Hydraulic function and hydraulic return

Freddy

Member

Plumbing in a loader on a 4020 and thought this was interesting. I have heard about the magical pathway from the rock shaft return to the main pump. Well Deere agrees there is a path but it's not magical. Makes a lot of sense.
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There is nothing magical about the system. The high flow systems returned the oil directly to the front pump. The reason being the transmission pump on the gear drive tractors did not have a high enough flow to keep up with the main pump at high flow rates.

This is why when plumbing a loader on a JD 4020 gear drive tractor you should feed it from just after the priority valve and return the oil to the filter housing. This way the oil is returned to the main pump directly not through the transmission pump. This really important when setting there with the cutch down using the loader. With the clutch down the transmission pump is not turning. So that is one reason that loaders ran by the tractors SCVs will chatter if ran long with the clutch down. The main hydraulic pump is starving for oil.

I also am wondering what manual you are posting this from???? I think it must be a later manual with the late model console tractors. The earlier models, with the SCV valves under the hood, did not return to oil directly to the filter relief valve. I am pretty sure this is true. IRC the later models with the rear mounted SCV valves did but the early ones did not return the oil the same way.

The long and short of it is IF your hooking a loader valve to a JD 4020 you should return it to the filter cup for better flow to the main pump. That helps prevent cavitation in the main pump from it being starved of supply side oil.
 
OK,

Is the filter on the discharge of the transmission pump?

So that would mean the filter goes to from pump, would assume it is outside in.
 
This a sm-2039 manual. Does not differentiate new or old just 4000 series on page 230-5-6. As Mike M said on this forum no need to drill a hole in the cover the rockshaft oil is going to the main pump after its cleaned first. If the pump doesn't use it it over flows back from the reservoir to the transmission housing! It goes there for cooling purposes.
 
Yes filtered outside in! The trans pump pumps oil to the filter. If filter is plugged it's forced right back to transmission case. That is the problem with a gear pump.. it always want to pump something even if it breaks itself. Hence the need for a oil filter relief valve. The pump through the filter supplies the forward reservoir and the main pump. If the main pump is not demanding the oil it fills the reservoir and overflows back to the trans case. This aids in cooling of the oil. Plus makes a reserve supply of oil for the main pump in case you are using big single acting cylinders
 

Important on the Waterloo and vital with a Dubuque or Mannheim. The utility tractors were built with too low of capacity transmission oil pumps .
 
That is an interesting point. Deere did not design it
for heavy constant use. A good system though if
used within its design.
 
"As Mike M said on this forum no need to drill a hole in the cover the rockshaft oil is going to the main pump after its cleaned first."

I am trying to figure out what point you are trying to make, talking about rockshaft return oil and drilling the filter cover in the same sentance????
 
Well I should have warned you to read his description first. I did not put in all the details like he did. He drilled and tapped the rockshaft return elbow. Which saved him $28 dollars. Most pictures I have seen have people just replacing it with a t fitting. That is what I did. Parts from Parker hydraulic was like $80 dollars. I'll list the parts after I am done
 
Yep, that was my best guess, that loader oil was being returned to the port where the rockshaft returns.
 
I did not drill and tap it so much to save $28.00 As much as it was quick and easy as I didn't think I could find the right part.
I had a JD500 parts machine which is a 3020 industrial with a loader and backhoe. JD returned the oil there so if they thought it was ok I sure was not going to doubt them. The loader valve from that machine was also a great choice to use.
I used a fitting from JD to get my pressure from up in front of the brakes. This system has been working very good since around 1992 ??
 

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