Catastrophic implement shaft failure!

[MOzarks]

Here's what happened: normal level ground, knee high grass, and zero obstructions while cutting- no rocks or stumps of any kind. Running an old Massey MF65 to an FMC Sidewinder 5x5 as I have done for the last 20 years. I heard a series of two or three loud bangs and looked behind me to find the shaft had totally failed with the yoke, separated from both my PTO and the implement shaft, laying on the ground. I limped both back to the garage to investigate and the rotary cutter was freely spinning with the shear bolt on the implement side of the shaft still intact! It is a grade 5 pin and should have broken prior to any shaft failure, I think, so my guess is some other cause than an impulse generated a problem.

Some quick forensics indicated that the overrun coupler on the back of the tractor (attached to the tractor's PTO shaft) had twisted like a tootsie roll before shearing off. That implies the implement shaft failed [u:43e3d5ff8e]first[/u:43e3d5ff8e], the free end spun around once or twice before binding on the tractor, and then sheared the overrun coupler.

Fortunately, after removing the destroyed overrun coupler, it appears the PTO in the tractor itself survived albeit there is a slight wobble on the output (which may or may not have been present prior to the incident). At this time I don't intend on replacing the tractor's PTO shaft as the bearing and seal are holding up well- unless you folks convince me otherwise. It's my intent on replacing the overrun coupler and getting a new implement shaft. If that's all I need to replace, then I feel pretty fortunate.

So my question is why would an implement shaft break in the first place without the shear pin breaking off first? Is fatigue failure ever a legitimate cause for an implement shaft to shatter like this? Do implement shafts have a lifespan and require routine replacement?

Long time lurker/reader (thanks for the help over the years!) and first time poster. Glad to be here.

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[Roger in Iowa]

Did the top of the hitch pin contact the implement drive shaft? Looks like it might have. Damaged shaft then failed.
Problem was ahead of the shear pin on mower, so it would not have failed.

 

[old]

Mo Ozarks as in your live in Missouri?? If yes I too live in Missouri the Lake f the Ozarks area

As for that shaft looks like some how it was forced to stop spinning but still had PTO power applied so something had to give

 

[MOzarks]

Good eye for detail! But the hitch pin handle had been damaged many moons ago by my late grandfather. I did inspect the handle after the incident and there were no new impact marks.

 

[MOzarks]

(quoted from post at 12:18:38 05/06/19) Mo Ozarks as in your live in Missouri?? If yes I too live in Missouri the Lake f the Ozarks area

As for that shaft looks like some how it was forced to stop spinning but still had PTO power applied so something had to give

Glad somebody noticed the handle! I'm a bit south and east of the Lake area closer to Mark Twain forest.

There was nothing under me to hit to induce any kind of stopping impulse. My initial thought was the gearbox seized on the cutter but after I was able to make it spin with a gentle touch that theory went out the window. Maybe stress fractures finally weakened the shaft enough, but I haven't heard of that happening to others.

 

[Roger in Iowa]

The pto shaft out of the tractor spins clockwise. When the power shaft failed, the part attached to the tractor continued to turn until it came around and stopped at the drawbar. The engine flywheel and engine continued to turn the pto shaft and then next to fail was the over running clutch shaft. Your PTO shaft may also be twisted ahead of the over running clutch. Check it. May also be twisted inside the tractor.

 

[MOzarks]

(quoted from post at 13:29:05 05/06/19) The pto shaft out of the tractor spins clockwise. When the power shaft failed, the part attached to the tractor continued to turn until it came around and stopped at the drawbar. The engine flywheel and engine continued to turn the pto shaft and then next to fail was the over running clutch shaft. Your PTO shaft may also be twisted ahead of the over running clutch. Check it. May also be twisted inside the tractor.

You're right- the remaining PTO shaft splines exposed and that still look straight were locked inside the over running clutch at impact, possibly hiding some twists inside the tractor. Bummer! I guess my next question involves what special tools are necessary to extract the PTO shaft, bearing, and seal? Since I'll be draining the hydraulic fluid, I'll be replacing all three.

 

[old]

I've lived here where I am since July of 1980 so almost 39 years in the same place. Yes I notice handles and there hidden meanings LOL

 

[MOzarks]

That's quite a while! You've seen that area grow. Good luck with the upcoming tourist season. You farm up your way? I just had 20 acres of overgrowth cleared and am now putting the old tractor back to frequent use.

 

[old]

I have 44 acres or land here. Have about 14 acres of pasture/hay land an the rest is mountain side and or caves or small lakes

 

[Eric in IL]

If you are without doubt that the pto shaft has a wobble, it needs replaced or at least inspected closer. If the rear bearing was starting to fail that could be the source of the wobble also. If the wobble is questionable, a dial indicator would answer the question. I would imagine the tractor shaft is made from much stronger steel than the steel in the over running clutch. Hopefully you will find the shaft to still be good.

I'm curious why you felt the need for an over running clutch on a tractor that has live pto.

 

[Leroy]

That is my question, why that over run coupler.. Mower should have one built it.

 

[Tx Jim]

(quoted from post at 11:04:38 05/07/19) That is my question, why that over run coupler.. Mower should have one built it.

Although I'm not personally familiar with a FMC Sidewinder I never seen a rotary cutter such as a pasture/brush cutter that came from factory with an over running clutch built in.

 

[PJH]

I use an over-running coupler on my rotary mower. It saves wear on the PTO brake.

 

[Eric in IL]

PJH, that sounds like a valid reason for your application.

A Massey 65 does not have a PTO brake though.

 

[Eric in IL]

PJH I have worn out a PTO brake on a newer Massey. My solution to avoid wear after mowing is to let the turbo cool off, then kill the engine with PTO still on. Let things coast to a stop, shut off PTO then restart tractor. Just a way to avoid using the brake but does take more time.

 

[MOzarks]

Thanks for the replies, folks! There is no built-in overrunning clutch on the mower, and the shaft that busted was a straight drive shaft with no slip clutch unlike what I'm finding in my search for a replacement (do rotary cutters even need a shaft with a slip clutch or is that for something else?). I think my late grandfather put the overrunning clutch on the PTO for safety reasons as much as to prevent wear on the drivetrain/PTO. Also, I just keep the PTO moving until I get back to the garage and kill the engine, letting the spinning blades wind down on their own.

In the meanwhile I ordered an equivalent implement shaft (hoping series 5 is the right rating), overrunning coupler (quick disconnect this time!), PTO shaft, bearing, and seals. Looks like I'll be spending a day playing on it all once the parts come in. I'm on the fence about retaining grade 5 shear bolts but the indication is fatigue failure, not seized blade motion, so maybe grade 5 isn't too strong.

One more thing- I am lucky enough to work with a metallurgist and he took a few minutes off-the-clock to look at the failed shaft. His opinion is a hairline fracture from some impact force many years ago that just eventually grew and weakened the shaft to the point of failure, based on visual indicators. The other mechanical engineers around here who saw it were impressed with the shearing force that led to the destruction.

 

[old]

You either need a working slip clutch or a shear bolt or you will end up sooner of latter having to have some major work done to the tractor it self due to broken parts. Had a JD1020 in my shop a couple years ago due to a bad slip clutch on the PTO an that in turn broken the PTO shiftier inside the rear end and that cost the guy a good number of $$ for the fix.

 

[MF#1]

I've bush hogged for over 40 years with 6 and 7 foot Bush Hog brand mowers, always with a Massey, and(fingers crossed) have yet to snap a shaft like that. And I mean HARD hoggin', locust trees, stumps, steel wheels, if the tractor would knock it down - it got chewed to pieces. I would take that broken over-run coupler off and throw it in the junk pile and not replace it, MF knew what they were doing when they designed their PTO system and it works
Before you attach that new shaft you may want to check closely for any slop in the driveline on the mower. Now would be the time to freshen up the front bearing if there is doubt. Whatever you decide I hope it works out for you, you don't need any more "surprises".

 

[4520BW]

My aunt and uncle have a place on the lake near Osage Beach. I use to go down and fish in the spring but have been to busy the past several years,plus its a 8 hr drive.

 

[Fritz Maurer]

I think you're right. Damaged tube failed. Some of the metal in the tear is rusty. That shaft been faulty for a long time.

 

[MOzarks]

I'd like to thank everybody for their thoughts and comments. I spent most of Friday night and all day Saturday extracting the old PTO shaft/seals/bearing and replacing the whole shoot-and-match with new parts. I realized that NOT having a shop press and arbor plates makes assembly a real pain, and the force required to pull out the old oil seal retainer was far higher than I could have imagined. Still, in the end, after putting the fluids back in and firing the old tractor up to witness a PTO shaft spinning flawlessly with ZERO wobble- really made the headache (and back ache, and arm ache, and...) worthwhile. It's back to business!