Got a Newholland that the left drive works great the right works great in forward but barely moves in reverse the joystick wont go all the way to the back either.
Visit www.messicks.com and look up your hydrostats on the parts fiche. See if it has separate relief valves for forward and reverse on each motor or the hydrosttic pumps.
You may just have a bad relief preventing it from making pressure in reverse.
Skidsteer.ca