What Is A Transfer Case And Why Is It Important?

Every four-wheel-drive or AWD vehicle has a transfer case. What are transfer cases? Why do transfer cases exist? Why do 4WD and AWD vehicles need them? If you're asking any of these questions, you came to the right place. We'll talk about what transfer cases are and why they're important.

What Is A Transfer Case?

If you look behind the transmission, you'll find a large oval-shaped part. That's the transfer case. It's supported by a frame cross member, and connected to both the transmission and the driveshafts.

A transfer case has several external components:

  • An input shaft
  • Two output shafts:
    • One output shaft spins the front driveshaft
    • The other output shaft spins the rear driveshaft
  • A cast iron, magnesium, or aluminum housing

Some transfer cases have a differential built in. The differential allows the outputs to spin at different rates. This prevents driveline bind on hard surfaces.

Different Kinds Of Transfer Cases

If a transfer case comes with a differential, the type of differential matters a lot. The transfer case's differential determines the type of 4WD your vehicle has.

  1. Part time four-wheel-drive: Many transfer cases are part time 4WD. That means you can operate your vehicle in 2-wheel-drive or four-wheel-drive. These transfer cases usually don't have an internal differential, but they offer both a high-range and low range output. These are typically found in trucks and SUV's. Because there is no internal differential, 4WD should only be used on slippery surfaces.
  2. All wheel drive: Transfer cases that are designed for AWD have an internal differential. An AWD transfer case sends power to the front and rear axles at all times. Because there is a differential inside the transfer case, AWD can be used on dry pavement. AWD is usually found in crossover SUV's and sedans.
  3. Active four-wheel-drive: A transfer case with an active 4WD has the most complicated design. Active 4WD is basically automatic 4WD. In other words, the driver doesn't have to switch to 4WD. The car will do it for them. The amount of wheel slip determines whether 4WD should be activated. When there's too much wheel slip, electronic or mechanical means are used to adjust the amount of power the front axle gets.

What Does A Transfer Case Do?

The transfer case serves as a link in the drivetrain system. Its job is to transfer power from the engine to all 4 wheels at the same time. Powering all 4 wheels is beneficial in a few ways:

  • Better traction
  • Better control in snow, mud, and water

How does a transfer case work, though? The process is quite straightforward:

  1. The transmission spins the input shaft.
  2. The input shaft splits the engine torque (from the transmission) between both output shafts.
  3. One output shaft delivers power to the front driveshaft and axle.
  4. The other output shaft delivers power to the rear driveshaft and axle.

What Happens When A Transfer Case Fails

Transfer cases are generally pretty reliable, but they do fail occasionally. The risks to your vehicle and the difficulty of repair vary depending on the type of transfer case:

Part Time 4WD - These transfer cases can fail completely, or they can fail to work properly. For instance, the unit may not want to shift into 4WD. In many cases, it is more cost effective to swap in a good transfer case rather than try to repair the old one. It's a pretty easy job, and you can replace it yourself with this tutorial. As authorized sellers of genuine OEM GMC parts, we offer transfer cases at wholesale pricing. That means you'll save quite a bit of money on an OEM transfer case. Win win.

AWD - If an AWD transfer case stops working properly, it can damage other parts of the driveline. For example, if the internal differential doesn't do it's job, u-joints and CV axles could be damaged. If you think something is wrong with an AWD transfer case, you should stop driving the vehicle until you can diagnose the problem. Transfer cases in AWD vehicles can be hard to access and swap.

The Importance Of Maintaining Your Transfer Case

If you have a GM vehicle with four-wheel or an all-wheel drive, it has a transfer case. It's important to maintain it. That means:

  • Replacing the transfer case fluid every 30,000 miles
  • Checking the seals and oil levels in regular intervals

It's important to make sure that the transfer case is properly lubricated at all times. If there's no lubrication, the gears within the transfer case will get hot and wear quickly.

Do you have any questions about transfer cases? We'll be happy to answer them for you! Just contact us here.