Deere 410 - No Hydraulics - Airlocked?

I have an original 410, with hydraulics completely down, i'm hoping someone may have some ideas.

Here is the sequence of events:
Initial Problem

1. Line from main Hydraulic Pump to Pressure control valve leaking excessively at PCV fitting
2. Remove Hydraulic filter/drain fluid to tighten fitting
3. Replace Hydraulic fitting and refill with 10 gallons of hydraulic fluid. Added some used fluid from another tractor that had some stop-leak in it.
4. Test system. Vibration/stuttering but bucket and dipperstick raised and lowered. Tractor able to move forward/backward.
5. Power off tractor and add additional fluid.
6. Attempted to move tractor – no hydraulics at all. No response on any stick, and no forward/backward.

Additional testing:

1. Remove Hydraulic filter, hydraulic bypass valve housing, transmission filter.
   1. Clean transmission sump screen (not very dirty, fluid looked good, no metal shavings)
   2. Check hydraulic bypass valve in hydraulic filter housing, moves freely.
   3. Found missing “mushroom shaped” spring loaded valve on hydraulic filter bypass. Replaced. I don’t know if I lost the valve when I drained the fluid, if it got pushed into a cavity, or if it was already missing.
   4. Replace filters (filters looked good)
   5. Refill with near 20 gal all new hydro fluid
   6. Test Failed/no change.
      
2. Test hydraulic pump with test gauge. 0 PSI on both high and low ports.
   1. Connect pneumatic brake bleeder vacuum pump to low test port and run vacuum while engine running. 1/2 qt fluid in 30 mins.
      
3. Disconnect line from hydraulic filter to main Tee forward of reverser unit and run tractor. No fluid coming out.

I then let it sit for a week while I tried to lift the loader bucket and dipper stick off the ground using manual means so I could move it. I managed to chain the bucket up about 12" off the ground and hoisted the dipper up about 8" to set it on blocks. Strangest thing is that someone came by to have a look at it, we started it up, and hydraulics were working - shuddering a bit but all functions worked, and even seemed to smooth out as the functions were exercised. Hydraulic fluid went from clear to very milky while running it and the level did not drop. I then raised the loader and boom and drove it to a new spot (where it wasn't blocking my driveway), and on the way lost all hydraulics again. I am now back where I started: No hydraulics whatsoever, no forward/reverse. I let it sit for a few days and still nada.

Based on the milky fluid I am guessing I have an air lock but I have no idea how/where to purge it out of the system or where to go from here.

Anyone have any ideas on how to ensure there's no air in the system? I am stumped as for what to do next.

I don't know that system, you say you have low and high ports, are these pressure test ports on/near the hydraulic pump? Is the hydraulic pump a two section that has the charge pump on the front of the radial piston pump? or does the charge pressure come from the trans? On a JD backhoe piston pump you need charge pressure, it won't suck fluid on it's own.

I hope there wasn't any water in the used oil bucket, pretty easy to pour in a quart of water that's sitting on the bottom of the bucket and not notice it, then the old bucket looks like it was just oil cause the water is gone.

That pressure control valve, is probably a "priority valve" which shuts off hydraulic pressure to the loader if the pressure drops (to allow you to steer and brake priority) but the backhoe is not shut off. That's one thing to check, if the backhoe works, as well as if the steering has any pressure, probably not because you had 0 PSI, but keep that in mind.

I'd guess you have an air leak somewhere in the suction line below the level of the fluid, which is why it will run and then stop, but that's a guess without a lot of info.

A picture of the machine, one of the serial number plate, and one of the pump would go a long way to figuring out what is going on here.

Delmer said:

does the charge pressure come from the trans?

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That hydraulic pump is charged by the transmission pump. Make sure the mechanical clutch is adjusted properly and that the clutch is not slipping. That would affect transmission pressure. If the lower test port on the front side of the hydraulic pump was tested and there was no charge pressure then the transmission circuit needs to be checked. Was the transmission pressure checked? If not check it and report the result.

Delmer, thanks - I am working on photos and answers to your questions - snowed here last night!

mg, thank you - I have not checked the transmission pressure - been trying to figure out how without a dummy filter they mention in the manual. In an older manual I have, it says there is a test port on the bottom of the reverser unit that is on the side of the transmission. I am thinking maybe that is the place to check? Reverser also has test ports on top, one for forward and one for reverse.

Ok Delmer, here is the serial plate and a pic of the front/right of the pump where the pump test ports are located..
When I put in all new fluid, I drained from both the transmission plug and the hydraulic filter so I think I got most of the old fluid out.

Yellow Paint said:

been trying to figure out how without a dummy filter they mention in the manual.

Click to expand...

You don't need the dummy filter to check pressure. That is only used for flow testing the transmission pump. There is a plug on the bottom rear of the transmission control valve on the right side of the tractor that is removed and you would place your gauge there.

That’s very helpful. It’s down in the teens today so i will do this in a few days when it gets above freezing!