Weak Hydraulics

[StevenDyche]

I have a 2007 John Deere 790 with a front end loader. The Hydraulics (3PH and FEL) became weak at about 300 hours so I replaced the fluid and all hydraulic filters. It is still very weak and I must run a high RPM to get decent performance, but still it was no where near what it was when I bought it (180 hours)(420 hours now). I can't afford to take it to a dealer, so I am hoping someone here can help me out. On a side note, I have also replace all fuel filters also.

Also, as stated above, it only has 420 hours, but all of the pins in the front end loader are lose. Is there a way to tighten them? It doesn't seem like enough hours for them to be worn out.

 

[PBettis]

Welcome to TBN! You might want to run a flow test to check out the hydraulic pump. You mentioned it took higher RPM's to achieve the same characteristics in the machine. If all filters/fluids were changed affecting hydraulics then it doesn't seem like anything else. Have you at least called a dealer to speak with a technician? They have a broad range of knowledge and may point you in the right direction from having seen this problem before on your model. They realize everyone can't bring their machines in for service and should still help you over the phone. Are you using the proper filters and fluids? You haven't given us much information other than you replaced filters, hydraulics are weak and the machine hours/model. Maybe one of the hydraulic hoses, if used in place of steel piping, has collapsed internally. "Sucked flat". Pump may not be getting enough return fluid to compress. "Starving" for oil. Just some thoughts. Most machines have internal "suction screens" that may stop up before going thru another "cartridge or media" type. May gain access thru access plate or by taking trans. cover off. As far as FEL pins, what kind of play are we talkin'? Won't grease take out the slack? Good luck!

 

[murphy1244]

:welcome:

 

[murphy1244]

see this thread http://www.tractorbynet.com/forums/john-deere-owning-operating/20118-790-maintenance-change.html

 

[StevenDyche]

Welcome to TBN! You might want to run a flow test to check out the hydraulic pump. You mentioned it took higher RPM's to achieve the same characteristics in the machine. If all filters/fluids were changed affecting hydraulics then it doesn't seem like anything else. Have you at least called a dealer to speak with a technician? They have a broad range of knowledge and may point you in the right direction from having seen this problem before on your model. They realize everyone can't bring their machines in for service and should still help you over the phone. Are you using the proper filters and fluids? You haven't given us much information other than you replaced filters, hydraulics are weak and the machine hours/model. Maybe one of the hoses if used in place of steel piping has collapsed internally. "Sucked flat". Pump may not be getting enough return fluid to compress. "Starving" for oil. Just some thoughts. Most machines have internal "suction screens" that may stop up before going thru another "cartridge or media" type. May gain access thru access plate or by taking trans. cover off. As far as FEL pins, what kind of play are we talkin'? Won't grease take out the slack? Good luck!

Thanks for the reply PBettis!
I have not done a Flow test, I will have to look up that process and work on that. I have called three dealers and they tell me to bring it in. At this time, I can't afford to bring take it in. I have only used JD Filters and fluids. I replaced one broken hose the FEL that had worn through. I am going to also check the screens based off of your advice. On the FEL pins, grease does not take out the slack. When not under a load they can be moved back and forth easily and the only way to describe it is that the FEL is noisy and sloppy while in use. You can see movement of the FEL on them while you are using it. I know that may not be alot of help, but I am new to all of this and I am doing my best to give you guys what you need to answer the questions. Thanks again for your help!

 

[PBettis]

Haha!....if you could give us enough information, you would discover the problem or solution yourself! I enjoy the challenge myself of the "hunt"! That FEL pin slop sounds very premature. Stumped on that one. The flow test I'm referring to is pretty easy if you can get your hands on a flow meter. Plumb it in where it goes on your model and set rpms where the procedure tells you to and see what gpm you're getting. Of course Safety First!!! Don't get hurt trying to save money!! Not worth it!

 

[J_J]

This is what you have for hyd.

hydraulics:
Type: open center
Capacity: 4 gal [15.1 L]
Pressure: 2050 psi [141.3 bar]
Pump flow: 5.4 gpm [20.4 lpm]
Steering flow: 4.2 gpm [15.9 lpm]
Steering press.: 2050 psi [141.3 bar]

Check fluid levels and clean screens and replace filters.

You could put one of the cyl hose in a 5 gal bucket marked ff in gal, and use the FEL lever to squirt some fluid in the bucket. If you can fill bucket to the 1 GAL mark in one min, , then you have about 5 GPM flow.

If you max out the cyl by retracting, you should be able to read the pressure,and the data for yor tractor says about 2050 psi

Install a 3000 psi hyd gage in a tee at the IN port of the FEL valve. Then use it to trouble shoot the hyd system.

 

[PBettis]

I was also going to suggest somehow pumping the oil into a container for 30 seconds and doubling that amount to obtain gpm but wasn't sure if that would be accurate. Your data suggests otherwise. Great information! Also the tee suggestion off the FEL connection to a hyd. guage is another excellent suggestion! As far as the FEL pins...I would take a few pins out and compare with new pins from the Dealer. Or mic the pin diameter and call the Dealer to get specs on new pins. Maybe someone changed them before you purchased at (180 hours). I keep saying it but this forum is invaluable for everyone owning equipment!!!

 

[Zebrafive]

You could put one of the cyl hose in a 5 gal bucket marked ff in gal, and use the FEL lever to squirt some fluid in the bucket. If you can fill bucket to the 1 GAL mark in one min, , then you have about 5 GPM flow.

One gallon in one minute = 5 GPM flow????? Sounds like 1 GPM to me :confused3:

 

[PBettis]

Everybody's head scratchin' now!!