Charging pump

I have a very old Case W7 loader that I saved from the scrap yard. I got the engine running last year and now I'm trying to get the transmission to work. I flushed out all the old fluids and filled it to the full marks with new transmission fluid. I do not hear any strange noises from the tractor at all. I put it in gear and nothing. No forward or reverse. Is it the charging pump? This is a HST system and like I said I have no history with this tractor other then just getting the engine to fire off again. I read somewhere that the charging pumps on these old tractors is the heart of the system. Would this explain the lack of any power to the transmission? I have a reading of 230 psi on the clutch pressure gauge and it never shows any temperature reading for the converter but that could just be a non functional gauge. I'm surprised to see any of these old gauges work. I'm hoping that someone out there still has any knowledge about these old workhorses. I would love to make it roll again. I have another one of these tractors that was retired because of the rear axle and extreme metal fatigue so parts would not be a problem to get.
Thank you for any help.

what pump does it have? I know the dannfoss and linde pumps use a charge pump. should have a guage to show charge pump pressure. without pressure you will screw up the main pump in a hurry.