Continuing 3pt Troubleshooting

Original problem was the 3pt on my 1801 (gas) was losing prime and wouldn't lift unless I pulled the plug on the pump.
My other tractor is an 1801D with working 3pt. It leaks hydraulic fluid between rear and transmission but the pump works and doesnt lose
prime.

I pulled the pump on my 1801 to inspect. I found round o-rings between pump and manifold and square o-rings between manifold and
transmission. I planned to replace the pump seal and inspect the shaft based on previous posts that the pump was losing prime. But one
bolt wouldn't break free after penetrating oil and some heat. I decided to swap pumps. I made sure to use square o-rings on the 1801.
Now, the 1801 has a working pump from the 1801D and I get nothing! I can pull the plug on the pump and nothing happens. I put pressurized
air through the dip stick tube - nothing happens.

The 1801 pump is now on the 1801D. Hydraulic oil bubbles up through threads on pump plug. I havent pulled the pump plug because the
diesel fuel filter is in the way. In all fairness it is low on fluid because of the leak. But, the 3pt doesn't work at all now.

The 1801 now has a pump that I know works and doesn't lose prime. It has the correct square o-rings. I looked in the reservoir and see no
fluid movement when moving quadrant lever. I looked into transmission and do see some bubbles when moving the quadrant lever, but cant say
for sure if its normal or a possible hole in the suction line.

Any suggestions?

Are you saying that the 1801 has a pump that should work and the 1801D has a pump now that was losing prime when installed on the 1801?

Yes, known working pump from 1801D is now on the 1801. Pump from 1801 that lost prime is now on the 1801D

I have had trouble getting the pump to prime on my 3600. I had to loosen the pipe on the pump outlet and start the engine. Shut off the engine as soon as oil starts showing, it will spray all over. Once primed, tighten the fitting.

I have removed the plug on the 1801 pump. Originally, removing the plug was how I'd prime the pump and the 3pt would start working. Now, I have the known working pump on the 1801 and when I remove the plug nothing happens. Fluid doesn't come out and the 3pt doesn't work at all. I think I'm going to put a little oil directly into the pump and see if that gets it going.

I would investigate those bubbles in the transmission. Those lines are sealed lines that run through the transmission for protection (in the NAA days the lines were external). It doesn't take much of a leak to cause trouble.

The transmission bubbles had me wondering too. I'm not sure how much is spinning around in there while the tractor is running and in neutral that might cause the fluid to be moving around. I already have a new suction line. Just waiting for the trap to arrive so I can cut some threads for pulling it.

What I don't understand is... If there's a hole in the suction line, why wouldn't the pump just pull transmission fluid.

Good point, all I can say is the service manual says to check that intake tube after all the easy stuff checks out O.K.

I think this is a case where you have to keep trying things until you stumble upon the problem.

The setup of the pump intake/manifold/tubes make it hard to bypass stuff for troubleshooting purposes.