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. Moving parts inside the transfer case are lubricated and cooled by a type of oil, often gear oil or transmission fluid.
A transfer case drain and fill is the process of removing the old fluid from the transfer case and replacing it with fresh fluid.
A transfer case drain and fill service is performed in a similar fashion to that of an oil change, or changing the fluid in a manual transmission or axle differential. The process is fairly straightforward; a technician removes a drain plug at the bottom of the transfer case, collects the old lubricant for proper disposal or recycling, and adds fresh fluid with a pump.
While the service might be simple, it is worth mentioning that your vehicle needs to be safely lifted and supported in the air for access. The correct type and amount of lubricant is essential. And some transfer cases require a special pressure pump to install the fresh fluid.