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4020 Air in Hydraulics

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RyanMAtwell

New User
A month or so ago I had a line leaking that ran from my Steering unit(steering wheel) going to the front end. We replaced the line. Now we can not get the air bled out of the system completely. Some times the steering works 80% or so but seems to air lock from time to time. We have bled the air out of the steering unit under dash and out of the brakes. The steering is working, but not 100% like before replacing the line. So far we have not been able to get the lift to start back working right. When I lower the lift arms they do not come back up for several minutes. Everyone keeps telling us that the system is airlocked. But how can we get it out. The tractor is a John Deere 4020 1972 model. Any help would be appreciated. Thanks
 

Air will work it's way out of hyd's just through operation except on the steering valve.
Have you bled steering valve according to the JD tech manual?

Slow to respond 3pt indicates lack of oil to rockshaft control valve due low trans pump pressure or a high pressure internal leak..

Have you ever checked stand-by psi??
 
We have bled the Steering and the brakes both. Brakes seem to work as good or better then ever. The past 2 days the guy that is helping me on it has been raking hay with it. Steering works pretty good but he said every once in a while it gets tight but then comes back to normal. He has been working the lift while raking to see if that will help work some of the air out too. It takes about a minute or so to come back up. He talked to a guy that use to work for John Deere that suggested that it might have some trash in the priority valve. That is our next place to look now. Thanks for the suggestings. I will check the psi as soon as we can and see what it checks.
 

It's possible that the stroke control valve isn't seating properly and if psi gets below 1600-1700 the priority valve will close shutting off rear hyd functions. Normally if all hyd functions are operable air isn't real hard to get out of system.
 
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