I have a 950f loader. When the boom and bucket levers are moved the machine vibrates like the pump is cavitating. The pump pressures are within spec. The problem is intermittent. Could something in the pilot circuit cause this? Any help would be great.
Check the rubber hose sections on the suction pipe from the tank. Tighten the hose clamps for the rubber section and replace the rubber if its really old and hard. Next check your hyd tank to ensure as the oil heats/expands the tank has pressure. Also seen where the tank wasn't pressurizing (filler cap missing a seal) and this cavitated the pump when the oil was hot
Thanks for your reply. I replaced both seals under the cap one was in the cap the other order the strainer. I also tightened the suction line on the tank. The machine is still doing the same thing. It's almost like the pump is starving for oil, but it only does this when it's warm. Just don't make sense.
Is there a pressure relief valve on the top of the hydraulic tank on that model..?
Next to check if the machine tank is holding pressure I would raise the boom all the way up and shut off the machine. Then slowly lower the boom down to the ground using the controls (it should have enough stored pilot oil to lower the boom). This should pressurize the tank. Loosen the cap and see if there is pressure there and if it holds the pressure for more than a minute or so. As Nige said check if there is a pressure relief and inspect. It should hold pressure but open any time there is a slight vacuum. Remove this from the top and it should hold air as you blow into it but allow air through when you suck. Next you could (I know easier said than done if you don't have a service truck handy) plumb in a regulator and put in 5-10 psi into the tank where the relief mounts on the top and pressure up the tank to check for leaks on the suction side. Does this machine have a 3 section (str., boom, pilot) vane pump with 1 main suction ? Is the tank on the R/h side (I assume so since its cavitating) or up behind the cab ?
I picked a 6YG S/N prefix for 950F at random - there are 6 different ones to choose from - and it has a breaker relief valve mounted on top of the hydraulic tank. That and to make sure the tank cap was sealing correctly would be the first places I'd be looking. If any other location in the pump suction side of the implement hydraulic system was leaking and causing the system to suck air, and if the tank was successfully creating and holding internal pressure with hot oil, surely it would manifest itself as a leak when the engine was shut off and there was positive pressure behind it...? Have you checked or changed hydraulic system filters recently..? Here's what I think the tank cap should look like. Does it have the metal plate (53) and the ball (54) in it..? 51 is a flat rubber gasket that holds the metal plate in place, 55 is the top flange of the strainer, and 50 is an O-Ring that fits under the strainer. Note that 51 & 50 are different Part Numbers. If the tank cap is missing any parts it will not seal and therefore not hold pressure correctly.
The tank cap is all there. I replaced both seals on the tank cap. On Monday I will raise the boom like you described and go from there. Thanks for the help.
If the tank cap is all there we have to assume it's sealing correctly, then as per Ben's comments above check the operation of the breaker relief valve on the top of the tank would be the next step IMO. If that valve is not maintaining pressure then the implement pump could cavitate under certain operating conditions. The valve is #33 on the attached illustration. If you remove it from the top of the tank you should be able to suck through the threaded end of it but not blow.
I've heard that description before and the usual culprit has been the ring in the vain pump. They get a rough spot or two and the vanes start popping over it causing the rattle that you can hear and feel in the controls. It is intermittent at first but if you continue running it will happen every time there is pressure when using a function. Nige and Big Ben are steering you right in checking the easy and cheap stuff first. I hope you find something without having to pull the pump. Pulling the cab to get to that component is not fun even if you have all the right lifting equipment to do it with. Good Luck!
The way I was always taught to diagnose hydraulic systems was to follow the oil. Its journey starts at the tank and therefore any diagnosis should start at the same place, eliminating everything in that location before moving round the system.
Nige mentioned the oil filter,,, I have a 950B and she won't take anything but a Cat filter... all others will collapse inside. Take it off and have a look inside of it.
I think you are right about the cause. It's just that most operators don't mention a little vibration to start with and when it gets worse, the damage is already done. I've seen them bad enough that the vanes break up and send steel down the lines. Suction leaks often don't show more than oily dirt on the hoses and may have a drip every few minutes. Crews coming in on monday might not even notice the oil on the ground under the machine. But what I've noticed is the noise coming off the pumps when they start after being down for a couple of days.
950F the pump comes out thru the floor by removing the seat. 950G needs the cab removed to get the pump out.
I raised the boom, shut the machine off and lowered the boom to the ground. I took the cap off the hydraulic tank and noticed some pressure, not anything considerable. Our tank don't have the breather on the top like the diagram shows above. The serial is 7zf00664.
7ZF machine does not have the breaker valve on the tank. I made a wild stab and got a different S/N prefix ..............
Replace the suction line