Have you ever wondered how vehicles are able to change from two-wheel drive to four-wheel drive? Well it happens because of the transfer case. The transfer case is designed to receive power from the transmission and then redirect that power to either the rear-axle, the front-axle, or both at the same time.
Transfer cases for passenger vehicles, the ones that most of us buy for daily use, use a chain to connect the two drive shafts internally. A chain-driven transfer case is lighter than, but not as strong as, a gear-driven transfer case that is used for large trucks.
Transfer cases are engaged by the use of a shifter in the passenger compartment of the vehicle. This allows the driver to shift from two-wheel to four-wheel drive whenever they wish to do so. Most transfer cases require that the vehicle is in neutral to make this shift. Some newer vehicles make this shift with the use of an electronic solenoid and it is activated with a switch on the dashboard.
There are also different types of transfer cases. Some only have two-wheel and four-wheel options, while some have different gear ratios that can be selected, like slow, which is a powerful, slow crawl, or regular speed driving. Usually these gears are called “high” and “low.” Using “four low” gives the driver a much slower speed but also gives much more control in slow situations and gives more torque. Four-high gives the driver the same driving gears as in two-wheel drive, but you get the control of four-wheel at normal speeds. This gear is usually used for snow and mud driving.
There are also some transfer cases that are in full-time, meaning they are always in four-wheel drive. There is a new process called “New Process 203” which switches out of four-wheel drive at 30 mph; otherwise it remains in four-wheel drive under 30 mph.
Deciding which type of vehicle and which type of transfer case is an individual choice that greatly depends on what type of driving you plan on doing. Someone who does a great deal of off-road driving will want a stronger transfer case as opposed to a driver who only plans on city driving in the occasional snow, ice and mud. Whatever the case may be, there is a transfer case for practically every situation.
Today’s lesson is brought to you by PDQ transmission parts, the experts in transmissions.
