Catastrophic Failure

[rbargeron]

Curt, Does the break look anything like the attached pic? On this one The back of the cylinder and rock shaft housing broke away with part of the gear housing. Maybe if yours isn't this bad it will help you feel a bit better.

I'm pretty sure the cast iron alloy they use is brittle and not weldable. You might find someone who could braze it together but it will never be strong enough to hold more than a coat of paint. You should ask your dealer to get the Kubota rep to have a look. Sometimes they help out with parts cost on major failures, where it isn't a clear case of abuse.

 

[SDT]

Most such catastrophic failures are caused by failure of the cylinder travel limit mechanism.

Such mechanism is generally internal on farm tractors but may be external on some CUTs. If external, the mechanism may have been damaged by driving over a limb, etc., or it could have been the random manufacturing defect.

SDT

 

[brain55]

Most such catastrophic failures are caused by failure of the cylinder travel limit mechanism.

Such mechanism is generally internal on farm tractors but may be external on some CUTs. If external, the mechanism may have been damaged by driving over a limb, etc., or it could have been the random manufacturing defect.

SDT

On Kubota's there is an external feedback rod. This in conjunction with the control valve shuts off the flow to and from the 3-pt cylinder and is how position control is achieved. The only limiting mechanism ouside of the control valve is the rear of the transmission case. This area is typically reinforced with some type of steel plate if it is an aluminum housing. Like I was saying once the control lever is in the full up position there should still be some upward travel left in the arms what stops this travel is the internal lever on the rockshaft hitting the transmission housing.

 

[Chilly807]

What Brian's saying is what I'm thinking too. I'm not sure the L2900 has a safety valve, but there's a good chance it does. They are designed to directly relieve excess pressure in the 3pt cylinder caused by external factors like fluid expansion or a heavy load being applied to the 3pt from another source, like a big rock being dumped into a carryall from another tractor, etc.

On mine, I think (memory reference here!) the safety relief setting is 3200 psi, significantly more than the 2250 psi the main relief and loader relief is set at. The WSM tells you to use an injector tester to get enough pressure to adjust the safety valve.

Either the OP's tractor failed at less than the safety valve pressure or it's not working right. Obviously, the safety valve will normally never open except under extreme circumstances. If there was condensation or water in the system at one time, it may have rusted solid and then refused to move when required.

Sounds like a freak occurrence to me, in fact I've never heard of something like this ever before. You'd have to have a lot of things happen together to make this occur if we're right in our diagnosis. First, the cylinder would have to be at the extreme limit of it's travel. Secondly, the relief would have to be "frozen", and third, the external force (either expansion due to heat or introduced mechanical load) would have to be there as well.

It's possible the relief is working normally but the cylinder failed below the set pressure too.

Sean

 

[DFB]

Does anyone know if Kubota (especially this unit) incorporates any type of thermal shock relief valve in their systems?

On my Deere its a check ball and spring asy designed for such circumstances. And its operation bypasses all other internal control valving and releases excessive rock shaft cylinder pressure from thermal expansion or shock load by dumping oil directly to sump.

 

[brain55]

That is the safety valve that I have been talking about. Kubota did at one time put them on their machines. I cannot swear one way or the other if that particular machine has one.

 

[DFB]

Yes mine is set for approx 500 psi over system operating pressure

 

[Chilly807]

I'd be surprised if it didn't have one, there's no other way to protect the system once the position valve is closed.

 

[joshuabardwell]

Would this relief valve also protect the system if one closed the descent-rate control valve on the three-point and then attempted to raise the hitch?

 

[PitbullMidwest]

Sure, we hope to able to pull it this weekend. His shop is unheated and it's 4 degrees today and high tomorrow is only in the teens. The spirit is willing but...

Well here's the pics. Didn't have a chance to work on things today, it seams like when it rains it pours, we spent the day repairing my other son's truck and replacing lockouts in yet another vehicle. Man I hate winter.

And just to clarify, it wasn't 4 degrees the day of the failure, it was 4 degrees the day of the posting.

 

[Leejohn]

That looks like there is water in you oil and some was on top of your piston. Cold weather freeze up.

 

[yelbike]

That looks like there is water in you oil and some was on top of your piston. Cold weather freeze up.

I don't see the water in oil. There may be water on the oil outside the case from precipitation. I doubt very much that a freeze crack as the tractor was warm and the oil would have been completely milky in colour.

The repair doesn't look to intensive compared to the jd 2305 case failures. Look up the for posts on it, it really sucks, trust me, don't ask how I know! As long as there is no internal parts damage, it looks like a relatively easy fix for a skilled FIYer. I would guess something physically pressed against the case(like an over extended cylinder) rather then a high hydraulic pressure. I would guess that a high hydraulic pressure would leak at seals before a catasrophic case failure. Just my uneducated guess though. Keep us posted please.

 

[DFB]

Wow looks like just behind where the rockshaft control valve bolts up. I would think your system pressure relief valve must be nearby. Mines located right below it

 

[Leejohn]

The reason I posted about freeze up is because my brothers BH just blew the top out of one of the L & R cyls. When it went it ended up about 60' away. The metal is about 1/2" thick.
Also the bucket is on the ground and it moved it about 2' until the dirt pile got to big.

 

[yelbike]

The reason I posted about freeze up is because my brothers BH just blew the top out of one of the L & R cyls. When it went it ended up about 60' away. The metal is about 1/2" thick.
Also the bucket is on the ground and it moved it about 2' until the dirt pile got to big.

Curious, was his oil milky in colour?

 

[Leejohn]

There was a little water that hadn't drained out of the piston. The BH was been setting for awhile, we well have to open the drain plug and see if water comes out now. I would say it is. It wouldn't take a lot of water if trapped on top of the piston like his was. What got me was how far the boom moved. If I think of it I'll try and get a picture.

 

[Chilly807]

Would this relief valve also protect the system if one closed the descent-rate control valve on the three-point and then attempted to raise the hitch?

It doesn't work that way, all the descent rate valve controls is the rate of fall. It's a check valve of sorts and is spring loaded. It has no effect on the raise part of the cycle, even if it's closed completely the valve will lift off the seat and allow oil to enter the cylinder unrestricted. Once it's in there, however, it's trapped and has no way out past the valve. I would think the safety valve would be plumbed directly into the cylinder to allow excess pressure to escape if the need arose. In other words, it shouldn't have to also pass through the descent rate valve to get out. That's the way it's shown on mine anyway.

The attached pics are from the WSM for my tractor, an L3400. It shows the cylinder safety valve being set for roughly 3000 psi (2845-3277 psi), which is well above the normal relief setting of 2250psi, and the hydraulic diagram shows where everything is plumbed in relation to each other. The lowering valve (6) is shown in green, the cylinder (7) is in yellow, as is the safety valve (8).



Sean

 

[Chilly807]

Wow.. quite the failure. I've never seen anything quite like that before. Sure looks like an overpressure situation, if that's the weakest point of the casting.

Sean

 

[radioman]

Wow.. quite the failure. I've never seen anything quite like that before. Sure looks like an overpressure situation, if that's the weakest point of the casting.

Sean

My thoughts exactly. You can see a clear line all the way where it broke. It appears to be following the thickness of the cast iron from the inside. I am willing to bet that once you get that cover off and inspect it from the inside with a strong light, you will see a dark color metal spot indicating an old fracture that was there way before you got the tractor and the gray paint covered it on the outside. If you dont see a spot of an old long time fractured spot, then either you have quite possibly found a manufacturing design defect or definately a failed relief valve. Time to inspect it too. By the way, its good to know that your oil was not milky- but even with contaminated oil you would noticed sluggishness with hst or loader as its using the same oil.

 

[DFB]

On my machine the thermal/shock safety relief ball check is located right inside the control valve itself.

Looks like a high pressure blowout to me. I once experienced a CAT skidder pump housing crack under pressure upon start up. It was freezing cold out.

Looking foward to seeing more diassembly