Just like motor oil, brake and clutch fluid, the oils in your transfer case and differential also degrade over time. And, like the other fluids, these oils also need to be replaced on a regular maintenance schedule
How often should I have my transfer case serviced?
It is recommended to have the transfer case on your 4WD vehicle performed every 2 years or 30,000 miles.
How often should I have my differential serviced?
Although this can vary from vehicle to vehicle, every 2 years or 30,000 miles is ideal for most vehicles.