John Deere 500c hydraulics

[chrisdvorak]

I have a John Deere 500c backhoe that suddenly lost hyd pressure while digging, no noises or leaks everything just got very slow and sluggish, steering, trans, and brakes still work ok. I parked the machine to change hyd filters and when i drained the rear end found some metal that I couldn't identify. Could be the problem or completely unrelated. No foam in hyd fluid like if pump was cavitating. Could a bad de stroke valve on the pump cause this? Any input would be appreciated

- thanks

 

[Tx Jim]

Pieces resembling wire are broken spring. Check frt hyd pump drive coupler to be sure pump shaft turns when engine is running. Yes faulty stroke control valve could be the problem.

 

[chrisdvorak]

thanks, I will check the pump drive coupler. whats the best way to test the stroke control valve? I guess there is no way to tell where that spring came from but it sure would be nice to know...

 

[Tx Jim]

You could install a gauge and check pressure which I think should 2250 psi or possibly a little more.

 

[chrisdvorak]

Thats what i was thinking also but wouldn't that just test the pump? any way to isolate the destroke valve itself? or is it just something that you replace?

 

[Tx Jim]

Please clarify are you desiring to isolate the stroke control valve or destroking screw? What are you attempting to accomplish when you state "isolate"?

 

[chrisdvorak]

I am trying to test the electronic destroke solonoid on top of the pump, but was not sure on how to test a bad or stuck destroke valve

 

[chrisdvorak]

the coupler from the engine to the front pump checks out fine. also had machine running for about 20 min and could not isolate any hot spots that would indicate internal leakage. I should add that when you use a hydraulic function there is no change in engine sound, (usually bogs a little at idle) which makes me think that no fluid or very little is getting to the valve body. so my next question, were is the stroke control valve located on the pump? and anything to watch out for when removing the valve for cleaning? I don't want to mess up the pumps pressure settings.
-thanks

 

[chrisdvorak]

I cleaned the stroke control valve, there was some junk in it but did not solve the problem I have heard there is a priority valve somewhere on the trans that when clogged will cause my issue, can anyone shed any light on where that valve is located?
- thanks

 

[Tx Jim]

Priority valve on RH side of tran is designed to give steering priority oil but has no affect on whether frt hyd pumps oil or not. Maybe they were referring to the hyd filter relief valve.

 

[chrisdvorak]

that may be it, were is the hyd filter relief valve located?

 

[Tx Jim]

Correction: I was thinking about smaller tractor when I stated RH side. Hyf filter relief valve is on LH side on a 500 series. I don't remember which valve is filter relief but I think it's either key 14 or 25.

 

[chrisdvorak]

I've attached a pic of the valve housing the plug closest to the rear of the machine is plastic and has an electrical connector on it. I did not see that in the parts diagram, would that be the relief valve?

 

[Tx Jim]

As I previously stated I don't which valve is the valve in question. You need to acquire a JD service manual for your tractor.

 

[chrisdvorak]

here's an update of whats been done so far
-filters changed/suction screen cleaned
-all valves inspected in trans housing including filter relief (clean)
-control valve on pump inspected (found bits of what I assumed was cyl chrome in it, cleaned but did not improve problem)
-replaced screen in front pump (little dirty but not too bad)
-replaced O-rings on electronic destroke valve
today I had the machine running and while I manually destroked the pump (T screw on top) and engaged it again I could feel/hear the pump kick in for a second but it would not stay engaged.
the loader barely moves at all now, the backhoe functions but very slow and weak.
I don't have gauges to check pressures but I have a hard time believing that the pump would go bad in a matter of seconds with no warning?
I am thinking i'll pull the control side of the pump apart and inspect it. anything to watch out for when splitting it?

 

[chrisdvorak]

well ended up pulling off the control side of the pump and found a hole plugged with chrome chips which was the problem.

 

[Tx Jim]

Thanks for update. I think you need to attempt to determine where chrome chips are originating from.

 

[chrisdvorak]

the machine had been sitting for a few years and the dipper cylinder in particular had some rust spots and I think that's were the flakes are coming from. I have since sanded/polished the spots down, I don't know how the flakes are getting to the pump though? I would think they would wind up in the filters or screen first.

 

[chrisdvorak]

well all was good for awhile now same problem again. pulled control side off pump and small holes were filled with metal pieces again BUT there is no metal in filters or screen in pump? would this mean that the metal was coming from the pump itself? also I checked pump pressures at idle it goes right up to 2200 psi but when any function is activated it slowly drops to 1000 is this normal? charge pump is 85 psi standby and never dropped below 50.

 

[Tx Jim]

I think trans pump pressure should be in the 155 psi range. Frt pump should be 2250 psi and hold that pressure IE not drop to 1000 psi. I think it's possible metal flakes are originating from frt pump possibly the shaft brgs.