Hydraulic Pump

bazman82 · Feb 20, 2020

It's time I tackle the hydraulic pump on my Farmtrac 795dtc. I am not getting the rated psi on my pump (2600). It maxes out at 2000 before dropping back down. I've narrowed the issue down to the pump because it seems like its leaking and I assume its leaking when I hit 2000psi. I can see the hydraulic fluid on the pump around the screws to the in and out pipes that lead to it. With modifications to some allen wrenches I was able to tighten down the 3 screws connecting each pipe to the pump. Then I would test again and to 2100PSI and would hold steady at around 2000. This only worked for awhile because after a days use of the hydraulics I would see the fluid build up again on the screws. The pipes are metal on metal connection to the pump.

Right now, I have a heavy weight hydraulic oil in there and while it does make an improvement when I first start, I lose the pressure when everything heats up. I was thinking the pump is warn out even though its not that old(it actually looked like someone had the pump off at one point because it looks like its been in a vice, marks on the flat side). Less than a 1000 hours on the tractor. Any ideas? I was looking at ordering the pump ($700 shipped) and having it on hand when I take everything apart so that I can just install the new one and be done with it. The other option I was thinking was to pull the pump off, clean everything up the best I can and put the pump back on with new allen screws and some locktight (would have to order). If the second option doesn't fix the solution then I'm back to option 1 with more downtime and doing the work a second time.

RNeumann · Feb 20, 2020

Wow I’d be checking the pressure regulator before I replaced the pump. If the pump couldn’t make pressure because of a leak I’d think it would be dumping a few gallons a minute on the ground......

bazman82 · Feb 20, 2020

I've checked the pressure relief valve and made adjustments there. The max I could get it up to and stay steady was 2100. I was able to achieve 2200 but then it would drop below 2000 right after.

The transmission and hydraulics all work off the same tank, open center I believe is what its called (could be wrong). There is a screen in the line between the tank and the pump according to the diagrams. Then it goes from the pump to the rear scv regulator. From there it branches off back to the front of the tractor for the loader scv. I have been testing the relief at the first scv the pump lines go to. Should I try replacing the first scv regulator that the pump line goes into? I priced the parts for the relief valve and well....it would cost more than the new hydraulic pump. Also, why would the screws on the pump have the buildup of hydraulic fluid on them after using. I can try and get some pictures of everything to help make it easier to explain and hopefully using the right terminology as this is definitely not my field of expertise.

RNeumann · Feb 20, 2020

What is the pressure before the relief valve? Does the relief valve require shims or can you simply tighten down the spring? Can you buy just a new spring for the relief valve- I’m thinking that part shouldn’t be too expensive?

oldnslo · Feb 20, 2020

bazman,
Does the hydraulic pump housing get hot quickly compared to the inlet and outlet lines when you are attempting to build pressure? If no the pump is not your problem since a pump leaking close to full flow will get hot very quick. Leaking around the bolts that hold pipes could be O-rings that have hardened and taken a set. These are easily changed if you can get the steel lines lose at both ends.

bazman82 · Feb 21, 2020

RNeumann said:
What is the pressure before the relief valve? Does the relief valve require shims or can you simply tighten down the spring? Can you buy just a new spring for the relief valve- I’m thinking that part shouldn’t be too expensive?

I've only checked the pressure at the rear ports. Not sure if that is considered before the relief valve or not. The valve can be tightened down and loosened and I've achieved different psi pressures doing this. When I tightened it to much the psi wont even reach 2100 psi if I remember correctly from my testing. There was a sweet spot during the testing to get the best usable result and thats what I have it set to now. I would have to try and find the paper that I wrote down the info on for the price on the parts.

bazman82 · Feb 21, 2020

oldnslo said:
bazman,
Does the hydraulic pump housing get hot quickly compared to the inlet and outlet lines when you are attempting to build pressure? If no the pump is not your problem since a pump leaking close to full flow will get hot very quick. Leaking around the bolts that hold pipes could be O-rings that have hardened and taken a set. These are easily changed if you can get the steel lines lose at both ends.

I never felt the housing pump but I do remember that one of the lines off the rear scv was really hot to the touch when in use for awhile. I would have to take a look at that line and see where it is going too or coming from. I will be using the loader tomorrow so I will try to remember to check.

oldnslo · Feb 21, 2020

is the rear scv the valve assembly with the valve you have been adjusting? If yes then I would suspect tank line is getting hot due to a leak path in the valve assembly. Some valves have a power beyond plug with O-rings on them. These O-rings have been known to fail which allows the pressure line to connect to tank like an orifice limiting system pressure.

bazman82 · Feb 21, 2020

oldnslo said:
is the rear scv the valve assembly with the valve you have been adjusting? If yes then I would suspect tank line is getting hot due to a leak path in the valve assembly. Some valves have a power beyond plug with O-rings on them. These O-rings have been known to fail which allows the pressure line to connect to tank like an orifice limiting system pressure.

Correct. The rear scv valve is the one with the valve I have been adjusting.