Automatic Transmissions are a very complex piece of equipment. Modern transmissions today generally have between four and eight gear ratios and are controlled by a computer to perform all functions required for the most optimal performance of a vehicle under all driving conditions.
There are numerous sensors and systems over the vehicle feeding information to the computer, including engine rpm, throttle opening, air and water temperature, road speed, cruise control, braking and stability control, air conditioning, GPS signals, power, winter / economy modes and gear selector. All of these systems use two way interaction where each changes condition dependant on input from the other. This can make fault diagnosis difficult as the cause of a problem can often be coming from another vehicle system. The transmission unit itself consists of approximately 1,000 components, and the operation of these is controlled by the computer through an average of three kilometers of wiring.
For efficiency and lower cost modern automatic transmissions operate with higher oil pressures and lower oil volumes, through operating temperatures which can vary from minus 20C to 140C. This places great strain on the oil and under some conditions its performance can degrade quite quickly leading to accelerated wear and transmission performance problems. Towing heavy trailers or caravans over long distances, particularly in hilly areas and / or in hot weather places an even greater strain on the transmission and its cooling system.
Recently manufacturers have introduced CVT or Constantly Variable Transmissions to the market. These units are completely different to a normal automatic transmission in the way they operate, using a belt and infinitely variable ratio pulleys, and are highly dependant on the qualities of the special oil used for correct performance and durability.
Regular servicing of modern automatic transmissions is recommended to ensure maximum performance and service life is achieved, and it is essential that you have highly trained personnel and the right equipment to meet the quality standards required.