PTO Soft Start

[gyro28866]

I have an M95S tractor and purchased it new in 2006?. Inside the cab is a PTO switch, that when you turn it on engages the PTO and suddenly. Last year I purchased a 20' Woods bushhog to replace my 15' servis bushhog. The sudden start has on 3 occasions twisted shafts out of the mower. The engine is at idle or slightly above idle. Is there a method to create a "Soft Start" on these PTO's.
That is what I am attempting to do. A soft start/slip clutches or something to get the mass of the mower moving before it fully engages.
Any Ideas???

 

[armylifer]

My tractor is not as big as yours but maybe I can suggest something anyway. For my tractor, the PTO seems to engage much smoother when I raise the engine RPM before engaging the PTO. It seems like the higher RPM make the engagement clutch slip a little instead of just banging into sudden engagement. The RPM that I find the smoothest engagement is at 2000 RPM. Yours may be different but with a little experimentation you should be able to find an RPM that works for you.

One other thing that I have tried in the past that worked with a little success is to engage and dis-engage the PTO lever for just a moment a couple quick times before full engagement. I no longer use this method though because I am not convinced that it is healthy for the clutch.

 

[SidecarFlip]

Both mine are as big as yours and I've never had an issue with starting an implement. I would adjust the slip clutch on the PTO driveline properly, that will negate any shock load. I know when I start both my bat wing and flat top chopper, both slip clutches will chirp. That takes the shock load.
In reality there should be very little anyway. Your PTO (and mine) are through a separate wet pack clutch and so long as the locking pressure is correct, the clutch pack will always slip a bit prior to lockup.

In my view, you have other issues contributing to your failures.

 

[Roadworthy]

Would it help to depress the clutch pedal, engage the PTO, then release the clutch?

 

[SDT]

Would it help to depress the clutch pedal, engage the PTO, then release the clutch?

No.

 

[SDT]

I have an M95S tractor and purchased it new in 2006?. Inside the cab is a PTO switch, that when you turn it on engages the PTO and suddenly. Last year I purchased a 20' Woods bushhog to replace my 15' servis bushhog. The sudden start has on 3 occasions twisted shafts out of the mower. The engine is at idle or slightly above idle. Is there a method to create a "Soft Start" on these PTO's.
That is what I am attempting to do. A soft start/slip clutches or something to get the mass of the mower moving before it fully engages.
Any Ideas???

Unfortunately, there is no way to feather PTO engagement with an electric over hydraulic PTO clutch.

Properly adjusting the mower slip clutches may help and should be done in any event but almost no one does this.

SDT

 

[SidecarFlip]

Unfortunately, there is no way to feather PTO engagement with an electric over hydraulic PTO clutch.

Properly adjusting the mower slip clutches may help and should be done in any event but almost no one does this.

SDT

I do SDT, yearly in fact. I loosen the springs and spin the clutch to remove any corrosion and then torque the hold down bolts to the required torque value listed in the implement manual

Only my disc mower has a sealed slip clutch and it takes a yearly greasing and thats it.

Mine are both mechanical engagement, via cable to the modulating valve on the transmission case.

 

[SidecarFlip]

Would it help to depress the clutch pedal, engage the PTO, then release the clutch?

it's an independent PTO so clutch or no has nothing to do with it.

 

[SidecarFlip]

My tractor is not as big as yours but maybe I can suggest something anyway. For my tractor, the PTO seems to engage much smoother when I raise the engine RPM before engaging the PTO. It seems like the higher RPM make the engagement clutch slip a little instead of just banging into sudden engagement. The RPM that I find the smoothest engagement is at 2000 RPM. Yours may be different but with a little experimentation you should be able to find an RPM that works for you.

One other thing that I have tried in the past that worked with a little success is to engage and dis-engage the PTO lever for just a moment a couple quick times before full engagement. I no longer use this method though because I am not convinced that it is healthy for the clutch.

It certainly isn't 'healthy' for the wet pack to engage it at elevated RPM either. If I did that sort of engagement, I'd be on maybe my 3rd set of clutch plates. You can see the wet pack by removing the rear PTO carrier cover (on my M's), but only see it. seeing and replacing are 2 different animals. Replacement of plates requires a split.

 

[armylifer]

It certainly isn't 'healthy' for the wet pack to engage it at elevated RPM either. If I did that sort of engagement, I'd be on maybe my 3rd set of clutch plates. You can see the wet pack by removing the rear PTO carrier cover (on my M's), but only see it. seeing and replacing are 2 different animals. Replacement of plates requires a split.

I agree that engaging at too high a RPM would probably cause premature damage, but so would the banging engagement that comes from engaging at too low an RPM. There is a happy medium, and I believe that I found it for my machine. I have to believe that the clutch pack is designed to take some slippage while engaging.

 

[GreensvilleJay]

re: Unfortunately, there is no way to feather PTO engagement with an electric over hydraulic PTO clutch.

If this 'system' is an electric valve that controls the hydrauic oil to control the clutch, then a 'softstart' module could be designed and installed. It essentially 'feathers','pulses' or 'ramps up' the power to the solenoid to gradually control the flow of oil. Similar to trailer brake 'controllers' that over a short time ,increase power to the electric brakes. I made a 'module' for my rider years ago as I never liked the 'bam-full power' to the cutting blades. with mechanical PTOs you can 'feather' the power.

 

[BAP]

Did this tractor always do this since new? If not, then something is not working right in the engagement mechanism and should be fixed. Check with your dealer and see if they are supposed to have some sort of built in feathering. Could be something has seized up or given out.

 

[SDT]

re: Unfortunately, there is no way to feather PTO engagement with an electric over hydraulic PTO clutch.

If this 'system' is an electric valve that controls the hydrauic oil to control the clutch, then a 'softstart' module could be designed and installed. It essentially 'feathers','pulses' or 'ramps up' the power to the solenoid to gradually control the flow of oil. Similar to trailer brake 'controllers' that over a short time ,increase power to the electric brakes. I made a 'module' for my rider years ago as I never liked the 'bam-full power' to the cutting blades. with mechanical PTOs you can 'feather' the power.

Did not mean to imply that such cannot be done, but rather, that it has not been done by the manufacturers of CUTs, SCUTs and utility tractors unless one wishes to consider the oil orifice in the clutch pack circuit.

Indeed, this issue is not limited to electric over hydraulic systems. The PTO clutch in my B3350 is engaged by a manually operated lever that apparently simply opens a valve to the PTO clutch. There is no way to feather PTO engagement. Engine RPM too low and the engine stalls. Engine RPM too high and all hell breaks loose, sometimes locking the blades requiring one to crawl beneath the mower to unlock. Around 1,200 engine RPM usually works but it still hammers pretty hard.

SDT

 

[gyro28866]

this tractor has always engaged the same since new. The only implement I have had any trouble with is the new to me 20' Woods Batwing mower. I have an old school maintenance shop locally. Two different mechanics with over 40 years experience have told me the same thing. These newer tractors with electric over hydrolic pto's will twist the shafts out of a 20' mower. Too much mass to sudden start. I have had to make repairs to the main gear box and a wing shaft and now the main shaft. These repairs have been near $1000 each time.
I have adjusted the clutches on the mower to factory specs. then I have backed them off and loosened them a little bit.
I was hoping someone here has had the same issues and found a way to soft start a large mower.
I really like my Kubota and use it mostly in the hay fields mowing and raking and even baling hay. It is the perfect tractor for loading out the hay. even great for feeding in the winter. It pulls my old 15' servis bushhog without any issues. I personally know 2 other local men that have had 20' mowers and after many very costly repairs to the drivelines, sold them and went back to 15 footers; because the newer tractors don't have the ability to soft start the implement.

 

[psdstu]

Is it possible to install an Over Running clutch on the mower drive shaft? My LP3712 has an ORC and no problems with PTO engagement.

 

[mcfarmall]

Is it possible to install an Over Running clutch on the mower drive shaft? My LP3712 has an ORC and no problems with PTO engagement.

An overrunning clutch only prevents the implement from back driving the tractor when you disengage it. They don't feather the power at startup.

 

[GreensvilleJay]

yeesh going from 15 to 20, is a 33% bigger unit. So the old guys are right..a LOT of extra mass. I wonder what Kubota says about size of implements for your tractor. I understand going to 20 should reduce seat time my 30%+- but at what cost ? expensive repairs and downtime !! Sounds like a case of 'bigger is NOT better'.

 

[MOfarmer]

Hard engagement is an issue on both my M7060 and M126GX with an electric PTO switch. The first year I had the M126GX it twisted the shaft off the main gear box on our New Holland 411 mower, engaging at idle. I have yet to find a solution that would adjust the electronic modulation valve. The work around we use today is cycling the switch on and off repeatedly until the PTO is fully engaged. Seems like their should be a better solution to this problem though. Would like to know if anyone has found a better way to address this for Kubota's electronic PTO engagement being so hard.

 

[Vigo]

As an automotive tech (ase master + L1 + L3 blah blah) it blows my mind that this type of PTO engagement even exists..

On car we call that a 'clutch dump'. Or, if it's a multiplate wet clutch like an auto trans, we call it a 'neutral drop'. And both are classic recipes for broken axles (ie shafts) among other things. Other than the foot pedal clutch on a manual transmission, every other type of clutch engagement on anything modern is usually 'pulse width modulated' which means rapidly switched on and off in a way that simulates releasing a clutch pedal properly. To me, it's sheer laziness that this isn't SOP on tractors with electric pto switches. I get why it's not a thing on riding mowers (to my knowledge?) because of the price point, but on tractors it just seems.. lazy!

Unfortunately that type of control is not something you can 'easily' implement because even if you built the control circuit to do it, you'd have to 'tune it' to function properly. A lot of work unless you're into electronics and enjoy that kind of thing. If it's a regular old electromagnetic dry plate clutch like a big version of what's on a riding mower, depending on how much current it flows you might be able to fairly easily rig up a lower voltage 'starting circuit' with a large resistor of some kind (coil ballast resistor or blower motor resistor pack are cheap car parts which could be made to work) and a timer circuit. It would start the clutch with the resistor in series, and then bypass it after a second or so. But would still require fiddling to find the right resistance. Or, a large capacitor in series with a resistor (both values would require experimentation). If you ARE working with a multiplate wet clutch or a band clutch applied by a servo you could install a variable restrictor into the flow path and mess with it until you like how it works. I used to rebuild automatic transmissions and this is anologous to a DIY 'shift kit'. Doable but requiring a lot of background knowledge and a major time/effort commitment to get working properly.

A slip clutch adjustment would be the easiest 'bandaid' if you already had a slip clutch. Other than that, no real EASY way forward.. sadly. Sucks that they even build them this way to begin with, in my opinion.

 

[troverman]

As an automotive tech (ase master + L1 + L3 blah blah) it blows my mind that this type of PTO engagement even exists..

Well, as the OP stated, he has run his 15' mower since 2006 without issue. Clearly the design is reliable and works fine. He is just running too large an implement for this particular tractor.