4520 Hydraulic Oil Circuit

[Farmboy1969]

I am trying to understand the hydraulic transmission pump to main pump circuit on this tractor.
My front reservoir tank seems to be leaking off and I'm trying to diagnose.
I've been into the relief valve body and checked it out and it seems to be ok.
What has me puzzled is that the transmission pump seems to push into the relief valve body through a check valve and then into the transmission block - I'm assuming through the filter - and then to the line to the main pump.
It would seem that there would have to be a check valve at the filter to keep the oil from just leaking back into the sump through the filter - but I don't see one anywhere in the parts diagrams and can not find in the TM.
I have a labeled picture to post if I can do it.
Any help would be appreciated.

 

[Tx Jim]

Welcome to YT
In order to limit spam posts new members must have a few posts before they are allowed to post photos. You can go to lower portion of home page to "site comments" & ask site moderator for permission to post photo.

Is your 4520 a rowcrop or CUT? If RC does it have Powershift or Syncro-range trans?

 

[Farmboy1969]

(quoted from post at 06:38:25 04/04/22)
Welcome to YT
In order to limit spam posts new members must have a few posts before they are allowed to post photos. You can go to lower portion of home page to "site comments" & ask site moderator for permission to post photo.

Is your 4520 a rowcrop or CUT? If RC does it have Powershift or Syncro-range trans?

It is a Row Crop with Syncro-Range Trans.
Thanks

 

[Tx Jim]

Hyd oil filter relief valve is above rear most plug(item 24) Common cause for lack of oil in frt oil reservoir is an internal hyd leak. A good place to check is the pto control valve. Disconnect & cap supply line then test hyd's.

 

[Tx Jim]

Photo didn't post & edit didn't function.

 

[wore out]

Look at the last post in the thread at the link below, by "Glen D Anderson" made on Fri Apr 23, 2021 8:18 am.


https://forums.yesterdaystractors.com/viewtopic.php?t=1460651

 

[Farmboy1969]

Thanks, Jim. Will give it some study.

 

[tim s]

I am thinking that you are losing pressure when you have the clutch pedal down ?? If this is the issue there is a strong chance the PTO operating valve is leaking off your stand by pressure..

 

[Tx Jim]

(quoted from post at 09:16:51 04/04/22)
Look at the last post in the thread at the link below, by "Glen D Anderson" made on Fri Apr 23, 2021 8:18 am.

Wore out
I could be mistaken but check valve referred to in Glen Anderson's thread is to keep oil from draining back to sump while hyd's are not operating not while the hyd's are operating such as farmboy's 4520.

 

[Farmboy1969]

(quoted from post at 08:33:10 04/04/22)

(quoted from post at 09:16:51 04/04/22)
Look at the last post in the thread at the link below, by "Glen D Anderson" made on Fri Apr 23, 2021 8:18 am.

Wore out
I could be mistaken but check valve referred to in Glen Anderson's thread is to keep oil from draining back to sump while hyd's are not operating not while the hyd's are operating such as farmboy's 4520.

That is what Im referring to.

 

[Tx Jim]

OOPS

 

[wore out]

(quoted from post at 09:27:14 04/04/22)
OOPS

It's amazing how often this issue comes up on here and also how much difference there is between the hydraulic and PTO systems between the early and late 4020's.

They are like two different machines, probably should have had different model numbers.

Of course, the later 4020's morphed into the 4520's and 4620's.

 

[tim s]

Yes, all the console 20 series have the same PTO valve,,and the same issue with loosing the hydraulic pressure when the pedal is down,,that very small line feeding the PTO valve will carry enough oil past a faulty valve to kill the pressure quickly..I know its not kosher, but I have been adding a 1/4 panel valve below the light switch,interrupting the flow,, when off it stops oil going the valve, eliminating the leakage, when on and your operating the PTO works, and the supply will deal with the leakage.

 

[Glen D Anderson]

As wore out suggested, go to the last post on this thread & read up on the bulletins: https://forums.yesterdaystractors.com/viewtopic.php?t=1460651

If the problem you are having is hyd. cooler bleed down after the tractor has sat for a while, the transmission pump check valve could be the culprit. It could have debris / crap in it preventing it from sealing or it could be stuck open due to the spool over-travelling. Depending on your S/N there is an updated plug with an extension stop that you can install to prevent the over-travelling condition.

(quoted from post at 06:20:37 04/04/22) I am trying to understand the hydraulic transmission pump to main pump circuit on this tractor.
My front reservoir tank seems to be leaking off and I'm trying to diagnose.
I've been into the relief valve body and checked it out and it seems to be ok.
What has me puzzled is that the transmission pump seems to push into the relief valve body through a check valve and then into the transmission block - I'm assuming through the filter - and then to the line to the main pump.
It would seem that there would have to be a check valve at the filter to keep the oil from just leaking back into the sump through the filter - but I don't see one anywhere in the parts diagrams and can not find in the TM.
I have a labeled picture to post if I can do it.
Any help would be appreciated.

 

[Farmboy1969]

I thought this might be helpful to others.
I think my leakage was past the transmission pump and return oil check valves.
Both springs were short and valve body a little worn.
Replaced the springs and the pump spool with improved spool that has a packing ring.
I'm putting it back together and will give it a try.

Thanks for the comments.



This post was edited by Farmboy1969 on 04/05/2022 at 05:48 am.

 

[Tx Jim]

That's an excellent explanation ID of valve body components. I wish photo was oriented the same as when mounted on tractor & in parts catalog. I think the different photo orientation will be confusing to an inexperienced repair person.

 

[Glen D Anderson]

Probably a little late to mention this now but I lightly lapped the trans. pump check valve to the valve body on our '72 4020 when I had it apart. The seat face is very narrow. IMO it's a poor design as the contact area should've been made larger and possibly even a steel seat installed but I guess one can't argue with the fact that these tractors have operated as designed for many years.

I thought this might be helpful to others.
I think my leakage was past the transmission pump and return oil check valves.
Both springs were short and valve body a little worn.
Replaced the springs and the pump spool with improved spool that has a packing ring.
I'm putting it back together and will give it a try.

Thanks for the comments.

 

[Farmboy1969]

Ya, I understand. I did it that way because I was trying to visualize how it fit up on the transmission casting and kept getting confused with it being reversed in hand. Hopefully whoever looks at it will read where it says flipped.

 

[Farmboy1969]

(quoted from post at 11:14:50 04/05/22) Probably a little late to mention this now but I lightly lapped the trans. pump check valve to the valve body on our '72 4020 when I had it apart. The seat face is very narrow. IMO it's a poor design as the contact area should've been made larger and possibly even a steel seat installed but I guess one can't argue with the fact that these tractors have operated as designed for many years.

I noticed the same thing - narrow and aluminum.