I have a Cat GP50 with two speed transmission and 4.3 engine. Lift will run fine, but will not move forward or reverse. Checked pressure on all three ports on the valve body and there is no pressure whatsoever in any gear. Pulled one transmission cooler hose as well and no movement of fluid either. Removed fill plug and do not see movement of fluid when idling. Lift was moving fine before and fluid shows no signs of metal or discoloration. Forward and reverse on this lift are completely mechanical so there is no solenoids. Torque converter spins fine and nothing visibly wrong from the outside. We do hear what sounds like a faint knock when lift is running. It sounds like it is coming from torque converter area. I have my suspicions, but would like to hear other people's ideas or if anyone has experienced this.