Transfer cases are found on 4 x 4 vehicles. Without a transfer case your car is a 2 x 4. So if you have four-wheel drive, you have a transfer case. We provide complete service for your transfer case.
How Transfer Cases Work
The purpose of the transfer case is to split the engine power and send it to all four tires via the front and rear axles. Without a transfer case, the engine power goes to either the front or rear axles depending on the vehicle.
If you look inside a transfer case, you'll find a few common components. There's an input shaft which is spun by the transmission. That input shaft is connected to two output shafts: One that spins the front driveshaft and one that spins the rear. Many transfer cases also have a differential. Just like the differential in the axles, this allows one output to spin at a different rate than the other to avoid driveline bind on hard surfaces.
The transfer case is the center of the drivetrain in a 4x4. Mounted to the back of the transmission, it splits engine power and sends it to the front and rear axles.
Types of Transfer Cases
There are many types of transfer cases. Most common have a second set of gears or a planetary gear set that produces low-range gearing when engaged. This essentially gives you the opposite effect of the gearing in your transmission, slowing the speed of the driveshafts relative to the speed of the transfer case input shaft. This is an important aspect of 4x4s, as the gear reduction multiplies the power delivered to the tires. It also slows the wheel speed. The result is more power delivered to the ground at a slower wheel speed, giving you more control.
Two common types of 4 WD that you might hear about are full time and active.
Full-Time 4WD: This is the simplest type of transfer case. It sends power to the front and rear axles all the time. To eliminate, or at least diminish, driveline bind on hard surfaces, these use an open T-case differential in high range. Some offer a 4Hi Lock position which locks the differential.
Active 4WD: Over the last decade or so, a variety of full-time and part-time systems have been developed that use electronic or mechanical means to adjust the amount of power delivered to the front axle according to wheel slip. They have a variety of names and levels of performance, but they provide some of the benefits of a part-time system without the owner every having to switch anything.
Because active 4WD was designed for smooth operation without any input from the driver, they can be found on everything from BMWs to Dodge 3500s.
Gear Reduction in Transfer cases
There are two different methods of gear reduction used in a transfer case. The older method uses traditional gears mounted on shafts, very similar to the way a manual transmission works. The gears may be either straight-cut or helically-cut gears. Both are extremely strong, with helically-cut gears generally being quieter.
The other way to produce gear reduction, and the method that nearly every 4x4 made today employs, is with a planetary gear set. Planetary gear sets are used in automatic transmissions, and they include a ring gear, planet carrier and sun gears. Securing the sun gear or the planet carrier produces different ratios. They key advantage of a planetary gear set is that they can be engaged at nearly any speed.