# Slip Clutch or Shear Bolt



## krone.1 (Jul 28, 2013)

In a PTO shaft type application that would allow either a disc type slip clutch or a shear bolt hub....

Which would you prefer?

Thanks!


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## hog987 (Apr 5, 2011)

I like a shear bolt, but lots of them are in a spot that is not so easy to replace to get the wrenches on. Slip clutches are nice but once they start to get a bit worn they can be a pain cause they keep slipping. Also when I was working in the shop when guys put in a new slip clutch they would either not tighten the bolts enough and the clutch would slip easier or tighten them too much and something else would go boom before the clutch would slip.


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## Vol (Jul 5, 2009)

I always preferred the simplicity of a shear bolt. Seems it is more capable of bumping the pto if needed...i.e. getting a baler to swallow a plugged wad of hay by bumping the pto shaft.

Regards, Mike


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## enos (Dec 6, 2009)

Ever notice that all drive line protection is usually close to tractor? Eg on first gear box or PTO directly behind tractor. I always figured it should be closest to operating part of machine, next to cutterbar, brushcutter hub, tiller shaft etc. Operator rarely slams PTO into gear at full throttle. If they do they learn about unemployment office in a hurry. Most damage is caused by unseen obstructions in tall grass, underground. Shock load has to travel back through shafts, belts, gears etc before slipping clutch, breaking bolt. As equipment gets older and used more stress fractures develope in yokes, shafts in one direction, shock load blows them apart before driveline protection can save them. Any part failure from hitting something i have dealt with has been past driveline protection if clutch etc has been set up correctly.


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## krone.1 (Jul 28, 2013)

We have a couple of applications where a shear bolt hub may be better than a slip clutch. Mostly due to the cost of repairing a slip clutch when it fails,,,, We are not sure what customer acceptance would be of a shear bolt hub..


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## enos (Dec 6, 2009)

On a disc mower for example, shear hub on shaft that goes down to cutter bar. I would buy a shear bolt over a gear box any day.


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## eam77 (Aug 4, 2013)

Shear bolts are OK only in places where they rarely are sheared. Some other applications must slip some. Now we (owners, operators) don't like to buy slip clutch parts, but some applications just require it. Examples: my 2615 batwing bush hog operated on moderately rough ground just must have slip clutches- a number of slips in every days run. I buy several clutch discs every year. On the other hand, my old baler has a slip clutch. I have never replaced a disc- I don't know that it has even ever slipped- 23 years of service--- obviously, a shear bold would have been fine.


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## mlappin (Jun 25, 2009)

On my round baler I much prefer the slip clutch. On our old square baler if I remember correctly it had both. Most slip clutches have a procedure in the owners manual to make sure they haven't seized up during storage.


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## Josh in WNY (Sep 7, 2010)

I think they both have their uses, but it is easier to tell when something is wrong when it's a shear bolt. Sometimes a slip clutch might be slipping, but not enough for you to know there is an issue that needs fixing. I also feel that shear bolts do a better job when it is a sudden shock to the drive line rather than a build up of resistance (where a slip clutch might be better).

Another thing, it's harder for someone to put the wrong grade of bolt in a slip clutch and really ruin a piece of equipment!


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## Tim/South (Dec 12, 2011)

I lean towards a slip clutch. On a lot implements the manual says to loosen the bolts and spin the clutch at the beginning of each season. The clutch disks tend to stick together over winter. I do not know many people who spin the clutch once a year.


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## FCF (Apr 23, 2010)

How about a toothed type slip clutch instead of disc style? Less likely to seize together in storage also makes noise when slipping just a little. I know this doesn't matter (noise) if you are in a closed cab with the radio turned up. It also doesn't take time like a shear bolt to replace but you still need to take care of what is causing the overloading, Just an idea,


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## urednecku (Oct 18, 2010)

They both have their place. Reference my 336 baler, the driveshaft has a slip clutch before the first gear, slips if there is too much load someplace, like a big plug going in the chamber the knife can't cut. But the flywheel has the shear bolt that works if something stops things suddenly, things don't get all twisted up before they can wind down.


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## jturbo10 (Feb 28, 2011)

Both. I rely on the machinery engineers to decide what is best if not both. Shear bolts are like idiot lights as they don't come on or shear until it is a major meltdown issue while slip clutches can deal with lesser issues multiple times. However, slip clutches have limited lives when it comes to operating like designed and they can become the salient problem if stuck, improperly adjusted, or worn out and affecting operational efficiency. Shear pins are pretty fool proof for the life of the implement unless you use the wrong grade bolt.


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## krone.1 (Jul 28, 2013)

Thanks for all the replies. The application in consideration is not a situation where there are load differentials between the tractor and machine which need to be absorbed by a slip clutch. The component needs to be protected primarily from impact or a severe overload.

With quieter cabs and more powerful tractors, a slipped clutch often goes unnoticed until it is too late. Even if you catch it as soon as it slips, the standard slip clutches typically used in the industry does not have a provision for adjustment, so at a minimum new discs are needed (usually happens at 3:00 on Saturday afternoon).

Our product and marketing departments are concerned that there is a perception that shear bolt type clutches are not considered to be good engineering by the end user. Just reading some of your comments, that doesn't seem to be the case?

Thanks again


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## Josh in WNY (Sep 7, 2010)

krone.1 said:


> The application in consideration is not a situation where there are load differentials between the tractor and machine which need to be absorbed by a slip clutch. The component needs to be protected primarily from impact or a severe overload.
> 
> Our product and marketing departments are concerned that there is a perception that shear bolt type clutches are not considered to be good engineering by the end user. Just reading some of your comments, that doesn't seem to be the case?


If it is just the shock/impact loads you are worried about, I think a slip clutch is better. There isn't the chance of the slip clutch being jammed without you knowing it.

I don't think a bad perception is the case, but I don't speak for everyone either. I have noticed that the people around me who complain the most about stuff like shear bolts are also the ones who replace them with grade 8 bolts from the hardware store and then wonder why something else (usually much more expensive) breaks. (FYI, you will never find me letting these people run or work on any of my equipment!) I just make sure I have a supply of proper shear bolts prior to using the equipment for the season. Each spring I check out the baler and there needs to be at least 5 shear bolts in the toolbox. I've never needed that many, but they're there just in case. Other equipment is similar, but the number of bolts on hand varies with experience.


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## hog987 (Apr 5, 2011)

One thing about a grade 8 bolt as a shear bolt is that in fact under a sudden shock they will break easier. High strenght steel is more brittle. But under an increase in load over time they will take a whole lot more stress and that is when other things begin to twist and snap and so on.


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