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John Deere F687 PTO Random Vibration

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MowJoens

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Discussion starter · #1 ·
First, I have been a long time reader and have always been able to find what I am looking for, so thanks to everyone for your previous help, but this one has me stumped.

I have a John Deere F687 with a 60" 7Iron deck, 23hp Kohler. The Electric clutch goes to a PTO shaft that attaches to a gear box running the deck blades if you are not familiar. I get really bad vibration on the shaft and deck when I engage the PTO approximately 4 out of 5 times. When I am going to mow with it I have to engage the PTO open the throttle and if there is vibration I back the throttle down disengage the PTO and try again. This takes several attempts until it finally will engage without vibration.

What has me stumped is if this is a balance issue why does it sometime go smooth and other times vibrates? The only thing that can change is the place in rotation where the clutch engages so it would have to be a cancelling of unbalance between the shaft and the motor which doesn't make much sense to me.

There is no slop in the PTO shaft or the clutch that I can find, it spins freely and engages solid. The clutch adjustments have all been checked and they are even and in spec for this clutch. There is a counter weight on one pulley but that I believe has been installed since factory.

I bought this unit with a leaking rear main so I tore it all apart before I could use it and am fairly confident that the shafts were all bolted back in the same positions.

The only thing I can think to do at this point is to move the counterbalance in 90 degree increments around the pulley and see if a bolted the shaft back to the engine out of position to the counterweight, but if that is the case I am confused as to why it would ever engage without vibrating.

Does anyone have any advice on what I can look for?

Thanks
 
#2 ·
Sounds like you are knowledgeable with things mechanical so I would recommend you remove the PTO shaft and inspect the u-joints if this unit has them. Pull each bearing cap off and look for damaged needle bearings. That’s all I got, good luck and let us know what you find.
 
Discussion starter · #3 ·
JoeRagMan said:
Sounds like you are knowledgeable with things mechanical so I would recommend you remove the PTO shaft and inspect the u-joints if this unit has them. Pull each bearing cap off and look for damaged needle bearings. That's all I got, good luck and let us know what you find.
Click to expand...
I should have added that I replaced all of the u-joints when trying to troubleshoot this issue so they are all new and in good shape.
 
Discussion starter · #5 ·
BigFish said:
I would check the gearbox bearings and shafts fer play. Also check the spindles. Belts good, tensioner pulley lubed on pivot, free to move, blades tight, not bent ??
Click to expand...
I will be replacing the seals on the gear box in a couple days (slow leak), I'll check for play. The blades are good and balanced and the spindles are good. I would think that if the blades or spindles were bad it would always vibrate and never smooth out.

The belt is good and the tension is good, strange thing with this deck that I have never seen before is once you set the tensioner spring to 5.25" you torque to bolts down so that it doesn't pivot anymore. That is what I found on the manual, which I have never understood why it would be done that way.

Thanks.
 
Discussion starter · #7 ·
JoeRagMan said:
Can you see the tensioner while it's running? The spring could be weak from age, allowing the tension arm to shake. Be careful while doing this!
Click to expand...
The tensoiner arm is locked in place. In the manual it shows to loosen the tensioner arm and drive the nut pulling the spring until the spring is 5.25" in length, then to torque the nut back down to 70ft.lbs. I have never seen a deck set up like this where the tension is fixed and there isn't a armature that is allowed to adjust, but this is my first John Deere.

I can say that I think after performing the belt adjustment as the Deere manual suggests I feel as though the belt is a little too tight and when operating there is more lashing in the belt than I would expect to see. However, this is the same regardless if the deck is vibrating or running smooth.

I have been tempted to leave the tension arm free moving so that it can flex but I have not broke from the instruction found in the manual yet.

Thanks.
 
#8 ·
MowJoens said:
. In the manual it shows to loosen the tensioner arm and drive the nut pulling the spring until the spring is 5.25" in length, then to torque the nut back down to 70ft.lbs. I have never seen a deck set up like this where the tension is fixed and there isn't a armature that is allowed to adjust,
Click to expand...
That don't sound right. Loosen it up and see what happens, right ?
Mayhaps give yer dlr a call or contact Deere.
 
Discussion starter · #9 ·
I will probably give it a try but I don't think the pivot arm is made right for that long term. I would need a nylon washer between locknut A and the arm plus the arm and the deck or I am going to have metal on metal rubbing. Plus locknut B holds one part of the gearbox bracket. (see attached picture)

Image
 
Discussion starter · #11 ·
Once the tension is set and the lock nuts torqued the spring is doing a whole lot of nothing. So I assume that this is the only version of 7 iron deck that doesn't have a floating idler pulley? I wonder if I could fit some sleeves around the bolts to allow for the torque to hold the bolt in place while allowing the pulley arm to float. I might mess around with this a little bit and see if it does anything or just starts throwing belts (an expensive lesson to learn). Either way, I don't think this is what is causing the vibration or it would always vibrate and never run smooth.

I'll reach out to Deere and see if I can't get an engineer on the line, but my previous experience is that they aren't going to stray from the guidance found in the manual. Although I am sure I'll hear the confusion in their voice.

I was also working with an engineer trying to troubleshoot the clutch, he suggested 15/1000" gap I might try to bring that down to 13/1000" and see if there isn't some imperceptible play in the clutch that can be reduced.
 
#14 ·
MowJoens said:
I get really bad vibration on the shaft and deck when I engage the PTO approximately 4 out of 5 times.
Click to expand...
You need to split the system..... take the belts off of the deck, engage the pto, if you get a vibration, then you know that the drive train up to the deck is bad. If you don't get a vibration, then you need to look at the deck for a bad spindle or idler pulley........
.
 
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Discussion starter · #15 · (Edited)
I finally stole some time today to work on this issue.

I removed the deck belt and engaged the clutch so everything through the gear box was moving but nothing on the deck was moving. Exact same thing, it would vibrate and if I engaged the clutch a couple times it would finally run smooth. Disengaged and engaged it was right back to vibrating. So we can rule everything in the deck out.

I replaced the seals on the gear box, everything is in great shape with the gear box, no play smooth running and everything is clean and as expected. It looks like u can rule the gear box out.

On the shaft the end from the motor to the clutch there is a pulley that drives belts for the pumps. There is a counter balance weight on the pulley. I took a piece of chalk and brought it up to the shaft until it barely touched, when I stopped the motor the chalk mark was in line with the balance. I took the balance off, repeated the chalk and it marked on the same place again. I installed the counter weight in the opposite side of the pulley and repeated again, still marked in the same place. There was no noticable difference in vibration from the engine. As far as engaging the clutch the vibration was exactly the same, vibrated most of the time but when it engaged smooth it was running smooth as butter.

I can't for the life of me figure out what could be wrong. If it was always vibrating then I would know something was bad, but why would it run so smooth occasionally?

I did notice that one if the u joints has about 1mm play side-to-side but pushing against the bearing it is tight. I have checked them in the past when trying to figure this issue out and there wasn't any play so I have doubts that is the issue but I'll probably be replacing it just to make sure.

This is a two piece sliding shaft pto and the two pieces have some play, I'm not sure if that could cause this issue or if that is more or less normal.

Thoughts?
 
#16 ·
1. Prolly gonna need to replace the clutch, have ya pulled it off and inspected ?
2. The U joint shouldn't have any play side to side.
3. How much shaft play is "some" ?
 
#17 ·
Also check the key where the clutch is, may be worn...
 
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Discussion starter · #18 ·
Image

So I noticed that the schematics all show the PTO shaft being assembled in the opposite direction from what mine is. The male shaft is on the deck side and the female shaft is on the clutch side where this shows the opposite. Might be a long shot but could this be why I am getting vibration? Regardless, when I replace the U-joints I am going to assemble it in the correct configuration but I was curious if anyone would have any input?
 
#19 ·
MowJoens said:
Might be a long shot but could this be why I am getting vibration?
Click to expand...
Probably not.
Unbolt the shaft assy from the clutch/ motor and see what happens with the vibration.
Check the clutch.

Use moly grease on the shaft splines.
You have replaced U joint bearings before, right ? They can be tricky, and a lot easier to install if ya have a big ass vise to press them in.
 
Discussion starter · #20 ·
BigFish said:
Probably not.
Unbolt the shaft assy from the clutch/ motor and see what happens with the vibration.
Check the clutch.

Use moly grease on the shaft splines.
You have replaced U joint bearings before, right ? They can be tricky, and a lot easier to install if ya have a big ass vise to press them in.
Click to expand...
I have replace u joints on trucks, the last time I replaced the u joint in this shaft was my first time with a pto shaft, I was a PITA but manageable. It seemed like I did it right at the time. I have a vise and it worked for the job last time.

I'll unbolt the shaft from the clutch and give it a whirl, if there is vibration that would mean I could rule out the shaft but I don't know if lack of vibration would necessarily mean it's the shaft simply because without a shaft you might not find the vibration noticable on the clutch. Either way it's a good next step and I'll be pulling the shaft off anyway.

I use John Deere sd polyurea grease, is that less desirable than a good moly?

Thanks for continuing to offer advice.

Caleb
 
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