Loader Joystick - Bucket goes down when trying to lift

[dm-in-mn]

Hello all,

I have a Kubota M4030su tractor with an M1000 front end loader. The FEL is controlled by a joystick. The problem I am having is that when the joystick is pulled back to lift the bucket, the FEL actually free falls for the first few centimeters of travel on the joystick - then the arms begin to lift. This makes lifting heavy items quite dangerous, as when the joystick is commanded to lift, it actually drops the FEL, then starts lifting.

Anyone ever encounter this problem before? My intuition would be that there is an O-ring inside the valve for the arm that probably needs to be replaced. Is this the right tree to be barking up?


Just to make some clarifications:
When the joystick is in the center position, nothing moves. The bucket stays solid, as does the loader arms. It's when the joystick is commanded to start lifting the FEL that it seems to internally bypass.
I have attached a simple diagram that hopefully explains where the issue is.


I appreciate the input. Thank you

 

[RickB]

The load check valve associated with the lift circuit has failed, is stuck open and/or has debris stuck in it.

 

[wdchyd]

One of your lift piston seals are compromised, you’ll need to rebuild lift cyls

 

[ptsg]

The load check valve associated with the lift circuit has failed, is stuck open and/or has debris stuck in it.

+1 for a bad check valve.

 

[dm-in-mn]

Thank you all for your replies. I do not believe that the list piston seals are compromised. When the valve in in the center position, the lift arms are quite solid.

Bad check valve, eh? Would this check valve be on the actual joystick body? I would look up the parts diagram for the joystick, but I cannot find a model number on it. I am guessing that the model number is between the valve and the mounting bracket. A failed check valve would make sense to me. I will use that as my working hypothesis going forward, and will dismount the joystick to see if I can find a model number.

I appreciate the help!

 

[ptsg]

Found a parts diagram for that loader over at Messicks website.

Here is the exploded view. Check valve consists of the parts #5, #4 and #6. Looks like there is one per spool, located in between the work ports.

As mentioned before, either a broken spring or trash holding the check valve open.

 

[Sportsman762]

One of your lift piston seals are compromised, you’ll need to rebuild lift cyls

When the joystick is in neutral bad seals in a piston will cause the cylinder to drift down. It does not cause a sudden drop when the valve is actuated. The check valve is the most likely culprit.

 

[LD1]

Thank you all for your replies. I do not believe that the list piston seals are compromised. When the valve in in the center position, the lift arms are quite solid.

When the joystick is in neutral bad seals in a piston will cause the cylinder to drift down. It does not cause a sudden drop when the valve is actuated.

This is incorrect information. Bad lift seals will NOT cause the cylinder to drift down. You could even remove the seals and when the valve is in neutral....it will be rock solid.

Bad seals "can" cause the loader to drop a bit though when trying to lift.....especially if you have a heavy load and are trying to lift/move very slowly. Heres why:

The base end of the cylinder is the side you are applying pressure to to lift the loader. The rod side is where fluid is expelled and returns to tank. So moving the joystick does TWO things. 1. Allows high pressure oil to enter the base end of the cylinder. 2. Allows oil out of the rod side of the cylinder to return to tank.

If you have bad seals....and they are leaking FASTER than you are applying high pressure oil.....the oil can go past the seals and return right back to tank.

Lets say you have bad seals that will allow 2 GPM past them. And your tractor is a 8GPM hydraulic system. If you are trying to feather the load (to lift slowly) you might only be allowing 1 GPM to enter the cylinder. But you have also given a path for 2 GPM (past the seals and back through the valve) for oil to exit the cylinder. So when 2GPM leave the cylinder and only 1GPM enter the cylinder....the result is the cylinder drops. ITs not until you move the joystick further and supply MORE than 2 GPM that it will actually start to lift.

The likely culprit is the check valves though. Sometimes called anti-drop valves. But BOTH those and the cylinders are easy enough to test.

First thing I would try would be Swap the lift and curl. (provided you have non-regen curl). Second thing I would do would be to test the cylinders.

 

[wdchyd]

Sorry if everyone out there feels like I’m wrong on the piston seals being bad, maybe I should just keep things to myself. After all anyone with a keyboard is an expert in guessing.
OP please enlighten us when you find the problem.

 

[LD1]

Sorry if everyone out there feels like I’m wrong on the piston seals being bad, maybe I should just keep things to myself. After all anyone with a keyboard is an expert in guessing.
OP please enlighten us when you find the problem.

I didnt think you were wrong

But there are a few people in this post that are completely wrong.

There are a few things it "can" be. But troubleshooting is pretty easy on all accounts. Hydraulics arent mysterious rocket science like some think it always is.