Caterpillar 302.5 Boom down/up pressure

[Daniel Paul]

I have a cat mini excavator serial 4AZ05894 302.5 has 1000 hrs on it. My problem is the main boom cylinder does not have a lot of down pressure and is falling several inches when I pull back on the stick. Going up it is also the same by moving the stick it will fall several inches before going up. If I leave the boom up overnight, it will be down by morning. Any help would be greatly appreciated.

 

[Nige]

Get the hydraulic oil up to normal operating temperature. Hang the stick vertical and raise the bucket about a foot off the ground then stop the engine. Mark the lift cylinder rod at a convenient location. It should not drift down more than 3mm in 10 minutes. Report your findings.

 

[SaarahMcgee]

I have a cat mini excavator serial 4AZ05894 302.5 has 1000 hrs on it. My problem is the main boom cylinder does not have a lot of down pressure and is falling several inches when I pull back on the stick. Going up it is also the same by moving the stick it will fall several inches before going up. If I leave the boom up overnight, it will be down by morning. Any help would be greatly appreciated.

It sounds like the seals inside your boom cylinder might be worn out, which is why the boom drops slowly during use and overnight. You can try a leak test to check for this, and resealing the cylinder should fix the issue. Also, take a look at the control valve for any damage or debris, as it could be part of the problem too.

 

[Daniel Paul]

Nige
I did the test and the boom drifted about 2" in the 10 Min.

SaarahMcgee
I had the cylinder resealed about 5 months ago and it started this about 4 weeks ago. I did not see any damage or debris around the control valve.

 

[Nige]

I did the test and the boom drifted about 2" in the 10 Min.

The next thing is you need to plug the line that carries oil to raise the boom and see if the cylinder still creeps down. If it does then it's the cylinder, if it doesn't you have to start looking further back in the system.

 

[Daniel Paul]

I will work on this over the weekend.

 

[shopguy]

Dropping when you pull to raise and seeping down sounds like you have a leaking load check valve

 

[Nige]

Dropping when you pull to raise and seeping down sounds like you have a leaking load check valve

Cat call it a load control valve, but it's basically the same thing. See attached. You need to first check if it actually has one. The LCV is an optional attachment.

 

[Daniel Paul]

Nige / Shopguy

So, from the PDF you attached looks like this would be mounted on the side of the cylinder I do not have anything on the side of my cylinder. The lines from the cylinder go straight back to the main block under the floor pan.

I will work on the test of blocking the line either this evening or tomorrow evening.

 

[Nige]

So, from the PDF you attached looks like this would be mounted on the side of the cylinder I do not have anything on the side of my cylinder. The lines from the cylinder go straight back to the main block under the floor pan.

OK, so you do not have that option on your machine. Back to Plan A, cap the cylinder line.

 

[92U 3406]

Normally load checks are part of the main valve itself are they not? The attached PDF's look like an optional holding or lock valve that attaches to the cylinder to prevent the boom dropping if a hose blows.

The load checks will hold the pressure in circuit until pump pressure is able to overcome the pressure in the cylinder. Without them the implement will drop until pump pressure gets high enough to hold and lift it.

Any chance there's a schematic of the boom circuit and/or control valve that can confirm that?

 

[Nige]

Any chance there's a schematic of the boom circuit and/or control valve that can confirm that?

Here you go.

 

[92U 3406]

Here you go.

Would the circled check valve be the load check inside the control valve slice? Looks like it may function as one.

 

[Daniel Paul]

The next thing is you need to plug the line that carries oil to raise the boom and see if the cylinder still creeps down. If it does then it's the cylinder, if it doesn't you have to start looking further back in the system.

so I done this test and found that the cylinder did in fact creep down so I ordered a new seal kit for the cylinder. I was able to get it installed last night and tested it today and that fixed my issue.

thanks to everyone for the advise and help.