John Deere 4020 hydraulic problem

John Deere 4020 hydraulic problem Problems

I have a John Deere 4020 Diesel with synchro transmission. With the engine idling, depressing the clutch cuts out the power steering and the power brakes are lost. Also, I don’t know if it’s related, but the 3-point settles quickly with the engine off, and is initially slow to lift.
Is the problem possibly the drive pump or check valve near the pump, or the cooler bypass valve, or could it be another check or relief valve in another part of the system?

John Deere 4020 hydraulic problem 2

Make sure you have the proper amount of hydraulic oil in the transmission. If the transmission pump were to fail, the foreline pump would blink because it would not receive enough hydraulic oil. Once the clutch is depressed, the transmission’s charge pump stops pumping. The charge pump is actuated when the clutch is engaged. I would check the pressure on the priority valve.

The priority valve sends oil under pressure to the steering and brakes first, then the rest of the tractor, it should have 2250psi, and when two hydraulic functions are engaged (i.e.Steering / SCV box) the pressure should not drop below 1500-1700psi. As for the 3 points, the first place to look is the rock shaft piston. If that doesn’t fix it, your steering axle control box needs to be rebuilt. Good luck.

I have a syncro 4020. Almost the same problems as the others. When it warms up, and generally while trying to reverse the wagon, the front pump screeches, the steering goes first, then the brakes, then all three points. So far we have:

  1. checked the screens and the front pump flow
  2. rebuild the foreline pump
  3. Open the transmission case and diassembled andchecked

the rear pump (almost no wear)

  1. 4. Dealer did a hot flow check (no help)
  2. Replaced relief valve housing (but not springs

and valves)

The tractor is now in my workshop. Is there a good way to check the bypass on the priority valve or the back pump relief valve? I would appreciate some help. It is a good old tractor, but I have spent a lot on the hydraulics.

I had the same problem. Mine started while rolling the hay. I lost power steering, lift arms, and pressure in the baler tailgate. I also had a hissing or fluid blowing noise in the transmission. If I removed the hydraulic rod from the transmission, the noise was louder and you could see the fluid spraying inside the casing. I removed the rocker shaft housing and also the rocker shaft piston and replaced all the gaskets and o-rings. I reassembled everything and was still having the same problem. So I removed the rock axle housing on the right side of the tractor and found an o-ring the size of a pencil eraser that was broken. I replaced this O-ring and the problem was solved.I hope this helps someone.

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