IMPORTANT: The differential lock rocker switch
is guarded to prevent unintentional switch acti-
vation. If the LED in the switch begins to blink
during normal operation, when the switch has
not been activated, this indicates an error condi-
tion. Bring the vehicle to an authorized Freight-
liner service facility as soon as possible.
When the differential lock switch is pressed, three
responses are possible: a normal response, a slow
response, and an abnormal response.
Normal Response:
The LED in the switch blinks until
the axle has responded to the request to lock the
wheels. At this point, the LED comes on steady and
stays illuminated. In normal operation, the wheels
may lock so quickly that the blinking of the switch is
barely noticeable.
If operation of the switch is not possible for any rea-
son (ignition is turned off, vehicle is moving faster
than 25 mph, etc.), the LED will stop blinking and
turn off.
Slow Response:
If operation of the switch is slowed
for any reason (vehicle moving too fast, low air pres-
sure, etc.), the switch will continue to blink until the
wheels are able to lock. As in the normal response,
the LED comes on steady and stays illuminated once
the wheels have locked.
NOTE: If the vehicle is moving too fast, let up
slightly on the accelerator. As the vehicle slows,
the wheels will lock.
Abnormal Response:
If the LED blinks for more than
30 seconds, the lock mechanism may not be fully
engaged/disengaged. Bring the vehicle to an autho-
rized Freightliner service facility for testing.
Differential Lock Operation
WARNING
Locking the wheels when the vehicle is traveling
down steep grades or when the wheels are slip-
ping could damage the differential and/or lead to
loss of vehicle control, causing personal injury
and property damage.
Lock the wheels only when the vehicle is standing
still or moving at very low speed, less than 5 mph (8
km/h). Never lock the wheels when the vehicle is
traveling down steep grades or when the wheels are
slipping.
NOTE: On some vehicles, the differential lock
system is connected through the low speed
range of the transmission. If this system is used,
the transmission must be in the low speed
range for the wheels to fully lock.
WARNING
A vehicle with locked wheels can still slip side-
ways, causing possible loss of vehicle control,
personal injury, and property damage.
Be especially careful when driving under slippery
conditions with the wheels locked. Though forward
traction is improved, the vehicle can still slip side-
ways.
If the vehicle is moving, maintain a constant vehicle
speed when the differential lock is turned on. Briefly
let up on the accelerator to relieve torque on the
gearing, allowing the wheels to lock completely.
When the wheels are fully locked, the turning radius
will increase because the vehicle understeers. See
. Drive cautiously and do not exceed 25
mph (40 km/h).
To disengage differential lock after leaving poor road
conditions, operate the differential lock switch as dis-
cussed above while maintaining vehicle speed. Let
up momentarily on the accelerator to allow the
wheels to fully unlock, then resume driving at normal
speed.
NOTE: If the differential lock system is con-
nected with the transmission in its low speed
range, shifting out of the low speed range will
also disengage the differential lock function. The
f350079a
02/03/2017
A
B
A. Turning Radius When the Differential Lock is
Engaged (understeer condition)
B. Turning Radius When the Differential Lock is
Disengaged
Fig. 8.22, Turning Radii
Drivetrain
8.30
