINE UNIVERSAL JOINT AND SLIP YOKE
Your vehicle may be equipped with universal joints that require
lubrication. Refer to the scheduled maintenance guide for maintenance
intervals. If the original universal joints are replaced with universal joints
equipped with grease fittings, lubrication will also be necessary.
AIR FILTER MAINTENANCE
Refer to the scheduled maintenance guide for the appropriate intervals
for changing the air filter element.
When changing the air filter element, use only the Motorcraft air filter
element listed. Refer to Motorcraft Part Numbers.
Maintenance and Specifications
246