I Still Hate My Tractor II

[moship]

Not true. It would have to be very badly designed if it worked that way.

There is max clamping pressure for the clutch pack, even at idle. Those things are set roughly 250 PSI. So there is always 250 PSI with the PTO either On or Off and at any engine RPM.

You better check the WSM and actually perform the test with respect to the Grand L40's and possibly the L60's to see the pressure is somewhat proportional to RPM's. Max pressure is definitely not achieved at lower RPM's. There has been several owners who operated their tractor as they did with the former design and got burned. Thus the general warning to make folks aware of the possibility. I will admit that perhaps in these situations the pressure was set too low from the factory or there was some other root cause that resulted in their clutch packs being burned up. There was also an error in the pressure settings in some of the earlier WSM. I do apologize for not specifying the model I'm referring to and implying all Kubota's are the same in my original post.

 

[ptsg]

You better check the WSM and actually perform the test with respect to the Grand L40's and possibly the L60's to see the pressure is somewhat proportional to RPM's. Max pressure is definitely not achieved at lower RPM's. There has been several owners who operated their tractor as they did with the former design and got burned. Thus the general warning to make folks aware of the possibility. I will admit that perhaps in these situations the pressure was set too low from the factory or there was some other root cause that resulted in their clutch packs being burned up. There was also an error in the pressure settings in some of the earlier WSM. I do apologize for not specifying the model I'm referring to and implying all Kubota's are the same in my original post.

I'll check the WSM for Kubota. :thumbsup:

Must be a Kubota thing though. On my Branson, when using the tiller, I have to go under lots of trees on the orchard. Since it's usually short runs, I use the throttle pedal all the time, so when going under a tree, I just let it idle while I use all my 4 arms and legs to move all the branches out of the way.

I haven't got any slippage on the PTO clutch whatsoever. In fact, when it's cold and the oil is also cold, I can hear the hissing from the fluid going through the sequence valve of the PTO valve to keep that clamping force right at any RPMs.

 

[LouNY]

I don't know of any tractors with hydraulic clutch packs for pto's or drives that require high rpm to work correctly.
If some of the kubotas do it just reinforces my thoughts that they must be way over rated

 

[DK35vince]

I don't know of any tractors with hydraulic clutch packs for pto's or drives that require high rpm to work correctly.

Nor do I..
I've run all my PTO powered attachments any where from idle to full throttle for as long as I've owned this tractor and never worried about that. (independent PTO)

 

[moship]

I'll check the WSM for Kubota. :thumbsup:

Must be a Kubota thing though. On my Branson, when using the tiller, I have to go under lots of trees on the orchard. Since it's usually short runs, I use the throttle pedal all the time, so when going under a tree, I just let it idle while I use all my 4 arms and legs to move all the branches out of the way.

I haven't got any slippage on the PTO clutch whatsoever. In fact, when it's cold and the oil is also cold, I can hear the hissing from the fluid going through the sequence valve of the PTO valve to keep that clamping force right at any RPMs.

Make certain you check the manuals for the Grand L40-3 models. They differ from the Grand L40-1 models. The dash 3 models use an electronic switch to turn pto on/off, while earlier versions (dash 1) use a lever. You'll also need to make certain the WSM is current as there was an error in pressure requirements in earlier versions.

Please note, I'm not saying the PTO won't function, but the clamp pressure will not be at 100% in these models and may have slippage in high torque applications (snowblower, tiller, etc...) when operating at speeds below 2,100 rpms.

I've taken the time to measure the supplied pressure across the RPM range along with testing at both cold and hot fluid temperatures. Based on what I've found supplied pressure to the PTO clutches is a function of rpm and temperature. Test one of these tractors and let me know what you find. Maybe your results will differ and there is an issue with my tractor.

I can't comment on Branson, Kioti or any other brand/model. As far as I know, I'm posting under the KUBOTA section.

Added in edit on 02-13-2020
Here was one person who had a problem a few years ago...
https://www.tractorbynet.com/forums/kubota-owning-operating/388585-kubota-l4740-pto-check-pressure.html?highlight=pressure

 

[aczlan]

Here are the relevant pages with specs from the other thread:
-3 WSM:

-1 WSM:

Aaron Z

 

[ptsg]

I still find it hard to believe. Specially coming from a well reputed manufacturer like Kubota. The only thing the manual says about the PTO (about 2 pages or so) is how to check and adjust the clamping pressure.

If there was slippage risk under low engine RPM, then would need to put warnings all over the place and we would see threads about this issue. Not all implements will need to work at 540 RPM.

I know on my tractor that the PTO valve is basically dead ending the flow from that comes from the steering valve, so there is always clamping force, no matter what RPM it is. The relief valve job is to keep that pressure at the entire RPM range. It will still vary slightly according to temp and RPM range but always within limits.

The Kubota does have some sort of regulating valve that seems to prioritize the PTO valve and sends the rest to the steering but it still maintains pressure for the PTO no mater what.

If I couldn't run under 2100 RPM, I would have serious problems as the 540E runs at 1800 engine RPM. So on most of my around 170 PTO hours would have the clutch slipping all the time.

I don't know. I might be missing something...

 

[aczlan]

I still find it hard to believe. Specially coming from a well reputed manufacturer like Kubota. The only thing the manual says about the PTO (about 2 pages or so) is how to check and adjust the clamping pressure.

If there was slippage risk under low engine RPM, then would need to put warnings all over the place and we would see threads about this issue. Not all implements will need to work at 540 RPM.

I know on my tractor that the PTO valve is basically dead ending the flow from that comes from the steering valve, so there is always clamping force, no matter what RPM it is. The relief valve job is to keep that pressure at the entire RPM range. It will still vary slightly according to temp and RPM range but always within limits.

The Kubota does have some sort of regulating valve that seems to prioritize the PTO valve and sends the rest to the steering but it still maintains pressure for the PTO no mater what.

If I couldn't run under 2100 RPM, I would have serious problems as the 540E runs at 1800 engine RPM. So on most of my around 170 PTO hours would have the clutch slipping all the time.

I don't know. I might be missing something...

I agree, I would stick a pressure gauge on it to test and verify pressure at various RPMs.

Aaron Z

 

[aeblank]

IMO, the (reduced) amount of power the engine is capable of at low rpm would match the reduced clamp pressure.

 

[MHarryE]

Direct acting relief - increased flow at higher rpm - the poppet needs to move more to allow the flow, which compresses the spring and increases the pressure. From my IH experience, they call for 270 to 280 psi at high idle, should drop no more than 40 psi when reduced to low idle. A problem with the bigger tractors is when running at lower speeds, the torque backup is so high that the torque transmitted can be higher than it is at max power and clutches fail.