JD310A Hydraulic Issue

CTaylor

New User
Need some advice on a 1977 JD 310A. Machine is one owner with 7500 hours. Recently
hydraulics stopped working. Machine had sump screen cleaned and filters/hydraulic
oil changed about 30 hours before hydraulics stopped. Pretty sure charge pump in
transmission is good because machine still moves forward and reverse in all 8 gears
with no issue and with same power as always. Loader, hoe, and steering are dead.
Stabilizers will move but very, very slowly and with no power.

Had already planned to change main pump because machine was getting weak and had one
on hand with a new destroke solenoid so we put them on, no change. Before new pump
was changed system was flushed and all possible old fluid removed. Used a magnet to
"sweep" the sump then filtered old oil and checked pump for metal. Found a less than
enough to fill a 1/8 teaspoon measuring spoon and most of that was in the pump on a
magnetic plug. Expected much more to be in a 43 year old machine.

So far, in addition to changing main pump, we have removed, cleaned, and put new
seals & orings on the pressure control valve on the side of transmission and the
filter relief valve on hydraulic system (the one that the cartridge is horizontal).
Planning to check, clean and reassemble the larger more complicated filter releif on
the other filter next. Have also ordered a set of test gages but am almost positive
we have a bypass or relief stuck open on the intake side of the main hydraulic
system. System has flow but does not enough to build pressure.

Any advice would be appreciated.
 
It would be my guess like you said that the pressure relief valve is letting the oil bypass.
AJ
 
Put a gauge in the reverser control valve plug and check pressures.. It should read 125 + lbs. oil pressure.. With the machine running , 8 speed gear shifters both in neutral , with a gauge with extension hose ty-wrapped to the front ROPS , Watch the gauge from idle to wide open throttle with reverser in every gear showing pressure.. If there is a substantial pressure loss-gain thru rpm range , I'd say the filter relief valve is partially stuck open with a very small particle holding the valve open. This is the valve that you can see from where the vertical filter was removed.. It doesn't take much to hold the valve open. I'm amazed what I find sometimes in the valve.. One job, I took the valve apart and had to look twice to see the minute particle that was the culprit. I put the particle on a fresh blue towel and set it aside for the customer to see. He was doubting my diagnosis until he tried the machine.
 
Thanks for the advice. How big of a pain is that vale to service? Looks pretty simple but sometimes its the simple things that cause the most trouble.
 
Roy, would that test procedure work the same on a 410 straight that was moving fine one minute and stopped moving the next? No bang or anything, won't even attempt to move at all. Sorry to hijack your thread...
 
the hardest part of the filter relief valve is getting it out of the bore it's in. with the side plug out, gently pry the valve from below, and try not to disturb the poppet valve inside.. It will either be seated all the way or held partially open..
 
Yes, That valve routes pressure oil to the hydraulic pump. Any loss of pressure will cause the front pump to
cavitate
 
Transmission filter relief checked and cleared. Got it out out, cleaned it and reinstalled, no change. The valve had some trash in it but was not stuck. Any other suggestions would be appreciated? Pressure guage will be here this week and I will have test pressures.

We did find one other symptom though. The loader is locked up. It will not go up or down even with external force. Tried to lift it with another hoe so we could move the machine. Held control lever to lift position but loader would not move. Lifted entire front end of machine off the ground no matter position of loader control. The hoe and stabilizers can be lifted like this.

Tip on getting the valve out after plug is removed. Take a long hook pick and carefully insert in the sleeve. You will be able to feel when you are beside the roll pin that is in there. Push in against the spring and rotate the pick and it will get caught on the roll pin. You can then hold the pick with a long set of pliers and lightly tap with a hammer. It will pop loose then you can pull it out by hand.
 
Loader's locked up ? Never heard of this.. Maybe try to remove the hoses from the lift cylinders and try lifting the loader again.. Watch out for oil spray if it moves... If it does move , maybe the valve spool isn't centering properly and trapping the oil. If the filter relief valve isn't the problem , put a gauge into the reverser ports to check if it's making oil pressure.. Test for leakage again with a gauge in the reverser ports and run the throttle up and down and watch for a major fluxuation on the gauge.. With gearshift transmission on neutral-neutral with wheels blocked so it doesn't roll.
 
Your backhoe may have stripped the clutch disc or input shaft splines from wear and tear.. If so , get in touch.. I have a real good short cut for that input shaft replacement..
 

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