Having the flexibility to shift on the fly from two to four wheel drive without having to get out and lock the wheel hubs is a luxury that most of us take for granted, especially during a snowstorm. Many of today's vehicles are equipped with part time four wheel drive systems, which will engage either manually when the driver selects a switch or automatically when the on board computer senses that wheel traction is reduced by weather or road conditions. The physical part of the vehicle that activates this action is the transfer case, which has an output shaft that delivers power to the drive axle. From time to time, the seals that connect these components together can dry up, wear out, or break. If this occurs, they will have to be replaced by a certified mechanic sooner rather than later to avoid further damages to the vehicle's drive system.

What is the transfer case output shaft seal?

The transfer case output shaft seal is located on the transfer case of four-wheel drive cars, trucks, and SUVs. The transfer case completes the activation between two-wheel drive neutral, to low four-wheel, and then to drive four-wheel. Inside the case are a series of gear reductions and chain drives that work together to accomplish their task of supplying power to the drive axles, making the vehicle four wheel drive.

The transfer case output shaft is the part that connects the case to the axle. The purpose of the transfer case output seal is to prevent fluid from leaking out of transmission, where the transfer case is connected by way of the transmission's input shaft. The seal also helps to keep fluid from leaking out of the front and rear output shaft to the differentials, which keeps all metal components properly lubricated for extended use.

If the seals leak, fluid escapes and is no longer able to properly lubricate the interior components of the transfer case. Eventually the parts inside will wear out and overheat. If this happens, the transfer case will be rendered useless and the four-wheel drive operation will not work. Over time the transfer case output shaft seal can fail, and when it does, will display a few symptoms that will alert the driver that a problem with this system exists. Noted below are a few of the common side effects of a damaged transfer case output shaft seal that should be replaced.

1. Difficulty shifting gears

The seal that keeps fluid inside the transfer case and thus the transmission is vital for the smooth operation of the vehicle's transmission. When fluid is leaking from a broken seal, it reduces the volume of fluid that is currently working inside the transmission. A loss in fluid pressure also occurs, which will make shifting gears more difficult for an automatic or manually shifted transmission. If you notice that your transmission is having difficulty shifting to higher or lower gears, you should contact a certified mechanic as soon as possible to inspect this problem and offer a solution.

2. Grinding noises coming from underneath the vehicle

When the output shaft seal breaks or wears out, it also can cause noises to appear from under the vehicle. In many cases, these noises are caused by the reduction of lubricants inside the transfer case or metal-to-metal grinding. It's pretty obvious to most vehicle owners that metal grinding together is never a good thing, so if you hear noises coming from the area where your transmission is located, contact a mechanic as soon as possible.

3. Vehicle jumps in and out of four-wheel drive

In some cases the loss of fluid will cause the vehicle to jump in and out of four wheel drive, when it is supposed to stay in this operation. This is commonly caused by broken parts inside the transfer case that control this operation. The parts become worn out prematurely due to the leaking fluid caused in many cases by the output shaft seal. When the seal leaks, you will notice reddish looking fluid on the ground under your vehicle. This is transmission fluid and an instant sign that a seal or gasket on your transmission case is broken and needs to be fixed. Anytime you recognize these warning signs, it's important for you to contact a professional mechanic so they can replace the transfer case output shaft seal as soon as possible.

This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing Transfer Case Output Shaft Seal and was authored by Timothy Charlet.


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