Slip clutch - shear pin ?

[Ultradog MN]

I still don't get the reasoning for the slip clutch vs non slip clutch having a lot to do with ujoint wear.
A 4' rotary is not only going to be narrower but also shorter than a 6'.
On a 4' the gear box will be closer to the tractor making for a shorter drive shaft.
So by the reasoning above a 4' should wear out u joints quicker than a 6' will.
But I don't think that is the case

 

[ovrszd]

The only advantage a slip clutch cutter would have over a shear pin cutter in regards to U-joint wear might be that the slip clutch protects the driveline from shock load better.

In regards to the length issue, a shear pin 4' cutter will have a longer driveline than a slip clutch 4' cutter. But I doubt that matters. My hiway driven Jeep has a lot shorter rear driveshaft than a 4' cutter.

 

[Dave M7040]

Sorry but there are just some basic engineering facts provided by the pto shaft manufacturers. You can believe their advice or ignore it.
Should you choose to ignore it they will be rewarded by you have to buy repair parts more often.
Dave M7040

 

[Ultradog MN]

Sorry but there are just some basic engineering facts provided by the pto shaft manufacturers. You can believe their advice or ignore it.
Should you choose to ignore it they will be rewarded by you have to buy repair parts more often.
Dave M7040

Got any evidence for that statement?
Let's say I have a 4' 3 point type cutter with a shaft length that is 44" long. Lets say it is a shear pin type.
Now if we put a slip clutch on that same cutter the shaft length might only be 38" long.

On the other hand, if I have a 6' 3 point, shear pin type cutter with a shaft length of 54" and I put a slip clutch on it I now have a shaft length of 48".
I seriously doubt the 6" difference in shaft length is going to make much of a difference in Ujoint life.
Maybe if we reduced their lengths by 2 Feet but not the average 6 Inches a slip clutch shortens them.

 

[ovrszd]

I'm a little "slow". Didn't quite understand the subject. But now I got it.

I think the driveline angle problems would be easier created by different tractor's configurations, rather than length.

For example, my neighbor has a 5' KK Rototiller. This Spring he asked to borrow my Ford 3910 to run it. That evening he commented that you can't lift it all the way on my tractor because the driveline binds and chatters.

So, for me, going back to my Jeep and Buggy world, the issue is maximum angles created more than length of the shaft. My Buggy has extreme flexibility in the rear suspension, each tire having 16" of travel. But I limit the center of the rear axle with a strap to avoid overloading the driveline angle.

 

[SPYDERLK]

Sorry but there are just some basic engineering facts provided by the pto shaft manufacturers. You can believe their advice or ignore it.
Should you choose to ignore it they will be rewarded by you have to buy repair parts more often.
Dave M7040

Im sure the info is true, but needs to be qualified by the specifics of test. ... For instance, was it continuous full load, full speed, no angle changes, no regreasing, no reverse loading? ... All having highly negative effect, and at variance to actual use on a pto.

 

[Fallon]

Tom Wood's Custom Drive Shafts - Driveline 101 indicates the same thing double the angle, half the lifespan.

In a lab a 4' cutter would have its U joints fail faster than a 5' due to the steeper angle. In the real world? To many variables to get a good answer. The extra couple degrees or fraction of a degree from loosing a few inches to a slip clutch will cause more wear. However as a practical matter I'd be a lot more concerned with poor greasing being a problem. It will also be a lot less of a problem with a long shaft like on a rotary cutter than on a short shaft like a tiller or flail. I'd expect a looser clutch on a rotary cutter would eat more shock extending the U joint life more than it takes off due to the extra angle.

I just ordered a new PTO shaft for my $100 Ford 917 as I couldn't even touch the half shafts together when they were mounted. I avoided a slip clutch as the belts on the flail will serve the same function & I have under 30" of PTO length at the shortest. I don't want to increase the strain on the U joints. Would it work with the slip clutch shaft that was cheaper? Probably, but why complicate things & put more strain on things.

 

[Dave M7040]

Get a piece of graph paper and drawing it to scale.
Measure the angles at the joints on the paper with a protractor just like in school.
I am not making the facts up.
Take a pto shaft you have with a manufacturers manual and post the manual here for all to see. Lets see what Your supplier thinks about joint angles.
I really am not trying to argue or downplay anyone's real world experience but rather enlighten those that are interested in the engineering facts that have a bearing on durability.
An example, when I buy a snowblower, I try and buy the one with the biggest fan. Why, because the center of the fan will be the height of the pto shaft. The closer it is in height to the pto shaft on my tractor, the lower will be the joint angles and the longer life the pto joints will have. Changing a joint in a snowstorm in the winter is not pleasant.
Dave M7040

 

[TripleR]

Dave, I think few are doubting the validity of the theory, just its implication to "real world experience". Your statements or the manufacturer's blanket statement that a slip clutch will dramatically reduce service life just isn't lining up with the real world experience of long term longevity of slip clutch equipped drive-lines.

I can accept increased angle can increase wear, but the extent and real life implications are a bit harder to buy into. My experience with slip clutches has been favorable with negligible difference in wear, so my preference will remain with them, I use them on SCUT, CUT, UT and Ag.

As always, results may vary.

 

[Dave M7040]

Dave, I think few are doubting the validity of the theory, just its implication to "real world experience". Your statements or the manufacturer's blanket statement that a slip clutch will dramatically reduce service life just isn't lining up with the real world experience of long term longevity of slip clutch equipped drive-lines.

I can accept increased angle can increase wear, but the extent and real life implications are a bit harder to buy into. My experience with slip clutches has been favorable with negligible difference in wear, so my preference will remain with them, I use them on SCUT, CUT, UT and Ag.

As always, results may vary.

Sometimes, I acknowledge my explanations fail to make a point clearly as can happen when you know a subject well.
My comments had nothing to do with the performance attributes of slip clutches compared to shear pins.
I was trying to convey that the slip clutches I have seen result in a shorter pto shaft which then increases the joint angles with the consequent reduction in joint life.
I will say it again, I have the utmost respect for those with a wealth of varied, real world experience. It is an engineer like me who is responsible for the Takata air bag recall! In Canada we wear an iron ring on our dominant hand little finger to remind us of a bridge collapse in Quebec city resulting from poor engineering.
Dave M7040