I’ve got a D8T where blade lifts up without command. Solenoids are reading correct. Lift solenoid valve has been replaced. Blade will stay down if put in float. As soon as you take it out of float it will lift on its own. Any ideas? No codes present. Other than trans, engine, and implement abnormal update rate.
How did the problem start.? Got a Serial Number and a list of Active Codes.? Do you have access to Cat ET to monitor output signals from the blade control lever position sensors.?
Not sure what the operator was doing when problem occurred. Serial number KPZ2067. No active codes. And yes I can monitor signals. All solenoids reading correctly. When in the hold position pump pressure starts climbing to 1200 psi and blade starts lifting on its own. The lift signal stays reading zero. Blade will start lifting while cranking over engine, like its a pump issue. When in float pump will stay in low pressure standby. As soon as it’s taken out of float blade lifts without command.
So the problem just appeared as opposed to getting worse over time.? If the position sensor signals from the blade control joystick all check out then it would appear the problem is hydraulic. Quite why the pump will stay in low pressure standby when the control is put into float is puzzling, especially as the joystick signals are apparently not the problem. Do you have access to service manual information.? A thought from left field. I wonder if it could be a resolver valve problem.?
Sounds to me like something happened to centering springs
You say that the blade cylinders lift on their own when the joystick is maintained in the HOLD position. Does the blade also raise if the joystick is moved to the RAISE position.? Does the blade "power down" when the joystick is moved to the LOWER position.? Attached info on the pump operation.
Yes all functions are normal except when joystick in hold position. That’s when blade will lift without command. I can move the joystick slightly to the lower positions to get blade to quit traveling. But yes all full travel at all speeds no issue. Was also thinking spool valve or a spring is week and pressure is overcoming. Signaling pump to upstroke.
Have you been into the blade control section of the implement control valve yet, looking for broken springs.?