sudden and violent PTO engagement with new Kubota MX5800

[Agvg]

Just that they doesn't design it right, soft start PTO is old news.

 

[TerryR]

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.

Yes, but why is that a problem?

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.

No, it is engine "braking" - the engine is slowing down the vehicle.

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.

Of course, that's the idea.

But there is no real benefit and there can be some potential disadvantages.

Sure there is a benefit - it slows down the implement more quickly, so it is more likely to be stopped by the time you get off.

What are the potential disadvantages?

 

[rbtjr]

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.

The mower is from EA and they are being very helpful and responsive. For example, they offered to replace the blades for free. I have declined because I don't think EA has any responsibility. The blades on the EA 72" rotary mower are 4" wide and very heavy--by design so that they store lots of energy when up to speed. I probably won't be able to prove this but I can see that with a sudden and violent engagement by the PTO and the extra inertia with the blades due to their extra width and weight, there could be enough force applied to the blades to cause them to get hung up when they wouldn't with a softer engagement. But regardless, the EA folks are being very helpful and supportive. And I have contacted our dealer. Our main contact at the dealer isn't aware of the MX tractors having a problem like this but he is checking for me. And thanks for the info about the electronic device made to ease PTO engagement. That sounds like an ideal solution if it could be applied to our MX. I will try to find it.

 

[kthompson]

I may have read the over rev comment wrong for what came to my mind was on tractors without separate clutch for the pto and when you push in the clutch running a high rpm rough cut mower it would really push the tractor. Been there more than once.

 

[rbtjr]

I mowed some today. Had 4 PTO engagements, 3 successful, the 3rd not. The first one pretty smooth, the others not. The tractor shut down on the 3d engagement. But the mower blades were not hung up, so the shutdown was due to the sudden load being put on the engine through the PTO. Makes me wonder if it would be better to engage the PTO at slightly higher rpms. I have read on TBN about others doing that--i.e., engaging the PTO at rpms higher than idle. The owners manual says that "to avoid shock loads to the PTO, reduce engine speed when engaging the PTO . . ." It doesn't say reduce the rpms to idle speed, which is what I have always done. Thoughts?

 

[ovrszd]

I have no solution. I've never had a tractor die when engaging the PTO. I always engage at idle.

Adding rpm will definitely stop the problem of engine stalling.

Not sure what that does to the PTO system long term.

 

[ericm979]

Thoughts?

What does the dealer say?

 

[rbtjr]

What does the dealer say?

I haven't asked the dealer about engaging the PTO at slightly higher rpms. I have told our dealer rep about the issues we are having. He said he is not aware of any problems caused by the electrically controlled PTO engagement on the MX tractors, but he is checking it out for me. We deal with a very good dealership, so if there is a problem with the MX and a fix he will find it for me.

 

[Turbys_1700]

I would engage at an rpm slightly above idle. It may be a combination of this specific cutter with the electric PTO. Have you tried it on a different cutter?

 

[rbtjr]

I would engage at an rpm slightly above idle. It may be a combination of this specific cutter with the electric PTO. Have you tried it on a different cutter?

I think that is exactly the problem--the unique combination of the tractor PTO electric control coming on suddenly, and the mower being a 6' heavy duty mower with 4" wide blades. The mower is great when it gets up to speed--actually, when it gets by the initial jolt. Yes, I used this same tractor a couple of times with a lighter duty 5' rotary mower with 3" blades. It shook a lot on the PTO engagement but worked okay and not as violently as the new mower. The new mower's heavy duty 4" wide longer blades create more resistance against rotating from the resting position, and that combined with the sudden PTO off-on engagement do not go well together. Since I may not be able to dampen or soften the PTO engagement, I'm going to loosen the slip clutch on the mower. Actually, Ted Corriher of EA recommended that I loosen up the slip clutch to the point at which it slips when mowing heavy grass, run it a short while like that, and then tighten the clutch to the point at which it no longer slips in the same mowing conditions. Makes sense to me. Actually, the PTO engagements with the mower seem to get getting a little better, a little less violent. I suspect that that is due to the slip clutch already getting worn in a little and therefore better able to help absorb the shock.