Transfer Case: Structure, Common Faults and How to Fix

The transfer case is an important part on vehicles using four-wheel drive (4WD or AWD).

This part not only helps the vehicle distribute torque to both the front and rear axles, but also enables the vehicle to overcome difficult terrain such as steep slopes, mud, or when wading. If the transfer case has a problem, the vehicle's performance will be seriously affected, causing difficulty in moving and potentially causing damage to the entire drive system.

What is a Sub Gearbox?

The transfer case is a transmission unit located behind the main transmission and connected to the drive shaft of the axles. Depending on the design of each vehicle, this part can be manufactured separately or integrated with the main transmission.

The transfer case helps transmit torque from the main transmission to both drive axles, allowing the driver to choose different drive modes depending on road conditions such as 2H, 4H, and 4L.

2H (2 High): Rear wheel drive, for dry street conditions.
4H (4 High): High-speed all-wheel drive, suitable for slippery terrain such as sand, gravel, or wet roads.
4L (4 Low): Low-speed four-wheel drive with high torque, ideal for climbing, rough terrain or wading situations.

Common Mistakes With Sub-Transmissions

Below are some common errors that four-wheel drive vehicle users may encounter when the transfer case fails:

1. Howling, Squeaking or Scratching Noises During Operation

When operating the vehicle in 4H or 4L mode, if you hear a howling, screeching or scraping noise from under the vehicle, it may be a sign of a problem in the transfer case. The cause is usually a deterioration or lack of transfer case fluid, or worn parts such as bushings and internal bearings.

2. The Vehicle Cannot Enter 4H Or 4L Mode

When the mode selector or knob is unresponsive, or the vehicle is stuck in one drive mode and cannot be switched, this is a clear sign that there is a problem with the transfer case. This could be due to a faulty electric motor controlling the mode, or a mechanical system that is stuck.

3. Vehicle Vibrates and Jerks When Changing Modes

When shifting between drive modes (from 2H to 4H or 4L), if you feel the vehicle shaking or jerking, there may be a problem with the sensor or control circuit of the transfer case. These faults may be related to incorrect signals from the sensor or drivetrain control module.

4. 4WD/AWD Error Indicator Light Is On

A clear sign that there is a problem with your drivetrain is the 4WD/AWD fault light on your dashboard. This could be due to things like a faulty sensor, an oil leak, or a problem in the control circuit.

5. Oil Leak From Sub Gearbox

If you see signs of oil leaking under the vehicle, especially near the driveshaft or seals, it could be due to worn gaskets, seals, or damaged internal components of the transfer case.

Solutions and Fixes

To fix problems with your transfer case, you first need to pinpoint the cause. Here are the basic checks:

Check Sub Gear Oil: The transfer case oil needs to be changed periodically to maintain effective lubrication. Old or insufficient oil can cause serious problems. Check the color and consistency of the oil for abnormalities.
Check Motor Control: If the vehicle does not enter drive mode or has problems shifting, the control motor may be damaged and needs to be replaced.
Sensor and Control Circuit Testing: A fault in the sensor or control circuit can cause shaking or jerking when switching bridge modes. Replacing the sensor or control module may help resolve the problem.
Mechanical Parts Replacement: In case parts such as gears, bearings, or bushings are worn, their repair or replacement is necessary to ensure stable operation of the auxiliary transmission.

When Should You Take Your Car to a Professional Garage?

If you experience any signs such as howling, shaking when switching between drive modes, the 4WD error light is constantly on, or the vehicle cannot switch between drive modes, you should take the vehicle to a specialized garage for inspection and repair. Regular maintenance of the transfer case and timely handling of problems will help the vehicle operate more stably and prolong the life of the drive system.

Summary

The transfer case plays an important role in the four-wheel drive system, helping the vehicle operate well in many different terrain conditions. When there are signs of abnormality, determining the cause and repairing it promptly will help protect the vehicle from serious damage and ensure optimal operating performance.

Always choose professional garages to check and maintain the transfer case, ensuring your car always performs at its best on every journey.

Why Choose Gartz For Gear Oil?

Although Gartz does not supply transfer case fluids, for vehicles using automatic transmission fluids, Gartz is a great choice. Gartz transmission fluids, manufactured with German technology, help protect transmission system components, reduce wear and improve performance.

Choosing a high quality gear oil like Gartz will help maintain the life of the main gearbox and related components, while protecting the engine from unwanted breakdowns.

To learn more about Gartz's premium gear oil products, contact us for more specific advice!