How can you tell if a PTO slip clutch is slipping correctly?

[sixdogs]

How do you know if your slip clutch on a PTO shaft is working? I've had slip clutches on PTO shafts forever and I can't recall ever hearing one slip. But I don't know if you can hear them slip. How do you know?

This matters now because I got a new to me slit seeder but no PTO shaft with slip clutch. And for the $1,100 they want for a new one, the odds are zero I'm getting a factory replacement. So I'm going to buy an off the shelf PTO shaft with slip clutch so I don't damage my gearing.

But first I have to figure out which one to get and then to make sure I get it adjusted correctly. Anyone know anything about this so I don't screw it up? I figure if I hear it slipping too soon I can snug it up a little. but how do I know if it's slipping or not and do most slip clutches ever slip? Lots of questions and I have no answers so any help appreciated.

 

[GManBart]

Good discussion on the topic below. The new shaft/clutch should come with adjustment instructions to get you started in the right direction.

http://www.tractorbynet.com/forums/attachments/119531-how-properly-adjust-king-kutter.html

 

[Poopdeck Pappy]

How do you know if your slip clutch on a PTO shaft is working? I've had slip clutches on PTO shafts forever and I can't recall ever hearing one slip. But I don't know if you can hear them slip. How do you know?

This matters now because I got a new to me slit seeder but no PTO shaft with slip clutch. And for the $1,100 they want for a new one, the odds are zero I'm getting a factory replacement. So I'm going to buy an off the shelf PTO shaft with slip clutch so I don't damage my gearing.

But first I have to figure out which one to get and then to make sure I get it adjusted correctly. Anyone know anything about this so I don't screw it up? I figure if I hear it slipping too soon I can snug it up a little. but how do I know if it's slipping or not and do most slip clutches ever slip? Lots of questions and I have no answers so any help appreciated.

Short answer is you typically take a straight edge and draw a line across both surfaces of the slip clutch. If it slips, you'll know it because the lines won't match up.

 

[Tractor Seabee]

I have not had luck trying to adjust it on the tractor. Take it off and do it on the bench. Mine stays out in the rain so it is a real PIA. the plates rust and seize up. I only have one. I am contemplating seriously of changing it to a shear bolt type.

Ron

 

[pmsmechanic]

I have a slip clutch on my rototiller. Believe me you know when it's slipping. If I get a rock caught between the tines and the frame the tines stop instantly, The tractor smokes and labours like crazy and if I don't get the PTO shut off in time my engine stalls. I never check mine and I haven't adjusted it in ages. I'll need to adjust in a year or so as the engine is not stalling as soon as it used too.

 

[oosik]

Although all my pto units are shear bolt I've seen the instructions for adjustment and checking slip clutches on many sites. Brown mfg for the slip clutches on the pto shafts powering their rear cutters; Bush Hog for the same thing; Land Pride for their rototillers etc. Finding instructions for a unit similar to the one you purchase plus the instructions that come along with the one you purchase should get the job done.

 

[Guesseral]

You will also have to know what the adjustment setting is for the factory unit so you can do the same on the after market unit, I think it is a tork setting. I only have one slip clutch it is on my tiller, I have never adjusted it or ever heard it slip of course I have never got a rock or anything else stuck in the tiller I am mostly sandy soil. I did read the instructions when I got the tiller and it included the adjustment for the clutch but I just don't remember what it said I am finding that the older I get the more I forget, wonder why!

 

[JRobyn]

That's a really good question. In my experience so far (Bushhog 286) there is really NOT any good way to tell if it is operating/slipping correctly. "Factory" settings don't get you much. Their instructions for maintenance are simply to loosen and engage to verify that it slips when loose. Given that the hog gearbox is rated for 90hp, I assumed that the slip clutch spring setting was for a similar HP/torque, which I surmised was TOO HIGH for my 40HP tractor. So I contacted Bushhog for a revised/lower setting. They could only advise using the "standard" spring length setting. I did once inadvertently have the springs way too loose, and could not tell that it was slipping excessively until after mowing for quite a while and getting into really thick weeds. Then, you could hear the blades slow and smell the roasting slip clutch disk! So, sound/smell is the only way I know. Sorry, not much help.

- Jay

 

[Baby Grand]

The line drawn across the friction surfaces is one way.
Also - it'll get hot if it's slipping much. A hand placed on it (engine OFF) will tell you some.
If it slips a lot, there will me smoke - lots of stinky smoke and there will be no doubt.

 

[newbury]

Good discussion on the topic below. The new shaft/clutch should come with adjustment instructions to get you started in the right direction.

http://www.tractorbynet.com/forums/attachments/119531-how-properly-adjust-king-kutter.html

That thread contains a good idea:

Comment and question:

Comment: Unless you have a cab, you'll usually be able to 'smell' if you've been slipping the clutch, that distinctive burnt brake/slightly electrical burn smell.

Question:
Does anyone sell an adapter for either a 1/2" drive, or maybe a 3/4" drive torque wrench to the drive shaft spine?

What I'd like to do is to hook up a torque wrench to the drive shaft, somehow prevent the implement from moving (generally easy) and finding out what torque the clutch slips at. If I know the HP, I can divide the HP by approximately .1028 (540/5252) (or multiply by about 9.7) and get the foot lbs of torque it should slip at. I have a 3/4" torque wrench good for 650 ft lbs. For each 10hp it is about 97ftlbs of torque so if I want it to slip at 20hp I could torque it and it should slip at 194 ft/lbs of torque. (These calculations assume 540RPM on the PTO).

Is this a nutty method or has anyone tried this?

One minor point also, the slip clutch slips on torque, not HP, so if you are running at less than 540, you'll get that much less HP unless you adjust for it. I.E. If I adjust the clutch to slip at 20hp at 540rpm, it will slip at 10hp if I was running half speed (If you half the speed you'd need to double the torque to maintain the hp).

Following that line of thinking - with a pipe wrench and a breaker bar giving me two foot of leverage, plus my 240 lbs I could put 480 lbs of torque on the drive shaft. Which is about what my 42HP M4700 would require.