Go BottomM5400 hydraulic problems
 | Karl Fletcher
Join Date: Posts: 1 
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2001-03-23 25778
I have a Kubota M5400 that releases hydraulic pressure thru the PTO clutch valve. Whenever I raise the front loader the pressure relief valve releases pressure and the loader will barely lift. The tractor has had this problem to a lesser degree from the day it was new. I wonder if anyone else has experienced this problem. Kubota will replace the valve under warranty, but I have yet to find a Kubota mechanic as experienced as I am. I am constantly surprised by the lack of quality service people in our local area. In other words I'm doing the trouble-shooting myself. I have talked to several Kubota people and they are lost. As a matter of fact the dealer I purchased the tractor from could not even find the part on his computer service software. I fianally found a dealer in Chattanooga, TN that could identify the part. My research indicates that Kubota improperly assembled the relief spring pistons from the factory. All mechanics that have examined the "support pto valve" body agree. Yet no one is sure if this is the only problem. HELP!Karl
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2001-03-24 25797
I'm not familiar with how the power-assisted clutch is plumbed into what I take to be a single pump open centred system. For example, I don't know if the clutch cylinder is fed from a priority valve, similar to power steering, so I may not be much help. However, I am curious if the slow loader only happens when the PTO clutch is operated, whether the same thing happens with the 3ph, and whether the power clutch works property. I guess the way I'm thinking about it is that a faulty relief valve in the clutch hydraulics could cause a priority valve to try and maintain pressure to the clutch hydraulics, which could rob flow from the remote hydraulics. In such a case, the power clutch probably wouldn't work properly, and the 3ph likely would be affected as well as the loader (provided the priority valve is plumbed ahead of the remote hydraulics). ....
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| Karl Fletcher
Join Date: Posts: 1
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2001-03-24 25806
Tom, at the time of disassembly I was not aware this relief valve was part of the PTO clutch. So I did not test the pto before disassembly. However, the 3ph worked properly even with implements attached. The 3ph has a separate relief vavle that appears to operating properly. The pto clutch engagement device and the faulty relief vavle are considered to be part of the "power beyond" device that allows remote use. The "pto clutch" is fed by a secondary line directly from the pump. The tractor has only one external hyd pump. I believe the pump has two large lines and a small line connected to it. I did trace the small line directly to the pto control valve. Late yesterday Kubota said they were going to send me the complete pto control assembly. I also received a breakdown drawing of the pto clutch. I am concerned about the replacement. It requires opening the side of the transmission. As long as everything stays in one piece, GREAT. But if something moves or falls, it will be a sad day in N. GA. :-) Your input is greatly appreciated. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2001-03-25 25839
Karl: Guess you've got a repair manual to tackle such a tear-down. It's a good idea to figure out any special tools or new gasket sets needed before starting.
I believe the relief valve in the 3ph (control valve assemblies also have them) are set for much higher pressures than the system relief valve and provide protection against load shocks. I'm not sure, but I think these valves see pressure only when a control valve is operated. Here's some theorizing. I know it’s long, but I hope it helps a bit. I'm still thinking about the plumbing in all this. Ordinarily, with one pump and power steering (don't know if the tractor has PS) there is a suction line and a high-pressure line on the pump. The HP line goes directly to a priority valve, and a HP line for the remote hydraulics and a smaller HP line, which goes to the PS, comes off the priority valve. Without PS, perhaps the line going to the PTO comes off a priority valve, and the priority valve appears as part of the pump. Don't know. I'm just trying to reason through this. Or, perhaps there's some unknown workings in the PTO clutch hydraulics that function similar to a priority valve. However, there has to be something, because components in open centre systems can't be simply connected in parallel without some sort of demand proportioning system. With power steering systems, there is a relief valve that can dump oil back to the sump, but it only operates when the steering is active. Attempts to lift a heavy load with the remote hydraulics will open the system relief valve. However, the high pressure developed may also open the PS relief-valve if the steering is active. It seems likely that the PTO clutch operates similar to PS. It's curious that the PTO clutch hydraulics is described as part of the power beyond system. As I am familiar with the term, PB refers to an auxiliary system on the remote hydraulics. Perhaps I'm mistaken, but I think of my remote system as starting at the hydraulic manifold block, which is after the priority valve. I don't think of PS as part of the PB system. Anyway, there remains a mystery in my mind. In an open-centre system, the loader and 3ph are often plumbed in series and powered from the auxiliary system. In a conventional system, only one function works at a time. If two control valves are operated simultaneously, only the first valve in the series gets much pressure. However, the plumbing to the clutch seems like it is ahead of the remote hydraulics, and a malfunction in the clutch relief valve should affect both the loader and 3ph.
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| Karl Fletcher
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2001-03-26 25901
Tom: I think your assumptions are correct. No, I do not have a service manual. I will have one before I go any further. I do have print outs from the dealer service software. The terms I have been using are "quotes" from Kubota paperwork. (i.e. pto clutch, power beyond, etc.) The tractor does have PS. I did not work on the tractor this weekend but I sure did miss not having it in operation. (the old MF135 is a little different) I will post my solutions when they arrive. (If I knew what I was doing it wouldn't be research) Thanks again! ....
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