In short, a transfer case is a part of a 4-wheel drive system that transmits the power from the engine to the front and rear axles of your vehicle. 

Transfer cases are also known as T-cases or Transfer boxes. 

What Is A Transfer Case And What Does It Do?

Generally, the transfer case can shift your 4WD vehicle from a 2-wheel drive system to a four-wheel drive system. It is a very critical part of the 4WD system.

In the case of 2-wheel drive vehicles, the engine power is distributed to the axles of the vehicle using a single prop shaft. However, for a four-wheel-drive vehicle, two different driveshafts are needed to transmit the power from the engine to all four wheels.

That’s when the transfer case comes to the scene because the transfer case is the spot where the connection between the rear and front axles, the driveshafts, and the engine takes place.

Simply put, the transfer case will accept the main drive shaft and then the driveshaft will be delivering the power from the engine to both the front and rear axles. Along with that, a transfer case is also necessary for attaining high and low torque transmission and aggressive traction off-road.

what is a transfer case

What Is The Function Of A Transfer Case?

In 4WD or AWD vehicles, the main function of the transfer case is to transmit the power from the engine to the front and rear axles. 

Normally, within a transfer case, there are 2 gear settings (high and low). The high gear setting is suitable for basic off-road driving conditions. For example, if you are driving in snowy, rainy, muddy, or dirt road conditions, then the high gear settings will come in handy because the high gear will offer aggressive traction.

On the flip side, low gears offer additional torque at a slower speed. This setting will come in handy in extreme off-road conditions. For example, if you are rock crawling or climbing a steep slope or hill, the low gear settings will be perfect for obtaining extra torque.

To be noted, the transfer case depends on many other parts of the vehicle for distributing the engine power to all the front and rear wheels at the same time. For example, it works in collaboration with the differentials, drive axles, wheels, transmission, driveshafts, and more. 

Also, the transfer case is impacted by any obstacles on the road, or how fast/slow you are driving, or any misalignment by the drive shaft, and so on.

Overall, you can say that the transfer case is assisting your 4WD vehicle move and stay aligned. It also helps in transmitting an equal amount of torque power to all four wheels of the vehicle. So without a transfer case, your 4×4 vehicle would not have its four-wheel-drive system.

what is a transfer case

How Transfer Cases Work

Part-time or Full-time/Different Modes

When it comes to a 4-wheel drive system, there are primarily 2 types of drive systems (part-time and full time). As the name suggests, a part-time drive system means that your vehicle remains in a 2-wheel-drive system most of the time. 

However, when you need the four-wheel-drive settings, you can turn the drive system from a two-wheel to a four-wheel-drive system with a push of a button or lever (depends on the particular vehicle). 

Some part-time 4WD drive systems can also switch from 2-wheel drive to a four-wheel-drive automatically, depending on the terrain condition. 

Generally speaking, most 4WD drive systems feature various modes like auto, terrain, 4-Hi, 4-Lo, etc. You can change the modes based on the driving conditions. 

On the other hand, a full-time 4WD system operates differently as you cannot usually switch between two-wheel and four-wheel-drive systems. However, you can change the gear and mode settings in the case of both part-time and full-time 4WD drive systems.

toyota troopy 4x4

What Are the Symptoms of a Bad Transfer Case

Trouble Shifting Gears

From the discussion above, you might have already guessed that the transfer case is very vital in shifting the gears of your vehicle. Shifting gears will not be a problem with a good transfer case. 

In contrast, if you have a bad transfer case, you will notice either grinding or whirring on the gears. You may also hear weird sounds coming from the vehicle while you are changing gears. In that case, the transfer case may be the culprit.

Unusual Grinding Sound

Another symptom of a faulty transfer box would be an unusual grinding sound. If you notice whirring noise coming out of the transfer case constantly, then there must be a problem with the transfer case. 

It could be that there is a lack of alignment inside the box. If you hear the unusual grinding sound occasionally, you should still consider checking the condition of the transfer box on your rig.

Erratic Four-Wheel Drive Driving

It is inevitable that if the transfer case is defective, your vehicle’s performance will worsen as well. The back wheels could fall out of alignment with time. This would put a lot of stress on the transfer case. 

As a result, the wheels could be damaged and the performance from the rear wheels will not be great. In general, you will start to notice inconsistent driving performance from your 4×4 rig. There will be problems with the transmission, gear shift, traction, and handling if the transfer case is faulty.

Smoke, Crack, and Fluid

If things go really bad, then you might even notice smoke coming from the back of your rig. If the smoke is from the transfer case, you must take care of the situation as fast as you can. 

The casing of the transfer box is made of strong metal. Still, it could get damaged if you run over a huge obstacle while overlanding. Debris could then get inside the device and damage the internal equipment, so look for cracks or crevices in the transfer case.

Remember, you need to oil the transfer case more often. There is also fluid inside the transfer case for running the gear setup smoothly. Unfortunately, if there is a crack in the T-case, the fluids could leak out. So, if you notice fluid is leaking out of the box, the transfer case could be damaged.

What Happens When A Transfer Case Goes Bad?

As we have explained above, a faulty transfer shows a few symptoms. For instance, the car will not perform the best, there will be problems with shifting gears, and you will hear unusual whirring or grinding noise from the transfer case. 

There could be smoke or fluids coming out of the transfer case as well. If any of these things happen on any of your cars, you should talk to a mechanic for repairing or replacing the transfer box as soon as you can.

Can You Drive With A Broken Transfer Case?

Yes. Technically, you can drive with a broken transfer case. However, we don’t recommend it, so make sure you have fixed the issue as quickly as possible.

How Can You Prevent Damage To Your Transfer Case?

Here are a few tips that will come in handy if you want to take care of the transfer box in your vehicle.

  • You should shift gears as gently as possible
  • Use the 2-wheel drive system whenever possible. If the terrain condition is perfect, the 2-wheel-drive system is enough
  • Follow the owner’s manual
  • You must check and maintain the transfer box more often if you are an off-roader
  • If possible, try to minimize off-roading with the 4WD drive system engaged
  • Do not put more stress on the transfer box by overusing it
  • If possible contact an expert mechanic in the field to check the transfer case now and then
Ferenc Elekes overlandsite

Ferenc Elekes has been a devout Overlanding enthusiast for many years. During that time, Ferenc has explored 75 countries on six continents, with overland travel involved in 40 countries on three continents. From his trusty 2006 Toyota Land Cruiser Prado with a roof-top tent, he’s blogged about experiences that can only be found in the remotest regions on Earth. Along the way, he's gained in-depth knowledge of the novel challenges overlanders encounter and practical ways to meet them. On his website, he shares informed opinions about everything from the best overland gear to how to get a vehicle unstuck. Ferenc has also written for Ih8mud, the Expedition Portal, the Overland Journal, and he is often invited as a guest to outdoors-related podcasts.