John Deere 2520 no charge pump pressure

[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