JD 750

[DeereDoug]

Hello,

I have a <2K hrs 750 compact tractor and I just replaced the hydraulic filter, fluid and cleaned the strainer. I found plenty of metal flakes in the strainer and some tiny pieces at the bottom of the pan which leads me to think that the hydraulic pump should be replaced as well.

My problem is that both the FEL and 3 point hitch seems to stall "screech" when lifting minor loads. I know from reading that both ends should be able to lift ~800lbs. and I have yet to meet this. My rear 60" mower ~500lbs. and I can just lift it a few inches at best.

I found a pump, but need to call to check if it is either rebuilt or new. Also, I am thinking about constructing a pressure and flow meter assembly to measure things, but kinda unsure on where to start with that. I do have a TM but its not helpful on building one or wear to attach such.

Any diagnosis or assistance would be most appreciated.

D.

 

[DT86]

Rebuilt or new, either pump should come with a warranty so does it matter?

What is a TM

 

[DeereDoug]

Rebuilt or new, either pump should come with a warranty so does it matter?

What is a TM

I wont know till I speak with both sellers.

TM, means Technical Manual

I think the screeching is the relief valve sounding off, but I am not completely sure. Perhaps it is cavitating due to lack of pressure? I beleive a pressure check on the system would help resolve this further.

 

[DeereDoug]

After I posted this, I obtained a 72" box blade and the rear lift works fine picking up a few hundred pounds so I am not worried about that. The finish mower must have its center of gravity back enough that my tractor struggles with it. Since creating this post, I have been able to lift bucket loads of dirt, but its slow so a hydraulic pump will be on my list of things to replace.

 

[matoyan]

Have you tried cleaning the screen? My 750 had the same issue and when I took off the hydraulic screen and cleaned it and that made a huge difference.

 

[DeereDoug]

Oh yes, I rinsed it out with a hose then left it to air-dry and changed the fluid. It seems a tad better, but should cycle much faster. This is why I believe the pump should be replaced.

 

[prs]

Doug, did you check the valve under the front of the seat. It should be fully open or fully closed. No in-between setting.

prs

 

[DeereDoug]

Actually I tried it on both settings with no noticeable difference, but will investigate it once more.

 

[sequoyah101]

That is usually a weak spring in the bypass valve.

You can check the pump pretty easy. You'll have to plug the suction line to keep it from draining your differential and tranny case.

My 750 is 33 years old and just keeps ticking. Only has less than 900 hours on it. Always in the barn its whole life. Need a new seat cover. Replaced the shaft from the steering to the pitman arm on the front axle but that is is for the last three decades. Yanmar builds good stuff or did back then.

 

[Tx Jim]

Doug, did you check the valve under the front of the seat. It should be fully open or fully closed. No in-between setting.

prs

May I ask why valve needs to be fully open as that would defeat the purpose of the "rate of drop" of 3 pt capabilities???? R-O-D screw was designed to limit lowering speed of 3 pt with a heavy load on 3 pt which can only be accomplished by partially closing the valve. I think OP needs to check system pressure with a gauge.

 

[J_J]

Hello,

I have a <2K hrs 750 compact tractor and I just replaced the hydraulic filter, fluid and cleaned the strainer. I found plenty of metal flakes in the strainer and some tiny pieces at the bottom of the pan which leads me to think that the hydraulic pump should be replaced as well.

My problem is that both the FEL and 3 point hitch seems to stall "screech" when lifting minor loads. I know from reading that both ends should be able to lift ~800lbs. and I have yet to meet this. My rear 60" mower ~500lbs. and I can just lift it a few inches at best.

I found a pump, but need to call to check if it is either rebuilt or new. Also, I am thinking about constructing a pressure and flow meter assembly to measure things, but kinda unsure on where to start with that. I do have a TM but its not helpful on building one or wear to attach such.

Any diagnosis or assistance would be most appreciated.

D.

The reason that you can't raise the rated load is that your hyd system can not develop the pressure required.

This could be due to several reasons.

Worn pump, worn piston seals, worn spools in the valves or a combination of problems.

The rate of descent is just that it will adjust the rate of drop for the load as you want.

It can be used for transport by closing off the valve.

You should have a flow and pressure check before tearing into the hyd system.

 

[prs]

May I ask why valve needs to be fully open as that would defeat the purpose of the "rate of drop" of 3 pt capabilities???? R-O-D screw was designed to limit lowering speed of 3 pt with a heavy load on 3 pt which can only be accomplished by partially closing the valve. I think OP needs to check system pressure with a gauge.

Jim, Because the Owner's Manual says so? The valve in question is a shut off valve on the main line going to rock shaft. The speed of drop valve is located, on the JD750, on an eccentric arm between the rock shaft lift arms.

Rooster

 

[DeereDoug]

I want to thank everyone's input on this, after I repair my MFWD repair I will investigate this. http://www.tractorbynet.com/forums/parts-repairs/339894-jd750-mfwd.html

I do understand checking the pressure of the system before tearing things apart, but unsure as to how to approach that. DO I ned to order a length of hydraulic line and pressure gauge, so as to screw it into the line somewhere? A walk through if someone is willing to write-one up would be most appreciative.

D.

 

[J_J]

Make a test gauge like this and insert it in series with pump IN flow to the loader valve.

Match up the QD's with your fittings.

 

[DeereDoug]

Ok... that looks fairly simple. I will look into this in-depth when I get a chance to. Thank you.

D.

 

[DeereDoug]

Found this: http://www.boltonhooks.com/hydraulics.html