JD 762 scraper charge pump

Hello, I have been fighting a problem with my JD 762 elevator chain that quits when put under a heavy load, it seems that the charge pump looses pressure and then the elevator chain stops, and the pumps howl at the same time, I took the charge pump apart and it looks like new inside, I also put a small shim in the pressure relief valve and the pressure increased on the gauge but still drops to zero under a load, I did pressure tests at the elevator motor test ports and I only get about 1500 lbs before it quits. I hate to buy a new hydrostatic pump and still have the same issue, I have replaced the inlet filter, and the oil level is full and I drained and replaced the oil with new JD hydraulic oil, My machine serial number is 002310T , and it has a sunstrand hydrostatic pump for the elevator system model 22-20 65H , I also shimmed the 2 pressure relief valves at the motor trying to find a solution? Can anyone please help?? Dave in Decatur

Welcome to HEF Dave in Decatur!

Did you get 1500 psi in both directions?

Charge pressure dropping to zero when the elevator is loaded is an indication of excessive leakage in the system. Since I doubt you have a flow meter to test the elevator pump, I would cap the lines going to the elevator motor (you may have to go to a hydraulic shop to get good caps to handle high pressure), and then operate the elevator. When it is stalling does the charge pressure still drop to zero. If yes, your issue is in the pump. If it holds charge, then the issue is in the motor.

Hello, and thank you for the reply, yes- 1500 lbs max in both directions, I will get some caps and test again. Question- is there anything inside the pump serviceable ?? Or would a person be better off to purchase a rebuild ??

David Friedt said:

is there anything inside the pump serviceable ??

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There used to be a time when you could buy anything inside. Now, nothing is available through Deere, new or reman, nor internals parts. So, if anything is wrong with either the pump or the motor, you will have to source parts or components elsewhere.

A very quick internet search shows plenty of parts are available. Sundstrand, Saur Danfoss. Rebuilding yourself isn't a big thing but a clean environment to do the job is.