Four-wheel-drive vehicles are designed to provide extra
power and traction for traveling at a slow speed over
rough or unusual terrain. Accidents and the high cost of
operating four-wheel-drive vehicles are, in most cases,
caused by abusive use or expecting the four-wheel-drive to do the impossible.
This chapter is intended to highlight safe, economical ways to get the most
out of
these vehicles.
Operators
Drivers operating four-wheel-drive vehicles must be
thoroughly trained and qualified (chapter 1, Authorized
Drivers).
Operation
The same general safe driving practices for standard
vehicles apply to four-wheel-drive vehicles (chapter 1,
Safety Rules).
Four-wheel-drive should be used only when greater
traction and power are required than can be provided
by a standard transmission in low gear. Use it in steep
off-road operations, in snow or on icy roads, in mud or
sand, or other conditions that require extra traction to
travel at slow speed.
The gear train will be placed under stress when vehicles
are driven on surfaced roads with four-wheel-drive
engaged. This causes difficulty in shifting out of four-wheel-
drive. To relieve this stress, back up a few feet or
drive off the surfaced road. This will allow the wheels
to slip.
Safety Rules
Four-wheel-drive vehicles usually do not perform as
well on surfaced roads as conventional-drive vehicles.
However, in most cases, four-wheel-drive vehicles
can be operated up to the legal speed limit on main
paved highways. Speed on unimproved roads should
never exceed the safe limits allowed by terrain and road conditions. Know
the limitations of the vehicle, especially on hard-packed snow and ice.
When
descending steep, unsurfaced mountain
roads with heavy loads, proceed with the four-wheel-drive
engaged. Place the hubs in the locked position. This
affords double safety in case one axle or drive shaft
should break. It is a good practice to descend a grade
using one gear lower than required to ascend the
same grade.
Do not allow the engine revolutions per minute to
exceed the manufacturer’s recommended limits,
particularly when the engine is under compression.
Use a constant steady application of the brakes to
maintain proper speed.
Be careful when driving on sidehills. Four-wheel-drive
vehicles have a high center of gravity and will
tip more easily than conventional vehicles.
Know the limitations of the vehicle and do not exceed
them. Most accidents and breakdowns occur within
that last one-quarter mile that should not have been
attempted.
When operating in rough or brushy terrain, do not
allow anyone to ride outside of the cab; in open jeeps,
drivers must be alert for limbs or brush.
Operating Procedures
Shifting Into and Out of Four-Wheel-Drive
For best results, do the following:
Review and follow the instructions in the operator’s
manual provided by the manufacturer.
A shifting device with position diagram will be
mounted in a conspicuous place in the cab of all four-wheel-drive
vehicles. Study the diagram carefully and practice shifting as directed before
driving the
vehicle.
If the vehicle is equipped with front hubs, lock them
into position before shifting the transfer case into
four-wheel-drive. Most four-wheel-drive vehicles of
current make employ a single-lever control for the
transfer case. The lever engages the front differential.
The lever normally allows the operator to select
four-wheel-drive high, four-wheel low, a two-wheel
high range, and a neutral position for power takeoff
equipment.
The operator can shift from two-wheel high to four-wheel
high, or vice versa, while the vehicle is stationary
or moving at moderate speeds. If the vehicle is
moving, let up on the accelerator before shifting.
To shift from two- or four-wheel high to four-wheel
low, bring the vehicle to a virtual standstill; four-wheel
low range should be used only in the most
severe conditions. When shifting out of four-wheel,
low range into two- or four-wheel, high range, the
vehicle should be stopped.
Analyze the terrain and select the proper gear before
attempting to travel over difficult terrain. Failure to
do so often results in a vehicle becoming stuck or
damage to the power train.
Front-Wheel Hub Locks
In addition to transfer case gear selections, the front
wheels of some four-wheel-drive vehicles are equipped
with locking hubs. These hubs are provided so that the
front axle can be disengaged when driving in two-wheel
drive. When locking hubs are used properly, the wear
on the front-end gear train is greatly reduced. Unlock
front hubs when appropriate.
Do not force hub locks in or out of the locking position
with makeshift tools; rock the vehicle slightly and the
splines will engage.
Some hubs are manually controlled. Other models
engage and disengage automatically. Be sure to check
the type on the vehicle.
Manually controlled hubs—Never shift into four-wheel-drive with
manual-control hubs in free position—drive train damage
could result.
Automatic hubs—Automatic hubs will engage when
the transfer case is shifted into four-wheel-drive.
Winches
When selecting a winch, choose one with a single line
rating at least 1½ times greater than the vehicle weight
rating. This allows the winch to pull the vehicle weight
and overcome the added resistance caused by whatever
the vehicle is stuck in. Never exceed the rated capacity.
Rigging a double line with a snatch block will reduce
the load on winch and cable by about half.
Avoid running a winch cable over rocks or wrapping it
around parts of the vehicle that could cause the cable
to fray or kink during winching. Never put the winch
cable around an object and hook back on the cable.
This will damage the cable.
Never pull at an angle to the load.
Always wear heavy leather gloves when handling
the winch cable.
If a tree is used as a solid anchor for winching, be sure
to use a tree truck protector.
Always drape a blanket or floormat over the middle
of a stretched winch cable to prevent the cable from
whipping back if it breaks or comes loose. A cable
that snaps under stress is extremely dangerous. Its
loose ends can sever a leg or kill a person. All persons
shall stand clear before the winch line is tightened.
When rewinding the cable after use, either drag a weight
until the cable is almost all rewound or use a helper to
hold the cable taut to ensure the cable is distributed
evenly and tightly on the drum. Never allow the cable
to slide through your hands. Do not allow the cable to
stack on the drum unevenly. Hook the cable to the
proper anchor on the truck, and draw it taut. Mashed,
pinched, or frayed areas on the cable severely reduce
its original tensile strength. For safety’s sake, replace
the cable when it is damaged.
Power Takeoff (PTO) Winches.
Check the PTO shift lever plate for the
correct operating positions. Always depress the clutch
pedal of the vehicle (disengaging the clutch) before
engaging the power takeoff.
When the winch is not being used, lock the shift
lever in neutral.
Never operate the winch above 1,500 engine
revolutions per minute.
Use the high-speed position of the winch when
pulling light loads and reeling in the cable.
Pay out cable by disengaging the sliding-jaw clutch
on the winch, then pull the cable out by hand.
Reverse gear may be used for lowering a load.
PTO winches are provided with shearpins as a
safety precaution to prevent overloading the cable
or winch. The shearpin is located in the yoke of the
universal joint that drives the winch worm-gear
shaft; it is designed to break before the cable or
winch. Never use makeshift pins to replace a
shearpin. Do not depend on the shearpin for
safety—a damaged cable may break before the
pin does.
Electric Winches.
Pull cable off the drum by hand, using the winch’s
clutch to free the spool, rather than using the
winch’s motor to unwind the cable. This saves time
and battery power.
On hard winch pulls, stop winching every 1 to 2
minutes to prevent the electric motor from overheating.
Do not operate the winch with the motor
lugged down to low revolutions per minute because
heat could build up rapidly, possibly damaging
the motor. Allowing the motor to cool with
intermittent operation will also allow time for the
battery to recharge while the vehicle engine is
running.
The electric remote control lead should only be
plugged into the winch during actual operation to
prevent accidental operation or injury. When
using the remote control lead from inside a vehicle,
always pass the lead through a window to
avoid pinching the lead in the door.
Parking on Hills
When parking a four-wheel-drive vehicle on steep, off-highway
grades, remember the following points:
Place the vehicle in four-wheel-drive low range, and
shift into the lowest gear.
Set the parking brake by first engaging the foot
brake and then applying the parking brake.
Park at a cross angle to the grade if the grade is not
too steep.
Tire Chains
When tire chains are required, they should be used as
recommended in the owner’s manual. Use tire chains on
all four wheels only under the most severe conditions.
When tire chains are used on all four wheels, excessive
maintenance costs can be expected. The user must be
prepared to justify such use.
Maintenance
Always keep the engine oil level at the full mark.
This may require carrying extra oil when operating
over rough, steep terrain. This is necessary to ensure
lubrication when the oil pan is tipped.
Check for water in the gearboxes and engine after
fording streams.
Because four-wheel-drive vehicles usually are used
under more severe conditions, they must be checked
and lubricated more often than conventional vehicles.
Check the logbook and reminder card or data plate
for lubrication, safety, and mechanical inspection
intervals. Under extreme use where mud, snow, water,
or heavy dust is excessive, it may be necessary to
service the vehicle daily.
Mismatched tires will cause early failure of the axle
assemblies and transfer cases and accelerate tire
wear. All tires should be matched to within 1/8-inch
circumference. Mismatched tires will result in a windup
of the gear train and can be detected by a locking-up
action when attempting to shift out of four-wheel-drive.
Rotating the tires, including the spare, when wear is
noted, will help keep the tire size as nearly equal as
possible. Never use snow tires, which are normally
larger than standard tires, on rear wheels only. If
snow tires are necessary, they should be used on
all four wheels.
USDA Forest Service, Technology and Development Last Modified: 10/15/2016 23:43:27
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