4020 hydraulic problem


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4020 hydraulic problem

Mike I have a John Deere 4020 Diesel with a syncro-range transmission. With engine idling, when you push in the clutch, the power steering cuts out and you lose the power brakes. Also, I don't know if it's related, but the 3-point will settle quickly with the engine off, and is initially slow to raise.

Is the problem possibly the transmission pump or the check valve near the pump, or the cooler bypass valve, or could it be another check or relief valve elsewhere in the system?

ross Make sure you have the proper amount of hydraulic oil in the transmission. If the transmission pump was going bad it would make the front pump chatter as it would not be getting enough hydraulic oil. Once you push in on the clutch the transmission charge pump stops pumping. The charge pump is driven when the clutch is engaged. I would check my pressure at the priority valve. The priority valve sends pressure oil to the steering and brakes first, then to the rest of the tractor, it should have 2250psi, and when you engage two hydraulic functions (ie;SCV Box/steering)the pressure shouldn't drop below 1500-1700psi. As for the 3 point, the first place to look is the rockshaft piston. If that doesnt' fix it, your rockshaft control housing needs to be rebuilt. Good luck.
Bob I have the exact same problem. The high pressure pump acts like it is starving for oil from the rear charge pump. The system is dumping oil to the resevoir somewhere. (Evens has a minor whistling noise telling me its blowing by somewhere)I will look at the priority valve as suggested but if it is starving the high pressure pump, it has to be dumping oil at the distribution valve? This is a very common problem, someone had to go thru this exercise many times before. Look forward to your suggestions. Thanks
Bob OK.. Found the problem. The steering valve was dumping oil causing the front pump to not keep up, stroke control oscillate, and pump chatter. What I learned from this:
1) Let the tractor run for an hour. Wherever you are losing oil will get warm. In my case it was the line from the front pump to the steering valve.
2) Be sure to check the inlet screen to the charge pump. You can access this by draining the hyd oil and removing the plug beneath the left side of the tractor under the floor board. It is a hex or square drive. When you remove it, pull the screen out and clean. It could be plugging the inlet to the charge pump.
3) Last but not least, if you find the problem like I did and correct it, you may still have to rebuild the front pump since it has taken quite a ride trying to keep up with the internal leakage. Hope this helps. Good luck.

Mark I have a 4320 syncro. Almost same issues as the others.When warmed up,and generally while trying to back up wagon,front pump chatters, the steering goes first, then brakes, then three point. So far we have:

1. checked screens and flow to front pump
2. rebuilt front pump
3. Opened trans case and diassembled andchecked
rear pump (hardly any wear)
4. Had dealer do warm flow check (no help)
5. replaced relief valve housing (but not springs
and valves)

The tractor is in my shop now. Is there a good way to check bypass at priority valve or rear pump relief valve? Would appreciate some help. Its a good old tractor, but I have spent a lot on the hydraulics.

Tim I had the same problem. Mine started while rolling hay. I lost power steering, lift arms and pressure to baler tailgate. I also had a whistling noise or fluid blow-by in the transmission. If you removed the hydraulic dipstick from transmission the noise was louder and you could see the fluid spraying inside the housing. I removed the rockshaft housing and also rockshaft piston and replaced all seals and o rings. Put everything back together and still had the same problem. Then I removed the rockshaft contorl housing on right side of tractor and found one o ring the size of a pencil eraser that was broken. Replaced this o ring and fixed my problem. Hope this helps someone.
John Gaukel Have a 1967 4020 Powershift. When the 3 point arms are lowered, there is a whistling or whining noise. The noise goes away when the arms are raised. Have had a JD tech rebuild the rock shaft valves and adjust. Still have the noise. Any suggestions?


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