A transfer case is part of the drivetrain of a four-wheel or all-wheel drive vehicle. The transfer case allows rotational power to be transmitted from the transmission to both the front and rear axles simultaneously. It also allows the front axle to be engaged and disengaged for application in specific conditions. The transfer case can be gear driven or chain driven. Moving parts inside the transfer case are lubricated and cooled by a type of oil, often gear oil or transmission fluid.
Transfer case service can range from a simple drain and fill of the fluid inside to a more extensive inspection or repair.
Most (but not all) vehicles that feature four-wheel or all-wheel drive come equipped with a transfer case. If your vehicle has a transfer case, it will be located next to the transmission and have two drive shafts extending toward the front and rear axles. The oil inside the transfer case needs to be serviced regularly as part of routine vehicle maintenance. But it might need more attention if you notice any of the following signs of a bad transfer case:
Repairs to a transfer case depend a good deal on the specific vehicle and problem. These repairs are far more involved than a simple transfer case service that includes merely replacing the fluid.
For that procedure, a technician will drain the old fluid in a similar way to draining old engine oil. A drain plug is unscrewed from the bottom of the transfer case and the fluid is collected for disposal. After the plug has been reinstalled, the technician will add fluid, usually with a pump, into a hole nearer the top of the transfer case. Once the fluid has reached its maximum level, when it begins to seep out of the upper hole, the technician plugs the hole and the service is complete.