# IH 784 hydraulic pump



## xrigger (Mar 19, 2020)

Hi all, have decided after much deliberation, to replace the hydraulic pump on my 784.
Have been advised that the pump is the likely source of my problems.
Does anybody know if the pump simply sits behind the filter can on the MCV and can be replaced without removing the MCV itself.


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## FredM (Nov 18, 2015)

I am only familiar with the 474 and 574 IH's and the hydraulic pump is bolted onto the other side of the MCV on those tractors and the MCV has to be removed to get to the pump, so I would expect that your tractor will have the same setup.


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## xrigger (Mar 19, 2020)

Thanks for that, is it a big job to remove the MCV ?


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## FredM (Nov 18, 2015)

Drain the transmission oil, there could be a control rod on a spool valve, remove that and undo the retaining bolts and remove the MCV with pump attached, use new gaskets/"O"rings on re-assembly.


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## xrigger (Mar 19, 2020)

Thanks for your help, doesn't sound too bad of a job !


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## FredM (Nov 18, 2015)

Save this to desktop if you have a full size computer, and then you can enlarge the size for better seeing, this covers your tractor and will show the oil circuits and valves in your system.


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## FredM (Nov 18, 2015)

I haven't asked, but why do you need to replace the hydraulic pump?.


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## xrigger (Mar 19, 2020)

At low engine revs no power steering . On engaging pto at lowish revs, takes several seconds to raise. Whilst cutting grass, the topper tends to drop unless the revs are fairly high. This gets progressively worse. 
With engine off and pto raised with topper connected, takes 4/5 hrs to drop.
There is plenty of hydraulic oil in system.
Am I jumping to conclusions ?


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## FredM (Nov 18, 2015)

I reckon I would be pulling the Main pressure regulation valve and the differential pressure valve beside it to the left and the two pressure regulation valves shown in the left side as viewed in the schematic, I would pull the two main valves first and check to see if the springs are ok and the spools are not sticking in their bores.

Study the schematic, look at the colour guides for the oil flow and see if you can nut out the flows.


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## xrigger (Mar 19, 2020)

OK sounds a good process of elimination !


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## xrigger (Mar 19, 2020)

Fred, have looked at the schematic you sent but unfortunately it is not clear as to the naming of the components !
I have found an identical one on the net and the parts are labled thus:
mcv which houses the main relief valve, to its right is the unloader and flow control valve, below this the auxiliary valve.
Or, are the valves you mentioned actually situated in the body of the MCV ??


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## FredM (Nov 18, 2015)

xrigger, it has been over 30+ years since I have seen a 474 and 574 IH tractor, if you have found a better schematic that is good then, if you have a look at the MCV there will be some large hex headed fittings screwed into it, these will be your main pressure regulating valve, the unloader and flow control valves supply pressure to the 3 point ram.

Would you be able to attach your copy so I can have a look.


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## Fedup (Feb 25, 2014)

I too would be interested in seeing that diagram. I've studied the one posted above more than once and have been confused. It appears to be an IH original, and evidently applies to many different models. I have trouble understanding certain parts of the flow charts, particularly the brake circuit. This diagram shows the brakes supplied with fluid from the transfer pump. My experience with 74 and 84 series has shown the brakes supplied from return flow from the power steering valve.


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## FredM (Nov 18, 2015)

Fedup said:


> My experience with 74 and 84 series has shown the brakes supplied from return flow from the power steering valve.


And so it does,


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## Fedup (Feb 25, 2014)

That's not how it's depicted in the above diagram. The brake cylinders appear at the top of the diagram and seem to have no connection to anything related to the steering valve which is shown neat the bottom. Pressure and return are shown in and out of ports on the MCV with no connection to brakes.


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## FredM (Nov 18, 2015)

I am happy with how I read the flows, green flow comes from the IPTO valve and from the steering supply and goes past the brake connection and if the tractor has a torque amplifier then that is supplied to the torque amplifier pump from the return line and after through the regulator valve and that oil bleeds through an orifice into the return line also after passing through the torque amplifier clutch pack and then through the gear train, and just above the transfer pump and above the branch to the transmission return line, there is another orifice.

I was always under the impression that the master cylinder oil supply was low pressure from when I had the two IH's in my care. 

What I have attached to forum is a flow chart of all of the capabilities that the IH models of this genre could have at the time.


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## xrigger (Mar 19, 2020)

FredM said:


> I am happy with how I read the flows, green flow comes from the IPTO valve and from the steering supply and goes past the brake connection and if the tractor has a torque amplifier then that is supplied to the torque amplifier pump from the return line and after through the regulator valve and that oil bleeds through an orifice into the return line also after passing through the torque amplifier clutch pack and then through the gear train, and just above the transfer pump and above the branch to the transmission return line, there is another orifice.
> 
> I was always under the impression that the master cylinder oil supply was low pressure from when I had the two IH's in my care.
> 
> What I have attached to forum is a flow chart of all of the capabilities that the IH models of this genre could have at the time.


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## xrigger (Mar 19, 2020)

Hey Fred did you get the photos ?


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## FredM (Nov 18, 2015)

I haven't seen any photos yet xrigger, did you try and attach them to this thread?.


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## xrigger (Mar 19, 2020)

FredM said:


> I haven't seen any photos yet xrigger, did you try and attach them to this thread?.


Will try again !!


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## xrigger (Mar 19, 2020)

xrigger said:


> Will try again !!


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## FredM (Nov 18, 2015)

Thanks xrigger, that manual will be a boon for you, it will explain the circuits and flows better than I ever could, best of luck with your fault finding, and could be as simple as a plugged screen.


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## xrigger (Mar 19, 2020)

FredM said:


> Thanks xrigger, that manual will be a boon for you, it will explain the circuits and flows better than I ever could, best of luck with your fault finding, and could be as simple as a plugged screen.


Cheers Fred, will have a go when I get time !! Weather has just started to break in Cornwall after weeks of unseasonal sunshine. Jim


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