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Discussion Starter #1 (Edited)
I have a question regarding the correct operation of a pneumatic PTO clutch.

I remember the manual saying that this clutch (green lever by the base of the seat) should only be operated briefly. Can somebody define "briefly" ?

I was planning to use the clutch in between blower passes to turn the PTO off. It would be more efficient than "normal" operation, i.e. 1 : operate the PTO clutch, 2 : put the pto speed lever to neutral, 3: operate the clutch again.
 

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Treat it in just the same way as you would a truck clutch or your mog clutch, I.e. you wouldn’t keep the clutch depressed for a couple of minutes sat at traffic lights but 30sec to 1min you would, but then agene if there is no specific need to disengage the clutch between passes then don’t, and if your going to engage drive do it at tick over or as low as possible engine RPM to avoid shock load.

Its to protect the clutch release bearing and the clutch plate heat from any drag, but that said if the PTO shaft is taken off and the PTO put in gear then operated so the PTO stub spins then you disengage the PTO clutch if you stub spins down and stops then this is no inherent drag to make heat as the slightest amount of drag would keep the PTO stub spinning, in which case your just protecting the clutch release bearing.

Is your blower a 540rpm or 1000rpm implement and is there an overrun clutch either on the end of the PTO shaft or on the input of the blower rotor?
 

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Discussion Starter #3
Is your blower a 540rpm or 1000rpm implement and is there an overrun clutch either on the end of the PTO shaft or on the input of the blower rotor?
It's 540rpm. There is an overrun clutch. There is also a sheer pin on the PTO shaft. This Blower is rated for tractor up to 75hp. So I'll have to watch miselft, to make sure I don't break nothing, being that the truck PTO is probably around 135ish HP.

b101uk, Have you ever "dynoed" your PTO ?
 

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No not dynoed it even though there is a tractor place 6 miles away with one!

In my “Unimog New models 427 - 437 - introduction to service” it says the PTO system loses 10% of the flywheel HP (DIN) by the time it gets to the PTO stub and that under DIN conditions which allow a further 5% for error (- 15% total) the minimum HP available at the engines rated speed should be in excess of >132.6HP at 2400rpm (-10% only = 140.4HP) and a bit less than that at exactly “540rpm” at the PTO stub

So really your looking at 132hp to 140hp though if we allow a little margin to account for diesel differences and for flow improvers in winter diesel I would say you really have nearer 130HP than 140HP at the PTO stub like you say at engine rated speed (2400rpm).

The 540/1000rpm pto box in our mogs will be 3.85:1 & 2.19:1 respective gear ratios so exactly 540rpm takes place at 2079rpm on the engine in the 540rpm gear, 1000rpm takes place at 2190rpm on the engine in the 1000rpm gear, also in the same 1000rpm gear you can make 540rpm at only 1182.6rpm on the engine, which would be <126HP, <129.5hp and <74hp respectively.

However I would stock up on shear pins or the recommended hardness bolts that act a shear pin, as you can never have to many in the cab even if you find you seldom brake them! ;)
 

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Discussion Starter #5 (Edited)
also in the same 1000rpm gear you can make 540rpm at only 1182.6rpm on the engine, ...

Is that a safe practice, to run in the 1000rpm gear at low revs to get 540rpm on the pto shaft ?

Would torque be affected since I would be playing in a different torque curve than at 2079rpm engine speed ? (edit : I would think so since I would be producing only 74hp at that speed)

Wonder how the blower would react if runned past its recommended speed of 540rpm ?
 

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Is that a safe practice, to run in the 1000rpm gear at low revs to get 540rpm on the pto shaft ?

Would torque be affected since I would be playing in a different torque curve than at 2079rpm engine speed ? (edit : I would think so since I would be producing only 74hp at that speed)

Wonder how the blower would react if runned past its recommended speed of 540rpm ?
I don't know, but this springs to mind!

 

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Is that a safe practice, to run in the 1000rpm gear at low revs to get 540rpm on the pto shaft ?
?
I run a 10kW PTO generator requiring 540 rpm on a 406, in 1000 rpm PTO position, then tune the engine speed by watching the output of the generator to give correct 220 vac and 60 Hz. The engine runs at a more comfortable speed, uses less fuel, and less wear and tear. But, even if the 10 kW genny was at full load (which it never is) that's only needing 14-15 hp plus whatever inefficiencies.

What kind of a blower is it? Snow? In the case of a snow blower which could easily load up and need peak hp, IMHO stick with the normal RPM and 540 position on the PTO. If you ever have to panic stop during one of those loaded-up situations, (if engine can't handle torque at that low rpm) cleaning out the blower will wean you of running in the 1000 rpm slot!!

Besides, 1182.6 rpm is way below the torque peak for that engine if you run in the 1000 rpm position.

Bob
 

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Discussion Starter #8
What kind of a blower is it? Snow? ...


Besides, 1182.6 rpm is way below the torque peak for that engine if you run in the 1000 rpm position.

Bob
Rear mounted snow blower it is.

Thought about it and like you said, getting 540 at the pto on the 1000rpm gear would be useful when stationary, but when moving about, a blip on the throttle and I'm past 1500rpm easily.

I'll stick with the 540rpm gear.

On another note, with the air clutch disengaged, I sometimes get a bit of grinding noise when I go from the neutral position on the pto speed selector level to the 540rpm setting. What gives ?

Do I have to match the revs or what ?


BTW, the blower is rated for a 75hp tractor.
 

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Discussion Starter #9 (Edited)
On another note, with the air clutch disengaged, I sometimes get a bit of grinding noise when I go from the neutral position on the pto speed selector level to the 540rpm setting. What gives ?

Do I have to match the revs or what ?
Did some test yesterday and I do have to bump-up the revs to around 1500rpm for the 540rpm speed to engage without any grinding noise.
 

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...chop...

On another note, with the air clutch disengaged, I sometimes get a bit of grinding noise when I go from the neutral position on the pto speed selector level to the 540rpm setting. What gives ?
...chop...
I am not speaking from experience here because I've not used the PTO air clutch on a mog. BUT, I don' think you should be shifting the PTO speed lever with the truck running. The normal procedure for shifting between 540-neutral-1000 (and vice versa) is to shut down the engine.

The air clutch, I think, is located down stream from the PTO gear box and does not stop the gears. You were only able to accomplish the shift because with the clutch disengaged there is minimized mass beyond the gearbox, mass that must be brought up to speed by the friction of grinding gears.

Bet the PTO gearbox will shift fine with the engine stopped.

Bob
 

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Discussion Starter #12 (Edited)
I am not speaking from experience here because I've not used the PTO air clutch on a mog. BUT, I don' think you should be shifting the PTO speed lever with the truck running. The normal procedure for shifting between 540-neutral-1000 (and vice versa) is to shut down the engine.

The air clutch, I think, is located down stream from the PTO gear box and does not stop the gears. You were only able to accomplish the shift because with the clutch disengaged there is minimized mass beyond the gearbox, mass that must be brought up to speed by the friction of grinding gears.

Bet the PTO gearbox will shift fine with the engine stopped.

Bob
I hope you are wrong cause it would involve major suckage to turn off the engine each time I have to stop the PTO.

I don't really shift gears on the PTO, I go from neutral to 540rpm and back, around 50 times pre hour,


Also, I think that the sole purpose of a separate pto clutch is to give the ability to shift it on the fly. I don't have my manual with me, but I believe that the wording was to that effect.
 

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No doubt I am wrong. I thought you were shifting PTO gears and referring to the PTO shifter on the left rear of the transmission, 'under the cab', that has 540-neutral-1000 positions. That one does need a stopped transmission to shift.

Apparently you are referring to the shift lever 'in the cab' that allows shifting the PTO in and out of gear (not the air clutch).

That air clutch in the PTO driveline lets you temporarily interrupt the PTO drive without hitting the foot clutch (therefore maintaining road speed), but leaving PTO in gear, right?

But, if you take the PTO out of gear, even with the air clutch disengaged, there will still be gear clash if you try to shift the PTO back into gear without the foot clutch. That's because the transmission-side gears are moving but the PTO output gears are not. Engage them, they will grind until the mass of the PTO output gears are back to transmission gear speed. There are no PTO gear synchronizers.

However you can take the PTO gears out of gear without clutching if they are not under load, just as you can bump a tranny out of gear when it's coasting. If under load, you will eventually kill your gears that way.

I still don't understand how the gears could grind if you are simply putting the air clutch back into 'engage'. The PTO gears should be remaining 'in gear', just de-coupled by the air clutch.

(I really do want to understand how that thing works!!)

Bob


I hope you are wrong cause it would involve major suckage to turn off the engine each time I have to stop the PTO.

I don't really shift gears on the PTO, I go from neutral to 540rpm and back, around 50 times pre hour,


Also, I think that the sole purpose of a separate pto clutch is to give the ability to shift it on the fly. I don't have my manual with me, but I believe that the wording was to that effect.
 

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Bob,

Just for information's sake, the MBU/SBU pto clutch setup with the double clutch and live pto transmission is a whole lot different than the one on the 406/416 series trucks. There are actually two sets of fingers and two throwout bearings in the clutch housing, along with two clutch slave cylinders (one hyd and one air), and each clutch disc is operated completely seperately. In other words, unlike on the 406 trucks, the pto will not stop at any point in the depression of the foot clutch, and the truck will not stop driving if the air pto clutch is "depressed" and the pto is brought to a stop. THe PTO transmission is completely seperate from the driving transmission on the square trucks, which makes all of this possible. This makes it really nice to engage and disengage the pto while on the move.

As far as mogish's question as to why his PTO gears are grinding while trying to engage, sometimes the pto clutch pressure plate will get rust on it from not being used and it will drag, and other times the cab must be tilted and the rod in the air slave cylinder needs adjustment (and sometimes the clutch plate is completely worn out, but you will get a slipping clutch under load in that case). I suspect that this is the first time that the pto has been used with an attachment since mogish bought the truck, so it may all clear up after a couple of good engagements under load.

Cheers,
Ben
 

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Discussion Starter #15
I still don't understand how the gears could grind if you are simply putting the air clutch back into 'engage'. The PTO gears should be remaining 'in gear', just de-coupled by the air clutch.

(I really do want to understand how that thing works!!)

Bob
The PTO makes a grinding noise when I go from PTO-neutral to PTO-540rpm, if the engines revs are under around 1500rpm. They will grind always, all the time if I would try to use the pto speed selector without activating the pto clutch first. I don't know if I would get the grinding without an implement hooked on the PTO shaft.

Now, I just bump-up the revs past 2000rpm, and it becomes one-finger shiftable.

I am definetly getting better at coordinating my hand on the direction lever, speed lever, gear selector, pto clutch, pto speed selector and 2 hydraulic spools while still looking in front, at the rear and in the mirrors. When I do snow work, I am a busy man in that cab.



In other news, still a tight fit but getting easier
 

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Discussion Starter #16
I suspect that this is the first time that the pto has been used with an attachment since mogish bought the truck, so it may all clear up after a couple of good engagements under load.
You are right, I never used the pto before.

When I pumped new grease "in" the pto spline zerk, brown rusty gunk came out

My 8 hour interval PTO grease service is up next week so hopefully, 8 hours of pto rotation plus new grease is gonna be good for my dear pto.

BTW, what would you use to clean out all that grease ?

Is there magical stuff that I can spray on there ?
 

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Next time you have 10 mins, remove the PTO shaft from the stub (mog off), start the mog and engage the PTO clutch and wait a moment for things to spin down, engage the 540rpm PTO gear then disengage the PTO clutch so the stub spins, then re-engage the PTO clutch and get out of the mog to observe the stub and answer the following,

Dose the stub spin down to a stop?

If it spins down to a stop there is no inherent drag within the PTO clutching system, if it continues to spin at quite a high speed then there is inherent drag within the PTO clutching system.

Next:

With the PTO clutch still engaged turn the mog off, exit and go to the stub if it has stopped turning grab the stub with 1 hand and turn it, you should be able to turn the stub with one hand thus showing there is no drag between the PTO clutch plate and pressure plate, if you have to use both hand and a lot of force or you cannot turn it then there is to much inherent drag between the PTO clutch plate and pressure plate.

Next:

If there is no inherent drag in the PTO clutch then you are probably not giving enough time between engaging the PTO clutch and shifting into the relevant PTO gear for the components in the PTO box to spin down, also there can be a small amount of inherent drag between the inner shaft pass-threw which goes to the main gearbox and the outer shaft which just goes to the PTO its self, in this case when selecting a PTO gear also engage the foot clutch which will insure both the inner and outer shafts (to main transmission and PTO) are stopped which will allow you to feed the PTO gear - if its between dogs thus the gear wont go fully in hold a bit of pressure on the PTO gear lever and raise you foot of the transmission clutch just so the little bit of drag will slowly turn the shaft/gears/etc so the dog can engage.

If its looking like its caused by to much inherent drag then you will need to raze the back of the cab 2ft to get access to the PTO clutch air slave cylinder so you can take measurements and set the correct gap between the push-rod on the end of the PTO clutch air slave cylinder and the clutch fork so you get the correct range of throw on the PTO clutch thrust bearing.
 

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Discussion Starter #18
Next time you have 10 mins, remove the PTO shaft from the stub (mog off), start the mog and engage the PTO clutch and wait a moment for things to spin down, engage the 540rpm PTO gear then disengage the PTO clutch so the stub spins, then re-engage the PTO clutch and get out of the mog to observe the stub and answer the following,

Dose the stub spin down to a stop?

If it spins down to a stop there is no inherent drag within the PTO clutching system, if it continues to spin at quite a high speed then there is inherent drag within the PTO clutching system.

Next:

With the PTO clutch still engaged turn the mog off, exit and go to the stub if it has stopped turning grab the stub with 1 hand and turn it, you should be able to turn the stub with one hand thus showing there is no drag between the PTO clutch plate and pressure plate, if you have to use both hand and a lot of force or you cannot turn it then there is to much inherent drag between the PTO clutch plate and pressure plate.

Next:

If there is no inherent drag in the PTO clutch then you are probably not giving enough time between engaging the PTO clutch and shifting into the relevant PTO gear for the components in the PTO box to spin down, also there can be a small amount of inherent drag between the inner shaft pass-threw which goes to the main gearbox and the outer shaft which just goes to the PTO its self, in this case when selecting a PTO gear also engage the foot clutch which will insure both the inner and outer shafts (to main transmission and PTO) are stopped which will allow you to feed the PTO gear - if its between dogs thus the gear wont go fully in hold a bit of pressure on the PTO gear lever and raise you foot of the transmission clutch just so the little bit of drag will slowly turn the shaft/gears/etc so the dog can engage.

If its looking like its caused by to much inherent drag then you will need to raze the back of the cab 2ft to get access to the PTO clutch air slave cylinder so you can take measurements and set the correct gap between the push-rod on the end of the PTO clutch air slave cylinder and the clutch fork so you get the correct range of throw on the PTO clutch thrust bearing.

Damn, you're good !

What would I do without you ?

Will try those steps next it doesn't snow...
 

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Next time you have 10 mins, remove the PTO shaft from the stub (mog off), start the mog and engage the PTO clutch and wait a moment for things to spin down, engage the 540rpm PTO gear then disengage the PTO clutch so the stub spins, then re-engage the PTO clutch and get out of the mog to observe the stub and answer the following,

Dose the stub spin down to a stop?

If it spins down to a stop there is no inherent drag within the PTO clutching system, if it continues to spin at quite a high speed then there is inherent drag within the PTO clutching system.

Next:

With the PTO clutch still engaged turn the mog off, exit and go to the stub if it has stopped turning grab the stub with 1 hand and turn it, you should be able to turn the stub with one hand thus showing there is no drag between the PTO clutch plate and pressure plate, if you have to use both hand and a lot of force or you cannot turn it then there is to much inherent drag between the PTO clutch plate and pressure plate.

Next:

If there is no inherent drag in the PTO clutch then you are probably not giving enough time between engaging the PTO clutch and shifting into the relevant PTO gear for the components in the PTO box to spin down, also there can be a small amount of inherent drag between the inner shaft pass-threw which goes to the main gearbox and the outer shaft which just goes to the PTO its self, in this case when selecting a PTO gear also engage the foot clutch which will insure both the inner and outer shafts (to main transmission and PTO) are stopped which will allow you to feed the PTO gear - if its between dogs thus the gear wont go fully in hold a bit of pressure on the PTO gear lever and raise you foot of the transmission clutch just so the little bit of drag will slowly turn the shaft/gears/etc so the dog can engage.

If its looking like its caused by to much inherent drag then you will need to raze the back of the cab 2ft to get access to the PTO clutch air slave cylinder so you can take measurements and set the correct gap between the push-rod on the end of the PTO clutch air slave cylinder and the clutch fork so you get the correct range of throw on the PTO clutch thrust bearing.
I really impressed myself by actually understanding what you are talking about...the lack of use argument makes sense also; some of us have large gaps of time between PTO applications. Thanks
 
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