After overhauling 4 of these now,
What I've learned so far: When you press the thumb bar down (actually a slight arc), it rotates the clutch plate approximately 90 degrees. This causes the cam plate (which is attached to the clutch plate) to also rotate. Somehow, a slanted nylon cam on the cam plate and flat nylon on the pinion yoke convert the rotary motion to linear motion in the direction of the crank handle. This disengages the pinion gear from the pin on the spool shaft, allowing the spool to move freely in either direction. The ratchet pawl is moved into position against the ratchet wheel to prevent the handle from being able to rotate in reverse or forward. The spring linking the body and the pawl doesn't seem to compress, it just changes direction 90 degrees. Its function seems to be to provide positional stability only. All that remains is for a forward wind of the crank (against resistance, which suddenly collapses), and you are back where you started. This forward movement of the crank turns the ratchet wheel against the pawl and, because the back side of the ratchet teeth are curved whereas the other sides are straight, the handle is eventually able to move free. The pawl is moved out of the way to its original position and the spring is also moved to its original position.
If this is all true, then I have one thing I am confused about. On some reels, there is another coil spring the function of which I'm not clear about. You can see it in the Lew's Speed Spool, for example. It's near the top of the reel, above the clutch plate. I can't see from videos what it attaches to at each end or what its function is. All I can see is that it doesn't compress either, it just changes orientation.