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rfazio 
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Joined: 29 Sep 2014
Location: Long Island, NY
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 Topic: AC 715D Backhoe Hydraulic Pump
Posted: 14 Oct 2014 at 9:25am |
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I was using the backhoe this weekend really for the first time. I got it cheap at auction and am realizing why. The hydraulics seem weak. It's a shame the unit looks pretty good everything works well. The backhoe bucket which should be the strongest thing on the machine is just weak. I would like to check the hydraulic pressure before I buy a new pump for the thing. I'm thinking to put a pressure gauge on it near the line that goes into the piston and read it when it stops under load and I have full open valve. Does anyone know what kind of pressure I should get from the pump? Supposidly Allis Chalmers used the Cummins motor in these backhoes from 1983 to 86? My engine was built 12/18/88. Makes me think it is an 89.
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Coke-in-MN
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Joined: 12 Sep 2009
Location: Afton MN
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Posted: 14 Oct 2014 at 9:53am |
Are all functions of hydraulics weak or just some ? Problems could be from leaking cylinders (internally) leaking valves or relief valves, restricted pump flow to bad pump. Later machines were CDS mfg and not AC . CDS became part of Ingersoll Rand . That was sold or merged with ???
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Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something.
"Challenges are what make life interesting; overcoming them is what makes life meaningful."
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rfazio
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Posted: 14 Oct 2014 at 10:33am |
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Good question! Seems ok on other functions but hard to tell. The front bucket seems good, and if I grab something and pull it drags the entire machine on the front bucket and stays. Thats why I want to check the pressure. Can I do that? Am I correct in checking at the piston or maybe the pump itself. I know some hydraulics today use 3000PSI. do these older machines use that high pressure?
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rfazio
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Posted: 14 Oct 2014 at 10:44am |
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I forgot, it also seems to make a lot of noise when I push the controls all the way. If I pull slowly she's fine, as I go more it gets noisy, hydraulic noise. Don't know if that's normal. The machine has 5200 hours on it. Should a pump last that long?
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Coke-in-MN
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Posted: 14 Oct 2014 at 10:49am |
The system will be high pressure - do not have service manual here to check actual reading . I had problem with crowd cylinder where the leakage by piston was enough to limit hoe power , also same on the extend a hoe cylinder . A quick test is when cylinder is at limit of travel and hyd pressure is still applied does engine lug down or relief valve sound from bypass ? If not, pump MAY be problem.
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Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something.
"Challenges are what make life interesting; overcoming them is what makes life meaningful."
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DonBC
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Posted: 14 Oct 2014 at 10:59am |
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From what you are describing it is possible that there is some restriction on the suction side of the pump. If there is no noise when the valve is partially open the low flow may not be restricted that much but when the valve is fully open the restriction becomes evident such as collapsing a suction hose and possibly drawing in some air and causing the pump to make a noise.
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Jack of all trades, master of none
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Dave A
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Posted: 14 Oct 2014 at 11:31am |
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will look in the service manual. when I get out to the shop. if I remember right, the pump is a two stage pump part runs the loader hydraulics and the high volume part runs the back hoe. if it makes noise. check the relief valve on the valve bank an spool alignment. the linkage might be sloppy. and not pull the valve all the way open
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Play the game for more than you can afford to lose... only then will you learn the game.
Winston Churchill
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rfazio
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Posted: 14 Oct 2014 at 11:33am |
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Thanks guys, I've got some checking to do. As a matter of fact I do remember the suction side hose not looking too good. It looked lt was cut too short and slightly kinked because of that. Wow that would be nice, a new hose and I'm done!
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ivan
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Posted: 14 Oct 2014 at 3:27pm |
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If you need parts call 989-379-2721 ask Ivan
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DiyDave
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Posted: 14 Oct 2014 at 6:20pm |
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It ain't necessarily the pressure, a lot of times a worn out pump's problem is flow. What you may need to do is put a flow meter on and check out how many GPM's the pump is putting out...
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Dave A
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Posted: 18 Oct 2014 at 8:16pm |
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pm'ed you the info on the dipper valveing, with the anti chatter circuit and a diagram of the system. Tractor has dual output pump one output is 25 gpm the other is 15 gpm. The low pressure hydraulics run at 2350psi the high pressure on the dipper is 3000psi. I know from experience. Spool alignment is important. Because part of the system runs a regeneration circuit off of the extend on the dipper. Meaning it takes the fluid, from the top of the dipper ram and put's it into the bottom of the boom ram. think the loader dose the same to keep the bucket level
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Play the game for more than you can afford to lose... only then will you learn the game.
Winston Churchill
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