JD4300 -- Catastrophic Failure of the Shift Shaft

[reasley]

Richard:

Glad to hear you got your rig back online without having to split the tractor. Should mine ever punk out like your did; it's a relief to know the repair can be done at home should I need to do it, and that the redesigned forks work better along with your machinist's improved shaft and lever.

Based on what you describe of the replacement lever you received from JD; it sounds like JD outsourced replacement parts manufacturing to our good buddies in China. That's a heck of a difference in dimensions you measured.

Matt

Good morning, Matt --

It is important to note that only the shift shaft can be replaced by removing the top plate -- to install the improved forks, the tractor still has to be split (Note the enclosed "shiftforks" picture -- the body of the forks is the red unit). Once I ascertained that my shift shaft could be replaced via the top, my next step was to carefully inspect the shift forks. I could find no evidence of any damage; they weren't bent, and the suction tube filter had no shavings of any kind, nor did the magnetic plug in the bottom of the case. So, at that point, I concluded that I didn't need the fork replacement. The smoothness and ease of shifting after reassembly provided further confirmation that there is no need for the improved forks.

On the dimensions of the JD shaft, I think that the machinist was right: I received a shaft which didn't get the polishing that it needed in the last step in the production process. I have enclosed a series of pictures that illustrate the original shaft's problems very clearly.

The first shows the newly-made shaft (no O-ring groove) versus the factory shaft (O-ring groove). The one that is called "originalfactoryshaft," in conjunction with "closeupofbreakpoint" clearly shows how easily the lever exerts tremendous force on the O-ring groove -- that is the problem with the transaxle as designed.

Richard

 

[mjncad]

Thanks for the clarifications Richard. That's the problem when I read TBN late at night, sometimes I miss something in the text.

That's quite an O-ring groove JD put in that shaft. It seems to me that it wouldn't take that thick of an O-ring to achieve an oil seal; especially on a shaft that doesn't see much movement as compared to a PTO shaft, etc, and in a low pressure environment to boot.

 

[reasley]

Thanks for the clarifications Richard. That's the problem when I read TBN late at night, sometimes I miss something in the text.

That's quite an O-ring groove JD put in that shaft. It seems to me that it wouldn't take that thick of an O-ring to achieve an oil seal; especially on a shaft that doesn't see much movement as compared to a PTO shaft, etc, and in a low pressure environment to boot.

Good morning, Matt --

Yes, I agree. It's almost as if the O-ring was put in as an afterthought with no consideration given to collateral effects. The oil level is about 2", give or take, under that shaft so the only oil that is going to be see is splashing, and probably little at that. And -- with the O-ring, everything to the outside of the ring gets zero lubrication and the shaft is still riding in the bore outside of it -- silly.

I spent all day yesterday using the tractor and it is amazing how smooth that it is now.

Richard

 

[dfkrug]

I spent all day yesterday using the tractor and it is amazing how smooth that it is now.

Hey, Richard. Is your shift shaft still working OK? No significant oil leaks?

 

[reasley]

I was just thinking about the shaft the other day -- it is working incredibly well. I have not even looked under the tractor to check for a leak until I had it in the stable the other day and noticed that there was no dripping whatsoever. I really don't think that the O-ring (and flawed groove in the shaft design) was ever needed, but it certainly weakened the shaft at that point. If you ever need to replace, I would not hesitate to have a shaft made at a machine sop -- it will be far superior to the factory shaft.

 

[ICGREEN]

Link to the quoted article:

John Deere's farm team - Apr. 28, 2008

 

[JohnDeere4300]

I'm glad you got it fixed!

I'm also glad that I found this thread so I can check mine out & keep an eye on it.

Mine is a 01 model and it has always been easy to shift from A through C, and it shifts so easy that i can take one finger and shift it.

Thanks for sharing your work!

 

[Kyle_in_Tex]

Hey Reasley, great thread!

As usual I have a few comments and questions....

1) I would like to see a closeup photo of your external O-ring setup.

2)Did you get your money back for the faulty oversized shaft? It looks like they forgot the final centerless grinding op. I'd hate to have my machine tied up at the dealership waiting on a correct shaft. I also wonder if the shaft you recieved might be what is used on newer models?

3)Did your machine shop check the hardness on the original shaft? You mentioned 4140 stainless. It can't be both. 4140 is a great steel hardenable to different levels depending on application. 4140 is not stainless. If they used stainless, I'm interested what type? I might have been tempted to use 17-4PH SST and hardened it H900 which would have been about 42 Rockwell. I agree fully that the Oring is the weakest link.

I would have done the same thing, omit the Oring groove.

 

[reasley]

Hey Reasley, great thread!

As usual I have a few comments and questions....

1) I would like to see a closeup photo of your external O-ring setup.

2)Did you get your money back for the faulty oversized shaft? It looks like they forgot the final centerless grinding op. I'd hate to have my machine tied up at the dealership waiting on a correct shaft. I also wonder if the shaft you recieved might be what is used on newer models?

3)Did your machine shop check the hardness on the original shaft? You mentioned 4140 stainless. It can't be both. 4140 is a great steel hardenable to different levels depending on application. 4140 is not stainless. If they used stainless, I'm interested what type? I might have been tempted to use 17-4PH SST and hardened it H900 which would have been about 42 Rockwell. I agree fully that the Oring is the weakest link.

I would have done the same thing, omit the Oring groove.

Good afternoon, Kyle --

Gotta love this wonderful Texas heat today, right?

I'll answer your questions in order from above:

1. I'm trying to remember what I did on the external O-ring setup. Note the enclosed picture and the external lever on the left side. I either put a small thickness O-ring between that lever and the transmission case or I coated the area with a liberal coat of heavy grease or both -- I can't remember. However, I am thinking that I simply put the grease there as a heavy barrier to oil egress.

2. On the shaft, it was clearly "unfinished." And - it was the correct part for the tractor -- JD is very specific with respect to part changes through their lines, so I don't think that this was the problem -- I think that the shaft simply didn't get finished, and I hope that was the only one!!!

3. I must be confused about what materials they used, that's what I thought they said, maybe they didn't. I do remember them talking about the hardness of the shaft that they were installing and they were confident that the new shaft, in addition to being better designed, was also harder than the original one.

Addendum: I still can't believe that the shaft had an O-ring groove at that location -- in the center of the machined part-of-the-case bearing. In addition to this location being the exact point where levarging forces are their greatest (and the shaft is weakest), the area is also a moisture trap and collected moisture which gravitated to the O-ring groove and hastened the shaft's demise.

Having said that, I have been on the tractor off-and-on today and it is an incredible little tractor. One of my boarders was talking to me just the other day about how much utility we get out of the fork lift that we made for it. I am well on my way to "palletizing" my entire property, from firewood, to basically all materials. I have a friend that bought a tractor several years ago and didn't get a front end loader/forklift and I truly believe that one is missing at least 60-70% of the utility of a tractor without one.

Richard Easley
China Spring, Texas

 

[dfkrug]

I might have been tempted to use 17-4PH SST and hardened it H900 which would have been about 42 Rockwell. I agree fully that the Oring is the weakest link.

I bought the OEM replacement shaft....it is quite hard, and not SS. JD
has used the O-ring slot seal strategy for both of their brake control shafts,
too, but not the diff lock shafts, and not the MFWD shaft. Go figure. The
latter shafts use conventional seals.

If you want to seal up a solid shaft like Richard has, I think the best way is
to slightly chamfer the hole, then use an O-ring around the outside of the
shaft, and a O-ring retainer that is bolted to the outside of the block. Not
an easy job unless the gearbox is out.