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Thread: JD 500C Hydraulics Quit after use

  1. #1
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    JD 500C Hydraulics Quit after use

    JD 500C Backhoe/Loader, Late Model, 4 cyl. Diesel. Engine runs just fine. Forward/Reverse control, OK. I rebuilt the Main Pump the end of 9/2008. I cleaned or changed everything in the Hydraulic system, new filters & screens. New radiator, cleaned the Oil Cooler. The hydraulic system slowly came to life (couple of minutes) after the rebuild. After a couple of hours of real use, the steering, brakes, and all hydraulic control, ceases to function. I drained the hyd. fluid. I checked the main filter screen for obstructions. It was clean. I refilled the system. The system then worked for about 8 hours over the next couple of days. It has now ceased to operate again. Thinking it might be an adjustment, I have tried to adjust the Stroke Control Valve handle. Nothing happens. I disassembled the Stroke Control Valve from the bottom on the Pump. I found a grease blob on the Valve, I cleaned it & reinstalled it. Still no Hydraulic movement in the Buckets, Brakes or Steering. What am I missing? What is my next step, to get the hydraulics back. I have both the JD Technical Manual & Parts Listing for this unit. No help in either one so far.
    Thanks, Lynn

  2. #2
    Senior Member Phil's Avatar
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    I'm not familiar with the JD's but I remember the older units had a charge pump to supply the main hydraulic pump. It had to supply a certain pressure, around 125-150psi minimum as I recall. If sounds like you were having problems with the machine before you rebuilt the pump. Did you have someone rebuild it? Might be a supply problem, just guessing. Phil

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    Senior Member bill onthehill's Avatar
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    http://www.heavyequipmentforums.com/...ad.php?t=10191 Try this thread. Similar issues. Never heard of a 500 backhoe from JD. A lot of the older ones used a charge pump to transfer fluid from the common sump/transmission to main hydraulic pump.
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    Bill, thanks for the heads up on the 410 post problem. My problem may be simular.

    Phil, My main pump was 110% woreout. The pistons and cam had huge radius's worn into them. I believe the machine was run for several hours with little or no oil, due to broken & leaking hoses. I rebuilt my own pump, and it worked fine after charging the system, several times.

    The 500 is the first version of the 500 series, builds started in '76, mine is a little later '79.

    FYI, all of the Hydraulic Fluid is in the Differential/Trans housing, approx. 19 gals. The units have a manual clutch transmission disengagement(dry), for engine starting. Newer units have an electric selonoid. The fluid is pumped from the reservoir via the internal transmission pump (might be referred to as a charge pump), thru valves regulated to 175psi. to the main pump. Once in the main pump, the fluid is dispersed to the steering/ brakes/loader/hoe/stabilizer system. The first items to fail will be the loader/hoe/stabilizers/pto. When the system fails, you should still have steering & brakes, due to their lower operating pressure, and being backed up by an accumulator. Forward/Reverse shifting are clutch free(refered to as a wet clutch system). Some 500's have complete gear speed shifting clutch free. The brakes are also in the hydraulic oil bath, again wet, they will usually chatter due to the anti-friction hydraulic oil.

    I am now draining my system in search of some foreign contamination in the hydraulic fluid(maybe an old caked build up). In my system their is a filter screen, in the bottom of the differential, at the pickup for the transmission pump. I am starting at the beginning of the hydraulic system, and testing after each check to see if I have main pump pressure. I will disassemble and clean pressure/relief valves as I go.

    Does anyone know how to adjust or set the Stroke Control Valve????
    Thanks, everyone

  5. #5
    Senior Member Phil's Avatar
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    I'm guessing the stroke control valve you mention controls the swash plate angle?http://en.wikipedia.org/wiki/Axial_piston_pump

    Is your tech manual an actual service manual? Usually they are pretty detailed.

    Checking out the charge pump system sounds like a good idea.

    What controls system pressure? Phil
    Last edited by Phil; 05-12-2009 at 10:15 PM. Reason: Added text

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    Phil,
    Thanks for the article information. It describes the stroke control function very well. It also made me think that the control is not the "T" handle on the top of the pump, but a screw w/locking nut on the bottom side of the pump. It is a heavy loaded adjustable spring valve, which I had out and cleaned last weekend. I still do not have an idea of how to make an adjustment to this vlave. It must be a system pressure setting.
    I wasn't aware that there is a service manual, what I have is a tech manual. Looks like I need to research this.
    I did drain the system, no chunks in fluid. I pulled the filter screen, it was very clean. I pulled the Hydraulic filter and the relief valve. Disassembled the relief valve, and found one of the spring ends broken off. It was only one coil, which could attribute to some loss of pressure, but not all of it. Today I will order parts, so I will be at a stand still until they arrive. I will follow up later. Thanks again.

  7. #7
    Senior Member Phil's Avatar
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    I found an old 'tech' manual or service manual for a JD 440 skidder, mid '70's era. It shows a piston pump out front under the rad. To check standby pressure install a 3000psi gauge in the pump pressure tap(3/8"-24UNF). Start engine and run at 2500rpm. Adjust stroke control adjusting screw to indicate 2300-2400psi. It shows this screw on the bottom front cover of the pump. The little valve with the T handle, used to dump pump pressure for cold weather starting, is shown on the top side of the pump cover.

    The relief valve, located in the pressure control valve, is set to 2700 psi.

    Whatever your relief valve setting is, as shown in specifications, I'm guessing the pump should be set about 300psi below it.

    I'm not an expert on hydraulics but as I recall a simple compensated pump is adjusted to give just enough angle on the plate, to maintain system working pressure, hence little heat produced, yet fast response. The only flow is through internal leakage in the pump and valves downstream. As soon as there is demand and pressure starts to drop, the stroke control valve changes the angle and pump flow increases. Phil
    Last edited by Phil; 05-17-2009 at 10:37 PM. Reason: added text

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    Phil,
    Great information. I guess my hunch was right as the the actual valve adjustment location.
    I know all of my other test are at 1900 rpm(diesel motor), so that is the speed I will test at. I do recall reading on the web the the pressure should be 2325 psi, and my book shows a test port on the pump which I can't get to without disassembling the front of the tractor. I think I might have found another port further down stream which might work. I don't know what the relief valve is set at yet, but I will find out soon.
    I have now worked my way up next to the main pump, so next weekend I should get to this test. Tomorrow night I will be pulling the Oil Cooler Relief Valve, which dumps into the main pump. I have now replaced a total of 5 valve springs, of which most were either broken on the ends, or shorter than the new ones.
    Now to add insult to the injury, I have an engine oil level three inches higher on the dip stick, than when I started my testing. It appears I have a leak in the Fuel Injection Pump, which is putting Fuel Oil into the crankcase. So I have to address this issue, before running up the engine again.
    Thanks again for the Stroke Control information.

  9. #9
    Senior Member Phil's Avatar
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    Do you have the Roosa Master pump shown below? I had to replace the seals on the pump main shaft on my 480C once. I think they face back to back(#3), Case part #R14711. I was able to slide the pump off the shaft, change the seals and carefully slide the pump back on. Phil
    Attached Images Attached Images  

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    Phil,
    My pump is probably one version older, but similar internally, it sets in vertically instead of horizontal. The one you pictured I believe is a DB pump, mine is a JDB431AL2401.Yes, I believe the back to back seals are the problem. All of the engine functions are fine. Its only that the engine manufactures its own crankcase oil. Maybe I could bottle it forsale. Or worse yet, I might spin a poorly lubricated bearing. I would post a picture of mine, but I don't know how to retrieve a copy of it. Thanks

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    1st time poster!
    Ican't say my problems are as bad...yet. When I first got my 410, I was told it needed a hydraulic pump. Well, I did some research with the manual, and found the pre-screen on the return side before the gear type trans pump which feeds the hyd pump. I took that out and it was blocked a little. Once I fired it back up, I didn't even have to raise the idle and I could see the difference and no chattering. A few weeks ago, I got the backhoe stuck in some mud only to realize my hydraulics are working poorly again. This time though, no chattering, just very week. I still have forward/reverse/steering and front/rear bucket operation, but very weak. Hence the reason I got a backhoe STUCK! I should have no problem pulling with the buckets and I should really be able to put this thing up in the air like a golden arch, but that's not the case
    I've checked the screen again, installed new fluid, checked filters, and removed/checked valve above the trans filter...all fine.
    Anyone have any ideas? I just got a 3000 psi gauge to do some pressure testing at pump, but what other items may cause this sort of problem. I'm hoping it's just a valve somewhere, but if it's the hyd pump I'll get one. Just need this asap since I was just about to start building the septic system on my new property Heck, if anyone lives near the New Ringgold, PA area that works on equipt and could cut me a good deal on diag, that would be great. Being a GM tech for 10years helps, but a tractor is a different beast that will take me longer to diag.
    Please let me know what you guys think it could be. Maybe with my concern we will figure out some of the other peoples as well.

  12. #12
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    on my 310a there are two ports on side of main hydraulic pump on right hand side top port is main pump pressure bottom port is pressure from charge pump your 500 should be the same. check these two when the hydraulics get hot and stop working you will need 0 to 3000 gauge for top port and 0 to 500 for bottom port. this would be a good starting point.

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    Thanks for the heads up on the pump ports. I will soon be getting to the pump, after I do pressure test in front of it.
    So far, I have pressure at the transmission & clutch. 0 PSI going to the main pump. Right now, I am disassembling the Regulating Valve Assembly, looking for broken, missing, or clogged parts. I will post, when I find a problem.

  14. #14
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    Finally,
    After a long summer, I finally returned to my "No Pump Pressure" problem. After removing/diassembling the Regulating valve, I discovered the following. The Pressur Control Valve had a worn out (somewhat compressed)spring, the Regulating valve was stuck open, an the regulating spring was missing. There was only one of the three springs in the pressure switch.
    Now that I have replaced all of the missing and defective springs, life is good. Everything is working again, as it should. This summer, I am going to try to repair the Hydrulic leaks at most of the joy sticks. Thanks to everyone who has given me help on this project.
    Lynn

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