Kubota 121-3 Excavator Weak Hydraulics

[banditbooker]

Hello, I have a Kubota 121-3 Super Series excavator and was using it on the job the other day and it was working fine. I shut it down and came back a couple hours later and it didn't have much hydraulic power. I changed the hydraulic suction and return filters in the tank and even a little one near the pump recommended by the dealer. Still don't have good hydraulic pressure. Was on the phone with the kubota mechanic and he said about pressure testing the hydraulic pump, so I got a gauge and plumbed it in where he said. With the machine running and no control input at an idle, the needle bounces around low at like 500 or less psi. When adding control input and going against a relief the most I can get is 2700 psi. Trying to figure out where the problem lies, whether its a pump issue or a relief valve issue or something else. I have heard of another guy who had similar problems but lost track movement all together and it turned out to be a busted O-ring caught in a relief valve. My question is number one, is that how I should check the pressure with it under load or at an idle and two, is where would the main relief valve be located so I can check it? Or if anyone else has any input or advice while I'm waiting to hear back from the dealer. I need to finish this job up and need the excavator. Also the machine will die down when bottoming out the hydraulics against the relief.

Thank You, Bill

 

[Dave M7040]

To check the pump and relief valve you want to install your gauge into a quick connector on its own and then send fluid to that connector and read pressure value.

Do you know what the relief valve spec's are?

Dave M7040

 

[banditbooker]

the pump pressure is 3555 psi, There is a main line (about 1in dia.) coming right out of the pump with a 90 degree fitting with an 1/8 npt plug in it. The dealer told me that is where I screw a 5000 psi gauge in to check it. When checking it, I dead headed the hydraulics and got about 2700 psi. I'm not sure about the relief valve specs, the manual for the machine says the hydraulic pressure is 3555 psi.

 

[Dave M7040]

I am going to back away from your problem because, after reading up on your machine, I realize that it has quite a sophisticated hydraulic system.

The fact that the problem suddenly appeared after short break and makes me think that a valve for something, tracks, swing, blade, or auxiliary hydraulics on the boom is partially open.

If there are quick connects, I would be re seating them, I would be looking closely for a damaged or pinched hose but beyond that I don't think it is wise to start messing with a relief valve as you may turn a minor problem into something major.

Perhaps someone with the same machine may offer more knowledgeable comments.

Good luck

Dave M7040

p.s. you might also try the other forum
OrangeTractorTalks | Kubota Tractor Tips, Classifieds, Specifications and Discussion
although I have never seem much excavator discussion there.

 

[Yankee Clipper]

Bandit,

I would not condemn the pump if you can get 2700 lbs out of it with clean filters on the work (discharge) port from the pump. I think you would do well before spending a lot of time and energy to get it to dealer as there are several different hydraulic systems on the KX 121-3.

The 3555 lbs is the overload relief - to protect the weldments (boom/stick bucket) from damage when they are overloaded as everything has a yield point. You will note this is always a higher value than the system relief pressure which you have obtained in your testing.

Good luck!

YC