OK, here goes: There are 2 places I know of where speed is governed on CC hydros. 1.) The hydro control/trunnion lever on the left side of the transmission. There are centering springs there that keep the speed constant. It would seem to me that if one spring for the forward position were taken out and a long spring or spacer was installed in the slot where the reverse spring is, it would result in more swash plate tilt and faster speed. The tractor would likely have no reverse. The farther the swash plate can be moved forward internally, the more volume the charge pump pistons will deliver to the hydro motor pistons. Same goes for reverse. 2.) There are three valves in the top of the hydro. Two are relief valves, one for forward and one for reverse. Carefully disassembling these (they are not made to be taken apart) and installing stiffer springs would hype the hydraulic pressure. There is a center pressure relief spring and ball. A stiffer spring there would also hype the pressure. I've never modified for more speed, but have seen these areas suggested as the trouble cause for a CC a guy owned that would do 30 or 40 mph in full forward. So that's where I'd start for more speed. You might also try posting on a pulling tractor site to see if they have any further input.
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