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bkolash
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2001-11-02          32912

I have a JD 750 4x4 w/ #67 FEL and #7 HOE. THe unit has sat (indoors) many years. It has only 390 Hrs. I recently purchased the unit and have been running the FEL & HOE. I notice a "squealing" noise when the hydraulics seem to run out of push. The loader will not hold up the tractor front end when using the FEL bucket to help stabilize the unit for digging with the hoe. It will slowly drift down (while the tractor is running) the hoe side supports will also drift and lose thier stability. When trying to reset same to position, I hear this "squealing noise" and can get no more lift from the hydraulics. Enough said, I am new at this tractor world and know little about hydraulics. Are the above symptoms normal, or is something wrong. I park the unit over a cement floor and notice no leakage, except a few drops from the right front bucket cyclinder. Ant input ? Thanks.

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lsheaffer
Join Date: Jun 1999
Posts: 1082 Northern Illinois
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2001-11-03          32917

Squeeling sounds like it could be the relief valve. If so it may be sticking due to lack of use. Are the hydraulics jerky? I'd recommend draining the oil. there is probably a pickup screen in the transmission housing . Remove & clean it. It may have gotten condensation from temperature changes while setting. ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2001-11-03          32924

Leonard's suggestion to change the oil and screen/filter sounds pretty good. I'd run the tractor with new oil and see if things improve. Various small hydraulic oddities disappeared a short time after I changed my oil and filter. Pressure relief valves operate to limit the pressure in high-pressure lines. There usually is a system relief valve and others to protect against load shocks in the 3ph, power steering, loader valves, and probably the hoe valve as well. It's normal for the system relief valve to open under high loads and when a cylinder reaches the limit of its travel. Hydraulic lift pretty much stops when the valve opens. If the relief valve opens during normal operation, it may need adjustment. Note that a tractor shouldn't be operated too long if the relief valve is opening, but also note that power steering sounds similar to a relief valve. I'd say lifting the front wheels with a loader would be considered normal operation in virtually all compacts, although some loaders don't go lower enough with the bucket flat for the loader to lift the wheels. I don't think my hoe stabilizers will completely lift the rear wheels, but I consider that within normal limits. I don't try to get the tractor completely off its tires. I usually set the bucket down fairly flat and with little down-pressure. I try for adequate, rather than rock-solid, stability because I believe that saves wear and tear on the tractor. I'm not sure how your hoe is plumbed into the hydraulics. However, a basic understanding of an open centred system might help. There should be various discussions in the archives. In many systems, valves for loader, hoe and 3ph are strung along a line in series. If several valves are operate at the same time, only the first valve in the line develops pressure. Before my oil change, I’ve had to jiggle valves to make sure they were entirely centred before everything would work. ....

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Art White
Join Date: Jan 2000
Posts: 6898 Waterville New York
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2001-11-03          32926

Come back to us after you check out your oil and filter. Has it been changed before? You could have some condisation in there causing the trouble. ....

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Roger L.
Join Date: Jun 1999
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2001-11-03          32930

That sounds like a relief valve squealing. All the symptoms are correct. The valves are designed to squeal in order to catch your attention. Like the 750, most tractors have a relief valve for the 3pt lift - located close to the lift cylinder under the seat. Loaders and backhoes have similar valves built into the control lever housing. The valve is composed of a poppet ball or valve and a spring which normally holds the valve shut. They can leak or fail from nothing more than sitting too long. I'd try the new oil plus running it for awhile.... but not be surprised if fixing it requires replacing the part. It's a $2.00 part, but I'm not sure where that valve is located on the 750. On older JD tractors it was right out on the side of the 3pt hitch and easy to get too. If it is like that, it is a 10 minute job to replace it. ....

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Paul Fox
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2001-11-03          32932

I have the same tractor (2250 hours), only with a Woods backhoe. The other folks are right on track with their comments. I'll just add a couple of points from my experience. I can pick the front end up at will, but it does drift down after a few minutes while using the backhoe. I have some leaks around the couplers at the SCV, but it's done that since day one. My hoe runs off it's own PTO=driven hydraulic pump, and I can run the stabilizers out to full extention under any conditions. With the #7 hoe running off tractor hydraulics, you're probably running up against the relief valve. Fresh oil and filter, some exercise, and perhaps a disassemble-clean-inspect-reassembe on the relief valve should take care of all your problems. It's a dandy little machine. I bought mine new in '88 and have ZERO mechanical failures that weren't directly related to operator stupidity. ....

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bkolash
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2001-11-03          32933

Guys, thanks for all the replies so soon. Regarding the oil and filter screen, I changed the hydraulic oil and cleaned the screen as specified in the JD manual right after I picked up the machine. Actually I changed all fluids and filters per the JD maintenance schedule. The tip on the relief valve, I will look into that. The hydraulics are not jerky, they seem to work OK, except for the symptoms noted. Working the machine, as suggested, I am doing now. I just finished digging out my neighbors footer drains, about 20 long and approx 5' deep, today and the unit seemed to do OK. The "squealing" does indeed sound like a power steering pump when its reached its limits. It seeme to be a great little tractor, perhaps I might be expecting too much. It is the first one I have owned. Thanks again for the replies. ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2001-11-04          32944

Bkolask: What I wanted to note by my power steering comment is that it's fairly easy to confuse the sound of power steering on a tractor with the pressure relief valve. The sounds usually come from different locations and the pressure relief valve sound usually is a bit louder. Most tractor power steering systems make a squeal whenever there is turning pressure on the sheering wheel. ....

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bkolash
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2001-11-04          32949

Tom G, My tractor doesn't have power steering. Since we have communicated I dissassembled the relief valve and cleaned it with solvent. I found a small piece of wire in it, like a bristle from a wire brush. I don't know whether this had any bearing, but the tractor will now raise the front end with the loader till the cyclinders are out of travel. It seeme to be working better now. The squeal IS the relief valve and it still will do it when the cyclinders are maxed out. Thanks for the help. ....

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Roger L.
Join Date: Jun 1999
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2001-11-04          32951

Congratulations; it sounds like you fixed it. That wire - or some other POC - would certainly explain the inability to reach full extention on the rams and also the slow leakdown.
It is normal for the relief valve to squeal when any hydraulic ram is fully contracted or extended "against the stops". That includes the backhoe, loader, 3pt, and power steering plus any other hydraulics that might be there. It sounds like yours is doing what it is supposed to now. ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2001-11-05          32952

Yep, a real good result. Congrats. I found a piece of rubber boot in a drain pan after I changed my hydraulic oil. One can only wonder how such stuff gets into the system. I'm just glad it stayed in the sump rather than ending up in the suction line or filter. ....

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