First post been reading forum for several years. my experience is life long farmer, ten years cat field mechanic, two years service manager, independent mechanic 12 years. Any help would be greatly appreciated. Vibromax vm106d requires excess force to rotate steering wheel. Steering system pressure is correct, both cylinder packings are good, hmu orbital motor new. return filter replaced. The orbital motor is open centered and return oil is charge for hydrostatic pumps. There have been no other operational complaints on machine. Back pressure is my belief but not sure how to determine due to return going into both hydrostatic pumps.