John Deere 2520 no charge pump pressure

   / John Deere 2520 no charge pump pressure #1  

Oregon2023

New member
Joined
Feb 10, 2023
Messages
15
Tractor
John Deere 855, 2520, 2040
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.
 
Last edited:
   / John Deere 2520 no charge pump pressure #2  
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
 
   / John Deere 2520 no charge pump pressure
  • Thread Starter
#3  
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.
 
   / John Deere 2520 no charge pump pressure #4  
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.
 
   / John Deere 2520 no charge pump pressure #5  
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?
 
   / John Deere 2520 no charge pump pressure #6  
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.
 
   / John Deere 2520 no charge pump pressure #7  
Rollover ? Any details ? You may have several problems . Kevin .
 
   / John Deere 2520 no charge pump pressure
  • Thread Starter
#8  
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.
 

Attachments

  • Screen Shot 2023-02-11 at 3.33.42 PM.png
    Screen Shot 2023-02-11 at 3.33.42 PM.png
    179.8 KB · Views: 51
   / John Deere 2520 no charge pump pressure
  • Thread Starter
#9  
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?
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.
 
   / John Deere 2520 no charge pump pressure
  • Thread Starter
#10  
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.
 
 
Top