I thought you guys might get a kick out of it. The patent date on it is Dec 5 1922. Its all mechanical.
The first pic is the whole jack.
The next pic is the foot peddle that shoots the centerpost up to take up the slack space as seen in the third pic. Kick the foot peddle the other way and the centerpost falls.
The last pic is in the razed position.
Nice thing about this jack is it can never bleed off, and its been working great for 80 years. Its also rated higher than the hydraulic jacks I was interested in, 5000 lb (2 1/2 ton)
Its only drawbacks are limited lift hight, sometimes its hard to lift the handle high enough to catch the next cog when its under the truck, and its big and awkward.
Hope you enjoy the pictures.