Soooooooo.....he changed the filters and fluid....same problem. We cut one of the filters open and there are metal pieces inside of it, small ones throughout the filter and some brass as well. He's figuring out his plan of attack. I told him to get someone familiar with hydraulics to do a pressure test on it and that should pretty much tell the whole story i would imagine....
Making up a gauge to do a pressure test probably won't cost 20 or 30 bucks. That's what I would do. If there is an hydraulic shop nearby they will have the right fittings. Tell him you want the gauge to fit an accessory circiut and also to be able to be put inline with say your pressure line to the loader valve.
A pressure test will tell some things, not all. For example there may be a way to differentiate between a worn hydraulic pump and a relief valve that has failed in the open position.....but I'm not sure I know off hand how to distinguish between the two. Read up in the shop manual too. As Hersheyfarm says,there are several pumps and a number of relief valves in the M59 hydraulic circuit.
For that matter there is a sort of hidden control below the FEL control on the M59 that turns flow to the front accessory circuit on and off. That's an example of a valve or circuit that could have failed and would show the same symptom - i.e. low pressure at low rpm rising to near normal pressure at high rpm.
I'll admit - it does begin to sound like a hydraulic pump wearing out.....but not totally worn if it will give pressure at high rpm. However keep in mind that it is normal for a hydraulic sump filter to show a surprising amount of metal and brass.
He will know a lot more when he changes the hydraulic fluid. After all, Kubota is using a common oil sump for a number of components that normally shed wear metal as they work... That metal is part of why you have three filters under there. That common sump will normally contaln wear metal from the the the rear end, the wet brakes, the transmission, the FEL, backhoe, the two speed axle shifter, and the differential lock. The brakes and diff lock both produce a lot of debris. If the tractor was ever used with rental hydraulic accessories on the front or rear hydralic circuits there can be particles from the oil that gets exchanged with those accessories. There can be a surprising amount including larger pieces. It's all why they have all those filters. And why it's good practice to add an extra inline filter huydraulic hose filter anytime you connect up any rental accessory.
Those are all good reasons to look at the hydraulic fluid itself when changing it. Good practice to save all the metal and a cup of the fluid that comes out when changing that fluid until you get a good diagnosis - there can be some real clues there.
Note that in the operator's manual it more than one plug to to remove to drain the common hydraulic sump (12.2 gallons). Pay attention to what fluid comes from which one. Might be a reason to use several containers.
My apologies for going over this basic mechanical procedure in such detail. I'm aware that any mechanic already knows all this and more. But sometimes it doesn't hurt to hear it from an old mechanic, too.
Good luck,
rScotty
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