JD 490 Excessive Hydraulic Temperature

[Knivens894]

I have a 409E with about 8,000 hours which suddenly went slow in all modes. The problem was no more than 2,000 PSI from main pump. Removed main pump for internal inspection by hydraulics shop, no issue found. During 4 months of searching, Replaced:

1. Main Pump solenoids.
2. Angle sensor
3. DP Sensor
4. Fuel filter
5. Cleaned hydraulic filters, air filters
6. Replaced PVC
7. Cleaned all connections
8. Service Tech finally showed up and found a broken spring in one of the main pump solenoids. Replaced that solenoid. Max main pressure then 3,800.
9. Tech returned and said engine injector pump was not meeting specs. Removed and had engine injector pump overhauled with no improvement noted. Tech says no issue with PVC or its sensors per his computer.
10. Overhauled the system main relief valve and replaced the surge relief valve with new. This allowed adjustment of surge and main pressure specifications.

Thinking I had solved the problem, I attempted to return the machine to service. Functions are weaker and slower than before with the engine wanting to stall. Operating temperature soon rose to near red line. The hydraulic oil was so hot steam came off the bucket cylinder when digging in water. I believe I have a hydraulic by pass somewhere. My question is how do I find it? Is it trial and error, or is there a methodical way to find it?

Any and all experiences and/or suggestions, short of throwing a match on, it would be appreciated.

 

[Tones]

One thing you haven't listed is pilot pressure and flow. If that is low then the main control spulls won't open fully and will create heat and make the engine labour.

 

[JonathanMA]

Those 2 pump solenoids control pump output-- 1 strokes pump for more output, the other de-strokes the pump-- they sort of fight each other while running to keep pump where it needs to be--normally you hear a clicking/pulsing when running at low speed and stand next to it. Does it sound like its under a load when you first start it? With all those parts thrown at it, could it be as simple as someone connected the 2 solenoids incorrectly and its trying to put out oil when its not asking for oil? They both have the same connectors. Also there are adjustments that need to be made to the angle sensor as well as the D/P sensor-- also if engine speed sensor isn't reading, it can do odd things as well.

 

[joeblow]

I agree with Jon. If you have a volt meter you can set the pump angle sensor and the dp sensor .W.e had a jumper or break out connector but you can make your own.Make a tee connection at the red/yellow wire going to the pump angle sensor and another tee at the black wire.Disconnect the 2 pump solenoids ,start machine at an idle and wait 3 or 4 minutes .You should hear the engine start to labor as the pump goes to full stroke.With the volt meter hooked in loosen the 2 screws on the angle sensor (leave snug) and adjust until you read 4.5 volts.Tighten the screws and recheck.It is a very sensitive adjustment so fiddle with it until you get 4.5. Hope fully that will solve your problem.If that adjustment is off the pump doesn't know to stroke or de stroke witch will account for the low pressure and the heat.Another useful tool to get is a temp sensor.Point it at the control valve and check what is the hottest.That should narrow down your search for what is bypassing.

 

[Knivens894]

Thanks for your inputs. Joe, my manual says 4.40 V on the angle sensor which is where it is set. The DP is set where found at 1.14V. The Tech recommended 1.0V on the DP. I installed a new DP set at the minimum manual recommendation of 0.5V and it made no difference. I read in the manual that turning the DP down slows the machine operating speeds. The pressures on the pilot circuit is according to manual.

With the PVC and all sensors functioning correctly according to the computer, i believe the problem is internal leaks pass one or more relief valves, with the dumped pressure creating the heat.

I read in another post on this site which offered, "I would suggest you look at the small solenoid valve box and reseal it. That is what did the trick for us in the end. I can't remember exactly what but think it had to do with how the valve box affects the load on the DP sensor. So too much pilot oil makes the DP sensor think more flow is needed and maxes out the pump and ends up being dumped as excess heat." That seems to be the situation with my machine, that is, pressure is being dumped creating excessive heat. Yesterday I ordered all the seals for the small solenoid box just behind the cab. They will arrive tomorrow and we will go through it. There are a total of 10 valves in the housing, so we will go through them all resealing, reset the pilot pressures and try it again.

I have purchased the harness from JD for use in setting the A sensor and the DP sensor ($135). I also have a temperature sensor gun accurate to 0.5 degrees. I also have the gauges and connectors to monitor and adjust the main and pilot pump pressures. I will reseal that solenoid assembly first and if that does not work, I will bring out the temperature measuring gun. There are so many relief's in the system, finding the internal system leak is a real pain. 4 months of searching, adjusting and repairing, two technician service calls, thousands in parts, and the machine is still not returnable to service.

 

[joeblow]

Sounds like you have been through the ringer with this machine.As I remember the biggest problem with the 490E was the relief valve getting contaminated and those pump solenoids calving.Since you have a manual, check #7 check valve and the unloading valve.Be sure to put a vacuum on the tank before removing unloading valve . Other than that I cannot think of another thing that would dump that pressure. The settings on the angle sensor and 0.8V on the DP sensor came from JD Detac.They also suggested cranking the pilot pressure up 100 psi. Good luck

 

[Knivens894]

Thanks again Joe for your reply and continued interest. These problems only started after my operator slid the machine into the pond we were digging. He was frantic to get the machine out of the water and I believe he overheated and/or overloaded the hydraulic system in the process. That one pull out cost me $750 for a very large wrecker. The machine has had problems since then, but for the past several years before that has performed reliably, just blowing a hose now or then. Additionally, in the past both track tensioner springs have been broken and replaced. We have replaced the pins and shims in the arm and bucket, installed new bosses on the bucket and painted the machine. Right after getting the machine 7 years ago, I pulled the pivot motor and replaced the main shaft seal to stop a major leak there (that is why the prior owner sold it). I also found the prior owner had removed the screen on the hydraulic oil return in the tank. Then the computer went south due to an angle sensor failure and the fact that the prior owner had installed a 5 amp fuse in the 1 amp slot for the computer. I do not blame the machine for problems caused by poor maintenance. I have put a couple of thousand hours on it largely trouble free until now. Tomorrow we will get into those valves. Considering the machine is 22 years old, new seals can't hurt.

 

[Knivens894]

Yesterday we pumped 15 gallons of hydraulic oil out of the tank and into new clean hydraulic oil buckets for reuse and to prevent loses while we removed and completely overhauled the pilot solenoid valve body. We found one broken O-ring, but all were hard. Each and every one was replaced with new and and the valve body has been reinstalled.

Today we are attempting to remove and overhaul the number 7 shuttle valve in the main valve body. The parts diagram shows only one O-ring, but it has a screen inside the valve body which I would like to inspect. Removing the shuttle valve cap was no major issue, but now we are having problems in determining how to get the valve body out without damaging it. All that we have tried does not work. Does anyone know how to get the valve body out without damaging it? ANY and ALL suggestions would be appreciated.

 

[Knivens894]

After further inspection, we found that the valve is threaded on the inside to allow insertion of a screw for removal. Full of hydraulic fluid, it was not easy to see. Careful on removal, once it broke free it went flying. Inspection of the valve body internal screen showed it was nearly blocked with fine particles of what appeared to be o-ring material. Would that cause problems with the DP sensor signal or cause a by-pass contributing to the overheating problem? We are now reinstalling the cleaned and resealed number 7 shuttle valve, then onto pilot pressure adjustments. I will post the outcome of this work.

 

[joeblow]

You may have found the problem.#7 shuttle valve sees highest work port pressure which is called load sense .That oil works on the DP sensor which tells the pumps to stroke or de stroke.It also works on the top of the unloader valve which dumps pressure relief oil back to tank.Since you have all the oil out of the tank it would be a good idea to pull the unloading valve spool and make sure it moves freely and the spring is in good shape.I think you are making some progress.
The E series was Hitachi first stab at computerization and were a steep learning curve for us old school mechanics. They went back to the dash 1 system in the dash 5 with a little more finess.One thing you have to say about the Japanese is that they learn from their mistakes.North Americans not so much.

 

[Knivens894]

Gentlemen; We completed the overhaul of the complete solenoid valve system. I increased the shims 0.10 attempting to achieve Joe's recommendation for 100 PSI on the pressure regulator. Only got an 80 PSI increase. The flow control valve after overhaul was erratic from 200 to 600 PSI, so I replaced it with new from JD. Now it is in the manual's range. We ran the machine for about an hour and still had the overheating problem with the hydraulic's. Using the heat gun, I looked for the source of the heat and found the arm control valve was hottest at 175 F. My question now is should I replace the relief valve for that function, overhaul the control valve for that function, both, or do them all? Scanning the hydraulic oil cooler, I had 134 F on the input, and 132 F on the output tubes. The auxiliary valve and the boom valves were about 7 degrees cooler, so I contributed that to heat bleed over. It appears the arm control valve is the source of the heat, so how should I address it? All advice will be sincerely appreciated.

 

[joeblow]

Ok ,I have a few questions.Did the pressure come up and the speed return? Did you pull the unloader valve? Is the machine functional now except for the heat?Does the arm drift or hesitate when you pull it in?What is the temp at the cylinder?Have you pulled the return filter and looked for contamination?
The 490E and the 790E have the same system and are prone to weird problems if you have any contamination.Since you pulled this machine out of the swamp you may have bent the arm cylinder (seen it happen).You can pull the shuttle valve for the arm the same way you pulled # 7 shuttle valve.Since you did find contamination in #7 chances are you will find it in the arm shuttle as well.If you have had any contamination producing event ( cylinder piling up ,propel or swing motor producing metal etc..)You can chase those little gremlins forever.I don't mean to dishearten you but for every problem there is a cause and you have to look back to where this problem started.

 

[Knivens894]

Joe, Yes the performance of the machine has returned. The first thing we did was remove and inspect the hydraulic filters, as well as the tank. No issue was found there. The problem now is the heat. Today we ran it some more (dug up a stump), and searched all over for the source of the heat again. We found that the flow control valve behind the cab is the heat source. It is returning the hot fluid to the solenoid valve body, heating it. The cylinders are cool, but the flow control valve body will burn you, particularly on the forward side. We are now removing hydraulic fluid again so we can remove that valve body and overhaul it. The infra red heat gun has been a valuable resource. It will be next week before we get'r done, but hopefully and prayerfully, this should finally solve the over heating issue. Today we should get the flow control valve removed, disassembled, inspected and get the parts ordered. I do sincerely appreciate your advice and assistance to date. I will advise of the success (or failure) of this effort.

 

[Knivens894]

Today we removed the flow control valve, disassembled, inspected and cleaned it. No issues were found there. It was reassembled and returned to service. Tomorrow I will remove and disassemble the left pilot control valve. That is where the hottest line was coming from. It is delivering hot hydraulic oil to the flow control valve. I will advise on the results. Continuing with the hydraulic over heating is not an option.

 

[Knivens894]

Yesterday I removed, disassembled, and inspected the left pilot control. I could not find any diagrams of the assembly or its internal parts listings. JD wanted $1,750 for a re-manufactured unit. The internals of the unit are fairly simple with a standard o-ring sealing in each control valve (replaced from my stock), and held in by the top plate. Unscrewing the control handle releases the plate Each valve is simply a piston with smaller internal end inserted slide valves actuated by a spring. The pistons are manufactured with one small (about 0.010 ) passages drilled through one side of each piston above the internal pin. Inspection revealed that three of the four piston's vent holes were blocked with black looking debris. I used a fine wire and acetone to reopen the vent passages and cleaned them and the housing thoroughly, then reassembled the unit. Each of the valves have a wiper seal on the exterior side of the operating plunger. Since none of mine were leaking, they were returned to service. Does anyone know if the blockage of those vent holes would cause an over pressure situation leading to heat generation?

 

[joeblow]

I don't think your heating problem is coming from the pilot control valve .If its not leaking leave it alone(they can be a bit of a bear if you have never done one before )If you do take it apart make sure all the plungers go back in the same holes and the little metering pistons go in the right way (small end up)
From the temps you are getting at the inlet and outlet of the hydraulic oil I would guess it was plugged(low air flow) There is also the cooler bypass valve that sticks sometimes but your main heating problem is not coming from the pilot circuit .I would say there is something in the main control valve heating the oil>

 

[joeblow]

Just read your last post while I was typing mine.Those little vent holes control your ability to meter a function as do the internal pins.The pilot system is open centre meaning that all the oil being pumped by the pilot pump has to flow back to tank.Have you checked the pilot filter? Is the machine a little jerky to operate?Hard to say where black looking debris is coming from but the pilot side is completely separate from high pressure side .

 

[Knivens894]

Joe; Again thanks for your reply. Yes the pilot filter has been checked with no issue there. I did not even know there was flow control valves in the oil cooler piping, but the low temperature differential across the oil cooler does seriously bring those valves and the cooler's operation into question. We have before externally pressure washed the oil cooler coil itself and it appears to be clear. Because of the heat, I have had the radiator boiled out and rodded. That made no difference either. I removed the engine thermostat and ran the machine with it out. Again no change in operating temperature. I will definitely get into that hydraulic flow control tomorrow. I see two hydraulic control valves in the system, one from the main valve control body at the tank and another in the cooler piping. What is the purpose of those valves?

The left pilot control valve has been out before (apparently by the prior owner), as indicated by markings on all the ports. I slowly went through it making certain everything went back as it came out. The operator reported he was getting feed back through that control. The hottest areas we could find with the heat gun were at the regulator valve body feeding back from the left pilot control, that is why it was investigated. We have not found metal anywhere in the system, just very small bits of what appears to be o-ring material. It could have been burned bits filling the pilot piston vents, but it was hard stuff. I intend to chase this rabbit until it is found!

 

[brianbulldozer]

In your first post you mention that you overhauled the main system relief valve. What did this include? The reason I ask is that years and years ago I had a Deere 490 excavator (no letter suffix, just straight 490, no computer, no pilot hydraulics) that developed a problem where in hard digging the functions would slow way down coming out of the hole and swinging, but release the controls for an instant and it would return to normal until the next cycle. And when it was doing this the hydraulic temperature went crazy. Dealer thought it needed a new pump, but it turned out to be a/the main relief valve. I think it was pilot operated relief, but can't remember as it was a long time ago. Anyway, there was a small cone shaped poppet that had a very slight annular groove worn into it by the seat. Slight, like visible but barely perceptible to a fingernail. I polished it out by chucking it in an air drill and dressing with a diamond file. Problem solved. I think what was happening was in a hard dig the relief valve would open and then not seat completely until the pressure dropped enough, which would happen each cycle when the bucket was dumping.

I don't know if this has any relevance to your problem, but thought I would mention it as it kind of sounds like you have oil bypassing somewhere.

 

[joeblow]

There are two bypass valves in the return section.One is used to create a back pressure to prevent cavitation at the swing motor.The other works when the oil is cold or the cooler plugs up and opens a straight return to tank,kind of like a thermostat in the engine (which you should never run without)The optimum temp for the hydraulic oil is 120 degrees F plus or minus 10 degrees. This depends on a lot of factors.Oil viscosity is a big one and should not be overlooked.Ambient temp is another one.In the Southern US where the temp stays in the higher range than it does up in Canada ( it sometimes gets too hot up here and igloos melt and homeless eskimos become a problem)sorry bad joke. ,A higher viscosity(thicker) oil would be recommended.
If your speed and pressure came back after you cleaned up shuttle valve#7 than you were probably heating your oil through the unloader valve. If it stays in the 125 to 130 F range then you should be alright. Deere recommended hydraulic oil be changed every 2000 hrs and if running a high heat producing attachment like a hammer then change it every 1000 hrs.When the oil becomes oxidized with heat and age it creates a whole new set of problems.Waxing is one of them that makes all your cylinders leak and all your valves get sticky. I know that you have already spent a lot of money on this machine but changing out the hydraulic oil will benefit you in the long run. A semi synthetic oil has a lot of advantages as it does not oxidize as readily as a straight mineral oil.And don't chase that rabbit down the hole ,thats how Alice got in all that trouble.