Hello Everyone! I have a 92 New Holland L785 with a Perkins motor. When I bought it, the machine had been sitting for a couple years. It appeared to run/drive good and when I brought it home the hydraulics were so sluggish that it would hardly raise the boom. The hydraulic fluid was pure white and the mesh prefilter was full of nasty white/grey snot. I cleaned it and the machine took right off. I've since replaced the hydraulic filters twice and cleaned the prefilter about 4 times, within about 16 hours of run time. It seemed to be running great for a while. Now the machine seems to have less hydraulic force than it should. Also when I raise the boom, the low pressure light (preset to 50psi) feeding the drive system will flicker. I installed a 3,000 psi pressure gauge just after the control valve feeding the bucket cylinders. The pressure seems to range between 150-1000psi and doesn't seem to be effected at all by the engine RPM's. When the cylinders are maxed out, you can get the pressure to pop up to around 2,000 and it sounds like the relief valve is opening. Does anyone have any ideas on what the problem could likely be? I was thinking the gear pump, but I would have thought the pressure would have gone up when the engine RPM's increase? Any idea's or advice would be GREATLY appreciated! THANKS! Ben
Hydraulic System Issues! Please Help!
- Thread starter gravinus
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skidsteer.ca
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No problem Ben, if it vanishes from here , check the NH section.
Your hyd pump pressures seems decent, but the light your refering to is for the charge pressure. This is created by choking off the return flow from the hydraulic pum until it reaches a pressure (generally) between 100 and 200 psi. This charge pressure feeds you hydrostatic wheel drives. A few machines have a separate pump for charge pressure but most don't.
It could be a problem whith the replentishing valve that creates this restriction.
I suggest you try tradebit.com to see if any manuals are available, also exploded parts views are available on sites like messicks.com
Thanks for the info! That is correct, it is the charge pressure light that is coming on. There is a 110psi check valve that directs the pressure to the wheel drives. The excess goes through a different filter and returns to the reservoirs on my machine. The odd thing is it only happens when raising the boom, which I assume puts a large oil demand on the system. It also only happens when the machine has been running for 20+ minutes and the oil is hot. I did replace all 25 gallons of hydraulic oil about 14 hours of run time ago, so I don't believe there is a quality issue with the oil. Would the fact that it only happens when its hot, mean it is more likely the gear pump vs the check valve? I would guess the check valve should operate the same regardless of the oil viscosity? Thanks again! I really appreciate the help! Ben
