JD 410 Backhoe loosing pressure when warm

[ChrisB]

Been doing some fine tuning on my pressures for my JD 410 backhoe. Main pump is new and has about 200 hrs on it. Trans pump is unknown age but last time I checked it was pumping well over 4 gpm. I got the standby pressure up to 2500 psi when cold. Pressure relief valve was a mess. Seems like parts where missing in the washer / shim area. Nevertheless I machined a new piece / cleaned it all out and it now cuts in at 1700-1800psi when cold.

When cold and running at the pressures above, the machine is unbelievable in power. Almost like new, and no leaks. Work it hard for a while and the pressure drops. 30 minutes of hard use and the standby pressure is at 1500psi and of course the pressure relief is using all of that 1500psi.

Filters where just replaced, trans pump screen cleaned and I have a newer main pump with no screen in it. I did have water in the system at one point, and only completely drained it once. Since then about 15 gals have been added thanks to filters changes/ blown hose / etc. I also just completely cleaned out the oil cooler fins.

I will admit to using the cheapest hydro oil and I am sure some will jump on me for that but I cannot imagine that a "better" oil will make a huge difference. No foaming in the oil and it does look clean.

I am at a loss as to why the pressure is dropping when warm and would to welcome to any thoughts on the matter. ?????????

On a plus note, I almost have the machine "dope free" when cold. Lucas fuel additive and a new thermostat along with the good advice from a few in here have helped me. I assume this points to a dirty injector somewhere.

 

[Tim [GA]]

Is the forward/reverser getting weak when you are losing hydraulic power. Change to the correct oil because cheap oil causes for reverser repairs. Use an oil that meets JD specs.

 

[ChrisB]

Tim,
Thanks for the help. No, the forward / reverser is not getting weak with a loss of pressure. On another issue last year I went through and rebuilt / cleaned the forward / reverser, so I doubt the leak would be in there. Although I could be wrong.

 

[Roy Suomi]

Time to start eliminating things..Start with the destroking solenoid on the hydraulic pump..Deere has a plug that replaces the destroking solenoid..By installing this plug it eliminates the unloading feature of the pump..Makes 'er hard to start unless you wiggle the steering wheel while cranking....Put a gauge into the reverser control valve and read the pressures at low rpm's then at high rpm's..If there is a considerable fluxuation in pressures , the reverser filter relief valve is hung up..I would install a JIC cap onto the output fitting right at the hydraulic pump [ dead head the oil flow]This will eliminate the pump if it carries good oil pressure when hot..Next , eliminate the steering valve by putting a JIC plug into the steering valve hose , or JIC cap at the Tee fitting..If pressure goes up to normal , the steering valve is leaking internally..

 

[Ed pap]

Hello Cris,
I would think your problem is in the stroke control valve on the main pump. I can see a few hundred pounds difference with hot oil but not a 1000 psi. a leak some where in the machine would realy heat up the oil but you should always have standby pressure.
The stroke control valve is not too bad to fix I always take the body right off the pump you can lapp the popets and seats and replace all the rubber. it dosen't take much of a leak in the valve to destroke the pump.
Good luck Ed
abcrepairparts

 

[ChrisB]

Thanks all for a ton for the help.

I am thinking I will proceed in this order.

1. Dead head the pump and check pressure when warm.
a. If pressure drops then the check pump stroke valve.

2. Bypass steering and check pressures when warm.
a. If low then attack steering valve.

3. Bypass back end pressure (front end loader, backhoe, pressure control etc) using "T" at steering hose.

Step 3 raises the question of where to proceed if the problem points to the back end. I remember how to block off the backhoe ( a real pain to get to as I have the Wain-Roy clam shell bucket) but am not sure where to block off the front end loader or if it is possible??

Also is it possible to block off just after the pressure relief valve? That way it would rule out the pressure relief valve, filter relief valve ,etc. More or less if I could block it off there, had good pressure then it would point to the backhoe or the front end loader????

Roy,
Per your excellent guidance last year, I had checked pressures at the reverser control they were good. Nevertheless I did rebuild the reverser control as well as cleaned out the pressure release valve.


Now that I think about it I might just try Ed's idea and pull the destroke valve. Clean, lap and new rubber as it is the easiest to get to??? I am getting tired of being under this thing and dumping/ replacing oil all over the place.