The transmission filter (also known as the "strainer" or "hydraulic filter") for a gearbox is a filtration element provided in a car transmission system.Its role is to preserve the oil by retaining particles and impurities that may be circulating in the system.The transmission oil in the gearbox actually lubricates the gears and other components.It is therefore important to filter out impurities, metal fragments and particles that may be circulating in the oil and damage the system.