I've done FOUR of them, all the same exact failure. Looked identical except they were all FOUR on the same tractor (MX5100). I know an MX5100 is different than the OP's tractor but the principles of operation are identical.
Of those 4 times, I asked the owner what happened and of course the normal answer was "well I was just driving across the field....". The LAST time it happened, I told him either someone's gonna have to give us better idea what actually happened, or we're gonna just have to refuse it the next time (and I was kidding about that last part, and he knew it). He said the same thing, he was driving across the field and it just broke. This was backed up by the kid who was watching his dad cut grass; but the kid went on to say that once the last row was done, he turned around, threw it in highest speed it's got and about throwed the daddy off of the seat several times. Ah-HAH!
Before we (or should I say "I") condemned the operator as the cause, I consulted with the kubota central division service manager at the time. Super good dude, excellent communication skills and superb knowledge-and memory. Explained the situation and the very first question he asked was this. Was the tractor driven at high speed on rough terrain?
Yup...confirmed it. BOUNCING.
Think about it. The weight of a 6 foot shredder is significant, but it's how far back the weight is hanging on the 3ph that causes the issue. It's 6 foot back, and acts like a long lever. Get it to bouncing and something's going to give, it has to. The lower links and their mounting points are pretty stout. The upper part is too, but it's not as strong as the lower. Secondly if the 3ph feedback linkage is out of adjustment and is pouring hydraulic pressure to the cylinder such that it bottoms the piston out in the bore, it is still pushing the rockshaft, and there is significant pressure pushed toward the rear of the tractor which combined with bouncing, something's gonna give and it's almost always the 3ph cylinder housing.
once we discussed this with Mr. Customer, he was totally understanding why it was happening. He'd get the tractor home, feedback link adjusted properly but to him, it was never enough lift, so he'd adjust it some more so the shredder would lift that last inch. Well then bounce it a little (or in his case a lot), and it broke the housing. Every time. Now that he's educated, he's slowed down and left the feedback rod alone, and to my knowledge hasn't had an issue since.
