JD4300 -- Catastrophic Failure of the Shift Shaft

[Kyle_in_Tex]

dfkrug, did your shaft fit?

 

[dfkrug]

dfkrug, did your shaft fit?

It is not installed yet, but after Richard's debacle, I miked it and it is
the same. This is one of several design deficiencies that I am not going
to fix. Keep an eye on yours.

 

[Kyle_in_Tex]

Almost forgot, YES Richard, it is HOT...

102 degrees

 

[reasley]

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.

I agree and your reply reminded me to clarify to those following this thread that when a manufacturer designs a product, they are faced with various constraints, not the least of which is the price/quality relationship. They have to provide a product that is 1) attractive to consumers, 2) competitive in the marketplace with others, and 3) returns a reasonable profit. Consequently, all of the things that we, as DIYers find that can be improved, could have certainly been designed into the product but the price point would probably be twice what we would be willing to pay! So, for the most part, improvements that we note in our products have probably already been considered by design engineers. Occasionally, something does slip through, though, and I think that this shat is one of those examples but probably only because of the extreme leverage that the gear lever can provide vis-a-vis the stubby shift lever on the side of the gear case.

I will try to remember to look under my tractor tomorrow and see if the "greasy seal" replacement for the O-ring and groove has prohibited oil leakage.

Richard Easley
China Spring, Texas

 

[passnbyu]

Hi, This is the exact thing that happened to my tractor. Do you have the measurments for the shaft so I can get someone to make me one? I think I'm going to get it made of stainless. Thanks for such an informing thread!!

Thanks Passnbyu

 

[reasley]

Hi, This is the exact thing that happened to my tractor. Do you have the measurments for the shaft so I can get someone to make me one? I think I'm going to get it made of stainless. Thanks for such an informing thread!!

Thanks Passnbyu

No problem. I don't have the measurements, but all you have to do is remove the old shaft (both pieces) and take them to your machine shop and they can easily make one for you.

Just used the tractor tonight -- the new shaft is still working great . . .

Richard Easley
Waco, Texas

 

[dfkrug]

Since this thread is getting resurrected....

My rebuilt 4300 has the OEM shift shaft, but I reduced the detent spring
pressure on the shift fork internally. This makes the shifter handle
move quite easily. A O-ring installed between the bellcrank and the
gearcase keeps water out (without chamfer). So far so good.

But....I just got another 4300 with a broken shifter. There is no way to
do what I did in the first one without taking the whole tractor apart.......

 

[reasley]

Since this thread is getting resurrected....

My rebuilt 4300 has the OEM shift shaft, but I reduced the detent spring
pressure on the shift fork internally. This makes the shifter handle
move quite easily. . .

Thanks for the reply. I don't think that the detent spring pressure is the causal factor for the broken shafts, though. Instead, I think that what causes the "O-ring-groove-weakened-shaft"s to break is *excess* pressure resulting from the incredible leverage that is inherent in the entire shifter "chain." First, the shift lever (to the left of the seat) is *very* long, providing "breaker bar" levels of torque, then this is transferred via linkage to the big "clunk" of metal that is attached to the shift rod lever outside of the case. Combine these things and *any* increased resistance puts undue stress on the inferior shifter shaft. My thinking is that, over time, if someone is trying to shift and the gears are not perfectly aligned, then there is a cumulative effect of this action that eventually results in a broken shaft.

Richard Easley
Waco, Texas

 

[dfkrug]

I think that what causes the "O-ring-groove-weakened-shaft"s to break is *excess* pressure resulting from the incredible leverage that is inherent in the entire shifter "chain."

Oh, I agree, its a bad design. All that leverage, and a weakened shaft.
In my case, the fix was to require lots less force to execute the shift. My
fix only makes sense if you crack the tractor, however. A stronger shaft
is the better fix. I may be doing that for this current tractor, as I am
not going to split it.

That shaft is so easy to break, it happens to lots of units that are not
in rental service, as mine were.

 

[rekees4300]

So far after 10 years the shifter on my 4300 hasn't broken but at times it is difficult to shift. After reading this thread I'm definitely going to limit shifting as well as not try to force it.