The wheels turn, but no other part of the hydraulic system is working. This happened once before a few years ago, shortly after we bought it. On that occasion a mechanic came from out of state and filled the back half of the main hydraulic pump, as shown in the photo, and then bled air from the lines using a valve we can't find. We have been unable to get hold of the same mechanic and have found no other who knows about these systems. In the manual, it shows these valves. None of them seems to be the one needed but nothing else has been located. My husband recalls there was something in front of the cabin, but can't find anything. Is there another valve for those lines somewhere? Is there a particular way of working it to bleed the air? The guys working on it are used to valves you pump until diesel is coming out, but they aren't familiar with hydraulic systems. I've been drafted to ask here because I speak English and they only speak Spanish. Any help appreciated.
Hola! Your english is excellent, but the hydraulic logic has been "lost in translation". The above doesn't make any sense to me on this system. There is nothing that should need to be bled or filled. If that is what the last mechanic told you then he may have gotten lucky and the problem resolved itself with him accidentally being there when it happened? I assume you mean the steering and brakes work, but no other hydraulic functions? Do you know how the lift arm lock works? that could be the valve in the cabin. That hydraulic pump needs charge pressure to operate, the charge oil pressure comes from the transmission. If you have pressure gauges, check the charge pressure, and the system pressure. I assume you have the service manual that page came from. That explains everything way better than I can, but I can point you where to look.
Thanks for replying. I passed along what you said. The main pump was sent away and completely rebuilt, because a problem was intermittently happening - the steering and all the hydraulics except the brakes would seize up, all the machine would do is go forwards and reverse. They handled it for some months by shutting down the machine for a while when it happened, after which it worked fine again for a bit. But finally it got too bad and he sent the pump to be rebuilt. Since they got the pump back, nobody has been able to reinstall it so that the machine works. My husband always suspected that the problem before was a sticking valve, but now he can't get anything to work. Because the pump was sent away and then reinstalled, he wonders if there might be air in the lines. The time this happened before we had just bought it, and it is quite likely the mechanic knew that the pump had been taken out and worked on before the grader was sold to us - the dealer sent him to us. My husband says during that repair the mechanic opened a t-shaped joint on a line between the pump and the oil cooler radiator. He added fluid to the system by pouring it in that line. After they had done that there was no change, so they did something with a valve - my husband doesn't remember where, just that they did something with a valve and then it worked. Here is a photo taken when the pump was removed. The line they have used to fill it with fluid is the one at the front in the photo, with the yellow tube going right and the blue one going down.
I'm 99% sure that pump is supplied pressurized oil from the transmission. Find the section in the service manual about "charge pressure" or "hydraulic pump charge pressure" and measure that. Maybe the valve they fixed was on the side of the transmission? Find the "clutch pressure control valve" or "transmission pressure control valve" in the service manual and see if that looks familiar. That valve is where the hydraulic oil comes from. before it goes to the hydraulic pump. If the steering doesn't work, then ignore the lift arm lock. There are several Deere professionals here, but not as many as Case or Cat, and they might not remember this grader either. I'm just an amateur, sorry, but I do recognize that pump, it's not complicated, just different than most others.
Yep, check charge pressure, and on the outlet side, Pressure control valve.
Okay, we were looking in the wrong section of the service manual. Once I searched for 'charge pressure', I realized there was a whole big part about it in a section called System Testing that I hadn't realized is 300 pages long, with 60 pages just on the hydraulic system. We'll go over that now and print out some sections so he can try that stuff tomorrow. This should be a big help. Thanks for the pointers.