310john deere backhoe slow hydraulics

I had posted awhile back about the hydraulics had just stopped working one day lost breaks lift and everything, and then starting working again. But were slow and weak checked pressure going to the main hydraulic pump showing around 110 pounds of pressure could not increase it with shims. So I put and new primary pump on put new seals in and new hoses and changed all the filters as well. Now it has around 125 pounds of pressure going to the main hydraulic pump. When it first starts hydraulics are pretty good but within minutes it starts moving slow and the hydraulic oil fills with what looks like millions of air bubbles. And the primary pump was checked out by a hydraulic shop it was fine. Thanks in advance for any advice
 
For what it's worth, air bubbles are caused by the pump starving for oil.. did you check the filter in the transmission housing, item #16 in the attached diagram.
https://partscatalog.deere.com/jdrc/sidebyside/equipment/82996/referrer/navigation/pgId/170966
 
Any information is helpful new screen put in the old one was fine, but since it was down I put a new one in, all suction hoses brand new and double clamped, now hopefully some will have a ideal why the pump is doing it. Thank you for your reply.
 
Aerated oil is due to either a suction oil leak or a high pressure oil leak [ like an o-ring or valve seat being held partially open.] Does your 310 have a destroking solenoid on the hydraulic pump front cover ? If so, check for blown o-ring or destroking solenoid not operating correctly. If you lost brakes, that tells me that return oil isn't refilling your brake valve [master cylinder]. 310, 310-A, 310-B ?
 
Did you set standby pressure on the hydraulic pump after installation ? 2350 would suffice. then check pressure when raising the loader to see where pressure control valve is set or stuck. Due to serial number breaks, I don't have that info due to me selling all my Tech Manuals. We do that when we get old and feeble..
 
Standby pressure is set at 2400, no destroke solenoid no need for one doesn't get that cold here. priorty valve has been pulled off and cleaned along with the oil relief valve. No lines getting hot or making noise. Brakes work good hydraulics work good till it fills the oil with bubbles then the goes down to nothing. machine is a straight 310 no letters.
 
Transmission pump should feed hydraulic pump via reservoir above hydraulic pump on front of tractor. Assume this is full? The 500b also has a booster pump that is run with the lever where the pto on a powershift 3020 would be. I dont know much about it and actually dont use it because Im afraid to break it but the uncle he flips it up and it is a whole different machine...I assume nothing got disconnected in this linkage if yours has it
 
When you run it , will the trans.oil dipstick show bubbles ? If so there may be a internal reverser oil leak. What does your hydraulic pressure show when you raise the loader without a load in bucket. Half throttle, full stroke not partial flow with the lever. stop it before it tops out the cylinders on the way up. Read what it says on the gauge. This will tell if the priority valve is set right. Shim adjustable. It's read with serial number of machine in tech manual. Was the orifice free inside the filter relief valve ?. Those shims get hammered and expanded inside the valve spool. That could cause aeration of oil. Sometimes that orifice will be held off it's seat just a titch, enough to keep the orifice from seating inside the valve spool. It doesn't take but a microscopic piece of crap to hold the orifice off the seat. All these could cause aeration.
 
yes the dipstick shows air bubbles its so bad it looks white there is just millions of them. The pressure control valve has been checked, along with the transmission relief valve only thing not checked yet is the filter relief valve on the horizontal filter and I don't think that has anything to do with it but I'm going to check it soon. Just setting and not moving the hydraulics no air bubbles the minute you use the hydraulics air bubbles start. Hard to check moving pressures the way the air bubbles start it throws off readings because of the air. My question to you Roy and it might be a stupid one since the primary pump bolts directly on with no gasket could I have a leak there. Because like if posted earlier the first minute before the bubbles start you have great hydraulics fast and strong. And again thanks everybody that has posted replies because there is some really smart people on this forum especially on the older equipment.
 
I have always used a THIN layer of Anerobic plastic gasket on these surfaces where the pump bolts. Service manual doesn't say this, just additional insurance. Did you have the plate that is inside the reverser control valve loose or off? If so , maybe one or more of the tubes have pulled out of the o-rings in the plate. Just trying to find the answer for you. It's tough to diagnose problems without being there to actually see what's going on. When you checked reverser pressures, did you do the idle to near wide open throttle pressure test ? This eliminates the vertical filter relief valve bypassing oil back to sump.
 
when the machine was put back together new packing and seals were placed, even replaced o rings on the reverser housing, could one be bad its possible, checking pressure at the reverser housing test port show same pressure idling or wide open no change. Five mechanics have looked at it and three of them worked for john Deere and two of them heavy equipment mechanics and they have all not been able to fix it. But one of them said its some little thing that is so simple and stupid we are overlooking it.
 
You're right. It's probably something really stupid simple. How about that pesky pin halfway down the clutch shaft on the front of the reverser housing. I've seen that pin wear and not allow the reverser to come to full pressure at times. This pin is midway from the pedal linkage to the reverser control valve. Now I'm really grasping at straws..
 
Now if feel stupid it was such a easy fix. Back in the 1970 john Deere let a few backhoes out of the plant that the filters would suck air if not extreme care putting the filter back on or use o rings instead of john Deere gaskets. This according to the engineer that used to work for them apparently it was a machining error, who I just happen to meet in a hospital waiting room. He told me to take the filters off and replace the john Deere gaskets with o ring that would fit tight against the lip of the filter housing, that should fix the air bubble problem. Then he said to pull the filter relief valve off and check for a piece of garbage holding it slightly open, and sure enough. The machine hydraulics are working great, only down side is he said that the pressure control valve orifice would probably have to changed due to the battering it took, it would try and hang open at times. And a big thank you to all the people that posted on this problem you are what makes the forums great.
 

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