hyraulics question

[oldnslo]

Matt,
did the spool move freely on the priority valve? These valves operate off of pressure drop across a control orifice. Any friction or binding will make them fail or hang up which is what you appear to be describing. If designed properly the springs should not be fatiguing in that few hours.

Did you have trouble steering the tractor at any time? This would normally be one of the first symtoms of a priority valve failing is either, loss of steering or erratic steering.

Roy

 

[Stonehaller]

Good to hear you have made progress. You may want to check and clean the forward and reverse relief valves. Make sure the valve spools move freely. Those valves have two functions, one to limit the pressure in the transmission and two, they have a low pressure check in them that opens when the internal pressure falls below the charge pressure.

 

[MattJ]

Good points and I'll check these. The priority valve seemed to move OK but did have a tiny amount of crude built up on it. I had cleaned it as well as I could and it made a little difference but the new one made a big jump forward.

As for the forward and reverse I was going to start by checking the relief pressure, but I would like to get in and inspect/replace these if needed. The biggest challenge is that it appears I need to take half the tractor apart to get to them! If it come to that I might go ahead and take the HST off and inspect that as well, and perhaps replace the fan that's missing one fin. Wish the design was better for access, but I guess thats the cost of a compact design.

 

[MattJ]

Also, sorry the question about the steering. No I didn't notice anything, but I wasn't really focused there either. You're right I should have taken a better look at that.

 

[MattJ]

So here's a new update. After replacing the flow priority valve the tractor had pretty good power and full charge pressure, could spin the wheels against a tree, but still had the chatter and lacked the power going up hills etc that I had when it was new.

I tried dropping it off at the dealer but they said it would be weeks before they could even test drive it. I took it home, opened up the WSM and starting taking the puppy apart.

About 4 hours in I had the HST on the workbench. Cracking it open, I found the problem. The motor was OK but the pump side was really worn. Pretty surprising for 500hr on it but at least I found it. I'm ordering the new pump, and while at it the HST fan since you can only get to it with the tractor apart (dumb design) and I have a few blades cracked off. I have a picture of the good motor and the bad pump for comparison. The pump was really worn into an oval shape in numerous cylinders. The IIRC bearing and the swash plate looked good.

- Matt

 

[MattJ]

Sorry, forgot to ask but if anyone has any idea why this would show up in 500hr of use please feel free to drop ideas. Don't really want to have to tear apart the tractor again.

Thanks

Matt

 

[leonz]

Sorry, forgot to ask but if anyone has any idea why this would show up in 500hr of use please feel free to drop ideas. Don't really want to have to tear apart the tractor again.

Thanks

Matt

Hello Matt,

do not be sorry Matt, I can tell you the oil filtration is the culprit.

Did the dealer tell you to order a new swash plate for the piston pump at the same time? If not their collective Pee Pee's need to be spanked.

the old pistons condition is a dead giveaway as far as the chattering goes as the oil is bypassing through the pistons going every which way on a lazy "I do not have to work" vacation


The swash plate is what directs the full flow of the pump to the forward or reverse direction of the tractor.


An axial piston pump requires a very high degree for filtration being 10 micron or less; chances are the filtration is 50 micron on your system.

Would you mind describing your tractors filtration system?

 

[MattJ]

I haven't ordered anaything yet. I haven't actually gotten much of any useful advice from the dealer since they seemed to be too backed up to test it or screen much of my questions.

The swash plate looked good as did the cradle bearing. I'm a novice here so I was wondering why that would need replacing?

For the filtration its the standard kubota setup. There is a suction screen and then the kubota supplied filter right before its charged into the HST housing. hhk20-36990 is the part number. I have no idea on the micron rating, its just expensive like all the kubota parts.

 

[leonz]

They are a wear part as well Matt; if you have the ball ends of the pistons exposed you will see this as well.

Everything that moves on a piston pump is a wear part :shocked: unfortunately.


They have to have a low micron rating for this and or the wrong filter is mounted on the tractor or the filter is damaged/ stuck open relief in the cartridge itself.


I wonder if you have a tuff torque transmission" assembly/axle set up in this tractor?

 

[Stonehaller]

Remember he had a bad priority valve causing low charge pressure. Who knows how long it had been running with low charge pressure. The low charge pressure may have caused pump cavitations which can also cause wear.