John deere 2940 hydraulic question

[CaptainQ]

I have a 1982 john deere 2940 with 5500 hrs it has a couple of issues that I need some advice on before I start trying to repair. 1.The hydraulics work fine when it is cold, but when the tractor warms up and you idle it down after about 10 seconds you can hear the engine change sounds and the hydraulics seem to unload or quit working until you rev. it up again and then it take about 10 seconds for it to start working again, you can hear the engine load a little and then the hydraulics are back. The only things I have done is to check the fluid and change the filter and no change.2. The other thing is when I turn the headlights on they run for 3-5 minutes then all electrical goes dead and if you stop the engine it will not start again, you wait about 10 minutes and it is like everything is fine. 3. I have a front steering cylinder and my 2 back remotes that are leaking and I wondered how hard the were to rebuild?

Thanks

Carl

 

[Gale Hawkins]

Carl I have a 1983 310B JD backhoe that when it gets hot the forward reverser works very slowly. The shop manual states to drain all the hydraulic fluid, change the two filter elements and clean a wire screen filter and refill with JD HyGard fluid as the first step to any transmission/lift issues with our model.

It states without these factors being known to be up to specs no testing of PSI at the test ports can be trusted as the reason this has to be done first.

Did you replace with new fluid when you changed the filters?

It sounds like the electrical issue may be a grounding problem perhaps.

I have not fixed any leaking cylinders or remotes. I HAVE replaced a few hoses and tighten some fittings to dry up the FEL and BH for the most part. Non dripping cylinder leaks on old equipment I just ignore.

 

[jd110]

Carl, There are many things that can cause your symptoms on hydraulics. The main hydraulic pump relies on the transmission pump to provide it's oil. It is kind of complicated, but the transmission pump can provide from around 3 - 8 gallons per minute depending on engine speed. The main pump can pump around 20 gallons per minute, so you can see the main pump can easily run out of oil. Some of the oil the main pump uses gets sent right back to the filter and straight back to main pump, so it is "recycled" with out the transmission pump having to work as hard. The transmission pump also provides oil to the independent pto clutch and brake, as well as the Hi-LO shift clutches, and transmission lubrication. If the pump is worn or there are any internal leakage in the clutches or pto brake, the oil to the main pump is less than needed and the leakage gets worse when the oil warms up and thins out. Also you can have an internal leak in the high pressure circuit(steering, three point hitch, scv's, loader valve, etc) That can cause the main pump to try and provide more oil than the transmission pump can provide.

I would try and start the tractor and let it run without using any hydraulics for maybe ten or fifteen minutes. Then starting at the main pump, touch the hydraulic line and feel for any heat. If the outlet line on the right side of pump is hot, then follow the line back and see where the heat goes. It tees off at steering first and then goes to three point and scv's. feel those housings and see what is hot. That is where you have a high pressure leak. That component will need repair. On the transmission pump side, try running with the pto on and off to see if hydraulics work any better in one position or the other. Also try running the Hi-Lo in lo for a while and then Hi for a while to see if that makes any difference. If one of those components is leaking, The hydrauics get worse when you use the leaking component.

On the steering cylinder leak and coupler leak, they are pretty easy for someone with moderate mechanical ability. Looking at the parts breakdown shows the parts involved. There were several styles of cylinders used(single, dual, 2wd or 4wd), so it is hard to describe disassembly without knowing which style you have. Let us know what you find out!

 

[CaptainQ]

Thanks Gale and JD 110, I will try some of the tests to see if I can come up with some answers. We have been running the tractor 2-3 days a week trying to get stuff done will this hurt the tractor? Again the only time it seems to do this is when you idle it down after it warms up, as long as you keep it over 1000 rpm's it seems to hold its prime or atleast does not sound like it quits pumping. Thanks for the help. Are we possibly looking at big dollars to get some of these things fixed?

 

[jd110]

As long as you keep rpm's high enough to keep oil to main pump, you shouldn't damage the pump. Depending on what is causing the problem, further damage could occur. Mainly, for example the Hi-Lo can get very pricey to repair. If it is already damaged and causing the loss of oil flow, further damage can occur to it. There is a compound planetary gear set in it that has needle bearings. So continued running can cost more money since the leak causes loss of lubrication to this planetary.

 

[CaptainQ]

Looks like I will be sending it to J.D. for repairs a little bigger and possibly more complicated than I want to mess with, if and when they crack it open will they be able to test and look at all of the components that may be causing the lose of pressure ex. pto clutch drive clutch, hi-lo, busted pipes and so on and is it a good idea to rebuild or replace certain items while they are in there? Any advice on what to let the dealer do and not do would be great.

Thanks,

Carl

 

[jd110]

They should be able to test hydraulic flows and pressures to isolate the problem before they go too deep. If they do need to split the tractor, I would recommend resealing the Hi-Lo, PTO clutch and brake, and also inspecting the transmision pump and oil lines. With all the labor to open it up, you might as well renew all the seals at a minimum. Good Luck!

 

[shaughnessy]

I have what seems to be a similar problem with a JD1140, with around 6500 hours on the clock. The hydraulics work fine when the tractor is cold, but become hesitant at low revs when the tractor is warm. I have a non-JD front-end loader, the brackets for which obstruct access to the high-pressure pump, but I'll try to implement the suggestion of following the warm pipes to see if there is an internal leak somewhere. A fiend of mine mentioned that he had been in a car crash in France when his brakes failed. The cause of the crash was traced to contaminated brake fluid, which contained too much water. When the brakes heated up, the water vapourised in the fluid leading to increased compressibility. Do you think something like this could be happening here? I doubt that the fluid in my JD has been changed for years, so contamination by water vapour would be a possibility, given that the internals of the tractor are effecitively open to the atmosphere, courtesy of the dip-stick tube if nothing else.

 

[Gale Hawkins]

After buy 10 gallons of the regular TSC trans/hydraulic fluid for the JD today I decided to use it in the dump truck and picked up their Renew version that is for older seals and can handle a higher water load.

Now if I will just drain, change the filters and pickup wire screen and try this new oil. As posted before this needs to be done before pulling any PSI test port readings per the JD shop manual.