Can I continue to us a slightly bent PTO shaft?

[Fargo]

So I have 2 mowers, a rough cut and a finish mower. For years my rough cut mower had a twisted PTO shaft that I could see wobble slightly as I used it. So I purchased a new one a year or 2 ago. Only to have it develop a slight wobble over the summer as well. The other night, I noticed that the PTO shaft on my finish mower appears to have a slight wobble as well. It does appear to be the actual shaft and not just the shroud. It also appears that I may have a small oil leak on the front of the gearbox. Is this related to the bent pto shaft?

So my questions are:
1) Do I need a new PTO shaft or can I continue to run with a slight wobble? How much wobble is normal?

2) Could my leaking gearbox be caused by the bent pto shaft?

 

[Mark_BX25D]

I don't have a lot of experience with PTO shafts yet, but I paid good money to have a truck's driveshaft balanced after an out-of-balance driveshaft trashed my transmission. RPMs are different, but the principle is the same.

The RPM difference is going to affect the severity of the problem, though, so how severe the wobble is and what it will do to you are going to be different. Maybe at 540 RPM it's tolerable.

I would bet your seal leak is due to the wobble.

 

[woodman55]

"How much wobble is normal", None. I am wondering what is bending these shafts. Are the pto shafts shortened properly to avoid bottoming out ? Are they hitting something when at max height ?

The seal could be failing due to the bent shaft.

 

[GreensvilleJay]

re: The seal could be failing due to the bent shaft.

or.... the bearing is 'bad'(missing balls) ,took out the seal, and a zillion rotates have bent the shaft(s) ?

Do the PTO shaft U-joints have ALL their needle bearings in them ? Are the U-joints 'tight' ?

Agree 540 isn't 'highway speed' BUT there's a lot of torque and inertia and 'stuff' that over time WILL destroy 'something'.

 

[Mark_BX25D]

or.... the bearing is 'bad'(missing balls) ,

Wait, the cops in Uvalde are another thread.

/ducks/

 

[Fargo]

Thanks for the input guys. The question of what is bending the shafts is a good question. My yard is pretty rough and the rough cut mover often hits gopher mounds and things like that. So that might be what did that shaft in. The finish mower is something I got from my dad a couple years ago. It was previously used on better lawn. So I'm not sure why it would be bent. Its not terrible, but I can see it wobble as it spins.

I've greased up the ujoints but I never checked to see how tight they are. I also need to check shaft length. It might actually be a little short on my tractor. I guess I have some places to start. Thanks.

 

[NCL4701]

So I have 2 mowers, a rough cut and a finish mower. For years my rough cut mower had a twisted PTO shaft that I could see wobble slightly as I used it. So I purchased a new one a year or 2 ago. Only to have it develop a slight wobble over the summer as well. The other night, I noticed that the PTO shaft on my finish mower appears to have a slight wobble as well. It does appear to be the actual shaft and not just the shroud. It also appears that I may have a small oil leak on the front of the gearbox. Is this related to the bent pto shaft?

So my questions are:
1) Do I need a new PTO shaft or can I continue to run with a slight wobble? How much wobble is normal?

2) Could my leaking gearbox be caused by the bent pto shaft?

1) Maybe and no.

I’d take some time to figure out why it’s wobbling before replacing the PTO shaft. They aren’t cheap and that might not be the problem.

Could be a bearing problem on the tractor end (unlikely) or gearbox end (more likely since you have a leaking seal there). Check for play with the shaft removed.

Could be a bent shaft. Removing the guards and checking straightness with a straight edge might be helpful there.

While the shaft and guards are off, check the U-joints thoroughly for play (shouldn’t be any).

Although unlikely, make sure it isn’t out of phase. I know many only go together one way but when I first started using my father’s brush hog, the PTO wobbled pretty bad. It is just two square shafts that go together any of four different ways. At some point it was put together with the U-joints on one end perpendicular to the other end (out of phase) which was causing stupid amounts of stress in the shaft as the two ends accelerated and decelerated at differing rates with every rotation. It created a whipping motion in the middle of the shaft. Ran it that way about 2 minutes before shutting it down and figuring it out.

Assuming you have full guards on it normally, while they’re off to inspect the actual shaft, if you haven’t isolated the problem I’d run it a bit with the guard off to make sure it’s the shaft wobbling and not just the guard wobbling. If it’s just the guard wobbling no need to do anything other than put it back on and watch it wobble.

2) Yes

 

[Magicman]

Could the shafts be too short and you are extending them beyond the point of being rigid?

 

[PoTreeBoy]

Is it actually bent, or just wobbling?

It's possible to lift some implements high enough that the drive shaft hits the implement. This can also be caused by crossing a ditch that raises the implement too high. A too long shaft is more likely to take out a gear box, but should be checked.

You can check for wobbling by lifting the shaft in the center (tractor off, of course). These are not high precision systems like a car, but if there is more than maybe 3/4 - 1" it should be corrected. Could be looseness at the u-joints or, as magicman said, too little engagement at the slide joint, or wear in the slide joint.

This was easier to check on old tractors before PTO brakes became standard, since you could turn the shaft by hand and watch it up-close.

 

[Biker1mike]

Shaft length and rough lawn. Raising my deck is not the closest point for my system. I have a couple of sections where the tractor is level and the finishing deck is almost 45 degrees. This is when the shaft is at it's shortest point. Going the other direction the shaft is at it's furthest. The range is amazing.

 

[mcfarmall]

Pull the guards off, run it and see if the wobble is the actual shaft or a sloppy guard. I have one that "wobbles" and it is the plastic guard at fault, not the shaft.

 

[Fargo]

Thanks guys. Lots of good points here. I'll need to make a list to run down all the items to check.

 

[Magicman]

Whatever you do, do not continue to use a wobbling PTO shaft.

 

[Fargo]

Whatever you do, do not continue to use a wobbling PTO shaft.

Why not use it? I assume it could damage seals or possible gears inside the tractor? I'd appreciate to hear your concerns.

 

[Magicman]

You answered your own question. I doubt that any harm would come to the tractor but I'm not going to wobble the seal, etc on my bush hog.

If you are aware of a problem, then fix it or assume the consequences.

 

[GeoHorn]

If the drive shaft is actually “bent” then it most likely is due to raising the implement too high until it contacts adjacent structure…or taking the implement thru a ”dip” or swale that results in contact between the drive shaft and structure.

 

[BAP]

Why not use it? I assume it could damage seals or possible gears inside the tractor? I'd appreciate to hear your concerns.

With enough wobble and time, there is a potential to shear off the PTO shaft on the tractor or the implement gearbox. I have seen that happen before. Tractor shaft is quite expensive.

 

[GreensvilleJay]

revisiting this post and seems he has THREE shafts with 'wobble' over time....only 2 now.
I'd remove both of them, toss on workbench, get a good straight bar( 2' level will work), and check the shafts for 'bends'. Yes, can be a bit of a challenge depending on PTO shafting.
Since it is both rough and finish, I'm wondering if at sometime 'something' got hit and the 'shockwave' bent the shaft ?

 

[Fargo]

Is it actually bent, or just wobbling?

...

You can check for wobbling by lifting the shaft in the center (tractor off, of course). These are not high precision systems like a car, but if there is more than maybe 3/4 - 1" it should be corrected. Could be looseness at the u-joints or, as magicman said, too little engagement at the slide joint, or wear in the slide joint.

This was easier to check on old tractors before PTO brakes became standard, since you could turn the shaft by hand and watch it up-close.

So I checked some things over the weekend. The guard on the back half of the shaft that connects to the mower was cut too short at some point before I had the mower So the bare shaft is exposed in the middle of the shaft giving me a visual on the bare shaft. That is how I saw the wobble.

I forgot to put a strait edge on the shaft, but I did notice that it extends and compresses very smoothly so it didn't feel like it was twisted or bent judging by how smoothly in moved.

When I lift up in the center of the shaft I have maybe 1/4"-1/2" of movement. So nowhere near the slop like you had mentioned. From what I could tell, the movement comes from the shaft fitting a little loose on the tractor PTO (maybe mower pto too). The locking pin is fully engaged, but the shaft doesn't seem to fit supper tight, at least not like a car driveshaft. So could it be the wobble I see might be normal movement?

 

[mikester]

PTO tubes are relatively cheap and easy to replace. Tractor PTO repairs are expensive and time consuming. Pick one.