Mid PTO shaft ujoints out of sync, how far is too far?

[Zebrafive]

That is a TOTALLY a rookie mistake!
I have shortened about a dozen and that is the first thing you have to check.
You don't get that tired!
I would not trust it because even if it seems OK it will wear on some other parts.
They screwed it up, they should move you to the front of the line.
It is only a 1-2 hour repair.

This is my response too. I would not even try it, I would have them fix it.

 

[Reb954]

Fix it now or fix it later. The problem with later is you may also be changing seals the vibration caused to start leaking.

 

[Industrial Toys]

I don't care how busy someone is. That shouldn't affect the quality of their work. To me, it speaks more about them, than how busy they are. Not a place I would plan on ever going again.

 

[rScotty]

It depends on the angularity of the shaft. If the whole shaft is installed straight, or almost straight, the phasing of the U joints become far less critical.

With significant drive angularity at both ends, the shaft accelerates and slows down each ninety degrees, and with perfect U joint phasing this effect is supposed to cancel out at each end and you get smooth torque transmitted with minimal torsional speed fluctuations. Its difficult to say exactly where being unacceptable starts. The length and weight of the shaft, and the rpm come into it too, as well as what is being driven. All you can really do is run it, and make the judgement yourself.

I like the Warpspeed answer. The answer to the question about "how much is too much out of phase vibration" depends entirely on how much the drive shaft is angled. It could vary from zero to unbearable just because of shaft angulation. There is also the "intensity" of the vibration which is going to depend on the PTO RPM.
I had one worse than yours, but it was on a posthole drill which doesn't spin very fast even though the angulation was high. It was usable, but barely. I was always afraid the shake would put wear on the PTO shaft output bearing - a much bigger job to replace than the price of a new PTO shaft.

The sliding fit does need to be a good tight fit. IMHO, those square tubing types of PTO shafts aren't all that great even when new. Automotive type splines are way better. That sliding fit problem you have would be the last word for me.

I finally bought new PTO shaft for mine and recommend you do the same. I think it was about $140 at the farm store. I'd buy it and then take it down to the welder and ask him how much he thinks he should pay on your new PTO shaft since he ruined the old one.
rScotty

 

[Fallon]

I didnt get the angle quite right when I rebuilt my PHD frame to fit on my quick hitch. If i lowered the 3pt before extending the toplink, it would hit the PTO shaft. I bent it a few inches out of straight a couple times. I gave up & just left it that way. Vibrated a bit, but not to bad & pretty low speed. 2,000rpm is a lot faster than the 2-300 I ran that at though.

 

[zzvyb6]

The error is LARGE and will shake your transmission AND the implement gearbox as well. A double Cardan shaft should be aligned so that the input and output parts of the driveline are co-linear (they lie at the same angles in top and side view) Otherwise you get a harmonic torque pulsation that's twice the input rpm.

I'd just saw it apart and reweld it. It's cast steel, so a good mig welder should be able to set it right. Best to fixture it.

 

[aczlan]

I put everything together tonight and tried it out. Where that u-joint sits (right at the back of the blower), it sees almost no deflection, 1-2 degrees at most.
I put it all together, turned on the PTO and wound it out full throttle.
No vibration, no wobbling, no issues that I can see. As such I'm just going to run it.
The other u-joint does see some deflection when you raise and lower the PTO, 3 to 5 degrees at most, but they did not design the PTO shaft to have an equal angle at both ends.

Aaron Z

 

[rScotty]

I put everything together tonight and tried it out. Where that u-joint sits (right at the back of the blower), it sees almost no deflection, 1-2 degrees at most.
I put it all together, turned on the PTO and wound it out full throttle.
No vibration, no wobbling, no issues that I can see. As such I'm just going to run it.
The other u-joint does see some deflection when you raise and lower the PTO, 3 to 5 degrees at most, but they did not design the PTO shaft to have an equal angle at both ends.

Aaron Z

Good on you for trying that. And thanks for posting the conclusion.
Agree that angular deflection is everything. After all, a straight shaft with zero deflection doesn't have - or need - any U joints at all.

Still.... I'll bet you and the welder are both particular about getting the phasing correct the next time that job gets done.

Some of us use the same PTO shaft on several implements. For mowing, we could probably get by with small some out of phase. But put that same shaft on the post hole drill and the error would show up right now.
rScotty

 

[Warpspeed]

Great stuff Aaron.
As I said in my earlier post, if the shaft is almost straight its far more tolerant to phasing errors.
I think I would still go back and tell the welder about the problem, it may save him and his next customer a lot of grief.

 

[aczlan]

They are actually the ones who pointed it out, they said that if it causes a problem to bring it back and they will cut it apart and weld it back together again in phase.

Aaron Z