FORD 2012 F-550 v.3 - Manual (Page 285)

If any steering components are serviced or replaced, install new
fasteners (many are coated with thread adhesive or have prevailing
torque features which may not be re-used). Never re-use a bolt or nut.
Torque fasteners to specifications in Workshop Manual.
A high crown in the road or high crosswinds may also make the steering
seem to wander/pull.
ELECTRONIC LOCKING DIFFERENTIAL (ELD) (IF EQUIPPED)
The electronic locking differential (ELD) is a device housed in the rear
axle which allows both rear wheels to turn at the same speed. It provides
added traction on slippery and/or off road surfaces, particularly when
one wheel is on a poor traction surface. The ELD may be locked or
unlocked by the vehicle operator and can be engaged or disengaged on
the fly. When the axle is unlocked it will function like a standard rear
axle. When the axle is locked it will not allow the rear wheels to rotate
at different speeds when turning. It is not recommended for use on good
traction surfaces such as dry pavement. Doing so may result in abnormal
driving behavior and noise while cornering and excessive tire wear.
The ELD is affected by the following conditions of your vehicle:
• On 2WD vehicles and 4WD vehicles in 2H (4X2) or 4H (4X4 High),
the ELD will not engage if the vehicle speed is above 25 mph
(40 km/h).
• On 2WD vehicles and 4WD vehicles in 2H (4X2) or 4H (4X4 High),
the ELD will automatically disengage at speeds above 25 mph
(40 km/h) and will automatically reengage at speeds below 19 mph
(30 km/h).
• On 4WD vehicles in 4L (4X4 Low), the ELD can be engaged at any
speed and will not automatically disengage.
Activating the electronic locking differential (ELD)
For vehicles equipped with an
electronic shift 4WD system:
Pull the knob on the 4WD control
toward you. The
indicator light
will display in the instrument
cluster.
Driving
285
2012 F-250/350/450/550 (f23)
Owners Guide, 3rd Printing
USA (fus)