If you've ever wondered what powered the logic of a hydraulic transmission back in the olden days, it's essentially a hydraulic computer with all sorts of compo

If you've ever wondered what powered the logic of a hydraulic transmission back in the olden days, it's essentially a hydraulic computer with all sorts of components which are analogous to diodes, transistors, even a pump-driven comparator to weigh input shaft speed and load against the output shaft to decide when to switch a gear. Do an image search for an automatic transmission valve body. It even looks like a big industrial circuit board. Some components are passive like a check valve, some are active like a valve which is operated by pressure from some other part of the circuit. Newer ones also have partial electronic control, with microcontroller-driven solenoids and actuators moving around valves to control hydraulic rams which finally engage or disengage clutches. But it all began with no electronics at all. Pretty neat trick if you ask me. I remember being a kid taking apart my first Ford transaxle and being amazed by the sheer complexity, almost to the point where it seems biological. My dad bought a really bad one for a couple bucks at a junkyard. We didn't need it to fix anything, he just wanted to feed my curiosity. It was a great parenting move. I recommend doing it yourself if you find a cheap busted one, just to get the ideas flowing.