Kubota KX41 revs dropping when hydraulics are activated

[Godhungry777]

See video explanation.
Revs drop from 3000RPM to 1800RPM when any hydraulics are activated.

Any thoughts?

Here's what I've done so far:

• emptied and cleaned fuel tank (had water, rust and gunk)
• replaced fuel filters (clogged with water and gunk from tank)
• replaced fuel lines (lines were brittle) - had injector pump and injectors tested - tested ok
• bled injector lines
• replaced engine oil and oil filter
• replaced thermostat and coolant (thermostat was stuck open)
• air filter had already been replaced - exhaust is clear
• checked governor spring, forks and flyweight. Worn but nothing broken or missing
• cleaned and flushed hydraulic tank, replaced both filters (both filters were very clogged), filled with new oil.

 

[K5lwq]

What happens when you move the controls at idle? Or lower RPMs? Then what happens when you dig or put a load on the hydraulics? Maybe even holding the valve open when cylinder bottoms out?

 

[oldnslo]

Do you have a hydraulic schematic for this machine?

Have you installed a pressure gauge on the pump pressure line?

Parts list indicate this model has fixed displacement gear pump or pumps depending on features. There should be minimal pressure with no functions be operated.

 

[JWR]

How many hours on the machine? I may have missed it if you said. Does the engine slow down or bog down when you move the machine around using the tracks ?

 

[Godhungry777]

How many hours on the machine? I may have missed it if you said. Does the engine slow down or bog down when you move the machine around using the tracks ?

4000 hours

Yes it does the same with driving the tracks. Everything is driven by the hydraulics so i don't really have a way of testing hydraulic load against any other type of load.

 

[Godhungry777]

Do you have a hydraulic schematic for this machine?

Have you installed a pressure gauge on the pump pressure line?

Parts list indicate this model has fixed displacement gear pump or pumps depending on features. There should be minimal pressure with no functions be operated.

Here's the schematic.
I don't have a pressure gauge.

 

[JWR]

4000 hours

Yes it does the same with driving the tracks. Everything is driven by the hydraulics so i don't really have a way of testing hydraulic load against any other type of load.

I am NOT experienced in this specific machine at all, BUT with 4000 hours on it and much of the overall operation of it using hydraulic pressure, I would have to guess your hydraulic pump is worn out.

Not sure how to test it but there must be others out there with high hours on one of these machines. The regional service rep for [AFFILIATE=1, nofollow=true, newwindow=true, title="Kubota"]Kubota[/AFFILIATE] (assuming they have those down under) should be able to comment and help you at least verbally on this... and that is his job. If it is a worn out central major part of that machine -- apparently is -- this is going to be expensive to replace it. Finding a shop that has done it before is likely to be your hardest search (and that won't be the local dealer who has never done it before...)

 

[oldnslo]

I am NOT experienced in this specific machine at all, BUT with 4000 hours on it and much of the overall operation of it using hydraulic pressure, I would have to guess your hydraulic pump is worn out.

JW
How would a worn pump cause the engine to slow down in RPM? Hydraulic function slower yes but engine ??

 

[oldnslo]

GodHungry
The schematic also shows your machine having fixed displacement pumps so unlikely the engine gradually slowing down is a hydraulic problem but I could be 100% wrong.

To confirm you need to have equipment to check system pressures or disconnect pumps from engine. This would 100% isolate engine from hydraulics. Most likely this is not feasible.

 

[Jerry/MT]

See video explanation.
Revs drop from 3000RPM to 1800RPM when any hydraulics are activated.

Any thoughts?

Here's what I've done so far:

• emptied and cleaned fuel tank (had water, rust and gunk)
• replaced fuel filters (clogged with water and gunk from tank)
• replaced fuel lines (lines were brittle) - had injector pump and injectors tested - tested ok
• bled injector lines
• replaced engine oil and oil filter
• replaced thermostat and coolant (thermostat was stuck open)
• air filter had already been replaced - exhaust is clear
• checked governor spring, forks and flyweight. Worn but nothing broken or missing
• cleaned and flushed hydraulic tank, replaced both filters (both filters were very clogged), filled with new oil.

Something is putting a big load on the engine via the hydraulics. Are the track drive bearings frozen, the brakes stuck ON, etc ?