Transfer Case Noise When Accelerating – What's This?

Noise from the transfer case when accelerating indicates a serious mechanical problem that needs urgent attention. Vehicles with multiple powered axles are designed to have a transfer case. It is responsible for transferring mechanical power from the engine to the shaft so that the vehicle can be driven in two or four-wheel drive.

Numerous reasons may cause a transfer case noise when accelerating. These include mechanical issues like a loose chain, damaged gears and snap rings, and bad bearings. A low fluid level may also be responsible for the noise and jerking.

Possible symptoms to pay close attention to include the vehicle jumping in and out of the 4-wheel drive. If this continues for long, it may further damage the transfer case and the transmission system.

Here are some of the questions I will attempt to answer within this article: 

• What is a transfer case, and where is it found in your car?
• What are the symptoms of a bad transfer case?
• What are the causes of transfer case noise when accelerating?
• How do you fix transfer case noise when accelerating?

Let's get right into our discussion!

What is a transfer case, and where is it found?

Put simply, the transfer case is a component of the 4-wheel drive system. It consists of a set of gears used in 4-wheel drive for transferring the power from the engine to both the front and rear axles of the car.

In two-wheel drive, the engine's motion is transmitted by a single shaft to the axles of the vehicle. However, this isn't appropriate for 4-wheel drive. The 4-wheel drive needs two different shafts to transmit motion to both axles. To achieve this, we need a transfer case. A transfer case is also useful for attaining low and high torque transmission.

So, how does the transfer case work?

The output shaft of the transmission system will act as the input shaft for the transfer case. The input shaft consists of a helical gear that constantly meshes with the gear of the lay shaft. Similarly, a gear in the lay shaft meshes with the output shaft's gear (of the transfer case). The output shaft is connected directly to the rear differential and has a fixed gear that rotates with the shaft. The output shaft sleeve is connected to an Auxiliary output shaft via a belt or chain.

However, most modern transfer cases are designed to be driven by a chain rather than a belt. This is because the chains are much lighter and quieter than extra gears. Although gear-driven transfer cases also have their advantage. They can withstand torque and stretch without breaking, unlike the chain driven.

Where is it found?

The transfer case is found between the transmission and each axle of the car via a driveshaft.

What Are the Symptoms of a Bad Transfer Case?

If you hear noise from your transfer case, especially when accelerating, it is a clear sign that it is bad or has developed a fault. Here are some of the symptoms you may notice when your vehicle's transfer case is bad: 

1) Noise from Transfer case

A clear sign of a bad transfer case is a loud noise coming from the system. These noises could include grinding, whining, humming, or erratic sounds coming from underneath the car. You want to pay close attention to these sounds. The sound is most evident, especially when accelerating or decelerating your car.

2) Irregularly shift from 4-wheel dive

A bad transfer case will prevent the vehicle from properly engaging in the 4-wheel drive. You may notice your vehicle is frequently popping out of the 4-wheel drive. It is also possible for a bad shift mechanism to cause this issue. It may also cause the car not to engage or disengage from the 4-wheel drive. Have your transfer case inspected if you are experiencing this problem.

3) Fluid leaks

As mentioned earlier, some causes of noise from the transfer case when you accelerate could be low fluid levels. Automatic transmission fluids are responsible for lubricating the transfer case components. When there is a low fluid level, friction is increased, and there is more grinding, causing the noise you hear. It is possible that there is a fluid leak leading to low fluid levels and increased friction. 

4) Difficulty shifting the gear

If you experience difficulty in shifting the gear of your car, the cause may be a low fluid level caused by leakage from the transfer case. When the fluid level is low, there is increased friction as the gears and other components rub against each other. This causes difficulty for the gear to shift from high to low or vice versa. 

5) Warning light

The warning lights are clear signs that something is wrong with your vehicle. In most cases, the check engine light may appear on the cluster dashboard, or sometimes, a 4WD warning light may be triggered. When you see this light, you should immediately take your vehicle to a services center for inspection.

What are the causes of transfer case noise when accelerating?

There is no single cause of a faulty transfer case in your vehicle. Some of the most common causes will be identified and discussed in this article. Some of the identified causes will help you diagnose and fix a damaged or bad transfer case. They are as follows:

1) A broken snap ring

Between the end of the transfer case output shaft is a  snap ring that holds it in place. Often, the cause of the noise you hear when you accelerate is caused by a broken snap ring. The ring allows the output shaft to sit in place and prevents the tail from having a loose end. There is a misalignment causing the metals to run again themselves, and hence the noise you hear from your vehicle. To fix this problem, you will need to replace the broken snap ring.

2) Low fluid level

Another major cause of a faulty transfer case is low fluid level. Fluids play an important role in the functioning of the transfer case and transmission fluid. Low fluids could cause further damage to the transfer case, such as damaging the pump system or causing excessive friction within the components. Sometimes, it is possible that the low fluid is because the fluid hose is disconnected from the pump, starving the entire components of the transfer case.

3) Loose chain or bearing or gear

As I stated earlier, your transfer case may be chain or gear-powered. It is possible that your chain or gear has become loose due to wear and tear from consistent movement. This would result in serious grinding noise coming from the transfer case, especially during acceleration. This loose chain or worn-out bearing needs to be fixed as soon as possible to prevent further damage to the vehicle.

4) Worn-out transmission motor or mount

When you hear rattling or clicking sounds coming from under your car, especially close to the transfer case, the most likely cause is a worn-out or broken transmission mount. These are rubberlike or sometimes metallic components that support the transmission from displacing when moving. Some people may mistake this issue for problems with the transfer case, so consider it before replacing the transfer case. 

5) Damaged skid plate

The skid place is the body of the transfer case. It is possible that the skid plate is dented in such a way that it interferes with the proper functioning of the system. You would usually hear a rattling or clunking sound coming from the transfer case in such situations.

How do you fix transfer case noise when accelerating?

To fix the issue with the transfer case, you will need to identify the main cause of the noise and assess the exact damage to the transfer case. 

The first step is to dismantle the driveshaft and other components to create space to work. Here is how you do it.

Tools you should have:

• A wrench set
• Tape
• Drain pan
• Pry bar
• Gear oil
• Part cleaner

Step 1: Remove the driveshaft and tail end

For older cars, you may want to spray penetrating oil to ensure that the nuts and bolts come off easily. Proceed to remove the bolts surrounding the driveshaft close to the differentials. When losing the bolts, take safety precautions to prevent the driveshaft from falling on you.  Also, do the same for the tail end.

Step 2: Identify and replace the snap ring

We have identified one of the causes of the noise from your transfer case as possibly a broken snap ring. I recommend you inspect the snap ring for damages and replace it if you spot any damage.

Step 3: Drain and refill the transfer case with the right fluid 

Contaminated fluids or low fluids may be responsible for the noise you hear. Begin with draining contaminated fluids from the transfer case and only refill with manufacturer-recommended fluids.

Step 4: Re-install the driveshaft, transfer case, and other components

Finally, install all components that may have been loosed removed in this procedure to their rightful position. Ensure that all bolts are tightened properly.