Have a 1999 Ranch King RK20H45a that after about 20-30 minutes will not move in reverse.
Anyone know where I can get the info on the hydrostatic unit to see what the problem might be
I'm not sure where exactly you can get it. I can tell you that most are a sealed unit, if you are lucky you have a fill plug for hydraulic fluid, check the level to be sure that the pumps are working with adequate supply. I have a Husqvarna which had similar problem. after about 30 minutes reverse was only possible if I was heading backward down a slight grade. Even worse, going forward up a slight grade maybe 10 degree was a major struggle. My hydrostatic transmission was sealed and not repairable. The dealer explained that with the unit, that sometimes the fluid overheats and looses it ability to pump adequately back and forth. Mine obviously was flawed from the manufacturer. Luckily under warranty, was replaced and works great now. Would have cost me $800+ if I had to pay for it out of my pocket.