Ideas for repairing a splined shaft/splined collar that is just a little loose

[TN Hillbilly]

Looking for ideas/suggestions. 

We have a New Holland haybine, and the output shaft of the wobble box (which drives the knife) is worn. The shaft is tapered splined (20 or so splines), as is the collar in the knife arm. The shaft has so wear, so there is now some back and forth play in the knife arm. If we keep running it, it will strip the splines off the shaft and also probably the arm.

 

I know. The "correct" repair is a full teardown of the wobble box and a new shaft. New Holland wants $1000 for the shaft, and I think it will be a pretty big job... There is just a little play right now, so I am looking for suggestions to take that play out as a "temporary" fix. I could weld the knife arm to the shaft, I guess but I kinda hate to so that... Any ideas/tips of how to tight up a splines shaft that is just starting to get loose? Right now, our best idea is to drill all the way through the splines collar and shaft, and put a grade 8 bolt or roll pin. There is also a castle nut holding this on, so whatever we do to take the play out won't be the ONLY thing holding it... Hoping a 3/8 grade 8 bolt might be tough enough?

Sorry, no pics right now. My hands were... ya know. Will get pics tomorrow if y'all need em. Thanks in advance for any ideas!

[Mudfly]

52 minutes ago, TN Hillbilly said:

Looking for ideas/suggestions. 

We have a New Holland haybine, and the output shaft of the wobble box (which drives the knife) is worn. The shaft is tapered splined (20 or so splines), as is the collar in the knife arm. The shaft has so wear, so there is now some back and forth play in the knife arm. If we keep running it, it will strip the splines off the shaft and also probably the arm.

 

I know. The "correct" repair is a full teardown of the wobble box and a new shaft. New Holland wants $1000 for the shaft, and I think it will be a pretty big job... There is just a little play right now, so I am looking for suggestions to take that play out as a "temporary" fix. I could weld the knife arm to the shaft, I guess but I kinda hate to so that... Any ideas/tips of how to tight up a splines shaft that is just starting to get loose? Right now, our best idea is to drill all the way through the splines collar and shaft, and put a grade 8 bolt or roll pin. There is also a castle nut holding this on, so whatever we do to take the play out won't be the ONLY thing holding it... Hoping a 3/8 grade 8 bolt might be tough enough?

Sorry, no pics right now. My hands were... ya know. Will get pics tomorrow if y'all need em. Thanks in advance for any ideas!

How many splines is on that shaft? 

Aluminum (beer can) shim?  Or maybe other thin shim stock could be formed into the splines.  I was thinking aluminum since it would be soft enough to form and stretch over the splines and shouldn’t damage anything.  
 

I’ve seen a lot of different temporary farm fixes like that last a good while, but there is a lot of vibration in that area.

[TN Hillbilly]

9 hours ago, Mudfly said:

How many splines is on that shaft? 

Aluminum (beer can) shim?  Or maybe other thin shim stock could be formed into the splines.  I was thinking aluminum since it would be soft enough to form and stretch over the splines and shouldn’t damage anything.  
 

I’ve seen a lot of different temporary farm fixes like that last a good while, but there is a lot of vibration in that area.

It's probably 20 or so, tapered.  Like the output shaft and stump jumper on a bushhog. We had thought about thin steel shim stock but weren't sure it would conform enough. I had not thought about aluminum, but that would be easy enough to try.

[Ihfan4life]

Try some of that epoxy metal stuff. It’s two part epoxy that you mix and then put on the surface. When it dries you can file/shape it to make the parts fit tighter. 
Option B, find a salvaged wobble box and replace the whole thing…

[Mudfly]

3 hours ago, TN Hillbilly said:

It's probably 20 or so, tapered.  Like the output shaft and stump jumper on a bushhog. We had thought about thin steel shim stock but weren't sure it would conform enough. I had not thought about aluminum, but that would be easy enough to try.

20 spline might be too much for anything to form around.  I was thinking it was more like 6 or 8.  

 

 

[IHC_1470]

You might try the fit of a new arm on the shaft. Think on the 5000 swather that did the trick. A little JB weld as it goes together will fill any void in the shaft itself. The other way would be to cut maybe 4 strips from the pop can and place best you can around the arm. Doubt you would need to completely fill the hole. 

[tractorholic]

I wonder if Kwik steel would work. I fixed a worn keyway on a shaft with it a few years ago and it is still working. 

[766 Man]

32 minutes ago, tractorholic said:

I wonder if Kwik steel would work. I fixed a worn keyway on a shaft with it a few years ago and it is still working. 

  The arm would have to be true onto the shaft.  if not the whole assembly will be out of dynamic balance.

[Little Red]

You say it’s a tapered shaft? What’s keeping it from getting pushed farther onto the tapered shaft, is the nut bottoming out on the the threads? Just curious if you could put another washer under the nut to push it farther on to the taper? 

On 5/15/2025 at 7:53 PM, TN Hillbilly said:

Looking for ideas/suggestions. 

We have a New Holland haybine, and the output shaft of the wobble box (which drives the knife) is worn. The shaft is tapered splined (20 or so splines), as is the collar in the knife arm. The shaft has so wear, so there is now some back and forth play in the knife arm. If we keep running it, it will strip the splines off the shaft and also probably the arm.

 

I know. The "correct" repair is a full teardown of the wobble box and a new shaft. New Holland wants $1000 for the shaft, and I think it will be a pretty big job... There is just a little play right now, so I am looking for suggestions to take that play out as a "temporary" fix. I could weld the knife arm to the shaft, I guess but I kinda hate to so that... Any ideas/tips of how to tight up a splines shaft that is just starting to get loose? Right now, our best idea is to drill all the way through the splines collar and shaft, and put a grade 8 bolt or roll pin. There is also a castle nut holding this on, so whatever we do to take the play out won't be the ONLY thing holding it... Hoping a 3/8 grade 8 bolt might be tough enough?

Sorry, no pics right now. My hands were... ya know. Will get pics tomorrow if y'all need em. Thanks in advance for any ideas!

Pictures would help too. You might have a hard time drilling through the shaft and I think the bolt would eventually wear and break 

[Binderoid]

Never  saw this configuration, so I'm kinda guessing here... 

If there  is a taper, it must be held on with a nut or bolt. The problem  would  seem  to be that  the fastener is getting  tight before  forcing  the two tapered surfaces  together. Is there any room for a short spacer with the  same I.D. as the shaft, to where it can apply clamping force to the arm before  the nut or bolt gets  tight?

   IF this were to be successful, you would still have the issue of the worn splines , which if installed dry, would have the potential  to either loosen  the fastener or further wear the taper until it was loose again. The thing would have to be glued together  with  a pretty  serious  adhesive to prevent  any wigglement in these worn out , less than perfect tapers. If you can keep  the pieces from  moving inside one another,  it will  stay tight. 

[Diesel Doctor]

We need a machinist to weigh in on this one?

[rustred]

that is machine shop work , or a new or good used replacement. when a spline is worn out its junk. that simple.

[IHC_1470]

I think on the 5000 that there was just enough wear that the shaft was sticking out past the arm which was preventing things from getting tighting up. It used a large nut. Most of the wear on mine seemed to be in the arm, and a new arm did get me through the season. I have since replaced the arm in the wobble box and everything is back to working like it should. I suspect the above design would be similiar. I think the shaft was around that magic $1000.00 mark and I believe that was an aftermarket shaft since there are very few parts available from the dealer anymore for the 4000-5000 machines.

[TN Hillbilly]

Thanks for all the replies and ideas. 

Yes, the knife arm is held on by a large castle nut. I am going to put another washer under it, but the design of the shaft and gearbox pretty much prevents "pushing it on further. 

Most of the wear appears to be on the shaft, not the arm (unfortunately.) So I don't think a new arm would solve it.

I think the plan, as of now is: shim with aluminum, maybe some JB Weld in a couple places, then tighten with the castle nut (plus extra washer) and hope for the best?

Pulled the 478 out of the "honored retirement row" and going to put it back in service too. It was parked  because of a couple broken chains. And then we got the much nicer condition 474. 

Will try to get some pics if I get time to work on it today.

[Takn4aFool]

24 minutes ago, TN Hillbilly said:

Thanks for all the replies and ideas. 

Yes, the knife arm is held on by a large castle nut. I am going to put another washer under it, but the design of the shaft and gearbox pretty much prevents "pushing it on further. 

 

could you grind some off the back of the arm so it could be pushed on farther/tighter

[augercreek]

I think taking a bit off the arm would be the way to go as it can then be pushed on further. And yes I'm a machinist.

[TN Hillbilly]

3 hours ago, Takn4aFool said:

could you grind some off the back of the arm so it could be pushed on farther/tighter

Hadn't thought of that.

Yes, probably a few thousandths. Might be enough...

[806JR]

5 hours ago, TN Hillbilly said:

Hadn't thought of that.

Yes, probably a few thousandths. Might be enough...

I did this with the knife arm on the gearbox on a New Holland 489 haybine and it worked great. I just used a flap wheel and kept sanding it down until the arm fit tight again.

[Binderoid]

23 hours ago, Diesel Doctor said:

We need a machinist to weigh in on this one?

Send it to Pakistan,  they can fix anything. 

[Lazy WP]

3 hours ago, Binderoid said:

Send it to Pakistan,  they can fix anything. 

According to the videos you see it appears so. 

[ray54]

7 hours ago, Binderoid said:

Send it to Pakistan,  they can fix anything. 

With the one minute warranty.

An old guy here use to say, if it make it to the end of the drive and the warranty is done. 

[Little Red]

4 hours ago, ray54 said:

With the one minute warranty.

An old guy here use to say, if it make it to the end of the drive and the warranty is done. 

Dad would call that taillight warranty, when you can’t see the taillights anymore warranty is expired 

[int 504]

We used to have 30-30 warranty. 30 feet or 30 seconds whichever came first.

[Ihfan4life]

Someone had a wobble box on marketplace… I don’t remember location.

[TN Hillbilly]

Well, got it back together. 

Here's what we went with:

Cut two shims out of a pop can. Probably long enough to go 2/3 of the shaft diameter. Was a real booger to hold them in place and slide the knife arm back on...But that tightened it up a lot, and gained us a few thousands before the knife arm bottomed out. THEN, we reinstalled the castle nut with a 24" crescent wrench plus a 24" pipe... So its on there. Now the knife arm has zero play. Now we're probably good at this point... but I had already mentioned to FIL the idea of drilling and pinning it... So, we drilled all the way through the whole shooting match (not fun but turned out okay) and pinned it with a grade 8 bolt. Not sure if this last step was good, bad, or indifferent, but we did it. I don't think the knife arm will be going anywhere anytime soon.

Sorry, few pics. Got to put a couple chains on the other machine, and both should be ready (if weather ever breaks!!) I'll try to get pictures of both machines then (if I don't forget!)

Thanks again for all the input and suggestions!