I have a Cat 279D track loader. Loader has no down pressure. Tilt cylinders will raise front of machine up. When trying to power down with the loader cylinders, it will actually reverse and start raising up. Then when I move the lever back to the neutral position the boom drops back down. Machine has new pumps. Loader has no problem lifting a load and no drifting. Any help would be appreciated. Thank you.
Why were the pumps replaced.? Did the problem start after the new pumps were installed.? Please supply a Serial Number.
Serial# CAT0279DVGTL01647 Pumps were replaced because boom stopped lifting. The charge pump (gear pump) and center pump (piston pump) were replaced. The piston pump had come apart which sent particles throughout the hydraulic system. I removed hoses and flushed them out. Valves were removed and flushed as well. Hydraulic tank was removed and thoroughly cleaned. Filter replaced. After reassembly machine was started and hydraulic functions were cycled and then I shut it down and changed hydraulic oil and filter and cleaned tank again. Everything seems to work normal except for not having any down pressure. I’m at a loss!
Based on that description my call would be that you still have contamination in the control valve. Maybe it has migrated from somewhere else in the system since you cleaned the control valve. Certainly that would be the first place I would look.
Unfortunately removing that valve again was my next move. Hopefully I will something obvious. Do you by chance know where the float circuit is on that system? I’ve heard some guys comment on looking at that as well.
Please post a Serial Number. I’ll see what information I can scrape up on the implement system operation.
Sorry I missed that you had posted it already. Attached the System Operation for both the standard control valve and the High Flow XPS control valve. One or other will be the same as what you have on your machine.
Thank You! I’ll take a look at this. I’ll get back to you when I get the valve removed and let you know what I find.
If there are any orifices or screens in that particular section of the valve then I would be looking there first for something wedged there that doesn’t belong….
If you have a load a mid level and slowly raise the boom, does it momentarily drop before raising? Reminds me a bit of one that had a damaged cylinder seal.
Ok. I’ll be looking. Thank you!
When I raise the boom, even empty, it drops like an inch when I go back to the neutral position. I had the same thought on the cylinder seals and went ahead and replaced them. Unfortunately it didn’t change anything. I’m getting ready to pull the main control valve off (again) and check it for foreign material.
Unfortunately due to system design all the garbage from a pump/motor failure ends up in the hyd oil cooler unfiltered. Only way I know of to make it clean is to replace it. Hyd oil samples are a must.
To which I would add that the samples have to include an ISO Cleanliness Code analysis, which is not necessarily a standard feature.