More than a few World War II veterans will tell you that the Jeep helped win the war, and more than a few Chicagoans wished they’d had a Jeep or other four-wheel-drive vehicle to do battle with this winter’s record snow storm.
Jeeps and other sport-utilities are among today’s hottest-selling vehicles, along with pickup trucks. Many have four-wheel-drive. Some mini-vans and cars also offer the technology.
Though there are two basic types of four-wheel-drive (often referred to as 4WD or 4X4)–part time and full time–there are many variations of both.
“Part-time four-wheel-drive is usually–and I emphasize, usually–on vehicles designed to go off-road,” says Greg Goodus, president of the Northern Illinois Jeep Alliance.
Part-time four-wheel-drive usually has a lever on the floor or in the dash to select two-wheel-drive, four-wheel high, neutral and four-wheel low. It’s usually found in sport-utes and pickups. Using a transfer case that splits the engine’s torque between the front and rear axles, the driver can switch the vehicle from 2WD to the 4WD ranges. Two-wheel-drive, it should be noted, offers better fuel economy and less tire wear.
Four-wheel high helps when traction is poor, such as in loose gravel, mud, snow or sand. Most modern vehicles can be driven on dry pavement in this mode though it wastes fuel and causes “crow hopping”–driveline windup that makes the wheels skip and the vehicle feel like it’s moving sideways when making a tight turn as in a parking lot.
“I would avoid using it on dry pavement,” says Bob Bubala, president of Iron Horse 4X4s, a club in Schererville. “It causes a lot of wear and tear on the CV (constant velocity) joints and universal joints on the driveshaft. Nobody wants a premature repair bill.”
To engage four-wheel-drive, the front wheel hubs must be locked to the axles.
On earlier part-time four-wheelers, the driver manually turned the hubs at each of the front wheels before shifting the transfer case into four-wheel high or low. This could be a bit inconvenient, especially if the vehicle was stuck in mud or in a stream.
Today, the hubs usually lock automatically when the vehicle is shifted into four-wheel-drive using a switch on the dash or a lever on the floor. And, it can usually be done “on the fly” without stopping.
Four-wheel low is strictly for off-road use, when torque is more important than speed. With the transmission in first gear and the transfer case in four-wheel-low, you can almost climb the side of the John Hancock Center.
It’s great for desert rock-climbing and jungle safaris, but the low range should never be used on dry pavement or above certain speeds, as indicated in the owner’s manual, because that can damage the system.
Vehicles with this system include full-size pickups such as the Ford F-Series; Chevrolet C/K (also the full-size Blazer sport-ute); and Dodge Ram, Dakota and Durango.
Full-time 4WD, on the other hand, is always active. The driver cannot disengage it.
But here is where the terms get a little slippery. There is one system known as full-time 4WD and another generally known as all-wheel-drive.
The full-time, or permanent, four-wheel-drive systems can offer high and low range, but not two-wheel-drive.
Though this system works well in snow and mud, it is not intended for off-road. It is often found in upscale 4X4s such as the Lexus LX470 and Mercedes-Benz ML320.
Unless the vehicle also has limited-slip differentials, all the power may be transferred without benefit to the wheel with the least traction. .
Some carmakers overcome this by including traction control, an offshoot of anti-lock brakes, that applies the brakes to the wheel that is spinning.
All-wheel-drive is commonly found on mini-vans and cars. These systems have a center differential in addition to the differentials at the front and rear axles. This system is the easiest for the motorist to use since it works without having to push a button or pull a lever.
The center differential usually splits the torque to the pair of wheels with the best traction. In other words, it can send more torque to the front or rear wheels depending on which are slipping the least. It is commonly found on mini-vans such as the Chrysler Town & Country, and cars such as Saburus and the Mitsubishi Eclipse.
Often these systems deliver the torque to the wheels with a viscous coupling between the front and rear driveshafts.
Normally, both shafts turn about the same speed, but when one turns faster than the other, a silicone fluid in the center differential heats up and thickens enough to bring the shafts to the same speed once more. (Some systems electronically or mechanically couple the center differential.)
AWD routes the torque to the axle that has the most traction. For example, if the rear wheels begin spinning, the power goes to the front axle, which has more traction.
Examples include the 1999 Jeep Grand Cherokee (when it is in the four-wheel high), which can also direct the traction to a single wheel with the most traction. Other examples include the Isuzu Trooper and Honda CR-V.
Though 4X4s can go places and do things no two-wheel-drive vehicle should attempt, they are not invincible and drivers can, and do, get in over their heads.
For instance, a 4X4 will not stop any quicker than its two-wheel counterpart. Since most vehicles with the system are trucks or SUVs, they have greater mass than many cars and may take longer to stop on slippery roads.
Ice is a great equalizer. Though the 4X4 may be able to get going on ice, it will still slide sideways, given the opportunity.
Just as driving into deep snow can cause a car’s wheels to lose contact with the pavement, this can happen to any vehicle.
Ground clearance may be a little better in a truck or SUV, but once the vehicle is suspended in deep snow it becomes no-wheel-drive.
And driving through a stream is a visual cliche in 4X4 TV commercials, but if the engine gulps a slug of water, it will stop running. And the vehicles don’t float.
For the motorist who wants the security of 4WD, almost any system will do. But for serious off-road use, the robust part-time four-wheel-drive system can’t be beat.
CLUBS CAN TAKE YOU OFF BEATEN PATH
If you want to have some fun with your 4X4 and socialize with others of like mind, you can join the club. Two in the Chicago area you may want to check out are Iron Horse 4X4s and the Northern Illinois Jeep Alliance.
Iron Horse 4X4s is open to everyone owning, or planning to buy, any 4X4–car, truck, sport-utility or van. Along with other events, they meet at 7:30 p.m. the last Wednesday of each month at Amarillo’s Road House on U.S. Highway 41 just south of U.S. Highway 30 in Schererville. Call Bob Bubala at 219-473-9102.
The Northern Illinois Jeep Alliance is open to Jeep owners only. However, new or prospective members are welcome. They meet at 1 p.m. on the second Sunday of the month at the Verdi Club, 782 N. Madison in Rockford. Call Greg Goodus at 815-332-3186.
