Cat 305C - Boom slowly going down when cold

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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!

 

[Nige]

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.

 

[Extra Fubar]

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!

 

[heymccall]

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.

 

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Hi heymccall! Thanks for your reply. The S/N is HWJ03046.

 

[heymccall]

Running your s/n, it looks like your machine doesn't have the load check manifold. If it does, it would look like this...

 

[Extra Fubar]

Thanks heymccall for your reply. The check manifold would be item no. 3?

 

[heymccall]

Yup. And, it's almost always an option.

 

[Extra Fubar]

Excellent - I'll check more closely this coming weekend (I don't have access to the machine during the week).

 

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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?

 

[heymccall]

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.

 

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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.

 

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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?

 

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Any opinions guys regarding the boom joystick (valve?) leaking oil?

 

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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.

 

[Extra Fubar]

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?

 

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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:

1. I had less boom lifting power than before (but everything else is perfect)
2. 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
3. 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!

 

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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$.

 

[Mark250]

swap these two valves first before you order one and see if it makes a difference
Mark

 

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Thanks @Mark250 ! Excellent idea. Hope that it isn't too hard to do.