We've heard a lot about four wheel drive cars and trucks over the years. However, there are lots of different variants out there. That means that many people have questions about how their four wheel drive vehicles work. Let's take a look at some of the current systems on the market. That'll help you have an easier time selecting the right car parts for your vehicle and understand how your car handles.
We've seen four wheel drive systems, also labeled 4WD or 4x4 systems, on trucks for a long time. These are the simplest system available. These vehicles may use a lever to shift them between two and four wheel driver, or a switch to shift modes. In two wheel drive, only the rear wheels are operational. When 4x4 mode is engaged, all the wheels drive at once. Since the front and wheel axles are locked together, use this mode on surfaces where tires may slip.
Don't use this mode on pavement surfaces, hard packed areas or other places which are very hard and smooth, because minor differences in tire size may cause the axles to turn at separate speeds. This can cause what's called windup or binding in the transfer case. If you keep driving with this occurring the transfer case or axles may be ruined. 4x4 mode has a reputation for being good is slick or icy conditions, but this binding can actually make corning difficult, since the tires don't use the same paths during a turn. That can make your vehicle slide out of control all of a sudden.
The automatic transfer cases you'll find in many SUVs and trucks make braking and cornering much safer. These systems have an auto position on their shift controls, and offer rear wheel drive and 4x4 mode, too. Select auto mode when you're driving on surfaces where traction may be uneven. This will allow the vehicle to operate in two wheel drive until the tires start spinning then switch to 4x4 mode. As soon as slipping stops, you go back to two wheel drive again. This prevents driveline binding. An ABS system makes barking much safer, too. Always use two wheel drive mode on the highway if you have one of these vehicles, since some binding can occur due to differences in tire size.
All wheel drive is another type of four wheel drive system, seen on SUVs and trucks, and on many models of cars. If you have a Jeep, the system may be called full time, instead. These systems have a transfer case that allows the front and rear axles to work at the same time, without locking them. There are a number of different variations on all wheel drive. Some types split the torque between the front and rear wheels, putting most on the rear. These systems, offered by Volvo, Subaru, Jaguar, Porsche and similar companies, provide excellent handling and traction on any surface.
Other systems use a silicone filled clutch inside the transfer case itself. This allows a few differences in axle speeds, but tends to lock up when the differences between the two are too great. There are still other all wheel drive systems that are mostly front wheel drive, but have rear drive as a backup. Honda's CRV requires the front wheels to slip before the rear ones kick in, which might make a difference on slick surfaces. Nissan's Pathfinder couples the rear axle at start up, then put torque on the front when no tire slip happens. This is more reliable for a slippery start.
There are lots of different variants on four wheel drive systems. Some work well on hard surfaces, while others should never be run on these surfaces. Some systems use four wheel drive at all times, while others work mostly as front wheel drive with an auxiliary rear drive as needed. Unfortunately, even many auto salespeople don't know the difference. Try talking to the service department, instead, or take the time to learn all about the differences yourself. In the end, you'll be glad you had this information. You could save yourself some high repair bills and avoid buying unnecessary car parts. Learning about your particular vehicle's type of four wheel drive is just a smart idea.