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I have a laggy boom and tracks everything else works fine on…

I have a laggy...

I have a laggy boom and tracks everything else works fine on a CAT 302.7D

Mechanic's Assistant: What is the complete model and serial number of your machine?

LJ700428

Mechanic's Assistant: Are you fixing this yourself? What have you tried so far?

Cat 302.7D Checked hydraulic level yes fixing myself possible to relieve pressure in hydraulics?

Mechanic's Assistant: Sometimes things that you think will be really complicated end up being easy to fix. The Heavy Equipment Mechanic I'm going to connect you with knows all the tricks and shortcuts.

Yea it just came from cat is very well maintained should be ab easy fix it is slow to rise, like takes about 2 to 3 seconds before it raises the boom

Mechanic's Assistant: Anything else you want the Equipment Mechanic to know before I connect you?

And then lowering the boom is also slow but not laggy just less power and slow and the tracks seems the same aggy laggy

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Answered in 1 hour by:
6/27/2020
Mechanic: Dan, Technician replied 2 years ago
Dan
Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 14,865
Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
Verified

Hi, It is Dan. I will be glad to help. We can follow up as needed on here, Give me some time to review your information and follow up with my responses. Professionals are not employees of the site but users of the site and help on here as time allows in between jobs, family,etc. Response time can vary depending on my work load each day but I will always respond back on my next available login. Feel free to respond back at anytime if for any reason we seem to get separated,for status, etc.

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Mechanic: Dan, Technician replied 2 years ago

Excavator hydraulics. If the problem is only isolated to those functions, it is most likely a problem within the control valve or your relief valve cartridges for those functions. Check your control valve spools for any type of metal or debris that would cause them to stick or malfunction. Also check your relief valve cartridges for any debris or damaged O-rings within your main control valve as well. Sometimes travel problems however can be a problem with the Rotary manifold or swivel seals bypassing internally causing a loss of flow to the travel motors. Despite the maintenance history, I still recommend inspecting inside your hydraulic filters to see if there is any sign of fine metal or debris that looks like glitter in the filter and oil which would indicate a potential component failure or pump failure occurring. This metal or debris can get pushed through the system and lodged in other components as well as your control valves creating further problems. For example, if you were to have let's say a drive motor failure that started producing metal into the system and then that metal started getting lodged within your control valve spools causing other functions to malfunction as well or the control valves and relief valve cartridges to stick and malfunction. If you check all of this and it is clean, you will want to get your pressures tested and confirmed whether or not they are within OEM specifications for your model and serial number machine. It is a pleasure to help anyway I can.

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Customer reply replied 2 years ago
Hi Dan thank you,The problem is only in the hydraulic boom. The boom lags for about 3-4 seconds and then finally picks up. After releasing the control arm up the boom still goes up slowly. Same thing going down, takes a few seconds to start going down and then also continues after releasing the control. There is also little power in the boom hydraulic.With that statement, and knowing everything else functions fine, can you please follow up with me.I will check the hydraulic filters at any rate.
Mechanic: Dan, Technician replied 2 years ago
Check and see if you have those boom and arm potentiometers which are sensors on both the boom and the stick that could affect boom or arm movement actually if they are malfunctioning or if there is a wiring problem. Otherwise check the control valve and relief valve cartridges as well as possible bypass within the cylinder seals.
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Customer reply replied 2 years ago
Can you tell me how you go about checking a control valve or a relief valve cartridge? I have the parts manual.
But how do you check them? you replace them with new? take a look and how can I tell if the part is bad?You don't think it makes more sense to be the seals in the hydraulic cylinder?
Mechanic: Dan, Technician replied 2 years ago
You remove the relief valve cartridge by unthreading them from the valve and inspect the o-rings for any type of damage as well as inspecting the relief valve cartridge popits for any type of scoring or damage and debris that might be stuck preventing the relief valve from closing on its eat bypassing pressure.
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Customer reply replied 2 years ago
if the machine and hydraulic oil is cooled down, I can safely remove parts to clean without draining hydraulic fluid everywhere? or is there some main shut off? It is all controlled through a series of checks and valves I imagine, but just wanted to check. thanks for your prompt replies. I really appreciate it Dan
Mechanic: Dan, Technician replied 2 years ago
You are going to lose some oil when opening up these components. You can use a vacuum pump adapted to the hydraulic tank filler to put the tank under a vacuum which will allow you to work on the control valve while the tank is under a consistent vacuum.you will still get some drippage but you won't lose as much oil. This will allow you to avoid draining the tank. I sometimes cheat and plug the ports with shop towels wrapped in plastic bags but you are still going to need a drain pan below.
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Customer reply replied 2 years ago
also is this relief valve related to the boom specifically, because again it is only the boom malfunctioning at this point
Customer reply replied 2 years ago
The boom lifts and lowers after about a 5 second delay. but is slow and less power.
Mechanic: Dan, Technician replied 2 years ago
In the first screenshot you have provided number one is a relief valve.the relief valve for the functions in question are going to line up with the hoses from those functions. Follow the hoses from your boom cylinders into the main control valve and the relief valve cartridges for those functions are going to line up with that valve Bank.
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Customer reply replied 2 years ago
ok, yea it is making alot of vibration specifically in those hoses. is that a symptom as well?
Mechanic: Dan, Technician replied 2 years ago

Yes that is a possibility. Also, it is not unheard of for a cylinder to start to come apart internally such as the piston loosening up etc. which would allow a bypass of pressure within a cylinder as well. If the cylinders producing metal you will likely find some of that metal at the hydraulic hose port where it connects to the control valve. That would be another thing, you may want to disconnect the hoses to inspect for any sign of metal at those ports and scoring within the hydraulic spools.

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Customer reply replied 2 years ago
Ok, so I have checked one relief valve cartridge I believe. Please look at the screen shot I have put an arrow on the part I believe is the relief valve for the boom. Please confirm.Also, I see it is more like 10-15 seconds for the boom to start raising, and then it will raise slowly and almost all the way up. The boom is the same going down about 10-15 seconds of lag and then it lowers, but stops and goes down further when you move it that way.I was saying a few seconds to raise and lower but actually counted.The place where the hoses connect to the control valve is below my arrow in the screen shot I believe, is there any other way to determine if there is bypass in the actual hydraulic piston?
Mechanic: Dan, Technician replied 2 years ago
That should be the one in line with that valve Bank. Also check the port where the hoses connect to see if there are any signs of metal within the port as well as any scoring of the hydraulic spool by shining a light and looking inside the valve. Your hand joystick controls also have four different plungers underneath the joystick handle plate. These plungers will push down to send pilot pressure for your functions and shift those Main spools. Check to make sure none of those plungers are partially stuck down due to some corridor corrosion buildup which could hold a function partially open by sending pressure to the end caps on the control valve spools. You could also pressure test your hydraulic cylinder using shop air with both lines disconnected. Pressurize one side and see if you get air coming out of the other Port as you should not.
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Customer reply replied 2 years ago
It was only my toggle between ISO and the other type of joystick controls, had somehow vibrated to a point in between the two setings, should have checked that first. Might be good advice. I ordered a whole repair manual and parts manual, thinking it was something big. Help us amateurs with the easy stuff
Mechanic: Dan, Technician replied 2 years ago
Thank you for the update and I'm glad to hear that you got this resolved.
Dan
Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 14,865
Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
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Category: Construction and Road Equipment
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Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.

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