Yet Another Death

[Tony_S]

Just down the road from me. A 15 yr. old. They are not sure yet why this happened, but it is tragic none the less.
Don't let your guard down around those driveshafts!!
Story in local Rockingham County Va newspaper.

Tony

 

[Bird]

That story indicates, in one place, that perhaps the entire PTO driveshaft came off, but it reminds me of something I saw in 1994. A guy was pulling out of a tractor repair shop on a John Deere tractor with a brush hog attached. As soon as he got out onto the shoulder of the road, he engaged the PTO and started mowing down the side of the road. And he didn't go 50 feet before the driveshaft came loose at the front end; i.e., it came loose from the tractor's PTO. Since the blades on the brush hog had gotten up to speed, they kept turning and that PTO driveshaft was flopping all the over the place; very noisy and impressive display before it finally stopped. I guess it could have easily slung the two sections apart, but at least it didn't that day. But I think every time I hooked up a PTO driveshaft, I thought about that and how scary is was, so I always wanted to be really sure I had mine all the way on and locked in place.

 

[N80]

My B-I-L has some old (mostly rust) JD 14 foot rotatry cutters and said his PTO shaft broke at the yoke on the mower end. He said it was all over the place before he could get it shut down. Not sure if one could flop up and hit the driver but I bet it still scares the pooh out of you.

 

[RoyJackson]

My B-I-L has some old (mostly rust) JD 14 foot rotatry cutters and said his PTO shaft broke at the yoke on the mower end. He said it was all over the place before he could get it shut down. Not sure if one could flop up and hit the driver but I bet it still scares the pooh out of you.

Yeah...one section of the shaft itself (the parts that slide to collapse and extend) could have flown off...basically travel like a spear.
Your B-I-L was lucky that didn't happen.

 

[Bob_Young]

Never seen a PTO shaft come unglued, but have thought about it a lot. One more reason to choose an operating RPM below Max PTO RPM...if it gets the job done. BTW, what does everyone think the minimum overlap between the two shaft sections should be when fully extended?

Hooked the old 5 ft. Woods M5 cutter to the L4300 (w/Pat's) the other day for a small job....first time on that tractor. Saw overlap between the two sections was only about 3.25 inches. Made me nervous....made me more nervous when the shaft seemed wobbly while running. Got another 3.75" when I removed Pat's EZ change. Hated doing that, but the shaft seemed to spin straighter. The female section of the shaft is pretty beefy on that cutter, but it's 30 yrs. old and I imagine too little overlap plus a shock load could split it...or twist off the end of the male section.
Bob

 

[Bird]

One more reason to choose an operating RPM below Max PTO RPM...if it gets the job done. BTW, what does everyone think the minimum overlap between the two shaft sections should be when fully extended?

I'd disagree with you about that being a reason to run less than full PTO speed. If it should come apart at half normal PTO speed, it would be dangerous, and if it's operating normally, hooked up correctly, etc., I see no reason to not go with full PTO rpm.

As for the minimum overlap, I think Bush Hog manuals recommend a minimum of 6" and I'd go along with that myself. Just simply would not use one with 3.25 inches overlap.

 

[AlanB]

I would have to ask again, but a couple years ago, my buddy mowing with an older tow behind type rotary cutter hit something, and instead of the shear bolt giving, the Front yoke broke.

Said it was scary as all get out, the RC momentum at that point was driving the driveshaft, and it was bouncing all over right behind him.

It all came out ok, but he got a new driveshaft and greases it regularly...

 

[Bob_Young]

The higher the PTO speed, the greater the momentum and energy in the system when something breaks. It's Physics. Following drive failure, this excess energy has to be dissipated somewhere before reaching a point of safety. The smaller the excess, the sooner the point of safety can be reached.

If you could be assured a smooth spin-down on part failure then it doesn't matter how much energy has to be dissipated. But it doesn't work that way. Shafts flail wildly, parts may fly off and, if you're lucky, only bent and broken metal will result. Worst thing is that the mayhem caused by this energy will be totally beyond operator control.

C'mon, Bird, you know all this stuff. Don't be dogmatic.
Bob

 

[Bird]

Dogmatic? Well, I didn't think so, but maybe. I didn't say there wouldn't be more energy to dissipate at higher speeds, only that I didn't see that possibility as a reason to operate at lower rpm. In other words, if it's defective and you think it might come apart, I wouldn't be using it at all, and if it's in good condition, properly hooked up, I'd run it at PTO speed.

You know in a car wreck, you're much less likely to get hurt if you keep your speed under 20 mph. Is that a good reason to never exceed 20 mph? Now, of course, for some drivers I've seen, maybe that would be a good idea.

 

[RoyJackson]

I'm with Bird on this one...a broken section of a PTO shaft might not fly as far or as fast at half PTO speed....but it'll still be going fast enough to do damage and serious injury.
I don't see much point in running at a reduced speed. Just check your equipment and make sure the wife keeps up with the insurance payments.