Hello everybody, I’m new here and I would appreciate any help that I can get. I recently bought a 1976 John Deere 410 D backhoe. When I bought it, I checked the hydraulic fluid level and the dipstick between your legs and the cab. It was about a foot above the line on the stick, but everything worked like you should. So I had thought it was the dipstick out of another tractor or something they had put in there. Anyhow, I had to replace the hydraulic coupler on the front of the engine were connects to the hydraulic pump. And after doing so I still don’t have hydraulics to the full machine. The back controls worked very slowly, same as the outriggers. I have no movement whatsoever in the loader controls being in the bucket tilt or dump or the loader arms going up or down. I have steering and I have brakes they work fine. I replaced the hydraulic filter and it was clean looking. Anyway, I was going to clean the transmission screen and in order to do so you have to drain the reservoir. I pulled the plug on the bottom of the case and drained off 15 gallons of oil. The book says the capacity is 10 gallons. I checked the dipstick and it is down where i oh Godt’s supposed to be at the line. I started it up and everything works fine other than the loader controls will not work at all and the backhoe controls are slow. I would greatly appreciate any help that I can get on this. If I had hair, I would pull it out. Thanks in advance!
Seems you let air in the system from your coupler replacement, and likely a separate loader valve problem.
When i say coupler I’m talking about the 2 piece clamp that connects the hydraulic pump to the harmonic balancer of the engine.
I had a 410C it was I believe a 1990 model. I'll guess the 410D wasn't built until after 1990. I feel you have a 410 if 1976. I had extensive trouble with a 410. There are many components uncommon to other heavy machines. 410 has a charge pump in the transmission supplies oil to the radial piston pump. Main pump is variable displacement. Instead of a crankshaft, it has a camshaft at center. Each revolution all 8 pistons are pushed outward. Spring force pushes them back to center. The center all piston bases are exposed to is pressurized. They won't return for refill with oil if pressure is too great. Nice system, makes for an unusually smooth operating hoe. There is a priority valve for steering. If pressure is low, it gives no oil to the loader. Backhoe wouldn't be in use while steering, so it isn't subject to the priority valve.
It’s a 410D. So are you saying its in the priority valve?
The machine in your photo is a 410. Strange way John Deere designated at the time. Dozers were 350-C describing a loader, or 350-? for a six way blade, or a 350-? for an outboard push straight blade dozer. Still not a 410D probably 20 years later. Complex hydraulic system. Mine, several mechanics prescribed a new radial pump. I reasoned that the pump on it was not the same color as the tractor. I felt it had been replaced already. I eventually spoke to a mechanic halfway across the country. He said: "You have oil flowing when it shouldn't be. Find an infrared camera. Start it up cold, watch what gets warm first." In my case it proved to be two of the six sections in the backhoe control valve. New Hampshire Hydraulics felt they were defective from the factory. My machine was 18 years old, John Deere didn't offer repair parts. Valve manufacturer was out of business. New Hampshire Hydraulics supplied a aftermarket valve. It was narrower than the original. I had to build a new joystick mechanism to make it work. It proved to be a very big deal! No. I don't assume your machine has the same ailment mine did. I do feel the people who fully understand this once advanced hydraulic system are aging, near extinct.
I have been watching this thread but not responding because I have not worked on one of these. I have worked on some of the ag version ones though. I am not an expert on their hydraulic systems. Two of the most important things when working on hydraulics is a service manual for the system and a set of pressure gauges. A flowmeter is important to. Without being able to see if the pressure is right you're just guessing. Working on a hydraulic system without being able to look at pressures is like trying to diagnose an electrical system without a voltmeter. A service manual should tell you how the system is set up and tell you where to start checking pressures.
Is it possible that a stuck priority valve could be causing this?
I'll guess you have little flow or pressure. The overfull condition is mysterious. That era John Deere had closed center hydraulics. Set up much like your home's water system, pressure is maintained to each valve. Any valve should function at any time. You can use two or more valves at a time. Most others in the day used open center systems. In those flow is constant, passes through each valve, through the filter, back to the tank. Mr. Wrench gives good advice. I suggest you seek a very competent hydraulic mechanic, or get a service manual & study.