Just like what motor oil is to the engine, transmission fluid plays a key role in maintaining your car's gearbox. Mainly, it provides lubrication between the many moving parts inside of a transmission, thus preventing them from grinding and wearing each other out. Plus, the transmission fluid also functions as a coolant, by both reducing the friction between the transmission's moving parts, as well as taking heat away from hot components. Therefore, driving without any transmission fluid is a terrible idea. Yet, it's still feasible to drive without it. Some say that you could still for up to 10 or 15 miles without any transmission fluid. However, that too isn't recommended, as you're only inviting serious and terminal damage to occur within the transmission.