How to drive an old JCB Hymac?

Presume you mean a "Backhoe loader"?
The "fluid flywheel" or torque convertor takes the place of a conventional clutch, so no clutch pedal to operate. With the forward/neutral/reverse lever in neutral, select an appropriate gear with the gear stick. Move the column mounted lever either up for forward or down for reverse, and increase engine revs. M/c should then move in the selected direction. You will also have a small pedal to the rear of the brake pedals. This is known as the "dump" pedal, and pressing this disconnects the drive without the need to select neutral, such as when changing gear on the move, or when "crowding" into a spoil pile with the front shovel.
This is a basic description of operation of the 3C and early 3CX models, with 4 gears selected manually. I hope we are talking about the same thing!

Mr. Toad
September 2009