Why won't my Caterpillar D9G move after a transmission oil change, and could the priority valve be the cause?

[Nicholas Villa]

I recently changed the transmission oil on my Caterpillar D9G, and now the machine won't move at all. Before the oil change, it was operating normally. While researching the issue, I found a similar case involving a D9H where the problem was traced to a dirty priority valve and a faulty pressure control valve. Before I start replacing parts, I'm hoping to get some advice from others who have worked on these older Caterpillar dozers. Could a stuck priority valve, pressure control valve, or loss of transmission pressure cause this issue after a fluid change? Any troubleshooting tips or experience with a D9G transmission not moving after service would be greatly appreciated.

 

[Chairmann Ringer]

I'd check transmission pressure first before replacing parts. Since it stopped moving right after the oil change, I'd suspect low oil level, wrong oil, a suction leak, or the pump losing prime before blaming the priority or pressure control valves.