DRIVETRAIN CONFIGURATIONS
Now that the basics of manual, automatic, and CVT transmissions are behind us,
let’s take a look at the different drivetrain configurations. It can be confusing
when you consider all the offerings, which include four-wheel drive (part-time,
full-time, and permanent), all-wheel drive, front-wheel drive, and rear-wheel
drive. What does all this mean?
Four-Wheel Drive
There are three different configurations to four-wheel drive (4WD): part-time,
full-time, and permanent.
Part-time 4WD is the most basic of all 4WD systems. With this setup, the
driver can choose when to drive in two-wheel drive or 4WD. In addition, it
offers the choice of either a high or a low range in which to operate the system.
At first this sounds pretty good—look at all the choices we have!—until you
realize that you can’t engage the 4WD on pavement unless it’s very, very
slippery. Why? Because when you engage 4WD with this system you lock the
front and rear wheels together through the transmission and transfer gearbox.
This is great for straight-ahead traction on slippery surfaces. However, on dry
pavement it makes for odd driving, cornering, and handling characteristics. Also,
you can harm the drivetrain components by driving in 4WD for extended periods
of time on dry pavement because there’s insufficient slippery surface to let the
wheels slip against each other. This causes the driveshafts to twist up and
exposes the transfer case to extreme mechanical stress.
So why would anyone want to choose part-time 4WD? Three reasons:
- It’s less costly to build and therefore to buy.
- It’s durable under the heavy stress of driving off-road or in snow, ice, mud, or
under other slippery road conditions. - When you don’t need 4WD you can disengage it.
Full-time 4WD is the most commonly used system on the market. Full-time
4WD offers a two-wheel-drive mode for summertime driving or dry-road
conditions and an automatic 4WD mode for changing road conditions. It also
offers 4WD high and 4WD low modes for when the going really gets tough. The
automatic 4WD mode is a convenience for many drivers. In addition to the
transmission and transfer gearbox, a center differential is used to couple the front