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.