sudden and violent PTO engagement with new Kubota MX5800

[rbtjr]

Lub your PTO shaft ...the inner on the outside....and the outen on the inside...to get a good slide for when shaft is not straight ,

Good idea--will help eliminate contributing factors. Along the same line of thought, we have Pat's quick connect system on the tractor, which of course extends the 3PH lift arms 4-5". As a result, I think that the overlap of the two components of the PTO shaft when the mower is hooked up to the PTO could be less than optimum. I plan on using a PTO shaft extension with the mower to eliminate this factor as well.

 

[Steve1300]

I'll let this thread serve as notice on what to expect. I use a flail mower and there is no shaking and noise when engaging my PTO at idle. I opted to not get a brush hog, so I don't have to spin that much weight on startup. Now, when I had a BX, starting the brush hog did take a few seconds to ramp up. I just thought it was normal so I was never worried about it.

 

[theg]

Low RPM, if mower has slip clutch make sure it is set correctly, start pto, start mowing. It sounds and feels bad but normal. Enjoy time on tractor.

 

[rbtjr]

Update: Today I added a PTO extension between the tractor PTO shaft and the mower PTO shaft. And I was very careful to engage the PTO at the lowest possible engine rpms (800 on our MX), to make sure the mower PTO shaft was aligned with the tractor PTO shaft, and to make sure that the mower blades were touching nothing. There seemed to be a slight improvement. I engaged the PTO three times successfully--still abrupt and pretty violent, but successful. On the fourth engagement the mower blades got hung up together again and the tractor shut down. I again went to the shed, raised the mower, put supports under the mower, got under the mower and used the light sledge hammer to free the blades. I checked the blades as best I could. They swing pretty freely, can be flexed up and down a little with downward pressure on the tips of the blades. So far as I can tell the blades aren't bent. I have mowed only 2-3 hours thus far with this mower and I don't recall mowing anything that caused a problem, and nothing larger than probably 1" in diameter. I manually aligned the blades so that they were pointing opposite of each other--i.e. you could draw a line lengthways through the blades and the line would run approximately down the middle of the two blades lengthways. Then I lowered the mower, went back out and engaged the PTO again to do some mowing, and the engagement was again pretty violent but successful. ???

Good point above about the slip clutch, which our mower has. I will look at an adjustment. I also intend to try the MX with another PTO-powered attachment. Also, in response to some notes, we have had three tractors before this MX and have used rotary brush mowers with all of them. All of these tractors had the PTO engagement via a clutch on the tractor. In hundreds of hours of mowing with rotary brush mowers with these prior tractors, we have never before experienced a problem with the PTO engagement like we are experiencing with our new MX. I think that the reason is that with our prior tractors and the engagement via the clutch, you could sort of feather the clutch to engage the PTO gently. No so with the electrically operated PTO engagement with the MX.

Thanks again for all of the responses.

 

[TripleR]

"Also, in response to some notes, we have had three tractors before this MX and have used rotary brush mowers with all of them. All of these tractors had the PTO engagement via a clutch on the tractor. In hundreds of hours of mowing with rotary brush mowers with these prior tractors, we have never before experienced a problem with the PTO engagement like we are experiencing with our new MX. I think that the reason is that with our prior tractors and the engagement via the clutch, you could sort of feather the clutch to engage the PTO gently. No so with the electrically operated PTO engagement with the MX."

Thanks again for all of the responses.

That was also my experience when I traded my L5030 for an L5740. I have learned to live with the new electric over hydraulic, but really prefer the "old style" lever engagement.

 

[TerryR]

Why do manufacturers now go for this design? It seems like such a poor idea, putting so much stress on the equipment, even to the point that some users have reported it breaking shear pins. I'd look to avoid it if I were buying another tractor, if that's even possible anymore.

Is it that much cheaper to build, or is there some other reason?

 

[Agvg]

Another good and pertinent thought. Based on my limited experience to date, I would probably run the risk of premature failure of the discs in order to eliminate the violent PTO engagement of the attachments, especially with the mower, which is my most often used attachment that requires the PTO power.

Don't think wet clutches wear that much, they run in oil and have quit large surface and the oil cools it down.

 

[s219]

I don't understand. How could it "over-run" the engine? The engine is already turning at full PTO speed -- the flywheel of the chipper can't make it speed up. It always seems to me to let the engine come down to idle speed so you slow down the flywheel quicker, then disengage and let the equipment come to a stop from there. (This of course if you don't have the old setup where the PTO can drive the transmission.)

If the implement has a giant flywheel or flywheel action, it is going to hold onto it's rotational energy a lot longer than the engine, and as a result it's going to transfer some of that energy to the engine and over-run it. You know from experience an isolated engine will drop in RPMs very quickly if you cut the throttle, since it has a small flywheel and lots of friction and losses to drag the RPM down. Not so for something large with a big flywheel and minimal friction losses.

Even if you slowly ramp down the throttle, for every drop in speed of the engine, the large-flywheel implement will lag behind and be pushing the engine.

You won't increase the RPM of the engine above the RPM of the coupled implement (taking gear ratios into account). But you will most surely increase the RPM of the engine above (perhaps way above) the normal RPM of the engine at the given throttle setting.

Best example I can think of is a car with manual transmission. Get up to speed on a downhill and take your foot off the throttle. The engine RPMs will then be driven by the inertia of the moving vehicle acting through the transmission, and most certainly be higher than the engine would turn at the same throttle (which would normally be idle speed). We think of this as engine braking, but in reality the inertia of the vehicle is over-running the engine through the transmission and gearing.

So if you throttle a tractor back with a large implement engaged and turning, you are in effect using the tractor's engine as a brake to hold back the implement and slow it down. But there is no real benefit and there can be some potential disadvantages. That is why when running my chipper, I clutch in and let the chipper and PTO slow down on their own while I independently cut the throttle and let the engine go back to idle on its own. There is zero reason why I'd need to be using the engine as a brake in that situation.

 

[ericm979]

With the independent PTO I just turn the PTO off first, then throttle down.

rbtjr- if the cutter blades are hanging up on each other that's a defect and you should talk to the seller. Also you should talk to your Kubota dealer about the PTO engagement. There may be an adjustment they can make, or advice they can give. If it eventually causes a problem that requires warranty work there will be a record.

Recently there was a post on this forum that linked to an electronic device made to ease PTO engagement. It works by sensing the PTO shaft speed and turning the PTO engagement on and off as the shaft is coming up to speed, similar to a PID controller for an electric heater. I have some concerns about it wearing out parts, and I can't find it now, but if you can find it, it might be an option. I'd only try after exhausting the options with your dealer.

 

[CobyRupert]

Why do manufacturers now go for this design? It seems like such a poor idea, putting so much stress on the equipment, even to the point that some users have reported it breaking shear pins. I'd look to avoid it if I were buying another tractor, if that's even possible anymore.

Is it that much cheaper to build, or is there some other reason?

Good question! :confused3:

PTO engagement was a huge factor in deciding what I bought. I wanted a independent hand operated lever only. Back then, it was a big reason I didn't buy a Kubota because they had a 2 stage pedal clutch to engage the PTO and/or transmission, and for me, even that was unacceptable.
Now, I see that even the current models of my Deere have gotten away from a hand clutch (lever) and gone to a suicide idiot switch. Why??!!!