The hydraulic pump on our 980G recently went bad, so we replaced it with a new pump straight from our Cat dealer. As soon as it was installed both the tilt and lift have been drifting quite noticeably. Before the old pump went bad, this loader had no cylinder drift at all. We have looked into the main control valve, ride control accumulator, now they are thinking of re packing the cylinders. Is there anything else we could try?
The pilot valves are very sensitive to dirt. You may have got some contamination down the pilot line to the MCV. Later machines have a screen where the line enters the valve. Confirm by exchanging valves from the lift side to the lower side. Did you do any other work such as exchanging the ECM? Have you tried calibrating the system?
The only part we have changed out was the Hyd. Pump. We haven't calibrated it yet, might have to try that. Will also check those valves, at this point we will try anything.
Well if the only work you did was to change the hydraulic pump, I'll put a dollar on contamination in the pilot valves.