weak hydro in one direction, rayco 1625

[MWALLIN]

My 1625 began giving me a fit when I want it to drive away from the blade. The pump belt squeals and it barley moves. All other function are normal just this.Rayco said it was the drive motor but after talking to some more knowlegable guys it made no sense. They think if one direction works it should work in opposite. I I've changed fluid and filter and taken apart the valve and the metal filters I could find with no success. I then found a metal block under the battery tray that has Allen head taps on one end. I was told this is some pressure relief thing so I took a guess and moved one a half turn and the machine worked great for a day then started acting up again. Can anyone tell me more about that relief block and which way turning does what since I guessed last fall and can't remember what I did? Thanks