The job of the car's transmission system is to transmit the power made in the engine to the wheels of the car. An automatic transmission uses both a mechanical and a hydraulic system to change the gears in the car automatically.
The automatic transmission gearbox is attached to a torque converter which fixes directly to the engine of the car.
The automatic transmission gearbox comes into play when the driver applies or releases pressure on the accelerator, by automatically selecting and changing the gears for the driver. The automatic transmission gearbox selects the right gear for the speed the car is travelling at, adjusting the speed of the car accordingly, while ensuring the engine can function as efficiently as possible. This all enables the driver to concentrate on driving without needing to manually change the gears. Generally automatic transmissions have 4 gears consisting of drive, first gear, second gear, park, reverse and neutral. The automatic transmission gearbox tends to be less fuel efficient than a manual transmission gearbox but offers the driver a smooth ride and the ease of not having to change gears manually.
The automatic gearbox transmission, although built to last will eventually wear down due to damage caused by heat and friction. If, when driving the automatic transmission gearbox is not changing gears smoothly; slow at changing gear or will not shift into gear; changes gears sporadically; judders; or produces unusual noises and vibrations, it will need looking at by a professional and you may need to replace the automatic gearbox transmission.