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As most auto shops are aware, 4-wheel drive vehicles require additional fluids to make them run properly. These fluids are known as "bottom fluids", and can be accessed from the under side of a vehicle. These fluids, just like those found in the standard Fluid Lock, are essential to a vehicle's health. Because of the severe duty 4-wheel drive vehicles typically endure, these fluids require faithful checking to improve health, and overall vehicle performance. 

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The typical sample tray will include a spot for Motor Oil, Transmission Fluid, Antifreeze, Power Steering Fluid, and Brake Fluid. Four wheel drive vehicles will require additional samples including: Front Differential Gear Oil, Transfer Case Fluid, GM Trak II, Rear Differential Gear Oil, and Clutch Fluid.