656 Hydro pressure

Got a call from the implement shop yesterday. They put the flow meter on the hydro to see why it is slipping and the mechanic told me the readings were 3,000 pounds in reverse and 1,800 in forward. He's sure the hydro is worn because he said it should be putting out about 5,000 pounds. My question is why are the readings so different in forward and reverse? He is going to take the high pressure relief valves out and look at them and also will check for a cracked line but I'm wondering if replacing the valves will help and if that will bring the pressure in the forward valve up to the same as the reverse valve. The hydro has adequate power the way it is for loader and mowing work so if they can get the forward pressure up to 3,000 I plan to run it that way until the hydro gets much worse. Is there anything else that could be causing the two valves to have that much variation in pressure?

Picking my old nogging, and believe the is dump valve, that would not let reverse in high range. also check dump valve at the foot and inch pedal (clutch) pedal. Fellow brought me a center section once that he removed from tractor, dissasemled could not find any thing wrong, low and behold it was the clutch dump valve.

Most likely your problem is scoring on the brass and steel plates for both the hydro pump and motor. Scoring allows oil to get between the plates and force them apart causing loss of oil pressure. They are highly machined surfaces to cleanly seal the oil as the plate turns and blocks off the holes the oil flows through.

Scoring on the hydro motor plates can cause the difference in pressure. The pump always turns in the same direction so the pressure loss should not change between forward and reverse. The motor reverses direction for reverse so it is possible to have different pressures before the plates separate.

The high pressure relief valves are pilot operated, controlled by the Foot-N-Inch valve (clutch pedal). Generally the valve will fail because of scoring and stick open. It is unlikely there is anything wrong with them. A cracked pressure line will surely cause a loss of pressure in one direction. It would be unusual to have both line cracked. Leaking check valves can also cause loss of pressure but there again it would be unusual for both of them to have failed. Both relief valves and both checks valves are the same for forward and reverse so it won't hurt to switch them. A positive check for cracked lines can be made by capping the fitting at the relief valves. You wont be able to get a pressure reading but if you drive it you can see if it makes a difference. WARNING!!! IF YOU DO THAT THE ONLY CONTROL OF THE HYDRO IS THE FORWARD/REVERSE LEVER.

Owen,
If the brass and steel plates between the motor and the pump are scored does the whole hydro unit need to be replaced or can just the plates be replaced?