Section 309 (Automatic Transmission): Pistons: Operation: Notes
WARNING: This page is about a different car, the 2004 Dodge Sprinter. However, it is still accessible from the selected car via links, so may be relevant.
The principal which makes this operation possible is known as Pascal's Law. Pascal's Law can be stated as: "Pressure on a confined fluid is transmitted equally in all directions and acts with equal force on equal areas."