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Discussion Starter · #1 ·
Hi, New Member here. Looking for guidance from anyone that knows tractor hydraulics. My tractor is a Ford 1910, 1986 with 770A Loader.
Problem: When I start cold, both the bucket and three-point hitch will lift (though the bucket has lost lifting strength). But once the oil gets warm, both the bucket and hitch fail to lift.
If I stop the engine and wait a minute, I can restart and get a lift for a second or two. But then it fails again. What I've tried: a) replace oil & filter (twice) - same thing. b) detach the front loader to eliminate that loader valving is a problem - (the same thing happens to just the 3 pt hitch once it warms up). c) sucking air out of the tank with a vacuum (this helps for a couple of minutes, then the same thing). d) checked for bad fittings or hoses (all seem fine). My suspicion at this point is the pump is handling oil when its cold and viscosity is thicker, but once the oil warms up and thins out, the oil is blowing by. I'd love someone to tell me I'm wrong and has a better idea. Prices on the pump are around $600.00. Look forward to any input.
 

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Howdy Joe, welcome to the tractor forum.

You may have a suction leak allowing air to enter the hydraulic fluid. After 10-15 minutes or so, depending upon the severity of the leak, the fluid becomes so aerated that it becomes useless as a hydraulic fluid. If you have a hydraulic fluid dipstick take a look at the fluid on it after the hydraulics quit. If you see almost milky looking fluid entrained with small air bubbles, that's your problem.

See attached hydraulics diagram:
https://www.messicks.com/nh/155874?sectionId=887037&diagramId=DA36B5C7-B8BF-E111-9FCE-005056875BD6

Possible points of air entry into hydraulic fluid:
#50 - gasket
#19 - o-rings (2 ea)
#13 - o-rings (2ea)
#10 - o-ring
#11 Filter seal??
Also look over the suction tube #12 for evidence of minor oil leakage. If oil can get out, air can get in. The suction tube has negative pressure.

Also, the pump could have a seal leaking, allowing air into the system.
 

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sucking in air on the feed side is the kiss of death, causes caviation of the pump........air does not compress efficiently...try leaving the lift fully extended when cold with a heavy load on it..... shut off the tractor......see if you find hydralic fluid "seeping out" anywhere in the pump high pressure side..and then the low pressure side...

Old harleys "wet sump" where oil flosw back through old oil pumps into the crankcase....when started.the spit oil out the crankcase breather.....new pumps with tighter clearances dont have that problem

A crappy pump will let fluid 'backwards" through the pump high side to the low side feed lines and it will leak out of any input line..........from the tank up to the feed line into the pump body
 

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Discussion Starter · #6 · (Edited)
Howdy Joe, welcome to the tractor forum.

You may have a suction leak allowing air to enter the hydraulic fluid. After 10-15 minutes or so, depending upon the severity of the leak, the fluid becomes so aerated that it becomes useless as a hydraulic fluid. If you have a hydraulic fluid dipstick take a look at the fluid on it after the hydraulics quit. If you see almost milky looking fluid entrained with small air bubbles, that's your problem.

See attached hydraulics diagram:
https://www.messicks.com/nh/155874?sectionId=887037&diagramId=DA36B5C7-B8BF-E111-9FCE-005056875BD6

Possible points of air entry into hydraulic fluid:
#50 - gasket
#19 - o-rings (2 ea)
#13 - o-rings (2ea)
#10 - o-ring
#11 Filter seal??
Also look over the suction tube #12 for evidence of minor oil leakage. If oil can get out, air can get in. The suction tube has negative pressure.

Also, the pump could have a seal leaking, allowing air into the system.
Thanks Big T. Great feedback. I'll start chasing down those o rings. I did find the oil was turning milky with bubbles. NO doubt about that.
 

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Discussion Starter · #7 ·
Good point Ultradog, I'lll do that to. Thanks
Just as you can't see electricity flowing through a wire without a meter or guage, you can't see oil in a hydraulic system.
Put a guage on it and Measure your pressure.
point
 

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Discussion Starter · #8 ·
sucking in air on the feed side is the kiss of death, causes caviation of the pump........air does not compress efficiently...try leaving the lift fully extended when cold with a heavy load on it..... shut off the tractor......see if you find hydralic fluid "seeping out" anywhere in the pump high pressure side..and then the low pressure side...

Old harleys "wet sump" where oil flosw back through old oil pumps into the crankcase....when started.the spit oil out the crankcase breather.....new pumps with tighter clearances dont have that problem

A crappy pump will let fluid 'backwards" through the pump high side to the low side feed lines and it will leak out of any input line..........from the tank up to the feed line into the pump body
Thanks Dominic,
 

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Discussion Starter · #9 ·
Howdy Joe, welcome to the tractor forum.

You may have a suction leak allowing air to enter the hydraulic fluid. After 10-15 minutes or so, depending upon the severity of the leak, the fluid becomes so aerated that it becomes useless as a hydraulic fluid. If you have a hydraulic fluid dipstick take a look at the fluid on it after the hydraulics quit. If you see almost milky looking fluid entrained with small air bubbles, that's your problem.

See attached hydraulics diagram:
https://www.messicks.com/nh/155874?sectionId=887037&diagramId=DA36B5C7-B8BF-E111-9FCE-005056875BD6

Possible points of air entry into hydraulic fluid:
#50 - gasket
#19 - o-rings (2 ea)
#13 - o-rings (2ea)
#10 - o-ring
#11 Filter seal??
Also look over the suction tube #12 for evidence of minor oil leakage. If oil can get out, air can get in. The suction tube has negative pressure.

Also, the pump could have a seal leaking, allowing air into the system.
Hi Big T, What about the Pump Gasket? (item #2)? You think there's any chance that could a source of air back into the system? Or before I start tearing things down further, what about the four (4) seals #41 at both ends of the rigid tube marked #40? What do you think?
 

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Hi JoeD,
Gasket #2 prevents engine oil leakage. You could have a leaking pump shaft seal, which might allow air into the system, but more likely leak hydraulic fluid into the engine.

The rigid tube #40 is your high pressure line. No chance of air leakage into the system.
 

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Discussion Starter · #11 ·
Hi JoeD,
Gasket #2 prevents engine oil leakage. You could have a leaking pump shaft seal, which might allow air into the system, but more likely leak hydraulic fluid into the engine.

The rigid tube #40 is your high pressure line. No chance of air leakage into the system.
Thanks. Understood. Really appreciate your guidance.
 

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I think you should try Ultradog's advice first: "Just as you can't see electricity flowing through a wire without a meter or gauge, you can't see oil in a hydraulic system. Put a gauge on it and Measure your pressure."

Put a pipe tee in the pressure line, and install gauge in the tee.

Also, have you observed tiny air bubbles in the hydraulic fluid when the system quits working??
 

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Sucking air from the tank does nothing because the tank is naturally vented to the air anyway. In a "open" hydraulic system the tank has to breathe air in as the fluid level in the tank changes slightly. Without venting to the atmosphere the suction caused by the pump could cause pump cavitation. Like others said too, sucking air into the system at leak points can cause pump cavitation. That all leads to pump element and pressure plate wear which lowers pump efficiency. When pump efficiency goes down it can't maintain pressure as the oil heats up and thins out. I agree a pressure test is 1st. Also since you say both the loader and 3-pt react the same its a good guess the issue is not the loader or 3-pt cylinder seals. My guess is the pump is bypassing due to wear.
 

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rule of thumb with a worn-out pump is that more RPMs should get it working as only so much oil will leak by the gears and seals.
gear pumps are pretty resistant to cavitation. vane pumps are not.

if air is turning the oil to milk, it almost has to be a leak on the suction side. the other potential cause would be the oil getting frothed up in the tank. the oil should not be spraying into the reservoir. it should be entering below the oil level. another unusual way for air to get into the system would be if you have the cylinder forced to move too quick (like dropping a heavy load quickly) it could suck air in through the piston seals.

check the tank for something like a broken off diffuser and look for an air leak at the inlet of the pump or in the line connecting the pump and the hose. I bet pressurizing the reservoir a bit would cause the air leak to leak oil.
 

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Yup. But if its a steel sheet metal reservoir, be careful with air pressure, you could expand the tank. Same for suction. I had a customer needed to change a 2" fitting on the bottom of a steel 50 gal reservoir. I said get a shop vac, some rags and really good sealing duct tape. Take out the filler cap and seal it up good with the shop vac hose into the filler neck, but not into the oil. Turn the shop vac on and you could see the tank sides go in. Took out the 2" fitting and a few drops of oil came out. Looking in the port you could see the oil, DONT TOUCH IT. Installed the new fitting and connected the hose. Turned off the shop vac and good to go.
 

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Discussion Starter · #16 ·
I think you should try Ultradog's advice first: "Just as you can't see electricity flowing through a wire without a meter or gauge, you can't see oil in a hydraulic system. Put a gauge on it and Measure your pressure."

Put a pipe tee in the pressure line, and install gauge in the tee.

Also, have you observed tiny air bubbles in the hydraulic fluid when the system quits working??
Hi Big T, Yes I have found air bubbles and it was milky the first time I turned over the oil. Interesting I can use a shop vacuum and suction through the top of the hydraulic tank for a while and get the system working again for a short bit, and then it'll fail once again. Little doubt to me its air getting in the system.
 

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Discussion Starter · #17 ·
Sucking air from the tank does nothing because the tank is naturally vented to the air anyway. In a "open" hydraulic system the tank has to breathe air in as the fluid level in the tank changes slightly. Without venting to the atmosphere the suction caused by the pump could cause pump cavitation. Like others said too, sucking air into the system at leak points can cause pump cavitation. That all leads to pump element and pressure plate wear which lowers pump efficiency. When pump efficiency goes down it can't maintain pressure as the oil heats up and thins out. I agree a pressure test is 1st. Also since you say both the loader and 3-pt react the same its a good guess the issue is not the loader or 3-pt cylinder seals. My guess is the pump is bypassing due to wear.
Hi Andy, Like I said in my reply to Big T, sucking air through the tank does have a very short term impact, which helped confirm to me air was involved. But like you said nothing of a solution. IM onto the pressure testing. Thanks for the input!
 

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Discussion Starter · #18 ·
rule of thumb with a worn-out pump is that more RPMs should get it working as only so much oil will leak by the gears and seals.
gear pumps are pretty resistant to cavitation. vane pumps are not.

if air is turning the oil to milk, it almost has to be a leak on the suction side. the other potential cause would be the oil getting frothed up in the tank. the oil should not be spraying into the reservoir. it should be entering below the oil level. another unusual way for air to get into the system would be if you have the cylinder forced to move too quick (like dropping a heavy load quickly) it could suck air in through the piston seals.

check the tank for something like a broken off diffuser and look for an air leak at the inlet of the pump or in the line connecting the pump and the hose. I bet pressurizing the reservoir a bit would cause the air leak to leak oil.
Hi, thanks for that input. Looking for a leak on the suction side seems to be the common thinking. Got my work cut out for me on that score. Never thought about pressurizing the tank but that's a neat idea. I'm going to try that. Thanks!
 
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