Overstressing PTO U-joints?

[Wagtail]

Here is a visual aid, because some shafts can be put together out of phase or a repair job may have welded the yokes on wrong.

View attachment 511017

Ta for that visual aid Xfaxman.

I read that the maximum working angle was 35 degrees.

 

[KYErik]

How can one bend a shaft? I'm really thinking that the thing was bent when I got it: always had a bit of a vibration to it. And most likely it was the bent shaft that caused the U-joint to fail (not my use).

Yes- you will need a bottle jack and a strong chain. Place the bottle jack on top of the outward bend and run the chain from one end of the shaft to the other and over the top of the bottle jack.

 

[Xfaxman]

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How can one bend a shaft? I'm really thinking that the thing was bent when I got it: always had a bit of a vibration to it. And most likely it was the bent shaft that caused the U-joint to fail (not my use).

The shaft can be bent buy lifting the bush hog with a top link that is set too long. The shaft will contact the front of the bush hog and bend. If the PTO is turned off, the operator won't know it happened.

 

[DieselBound]

Regarding Bush Hog making cutters for 50 years, they might have been making them for only 30 years when this unit was made Lots of manufacturers have been making the same product for decades and yet they will still produce some poor designs. While this is possible it's probably, in this case, not probable.

Rick, I have the manuals, thank you: that's where I got the HP specs; I had tracked the service manual so that I could get the specs for setting the slip clutch (before I first used the cutter). The ratings that folks here are stating for the shaft are all over the place/spectrum. "35 hp." And "There's nothing special or unique about connecting a 286 to an NX 5510" ( it "connects," yes, but the issue is whether it can operate at full range/power- so far it's proven not capable, though the question is whether it had a pre-existing condition that I wasn't aware of).

I've never had a PTO issue up until now. And now all of sudden I've got a mess. I always look to blame myself first but in this case I'm almost convinced that the previous owner (who ran a business clearing land) likely screwed this thing up.

Just want to make sure that if I shell out for a new, complete, PTO shaft that I won't be posting back here that it failed again.

 

[countrybumpkin]

You said the shaft had been replaced before you bought it, just curios if it was replaced with a smaller cheaper shaft, that has gotten bent and can't handle that size cutter?

 

[aczlan]

You said the shaft had been replaced before you bought it, just curios if it was replaced with a smaller cheaper shaft, that has gotten bent and can't handle that size cutter?

That is what I would look at first. If there isn't a part number, here is a page to help you figure out what model it is and from that you can check that it is rated for the HP that your tractor puts out: Royal Brass and Hose Blog

Aaron Z

 

[RickB]

Whatever. That machine is probably 10 to 15 years old at the most. That would be about half as long as I've been using, professionally repairing, and selling parts for Bush Hogs.
Good Luck to you.

 

[DieselBound]

Xfaxman, thanks for that input, that's kind of what I was after. How would one check for this? I don't have a quick hitch, and if anything I was tending to operate the cutter more with the tail end raised than drooping. I suppose that operating at near the minimum overlap (approximately 6 1/2") that with a replacement shaft I should be looking to have a greater overlap (ensuring, of course, that it's not fully collapsed when the top link is at its shortest).

country, I just don't know what the previous owner did. I'll try to do some more forensics on this thing: I've been busy with a bunch of other things and haven't had time to really scrutinize.

Aaron, that's an excellent link, thank you!

At this point I know that it's an Italian/Metric, class four shaft.

The more I think about this the more I'm almost positive that the shaft was bent when I bought this thing. The reason I suspect this is because the U-joint (tractor side) had one (or two) of the cups showing cracks (might even has been a small chunk missing) on the cup edges. Seems that a bent shaft would put a lot of stress on the U-joints.

 

[Xfaxman]

Xfaxman, thanks for that input, that's kind of what I was after. How would one check for this? I don't have a quick hitch, and if anything I was tending to operate the cutter more with the tail end raised than drooping. I suppose that operating at near the minimum overlap (approximately 6 1/2") that with a replacement shaft I should be looking to have a greater overlap (ensuring, of course, that it's not fully collapsed when the top link is at its shortest).

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The more I think about this the more I'm almost positive that the shaft was bent when I bought this thing. The reason I suspect this is because the U-joint (tractor side) had one (or two) of the cups showing cracks (might even has been a small chunk missing) on the cup edges. Seems that a bent shaft would put a lot of stress on the U-joints.

Adjust the toplink out as long as it will go. Don't turn on the PTO, slowly raise the 3 point watching the distance between the PTO shaft and the front edge of the mower deck.

The previous owner may have had a hydraulic toplink and forgot to retract it some after backing onto a down slope.

 

[DieselBound]

OK, will check!

Hydraulic top link kind of makes me nervous now. I actually struggled to get the rear of the mower adjusted correctly (keep in mind that I'd only operated it about three times) and just dropped the tail wheel bracket down in an effort to get the tail end up a bit more. So, if anything, I've been tending to get the tail UP more so than down.

The previous owner worked the snot out of this thing. Pretty sure that the additional 1/4" plate steel on the deck is because the deck had been ripped up: looking on the underside one can see this. Breaking U-joints and such... my money is on this thing having been very ABUSED: if I can get this PTO issue resolved I figure that I'd still be coming out ahead (vs buying a new one).