Mowing Kubota PTO Breaking

[Adryan]

Hi,

I've worked for 10 years at a factory wich produces aggric. machines and we had a fair amount of sheared off PTO stub's.

there are normally 3 possibilities:

1) length of PTO shaft is incorrect. PTO shaft to long and will put force on PTO stub shaft.

2)not greasing the PTO shaft tubes enough, giving the same effect as a shaft wich is to long.

3)incorrect angles of the outputshaft of the tractor and the input shaft on the machine. Both shafts should be at the same angle relative to the horizon. Meaning if the tractor PTO outputshaft is horizontal, the inputshaft on the machien should also be horizontal!

 

[weldermike]

I have had hair pulling experiences with steel in the past. Everything that has been posted so far has gone thru my head, and evthing seems very well justified that you and your workers are not doing anything wrong. I could only suggest that if you have a local machine shop that has a rockwell tester, which will test the hardness of a piece of steel, test the outside hardness of the shaft, then test the core of the shaft and see what the differance is. Steel will work harden as well, so maybe cut it back a little on a bandsaw or whatever you have available, prior to testing. I am a very big fan of kubota, but may be a problem on there end with there tempering, which can get tricky at times.

 

[Max Power]

it would not surprise me that the pto shaft is a weak link so the damage is less costly ...and maybe too weak in some cases.

 

[weldermike]

I agree, but with slip clutches, and shear pins, soooo hard to tell. Tempering can be mind bogglin sometimes, b/c have to allow for work hardening. Can get tricky, but even big corps get caught up in it as well.

 

[Keith55]

I have a 9960 that has 105 Hours on it and already 2nd PTO shaft broke. Pulling a 15' Brush Whacker, breaking in same place. Dealer said checked and not issues in fleet. Any other Kubota users having the same problem with shaft breaking?

 

[JWR]

1. Check your slip clutches
2. Check your pto length with the tractor parked on the uphill of a dip and the mower on the down hill. Make sure the shaft isn't bottoming out, it will push the output shaft down and break it.

Takes a lot of force to do that, whatever the source.
1) Seems to me the problem is almost certainly the cutters and drivetrains outside the tractors. BUT, Have you checked the overrun clutches on these tractors ? Do they let the pto coast cleanly after power is shut off?
2) With that large a cutter there is probably not much actual lifting via 3pt hitches but when there is some raising and lowering action does the driveshaft clear the mower housings ? Almost seems like sideways force is coming from somewhere.
3) The operators SHOULD be a big help with clues so long as they do not feel they are being accused. Have you asked them WHEN the break occurs ? e.g. at shutdown ? when raising or lowering ? when "grounding out" contacting the ground and lugging down the machine ? Seems to me they are bound to know the answers to those questions.
4) These are pull behind cutters of course, being that big. Are these cutters configured such that VERY sharp turns might be made, putting the U-joints at impossible angles ? That is actually my first guess at the problem unless you know why not. Of course if that is the case, operators might be very hesitant to admit it.