As I've already mentioned, I had to do quite a few repairs, and fixes recently, on the tractor/mower. A word I kept coming across, in relation to these machines, was 'hydrostatic drive'. It meant nothing to me, and I just assumed, wrongly, that it was just a fancy name for the variable speed belt drive, similar to the old DAF car with the horrible CVT belt drives. With a bit of spare time last night, I decided to research 'hydrostatic drives', and the result was absolutely fascinating....
It is actually a rather clever design of hydraulic drive, built into the back axle. It uses the usual crown wheel, to allow the two rear wheels to rotate at differing speeds, when it goes round corners, but includes the ability to hydraulically switch from forward, to reverse drive, and some versions include hydraulically variable speed too. All done using little pistons.
A rotating shaft, with not much movement, sets whether the drive is in F, N, or R. I originally thought that somehow, moved cogs, in and out of engagement, in the diff., but no, it alters the hydraulic passages.