1983 jd710b backhoe/loader. all the hydraulics move and work. they also speed up with engine speed. pump was making noise so took that off and had it rebuilt. ive checked the screen and put new fluid in tranny. put a new hydraulic filter on and check the rubber piece between crank and pump. everything is good. put new pump back in yesterday and the problem still is when i go to use the loader or backhoe or side posts, they will go up and down but when i go to actually use it like for it to lift machine up or work, it just gives out. it will lift itself right back up but will not allow to put any load on it and motor does not grunt. so i cant use the loader really and really cannot use the backhoe. is it a priority valve? i dont know what else to check? i have service manual.
forgot to add even if you hold the stick in the same direction like putting bucket down it wont lift the machine off the ground. u can keep doing it in the same direction and does nothing but if you use any other direction it will move. same for loader and backhoe controls??? i will do some more testing today
Sounds like you have a broken or contaminated check valve.
The pump in the transmission supplies the ext. pump. If it is weak, it may not be sending enough fluid to the front pump.
where would this check valve be? talked to my friend seems like relief valve spring but i guess that is the priority valve?
With this closed center system if the relief valve in the priority valve is leaking then it will be leaking all the time and heat up fast. Same with any of the other valves, if they're leaking they'll leak at standby pressure constantly and warm up. This is acting the same way it was acting before the pump rebuild, right? Does the engine lighten its load when you use tilt a bucket or swing the stick freely?
yes, lighten its load? the motor grunts right up till you try to do real work with it like curling backhoe bucket or lifting machine off ground then it runs as if you were doing nothing but i keep moving the stick in that position. its sound like the priority valve is sticking? i cant buy a new one so i guess im ripping it apart?
The priority valve has three functions, first it's a manifold that connects the oil lines to the different valves. Second it has a relief valve that drains to low pressure. Third it "prioritizes" everything else over the loader valve (shuts off only the loader valve below a certain pressure- to maintain brakes and steering). If the relief valve is leaking at too low a pressure then it will leak all the time at standby pressure (max pressure). The "priority" part of the whole valve assembly only affects the loader, not the hoe so that's easy to diagnose. If the hoses are hooked up and not leaking then it's serving it's purpose as a manifold. Does the motor sound the same running with no functions as when you are moving a function with no load? And then lightens when you hit resistance? It will sound like it's doing nothing when a cylinder is stopped because it's a closed center system, the pump sees the "standby" pressure and stops pumping so there's no load on the engine even though there's force on the cylinder. Are you sure the standby pressure was set right on the pump? Did the functions not have any power with the old pump also?
great explanation. no one could tell me what it does. motor sounds about the same with no function or function with no load. rpms lower a tad when you move something because of the flow but as soon as you hit resistance it just stops. im not sure standby was set right but i had a professional place that does these pumps rebuild it so it should have been done right. before we rebuilt the pump, the machine did the samne thing when hitting resistance, it just stopped but would work if you do anything other functions with the controls. pump was struggling before but seems strong now. i need to figure this out. can i do any certain tests or help you figure out my issue?
How long have you had this machine and has it had this weak hydraulics the whole time? Also, when you put the outriggers down and hold it, they will just stop? instead of slowing way down but lifting all the way eventually? If you can figure out how to do it safely, there should be ports on/near the hydraulic pump to test the pressure. One should be about 100psi "charge pressure" and the other should be about 2,500psi. The 100 psi is just as important as the higher pressure. The operation and test manual would be a good investment at this point. I have one for 610B but I think the 710B has an engine driven charge pump instead of transmission? (you could probably tell by looking where the hydraulic line going to the pump comes from)
The 710B does have a transmission charge pump. ( I have mine apart for rebuilding now) I have the service manual for the 710B in PDF form. Shoot me your email and I will send you a copy.
so we have done some testing with the help of kin-tec industries. this guy is great! also thank goldknight! i bought some gauges and we have tested the charge pressure of the pump is around 80psi. he said thats low and should be about 100-125psi. when i tested the high side of the pump, we got about 1500 ton start so i kept turning screw in pump till we have about 2300 standby pressure at idle. -if the transmission drives fine, is the charge pump still an issue? -how hard is it to get to charge pump? they make a rebuild kit? -since charge is low, i am going to check filter relief valve, maybe stuck open? what else could make charge pressure low?
on the left side of the transmission there is a pressure regulator. 3 springs and pistons are in there. I had to replace all of mine. ( not to expensive) By adding small washers or removing them you can adjust the pressure a bit. To rebuild the charge pump you have to remove the transmission. (and it heavy 800lb) No need to split the tractor on this model. Its the first part you can take off inside the bell housing. I believe the rebuild parts are close to 3000 dollars just for the pump. I got lucky mine was fine. And yep the tractor will move fine in lower gears at 80psi but may slip in higher gears on hills. Read through the manual in the transmission sections, There is a suction screen in the bottom of the unit that if plugged will limit the flow to the charge pump, Thurston
Just got mine back together and ran into no hyro functions. The loader and backhoe were dead. Turns out i bent the electric destroke valve on the front pump. You may want to pull yours and see if its functioning perfectly. If it is slightly bent it will let some fluid slip past and that would stop your buckets from moving.
i am finally got the pressure valve on the side of the tranny and have put in all new shims, seals, washers. all the springs seems to be ok. everything looks ok. will try tomorrow.
if there is anyone in the area, i would pay someone to diagnose or fix this issue?
Did you ever find out what was causing this issue? I have looked at 8 710d machines and all operate just like you describe. Did your machine always operate like this or did it progress to that point.