6420 no hydraulic power to (3)rear 300 series SCV'S

[KCinNMO]

Rear Selective Control Valves have no hydraulics. No hydraulic pump 'groan' when operating remotes.
Connected hose to quick disconnects in both connectors for all THREE SCV'S. Put hose in bucket and tried all three remotes in both positions. No hydraulic flow.
Bucket operates correctly, tractor drives good FWD and BWD. PTO works.
Any help or troubleshooting suggestions appreciated.

 

[wore out]

Rear Selective Control Valves have no hydraulics. No hydraulic pump 'groan' when operating remotes.
Connected hose to quick disconnects in both connectors for all THREE SCV'S. Put hose in bucket and tried all three remotes in both positions. No hydraulic flow.
Bucket operates correctly, tractor drives good FWD and BWD. PTO works.
Any help or troubleshooting suggestions appreciated.

Hos did this come to be, worked one day and not the next, quit while you were using it, or is "new to you" and you don't know when they last worked?

I'm wondering about the steering priority valve being stuck or pump pressure simply being low, but you state the "bucket" works O.K..

There are several ways "power beyond" for the loader controls cold be sourced, making this even more difficult/interesting.

There are a number of "dime valves", one-way check valves on the various hydraulic functions that direct pressure feedback control to the PFC hydraulic pump.

Also, what is the "standby pressure"?

There are 3 pressure test ports on the rear valve stack, one for system pressure, one for steering pressure, and one for "feedback pressure" that is plumbed to the hydraulic pump. Offhand, I don't remember which is which, you REALLY need a factory manual with "flow charts" when digging into this complicated system

 

[KCinNMO]

I apologize for not going into detail about the history. I have gone on many forums for help. Not getting any response at all I just started abbreviating the problem as no one was even answering. In reading here it seems you have a lot of 6420 knowledge so I thought I’d give it a shot.
The rest of the story:
In the beginning SCV #2 would not hold the brush cutter or disc wing up, it would slowly lower. I changed the 3 position adjuster several times to see if that made a difference. It didn’t so I removed the SCV to see if I could find the problem. I removed the long ‘poston’ being careful to not lose any parts. I found a broken pin (indicated on the parts diagram) I replaced the pin and put the SCV’S back in. (Making sure the ‘dime’ pieces were in place) I -did not disassemble- any of the operating parts. <No hydraulics>
I again removed the SCV’S (#1 & #2) to see if the ‘dime’ pieces had dropped out even though I didn’t see them on the cloth I had placed below the SCV to catch any parts. They were still in place but I again put some grease on them to hold them in place. The large o-rings (which I replaced) looked good. The end cap o-rings looked good. There is no ‘dime’ valve plate on the end cap. <Still no hydraulics.>

 

[WTW]

Rear Selective Control Valves have no hydraulics. No hydraulic pump 'groan' when operating remotes.
Connected hose to quick disconnects in both connectors for all THREE SCV'S. Put hose in bucket and tried all three remotes in both positions. No hydraulic flow.
Bucket operates correctly, tractor drives good FWD and BWD. PTO works.
Any help or troubleshooting suggestions appreciated.

When you say bucket operates correctly?? Are you saying both loader function work correctly and just the rear SCV do not work?? Does steering also work OK? If this is correct?? Pump and Priority valve are OK and there is most likely an LS leak / issue with rear valve stack functions that needs to be diagnosed. A quick test to confirm this is a LS issue or not, simply stall one of the working loader functions (bucket or boom) and while holding pump stalled does the rear SCV's now work? Let me know and I can continue to narrow your problem down. DW

 

[KCinNMO]

Duplicate response

 

[KCinNMO]

When you say bucket operates correctly?? Are you saying both loader function work correctly and just the rear SCV do not work?? Does steering also work OK? If this is correct?? Pump and Priority valve are OK and there is most likely an LS leak / issue with rear valve stack functions that needs to be diagnosed. A quick test to confirm this is a LS issue or not, simply stall one of the working loader functions (bucket or boom) and while holding pump stalled does the rear SCV's now work? Let me know and I can continue to narrow your problem down. DW

Hydraulic fluid level good. Bucket operates correctly, tractor drives good FWD and BWD. ( I haven't taken it for a high speed drive) Power steering functions good.

Connected a hose to a rear SCV. Stalled and held the loader both boom and bucket.
While operating the lever -no hydraulic fluid- out of SCV.

 

[KCinNMO]

Hos did this come to be, worked one day and not the next, quit while you were using it, or is "new to you" and you don't know when they last worked?

I'm wondering about the steering priority valve being stuck or pump pressure simply being low, but you state the "bucket" works O.K..

There are several ways "power beyond" for the loader controls cold be sourced, making this even more difficult/interesting.

There are a number of "dime valves", one-way check valves on the various hydraulic functions that direct pressure feedback control to the PFC hydraulic pump.

Also, what is the "standby pressure"?

There are 3 pressure test ports on the rear valve stack, one for system pressure, one for steering pressure, and one for "feedback pressure" that is plumbed to the hydraulic pump. Offhand, I don't remember which is which, you REALLY need a factory manual with "flow charts" when digging into this complicated system

I posted a reply but it wasn't directed to you. Sorry about that..
Novice learning how to use this forum.

 

[WTW]

If the loader valves works and other SCV's do not when stalling a loader valve this indicates the SCV's that do not work, are not getting supply oil from the common hydraulic supply circuit that supplies pump pressure oil for all SCV's. The most likely reason, knowing your tractor has mechanical / cable operated SCV valves, is the compensator spool valve in the problem valve sections is stuck shut or malfunctioning. The compensator valve controls inlet oil from pump to the SCV control valve spool. We know the control valve is moving because it connected to the control lever via cable. If control valve is moving and pump does not build pressure. it is because of lack of LS pressure / message from control valve, this indicates there is no supply oil from compensator valve to main control valve. The compensator valve resides in same bore as the flow control valve assembly. This is where I would recommend to start looking.

 

[KCinNMO]

If the loader valves works and other SCV's do not when stalling a loader valve this indicates the SCV's that do not work, are not getting supply oil from the common hydraulic supply circuit that supplies pump pressure oil for all SCV's. The most likely reason, knowing your tractor has mechanical / cable operated SCV valves, is the compensator spool valve in the problem valve sections is stuck shut or malfunctioning. The compensator valve controls inlet oil from pump to the SCV control valve spool. We know the control valve is moving because it connected to the control lever via cable. If control valve is moving and pump does not build pressure. it is because of lack of LS pressure / message from control valve, this indicates there is no supply oil from compensator valve to main control valve. The compensator valve resides in same bore as the flow control valve assembly. This is where I would recommend to start looking.

You will have to enlighten me as to where “the compensator spool valve in the problem valve sections” is.

You seem to be have a lot of 6420 hydraulic knowledge.
I didn’t want to add something to confuse the problem, but.

Just previous to working on things I had a strange –anomaly- that may or may not be important . . . . while using a connected brush cutter the SCV hoses started –blowing off/out of- the quick connects. Different SCV'S, different pots (upper/ lower). I would swap locations but nothing was location or hose specific.
My thinking at the time-It was like there was too much pressure.

 

[KCinNMO]

The most likely reason, knowing your tractor has mechanical / cable operated SCV valves, is the compensator spool valve in the problem valve sections is stuck shut or malfunctioning.

I'm confused about what was said.
-If- I am correct about where this valve is {N}? (I think it may be in each SCV. . . I have 3)
Why would -NONE- of the (3) SCV'S work? I don't think -all of them- would have stuck valves.

 

[WTW]

Yes it is odd that all three is giving problems. But it the only thing between what is working / that has pressure and what does not based off your information??
Lets try this again. You have Three SCV's at the rear of tractor that do not have any (ZERO pressure at coupler)? This is tested with a pressure gauge?? If so What is pressure at the P port lower DR on the PV (priority valve)? You should have standby pressure with all controls in Neutral around 500 to 600 psi. Ten when you stall a working loader valve you should have around 3000 psi? What are these pressures? Also If the loader valve works is it a factory installed valve? (No aftermarket) Loader valve is supplied pressure oil from the PB manifold on the rear valve stack? Or is loader valve part of the rear valve stack?

 

[KCinNMO]

Yes it is odd that all three is giving problems. But it the only thing between what is working / that has pressure and what does not based off your information??
Lets try this again. You have Three SCV's at the rear of tractor that do not have any (ZERO pressure at coupler)? This is tested with a pressure gauge?? If so What is pressure at the P port lower DR on the PV (priority valve)? You should have standby pressure with all controls in Neutral around 500 to 600 psi. Ten when you stall a working loader valve you should have around 3000 psi? What are these pressures? Also If the loader valve works is it a factory installed valve? (No aftermarket) Loader valve is supplied pressure oil from the PB manifold on the rear valve stack? Or is loader valve part of the rear valve stack?

I do not have a pressure gauge.
I might be able to get a gauge shipped to me in a week or two if I knew what type connectors I need. Even if I had one I don’t know where to check any pressures.

The way I check the SCV(S) is to plug an open ended hose in and operated the levers to see if there is flow. Wouldn't this mean I have no –standby pressure- else I would have -some- hydraulic flow???

As earlier said---- I removed SCV #2 to see if I could find a problem. I found a broken pin (indicated on the parts diagram) I replaced the pin and put the SCV’S back in following the Repair Manual instruction. (Making sure the ‘dime’ pieces were in place) I -did not disassemble- any of the operating parts. Back together and <No hydraulics>

I again removed the SCV’S (#1 & #2) to verify the ‘dime’ pieces had not dropped out . They were still in place so I again put some grease on them to hold them in place. The large o-rings (which I replaced) looked good. The end cap o-rings looked good. <Still no hydraulics.>

Question: What would be the result if a ‘dime piece’ was missing???? Just to verify they are in place.

 

[WTW]

Are the SCV's cable or electro hydraulic valves? I assumed they are cable controlled valves based off the parts picture you posted?? If a LS shuttle check valve was left out you would have flow out open hose / coupler if there was standby pressure. Pump would not build high pressure out SCV if a LS check was missing but, would flow low pressure. The pressure reading at the bottom DR (Diagnostic Receptacle) test port on the PV would tell me if there is pump / supply pressure to the PV that then supplies the individual SCV's. Have you pulled the PV spool to confirm it is in one piece and not stuck in bore? It should be OK if tractor loader is a factory installed / plumbed loader knowing loader functions??

 

[KCinNMO]

Are the SCV's cable or electro hydraulic valves? I assumed they are cable controlled valves based off the parts picture you posted?? If a LS shuttle check valve was left out you would have flow out open hose / coupler if there was standby pressure. Pump would not build high pressure out SCV if a LS check was missing but, would flow low pressure. The pressure reading at the bottom DR (Diagnostic Receptacle) test port on the PV would tell me if there is pump / supply pressure to the PV that then supplies the individual SCV's. Have you pulled the PV spool to confirm it is in one piece and not stuck in bore? It should be OK if tractor loader is a factory installed / plumbed loader knowing loader functions??

Manual / cable attached SCV'S. #Everything is factory installed.
Again I have no pressure gauge but I can order one from somewhere. What type connection adapter must it have? What would the max pressure requirement be?
I -assume- an "LS? shuttle check valve" is what's called a 'flat valve' in parts? Referred to as the 'dime' valve by many.
I need a picture of where the DR test port is. As I don't know what the "PV spool" is I can't say if I have pulled it or not. I don't know the acronyms or names for anything. I would need everything simplified (and pictures if possible) so I know what you ask me about.

 

[KCinNMO]

Are the SCV's cable or electro hydraulic valves? I assumed they are cable controlled valves based off the parts picture you posted?? If a LS shuttle check valve was left out you would have flow out open hose / coupler if there was standby pressure. Pump would not build high pressure out SCV if a LS check was missing but, would flow low pressure. The pressure reading at the bottom DR (Diagnostic Receptacle) test port on the PV would tell me if there is pump / supply pressure to the PV that then supplies the individual SCV's. Have you pulled the PV spool to confirm it is in one piece and not stuck in bore? It should be OK if tractor loader is a factory installed / plumbed loader knowing loader functions??

I don’t know anything about how the rear SCV’S operate. I don't even know how the low pressure/ high pressure thing works.
Could you spare the time to educate me on the basic operation of the SCV ? I would really appreciate it to understand how things work. It may help me in answering questions and in getting this fixed.

 

[used red MN]

Manual / cable attached SCV'S. #Everything is factory installed.
Again I have no pressure gauge but I can order one from somewhere. What type connection adapter must it have? What would the max pressure requirement be?
I -assume- an "LS? shuttle check valve" is what's called a 'flat valve' in parts? Referred to as the 'dime' valve by many.
I need a picture of where the DR test port is. As I don't know what the "PV spool" is I can't say if I have pulled it or not. I don't know the acronyms or names for anything. I would need everything simplified (and pictures if possible) so I know what you ask me about.

I no expert on this system but I will try to help you out with definitions. Looking above and from experience with other hydraulic systems the PV is the “priority valve“ in most systems this gives pressure and flow to safety and critical systems first such as brakes, power steering and transmission or clutch pressure if this applies to your machine. I assume you are getting those diagrams from the online parts catalog, search “priority valve” and it should show up. It must be called an “inlet priority valve” I would link it but I am not sure which variant of the tractor you have. The wording Wore out uses is usually pretty “spot on” so saying PFC being “Pressure feedback control.” WTW shifted gears on you using a generic term LS which means “load sense.” I believe these two mean essentially the same thing. A hydraulic circuit is telling the pump when and how much to pump. I cannot explain exactly how this is done on your tractor. I am not a 100 percent certain but I think that you are correct in saying what WTW was calling a “LS shuttle check valve” is a “flat valve or dime valve”
I can’t find anything on the specific location of the “DR diagnostic receptacle” on your tractor. It looks like it is a miniature male plug similar to a male hydraulic hose coupler to allow a quick connection to a hydraulic test gauge. Do a web search and it should show what I am talking about.
If you are near KC go to Northern Hydraulics and get a 5000psi hydraulic gauge and adapt it to a male SCV fitting. At least you will then have some idea of what you have going on. Hopefully I am close on all this. You never know someone that is an actual expert may come along and blow all my explanations completely out of the water. I would tell you to get a manual but JD manuals are big bucks and I don’t feel good about recommending any other substitutes.
Here are some videos that may help, the last one is maybe a bit complex.
Edit to add: An SCV is basically a 4 port 3 position valve as explained in the last video. There is an additional position and other porting if your valves have a float option, but the description above covers the basic functions needed to extend and retract a cylinder.
Axial Swash plate pump
Result of adjusting the swash plate
Pressure compensating pump
spool valve operation (SCV)

 

[wore out]

I no expert on this system but I will try to help you out with definitions. Looking above and from experience with other hydraulic systems the PV is the “priority valve“ in most systems this gives pressure and flow to safety and critical systems first such as brakes, power steering and transmission or clutch pressure if this applies to your machine. I assume you are getting those diagrams from the online parts catalog, search “priority valve” and it should show up. It must be called an “inlet priority valve” I would link it but I am not sure which variant of the tractor you have. The wording Wore out uses is usually pretty “spot on” so saying PFC being “Pressure feedback control.” WTW shifted gears on you using a generic term LS which means “load sense.” I believe these two mean essentially the same thing. A hydraulic circuit is telling the pump when and how much to pump. I cannot explain exactly how this is done on your tractor. I am not a 100 percent certain but I think that you are correct in saying what WTW was calling a “LS shuttle check valve” is a “flat valve or dime valve”
I can’t find anything on the specific location of the “DR diagnostic receptacle” on your tractor. It looks like it is a miniature male plug similar to a male hydraulic hose coupler to allow a quick connection to a hydraulic test gauge. Do a web search and it should show what I am talking about.
If you are near KC go to Northern Hydraulics and get a 5000psi hydraulic gauge and adapt it to a male SCV fitting. At least you will then have some idea of what you have going on. Hopefully I am close on all this. You never know someone that is an actual expert may come along and blow all my explanations completely out of the water. I would tell you to get a manual but JD manuals are big bucks and I don’t feel good about recommending any other substitutes.
Here are some videos that may help, the last one is maybe a bit complex.
Edit to add: An SCV is basically a 4 port 3 position valve as explained in the last video. There is an additional position and other porting if your valves have a float option, but the description above covers the basic functions needed to extend and retract a cylinder.
Axial Swash plate pump
Result of adjusting the swash plate
Pressure compensating pump
spool valve operation (SCV)

DEERE defines "PFC" as "pressure and flow compensated".

 

[620 John]

The coupler used to plug into the Diagnostic Receptacle is called a PD242 series. What I use at work is a 1/4" hyd hose with 1/4" pipe thread fittings on each end with a gauge on one end and this coupler on the other.

https://www.ebay.com/itm/375290712982?


Like Used red MN said go to Northern Tool and get a 5000 and maybe a 3000 PSI gauge as well.

https://www.northerntool.com/categories/hydraulic-gauges

In case you need to install a DR in a certain plug (which I don't think you'll have to do) here's where I get my DR's from: https://www.hydracheck.com/catalog/diagnostic-quick-disconnects/pd-series-test-nipples/

If I remember correctly most of the test ports used in your scenario will be M14X1.5 thread size DR.


If get more time today or tomorrow I can post some diagrams pictures from the tech manual on hos the SCV's work and show where WTW is telling you to test.

 

[KCinNMO]

The coupler used to plug into the Diagnostic Receptacle is called a PD242 series. What I use at work is a 1/4" hyd hose with 1/4" pipe thread fittings on each end with a gauge on one end and this coupler on the other.

If get more time today or tomorrow I can post some diagrams pictures from the tech manual on hos the SCV's work and show where WTW is telling you to test.

Happy St Patricks day. Erin Go Bragh !!
- Kerry

Thank you ‘used red MN’, ‘wore out’, and ‘620 John’ for all the information. I have a Cat excavator so I am –somewhat familiar- with hydraulics and pump operation but I do not understand the SCV workings.
Also I do not know where to connect –anything-.
The PD242 information is what I need to know when I buy a pressure gauge. I live120 miles North from KC, everything will be online purchased. (my initials happen to be KC)

My main goal in trying to understand the SCV is to figure out if my removal and reinstall of SCV #2 is the cause of the –no pressure-. Until I removed SCV #2 the pressure was good so I’m thinking the -no hydraulics- was my fault. But from what I currently know about the SCV operation I can’t see what I could have done to cause this. I even removed the SCV –again- to verify big the o-ring seals and the flat valves were in place for SCV #1 & #2.

FYI: the tractor is 6420 - 6320, 6420 (North America Edition) - PC4357

 

[620 John]

Don't know if these help or not. Just to give you an idea of how they work. B and C are where your hydraulic couplers are at.

I think this is the test port WTW is telling you to test.

Minimum pressure at this port with all valves in neutral should be about 400-480 PSI. Max pressure with any SCV stalled should be 2830-2970 PSI