The HMU is a small hand driven pump that sends pilot flow to a valve. Turn, flow shifts the valve, valve directs oil to cylinders, machine turns, stop turning, centering springs center valve, flow stops. It’s all hydraulic, no feedback to the steering wheel like on power assisted steering like a rack and pinion. When hydraulic pressure drops below a specific pressure, flow from the gerotor pump flows directly to the cylinders to provide ability to steer if the engine dies. This is the system on the machines I’ve engineered my whole career, and as described in my WSM (checked to see if there was something new under the sun). I read directly from my
L6060 WSM. “When the engine is not operating, and the steering wheel is turned, gerotor(1) rotates to supply oil to the steering cylinder (2). Thus the machine can be steered manually.
The WSM covers all Grand L 60’s sold in USA. I do not believe this same unit is marketed in Europe because EN500 requires cross over reliefs so if you hit an object with a tire at and angle, feedback will create a pressure spike that can burst a hose. We needed to use a different HMU for Europe, a bear to keep straight on the assembly line. I thought Kubota might have commonality. My old M135GX has the North America, Oceana, and European versions in its manual.
So OPs tractor is full hydraulic, will have steering wheel rotate a little continual due to leakage (likely worse when hot), perfectly normal within limits. I don’t find those limits in the WSM. The difference between full hydrostatic steering and power assisted is described in my M135GX WSM. It concludes with all hydraulic, no feedback to steering wheel on position. I think they left off same as everyone else in this class, likely HMU from same supplier, live with it.
