John Deere 2520 no charge pump pressure

[Oregon2023]

I have a John Deere 2520 that I had to remove the charge pump and valve block to replace the transmission input driveshaft that couples to the engine due to the end of it breaking off after the tractor tunnel section cracked due to rolling over. I very carefully and cleanly reassembled the pumps back into the transmission housing using diagrams and lubricating with hydraulic oil. After reassembling the tractor and priming the hydraulic charge pump I’m not getting enough charge pump pressure to run the steering or feed the rest of the hydrostatic system. If I open the test port when turning it over oil gushes out. If I crack the steering pressure line I get nothing. I have disassembled, cleaned, inspected, and resealed everything 4 times now (including splitting the tractor) and it still comes down to no charge pump pressure. The tractor has just over 400 hours and the charge pump components measure within spec according to the John Deere service manual without any major visible wear. Everything was driving fine before disassembling. Any help beyond the obvious would be much appreciated.

 

[MTGreen]

I would look closely at your pickup screen and associated plumbing assembly to make sure you're not sucking air and losing prime immediately. I would look closely at the gaskets and on some models there are rubber connectors or elbows that are prone to cracking/leaking and sucking air which may not show as a frank oil leak.
Some of the hardline could also have been cracked or tweaked in the roll over

 

[Oregon2023]

I would look closely at your pickup screen and associated plumbing assembly to make sure you're not sucking air and losing prime immediately. I would look closely at the gaskets and on some models there are rubber connectors or elbows that are prone to cracking/leaking and sucking air which may not show as a frank oil leak.
Some of the hardline could also have been cracked or tweaked in the roll over

Ok, I’ll look over all the lines and fittings again. I do know the charge pump oil is supplied through a passage in the transmission case directly from the spin on hydraulic filter. When I removed the power steering pressure regulator in the side of the charge pump block and turned it over about 3/4 of a gallon of hydraulic fluid shot out in 2-3 sec. (I know because that’s what it took to top it back off, lol). So I know the charge pump is pumping oil, it’s just not pressurizing which leads me to think there’s some type of internal leak or crack somewhere between the valve block and the transmission case. A crack could have theoretically happened as a result of the same pressure that broke the input driveshaft when the tunnel section broke.

I just hope I didn’t trash the hydrostatic drive motor and pump running it with no charge pump pressure.

 

[oldnslo]

I agree from what you have posted the charge pump is working but the flow is escaping somewhere. Does the oil flow to steering and then back to filter and charge for HST or through the filter to steering? Is there an external line from steering pressure regulator to steering valve? Do you get any oil is this line or is that the line you removed and say no flow.

Does same pump supply PTO circuit? If yes is there any pressure in that circuit?

Reason asking is that my Branson oil flows from pump to steering, then through oil cooler, then through HST filter to charge circuit of HST. I do not know how your 2520 is plumbed.

 

[MTGreen]

There are test ports on the hydrostat & JD has a procedure and pressure specs. This may be where to go from here

The input shaft 41 from the motor is directly coupled to the variable pump 35 with the fixed pump directly below coupled with gearing. Are both of those not working? Did you look for cracks in the hydrostat housing 30 where the input shaft goes in? Also are you sure on your model the charge pump runs the steering also?

https://partscatalog.deere.com/jdrc/sidebyside/equipment/74954/referrer/navigation/pgId/22128359

 

[oldnslo]

I just hope I didn’t trash the hydrostatic drive motor and pump running it with no charge pump pressure.

Have you tried to drive the tractor under this condition? The charge pressure does two things.

1) provides pressure for hydrodynamic bearing lube between rotating group surfaces while at standstill. If run a length of time with any pressure you can score the wear surfaces.

2) provides make up oil for leakage in the HST circuit during operation.

 

[kevin37b]

Rollover ? Any details ? You may have several problems . Kevin .

 

[Oregon2023]

I agree from what you have posted the charge pump is working but the flow is escaping somewhere. Does the oil flow to steering and then back to filter and charge for HST or through the filter to steering? Is there an external line from steering pressure regulator to steering valve? Do you get any oil is this line or is that the line you removed and say no flow.

Does same pump supply PTO circuit? If yes is there any pressure in that circuit?

Reason asking is that my Branson oil flows from pump to steering, then through oil cooler, then through HST filter to charge circuit of HST. I do not know how your 2520 is plumbed.

Yes, the charge pump does supply the PTO clutch/brake system. The PTO systems have no pressure either. The charge pump circuit draws oil from the spin-on filter, pressurizes in the pump then supplies oil to the PTO clutch/brake, hydrostatic drive system, and the steering system all independently. Attached is a diagram of the flow going through the charge pump.

 

[Oregon2023]

There are test ports on the hydrostat & JD has a procedure and pressure specs. This may be where to go from here

The input shaft 41 from the motor is directly coupled to the variable pump 35 with the fixed pump directly below coupled with gearing. Are both of those not working? Did you look for cracks in the hydrostat housing 30 where the input shaft goes in? Also are you sure on your model the charge pump runs the steering also?

https://partscatalog.deere.com/jdrc/sidebyside/equipment/74954/referrer/navigation/pgId/22128359

I did not see any cracks. The hydrostatic pump and hydrostatic drive are spinning but not pressurizing due to air in the system from the charge pump not pressurizing. I have tried bleeding the entire system with the back end of the tractor on jack stands with the rear wheels off the ground. There is zero movement of the rear wheels.

 

[Oregon2023]

Have you tried to drive the tractor under this condition? The charge pressure does two things.

1) provides pressure for hydrodynamic bearing lube between rotating group surfaces while at standstill. If run a length of time with any pressure you can score the wear surfaces.

2) provides make up oil for leakage in the HST circuit during operation.

I have not tried to drive it. I have only attempted to bleed the hydrostatic drive system with the rear wheels off the ground and the 4x4 disengaged.

 

[Oregon2023]

Rollover ? Any details ? You may have several problems . Kevin .

The tractor originally rolled on its side and hydro-locked the engine with oil. That was easy enough to fix and the engine runs great. When it had rolled it apparently broke the tunnel section between the engine and transmission. When I drove it shortly after getting it running after tipping over, the tunnel system collapsed. Not a good feeling to have the steering wheel pushed into your lap. When I disassembled it to replace the tunnel section that is when I found the broken transmission input driveshaft. I carefully removed, cleaned, and resealed the hydrostatic pump, drive motor, charge pump, and valve block in the process of replacing the input driveshaft. I marked the locations of all the components and properly reassembled using the John Deere service manual for this model of tractor. I've never had one not pressurize and work after bleeding which leads me to believe there has to be further damage to the valve block or charge pump housing.

 

[Oregon2023]

I will split and disassemble the tractor for the 5th time and completely disassemble and inspect the entire hydrostatic drive system for cracks or other damage. I will keep everyone updated with what I find.

 

[MTGreen]

Yes, the charge pump does supply the PTO clutch/brake system. The PTO systems have no pressure either. The charge pump circuit draws oil from the spin-on filter, pressurizes in the pump then supplies oil to the PTO clutch/brake, hydrostatic drive system, and the steering system all independently. Attached is a diagram of the flow going through the charge pump.

So it looks like the test port at B is directly connected to the output of the charge pump itself. Seems like you need a pressure gauge reading here. You could differentiate between low pressure from the pump versus sucking air which would mean almost zero pressure. No pressure output from the pump means you don't compress either one of those springs which means you don't get any pressure to the steering or PTO.

Also I wonder if there was a chance that something got assembled incorrectly in the charge pump when you had it apart

 

[Oregon2023]

So it looks like the test port at B is directly connected to the output of the charge pump itself. Seems like you need a pressure gauge reading here. You could differentiate between low pressure from the pump versus sucking air which would mean almost zero pressure. No pressure output from the pump means you don't compress either one of those springs which means you don't get any pressure to the steering or PTO.

Also I wonder if there was a chance that something got assembled incorrectly in the charge pump when you had it apart

It is possible something was assembled incorrectly. The rotor and idler each have a small arrow on their face that was facing to the rear of the tractor when I originally disassembled it. These arrows don't seem to line up with anything and it wouldn't matter anyhow since the rotor and idler spin and change position in relation to each constantly while in motion.
The charge pump is definitely moving liquid, but I haven't taken another pressure reading since I put it back together this last time (it was previously 0). If I remove the test port plug or the steering system pressure regulator, oil shoots out. It just doesn't seem to be building enough pressure to open any of the pressure regulating valves. It's moving liquid and its going somewhere, just not under pressure through any of the pressure regulator valves.
The last charge pump seal I removed was deformed and blown out the bottom of the housing despite me verifying for sure that it was properly seated when assembling which leads me to believe that the pump housing may be warped from the tractor breaking in half. We will see when I get it apart again.

 

[oldnslo]

Oregon
Does your Deere manual list the dimensional tolerances for the charge pump bore? If the outer gear has scored the bore this style pump will lose pressure pretty fast. Shaft being pushed out would also indicate excessive internal leakage.

Would you see steering pressure unless wheels are cranked to the stops? You should have PTO and charge pressure all the time but not sure on steering.

Port H goes to a system relief. I presume you have verified that connection and valve.

Wishing you the best of finding the problem.

 

[Hoss710]

could there be a stuck open bypass or pressure regulator? is there anywhere the fluid is going in a another circuit that could be dumping pressure? or a crack in a housing?

 

[Oregon2023]

I split the tractor and removed and disassembled the entire hydrostatic drive. The charge pump components all measure well within specs. There’s a little wear on the parts, but nothing you could even feel with your fingernail. All seals were intact. I also removed all the valves and everything was pristine. I used compressed air to make sure the charge pump pressure regulator doesn’t leak. None of the blocks or housings are cracked or warped. I’m stumped as to why the charge pump still won’t create pressure. I guess the next step is just buy a new pump assembly.

 

[Hoss710]

keep us posted . I'm curious what you find. and good luck.

 

[oldnslo]

New pump is awful expensive might fix it solution but I do not have a better idea since you have inspected everything.

 

[MTGreen]

I can't help but wonder if something was misassembled or you're missing a part that's not readily apparent