IH 784 Hydralics went from strong to weak overnight.

Hey guys, I'm very good with engines, electronics and mechanical issues but I'm not Hydraulic savvy. I bought this tractor (IH 784, 4wd with 2250 loader) a couple years ago and the hydraulics were weak. I replaced the pump, filter and hydraulic oil and the hydraulics have been very strong ever since. This fall, I discovered coolant in the oil and so did a major engine overhaul. When I drove the tractor out of the shop, all hydraulics were as strong as ever. I attached the loader and mounted my snowblower. I ran the 3pt hitch up and down and the hydraulically controlled directional chute. Also the pto. All worked excellent. We got our first major snowfall here a couple days ago and so I fired her up. I discovered that the 3 pt hitch and the loader would not lift. I increased engine rpm and it was over half throttle before either struggled to lift. I figured everything was cold, though it was only zero degrees (32 for my american friends)so I let it warm up a long time. No difference. I pulled it into my heated shop and discovered the steering would not work below half throttle either. I left it overnight and next day no difference. I drained the hyd fluid and it's slightly cloudy but not what I would call bad. I removed the filter, put the hyd fluid back in and tried it again to eliminate the filter. No difference. I pulled out the relief valve and disassembled it. Spring looks good as does the seat etc. I cleaned and reassembled and still no difference. I pulled the valve beside the relief and started the tractor... Lots of flow. No difference. I pulled the pump off and checked the gears. The woodruff key is still intact and I cannot make the drive shaft for the pump slip in the pressure plate (this would be loud when running anyway and there is no such noise). I am now at a total loss... All signs point to pump except that it happened overnight and besides that, the pump has maybe 200 hours on it. Anyone have any input on this? Sorry for the length but wanted to supply as much info as possible. I need this tractor....

did you check the screen in the filter cover?

check the flow divider valve, or sometimes called a priority valve. the valve works in a way so the most important functions, like steering get oil first,then hydraulics, then hitch, then brakes and lubrication.

Hi Ben,
Has an O-ring blown out of the MCV somewhere allowing the Hytran to bypass the power steering or 3pt hitch circuits?

JimB

Can we assume that you bled the air out of the system? Air is compressible where fluids are essentially not (only one half of one percent, I think). So, if some air has found its way into the system while it sat, everything will seem to be sluggish or simply will not work.

@mstas: I removed the filter and this screen for diagnostic purposes and there was no discernible difference in performance. Filter and screen ruled out.

@thefarmhand: All o-rings that are in or around the MCV have been replaced and all still look ok.

@JimB2: I don't know how this valve works, but it seems to me that if it were malfunctioning, I would lose steering pressure while lifting the loader but is it also possible I would lose pressure everywhere? When the pump got weak initially, I always still had steering and the loader would still go all the way up and down just off idle. It just didn't have any lifting power. Now, no hydraulics will work at all between Idle and at least half throttle. No steering, no 3pt hitch, no loader, no aux... the pto is good and strong though I have no idea how this is engaged.

@Harold Evans: The only way I know to bleed the air is to remove the flow divider valve and start the tractor until fluid flows continuously. Which I have done... is there more to it?

Thanks,

-Ben

Ben, first, I'm in my late fifties, currently disabled but still work a little on tractors. I currently serve as director/advisor to the technical college in my area in the diesel and ag mechanic's dept's. So on that, I was service manager at an IH/CaseIH dealership for fifteen years so, I do have a lot of experience in these. Your problem is not strange but, I need a lot more information first. Is the tractor making a howling noise? Does the hyd oil, if you run it into a bucket from the couplers foamy or a solid stream without any foam? Next, you said you replaced all the gaskets and o-rings on the SCV, right? What about the pump? I was reading your problems and got mixed information as the SCV regulates flows and pressures. The main thing I was wondering is it the rear hyd, "three point and aux hyd" or is all hyd, which is the steering brakes, etc? If you want to talk more, just email me your answers. I can help out on this but, need more info. to analyze. Thanks, and good luck. my email is [email protected] if you want to contact direct.

Ben, the PTO is engaged by a spool valve covered by a rubber boot on upper right of MCV.

Reference 784 MCV parts diagram.
1)Bottom left front Items 4-12is Power Steering, Oil Cooler, Power Brakes outlet and relief valve at 1500 PSI, item 1-3, 13 are priority valve that diverts 3 GPM to PS,PB and Oil Cooler.
2) Item 39-42 is main relief valve at 2500 PSI
3) Items at top right are to do with PTO.
Not shown is 3PT pressure and return connecting on back right.

I still believe that somewhere the Hytran is bypassing the pressure lines to the PS,PB and 3PT and wherever the bypass/leak is by reving the engine there is enough flow to operate the PS, PB and 3PT at reduced capacity.

JimB
784 MCV

Just fixed this today. Oil seal was blown out of my new pump. (the seal keeper was pinched from the factory).