I picked up a front wheel drive GM automatic transmission at the dump, and stripped it totally so I could melt the aluminum casing down, for casting.
The transmission is a "Hydra-matic", circa 1986. It takes power off the engine right after the flywheel, moves it over with a *fat* chain drive, then runs it through the usual planetary gear system to drive both front wheels. It was in the dump because of two fatal problems: first a lot of water in the transmission fluid causing rust, and second (probably caused by the first) a broken mounting flange on the main hydraulic pump.
An automatic transmission is a hydraulic computer, with little diodes (one way valves, a ball bearing on a spring), transistors (pistons), and all manner of cool 3D cast-in routing.
The transmission computer's outputs are to pump fluid into pistons, which press down on two drum-brake-style immobilizers on each end of the planetary gear system. Probably the four gears are the binary combinations of the immobilizers.
Cool things are the little ring magnet, used to pick up metal shavings. It's got some awesome magnetic goo attached.
I had a really hard time cracking the star-headed mounting bolts loose. I actually had a well-fitting tool, but it was a 1/4" hex bit. Mounting a 3/8" to 1/4" socket reducer just detached the 1/4" socket head. Mounting a craftsman box-end wrench on just bent the wrench. I finally grabbed the bit between the jaws of my 14" crescent, which worked for all but two of the bolts, which I ended up just drilling off (it'll all be melted down anyway!).
Tons of high-quality metric bolts, in 8mm and 6mm(?) sizes. Tons of weird springs in different sizes and shapes. Tons of high-quality shafts and ball bearings. An amazing amount of mechanical genious went into this object.