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Driver-Operator Guide

Chapter 2—Four-Wheel-Drive Vehicles



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

  1. 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.

  2. 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.

  3. 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.

  4. Be careful when driving on sidehills. Four-wheel-drive vehicles have a high center of gravity and will tip more easily than conventional vehicles.

  5. 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.

  6. 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:

  1. Review and follow the instructions in the operator’s manual provided by the manufacturer.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  1. Manually controlled hubs—Never shift into four-wheel-drive with manual-control hubs in free position—drive train damage could result.

  2. 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.

  1. Power Takeoff (PTO) Winches.
  1. Electric Winches.
Parking on Hills

When parking a four-wheel-drive vehicle on steep, off-highway grades, remember the following points:

  1. Place the vehicle in four-wheel-drive low range, and shift into the lowest gear.

  2. Set the parking brake by first engaging the foot brake and then applying the parking brake.

  3. 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

  1. 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.

  2. Check for water in the gearboxes and engine after fording streams.

  3. 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.

  4. 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.

  5. 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.
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