Hi everybody! I've recently purchased a Cat 305C CR 2008 with 4100 hours on it. Overall the excavator seems in pretty good shape and was correctly maintained. I'm new to this nonetheless and I've noticed that after starting the excavator (only tested on cold temperature so far - like 30-40F), whenever I lift the bucket with the boom, it very slowly drops down. When the excavator has been running for a few minutes (2 to 4), this seems to go away entirely. What could be wrong? Anything to adjust or check? Anything to worry about? Thanks guys!
Generally the test for cylinder drift is done with the hydraulic system at normal operating temperature, which would equate to operating the machine for at least 30 mins from cold in ambient temps of 30-40F. If as you say your probem goes away after a short time I would say there is nothing to worry about. It may be worth your while finding out when the hydraulic oil was last changed and what grade of oil was actually used in it. An oil with too high a viscosity might possibly be the culprit.
Hi Nige, Many thanks for the response - it's really appreciated as I'm slowly learning to work on the machine. I'll try to get in touch with the seller of that machine to know about the hydraulic oil that was used. Perhaps it would be a good thing nonetheless to start "from scratch" and replace it entirely. Thanks!
I'm leaning toward a sticking load check valve, assuming the boom is equipped as such. How about a serial number? At least the prefix.
Hi heymccall ! Thanks for your reply. The S/N is HWJ03046.
Running your s/n, it looks like your machine doesn't have the load check manifold. If it does, it would look like this...
Thanks heymcc all for your reply. The check manifold would be item no. 3?
Yup. And, it's almost always an option.
Excellent - I'll check more closely this coming weekend (I don't have access to the machine during the week).
I definitely don't seem to have a check manifold and this past weekend, the boom has been going down by itself a lot faster than it used to. Power seems to be good but I seem to hear a small "whistling" sound when I lifted big rocks - I don't recall hearing that sound that much before. I haven't done my homework to check if the hydraulic oil needs changing. I guess it's time now to replace all hydraulic oil, right?
Changing the hydraulic oil wont solve that. My money is on the cylinder bypassing internally. Not hard to reseal/ repack a cylinder that size if you have a stout vise and larger sockets.
Hi heymccall - thanks for your response. You mean that cylinder (pointed by the red arrow)? Looks like I might have to call a pro for that one.
I spoke to someone who did some repairs on my excavator a few weeks ago (changing hoses). He said that the problem could be the joystick "leaking" oil. One test he asked me to do is to lift the boom and then, lift the security leaver to disable the controls. If the boom doesn't go down, it might be the joystick. I noticed this yesterday when I was working with the excavator. The boom would go down quickly (like 30 seconds for the bucket to reach the floor when it was 6' high) but when I lifted the security leaver, it wouldn't go down (well, it took like 15 minutes to reach the floor when it was 6' high). Could that be the issue?
Any opinions guys regarding the boom joystick (valve?) leaking oil?
I did some testing today. First I opened the hydraulic oil tank. When I twisted the cap, I paid attention to the air relief in there and there was some. I also made the test with the security leaver and that didn't change anything. The boom seemed to go down a bit more slowly today, I don't know if it's because of the air relief from the hydraulic oil tank.
I made a test today - ie., lifted the boom, disconnected the top hose from the cylinder and oil was leaking quite a bit from the cylinder - so I guess that means it has an internal leak. I was also surprised that it was leaking a lot too from the hose itself. How much can it generally cost to get that fixed?
I had a guy specializing in hydraulic machines do some test last week, and he redid the cylinder leak test and said that it wasn't that. He also did some tests and notice that the boom would stop going down by itself when the machine was turned off completely. He suggested to me use the machine this weekend in order to try to narrow down the issue. So this week, while moving big rock around I found that: I had less boom lifting power than before (but everything else is perfect) I couldn't anymore lift the front or read of the excavator off the ground entirely like I was able to about 1 month ago I heard a good amount of whistle sounds when lifting big rocks Anyone got any more ideas? This issue is frustrating and starts to impact the machine's performance. Thanks!
Sorry for the noise... but I called Caterpillar today and explained them my issue. The nice gentlemen told me that it is likely the boom relief valve that is broken. From the parts manual, it looks like it's part 272-7832. Should I change this preventively and at least, eliminate one potential place to look at? That thing is about CAD 300$.
swap these two valves first before you order one and see if it makes a difference Mark
Thanks @Mark250 ! Excellent idea. Hope that it isn't too hard to do.
On my larger Cats, the relief cartridges have (had) a design flaw. When using the machine improperly (beating rock or any action that would cycle the relief valve open repeatedly and rapidly), the back and forth oil would pull the spring coil of the integral makeup valve into the relief seat, causing the relief to slowly bypass. For years, I'd disassemble the valve, flip the makeup spring over and reassemble. Sometime in the last couple of years Cat revised the cartridge to prevent the makeup spring from unwinding/ fouling the relief seat. I could leave the relief setting intact, and just separate the lower half to inspect. If that was the issue, the makeup spring would be in the relief seat. I dunno know if the minis have the same "flaw" or not. But, if it were the relief cartridge, it wouldn't matter if the machine was running or not.
@Mark250 Can you confirm it's those two valves to swap?
the one on the left is the boom head end line relief the other is the rod end .you could swap the one on the left with any of the other line reliefs as they are the same pressure setting
@Mark250 Ok - I did the test. Nothing changed by swapping valves so it's not that. Then, I re-did the cylinder internal leakage test. I disconnected the top hose (to lower the boom) from the cylinder. Whenever I try to lift the boom, there's quite a big amount of oil getting our of the top hose, continuously - like one liter in 15-20 seconds. If I try to lift the machine with the boom, I can hear a whistle sound from the boom cylinder. I guess its internal o-rings and stuff are damaged and need replacement.
I am assuming the guy that did your original cylinder bypass test would of done the test at each end of boom cylinder travel .this test does not account for bore damage or swelling along the cylinder barrel length. there is another way to do that you said oil is coming out of the top hose. did you mean the hose that goes back to the machine or from a hose that comes from the cylinder. if from the latter it sounds like you are on the right track Mark
Hi Mark, thanks for your response. I mean the top hose that is connected in the cylinder. When I removed the hose, lifted the boom and was trying to maintain it the highest I could, oil was coming out from the cylinder hole (where the hose was connected) at about 1L of oil per 15-20 seconds. That was messy. Thanks
hope the guy that said your cylinder was ok didn't charge you .if that was my call I would be very embarrassed. Mark
Final update on this. I've got my boom cylinder back yesterday which was rebuilt (new seals, new piston rod, etc.). That fixed my issue - the machine now works perfectly well. Thanks to everybody for your great help in identifying the issue.