Go Bottom755 hydro problem
 | deerecrew
Join Date: Jul 2003 Posts: 17 Pasadena, MD 
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2002-11-25 45388
My 755 started "surging" when moving forward yesterday; the tractor struggled to pick up speed. I stopped it immediately and rechecked the front and rear dipsticks...both levels were OK but the front unit seemed to have bubbles in the fluid. I cranked it back up again (the engine runs great) and then tried to lift the front end with the FEL, but found that it wouldn't do so.
I shut it down again, pondered some, and then put it in 2WD and gently got it back to the barn. It did not surge on the way back, and upon arriving, the FEL lifted the front end just fine. This morning I rechecked the fluid levels and everything looks OK (levels good, color good, etc.)
Anyone have any clues to what could be causing this? Any help would be greatly appreciated!! Thanks in advance,
Dan
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2002-11-26 45407
The front dipstick on my Ford would refer to the front axle and rear would be the TX/hydraulic reservoir. I don't know if that would be the same on a 755.
If the front dipstick checks the level of a reservoir that feeds the hydraulics and HST, it sounds like a suction line problem. I'd change the filter and clean all screens. Clogged filters or other obstruction as well as a break in the line can do about the same thing. More air is put into the oil than can bubble out in the reservoir before it gets pumped again. Air in loader cylinders and the HST motor would cause weakness and surging. The air bubbles out if the tractor sits awhile and operation returns to normal but deteriorates again after a tractor is operated for awhile.
If it's pump cavitation caused by clogged filters, the oil probably also gets hot and the pump will be damaged by prolonged operation.
I'd have to do a rethink of this idea if the front dipstick is for the front axle. I'm not sure if changing to 2wd drive made any difference or not.
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| deerecrew
Join Date: Jul 2003 Posts: 17 Pasadena, MD
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2002-11-26 45422
Thanks for the insight Tom. The front dipstick on the 755 is on the front axle. I didn't get a chance to look it over today...I'll check the book and review the filter situation tonite.
Thanks again for your help,
Dan ....
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| Don M
Join Date: Feb 2002 Posts: 120 myLocation
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2002-11-26 45427
Believe it or not, new oil (and filter) can cure hydro problems like that. I experienced it first hand on a large garden tractor. I did not believe an oil change could make that difference, but it did.
-Don M ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2002-11-27 45437
I don't think I've ever checked my front axle dipstick right after running in 4wd. I'd guess that the differential gears churning away would beat some air into the oil. Some bubbles in the oil right after operation probably is normal. I know that my front axle is slightly pressurized for awhile after operation--at least there's a slight hiss when cracking the fill cap but I think that's normal.
At any rate I can't think of a relationship between front axle oil and HST and loader weakness and surging right now. I'll try to think harder if filters etc. doesn't fix the problem. New oil in my used tractor cured several occasional hydraulic glitches for me even if it wasn't time for a change on the hour meter. The former owner probably skipped a scheduled change.
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 | Art White
Join Date: Jan 2000 Posts: 6898 Waterville New York
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2002-11-27 45440
The air bubbles naturally would be caused from air in the circuit. You might try a good oil change with filter. While looking underneath the tractor look for leaks. If oil can come out than air can get in! Look also for any dents in lines or housings as they to could be leaking air in and still not leak oil out. Yes old oil might have lost it's ability to prevent aireation of oil. To idle the tractor or run at lower rpm's would have allowwed it to purge the air out of the cylinders and hydro and give you good performance within a matter of minutes. ....
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 | Peters
Join Date: Feb 2002 Posts: 3034 Northern AL
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2002-11-27 45480
Nature and hydraulics abhores a vacuum. If there is a small leak on the negative side of the pump the air will bleed in, it takes only a small leak to create a large amount of air. ....
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| deerecrew
Join Date: Jul 2003 Posts: 17 Pasadena, MD
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2002-11-28 45498
Thanks for all of the incredible feedback! I am somewhat relieved; it seems that all of the suggestions are relatively simple to check/fix/correct. I was having nightmares of $5K transaxles, hydro pumps, etc. Will tackle this over the weekend. Thanks again and I'll keep you posted,
Dan ....
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