Rear PTO seal blowing out

[tranas]

The PTO seal has blown out twice (within 1 hour of working with the replacement seal) on this M5112 tractor - which has less than 1000 hours since it was purchased. Dealer simply replaced the seal under warranty. The dealer now seems to think this may be caused by a plugged breather (transmission) - however the dipstick, which is less than 100 mm from the seal, would certainly be expelled much more easily than the seal itself, so the breather theory seems bogus at best. Anybody have any experience with the bearings failing on the PTO output shaft? There are 2 bearings on the output shaft and two on the countershaft. My best guess is that one of the output shaft bearings has failed and the misalignment/friction is forcing the seal out. See attached pics. Any additional input would be appreciated.

 

[Motion]

Measure the seal and bore to confirm fit. Indicate the PTO shaft to confirm straightness. Leave the fill cap off when a new OEM seal is installed.

 

[Old Machinist]

The breather/vent theory is valid. That would be the first thing I would check for any seal leak. I have seen seals STOP leaking just by cleaning a stuck or clogged vent.

My old JD855 was pushing oil out of the hydro side shaft. Dipstick remained in place. Found the breather tube clogged and cleaned it out and the leak stopped. Had a similar experience on a Mustang axle seal except it didn't have a dipstick. BUT cleaning the stuck vent stopped the leak without doing a seal replacement.

 

[tranas]

Appreciate the responses.

For the record, Kubota has issues with breathers - simply bad design and poor location for such theoretically critical items - already resulted in a collapsed fuel tank. Bad engineering.

Breather theory was, in fact, bogus. Nothing plugged. Once the tech grudgingly confirmed that, he bit the bullet and the rear PTO case came off.

The failure is now obvious, however the cause is not. See attached pics.

The retaining nut on the PTO output shaft failed or was damaged during installation. The nut and washer were lying in the bottom of the case. Will have to await a response from Kubota warranty, but this is clearly not a simple failure. Number of theories why this occurred on such a new tractor with so few hours on the PTO. Some possibilities:

1. Japanese workers are not all 'legendary', and over-tightened/stripped the nut on installation;
2. Retaining nut was not manufactured to spec - bad metal;
3. inexplicable load on the PTO output shaft (unlikely, imho) - your guess is as good as mine.

Some things to note:
1. the nut was swedged as designed - unlikely it rotated off - it rattled for a long time;
2. the nut is stripped, but the shaft, although damaged, is not nearly as bad;
3. the seal failure was likely caused by the shaft moving in and out of the gear/bearing stack;
4. unlikely the output bearing failed (no play at the output) - but will have to await teardown;
5. output and countershaft gears appear clean with no apparent damage;
6. gear oil was clean - no stardust.

Any additional ideas/comments as to the cause of the failure would be appreciated.

 

[tranas]

Just one additional clarification - the oil leak was between the seal and the case - not between the seal and the PTO shaft. The seal was physically expelled from the housing - visible in the pic with the first post.

 

[Old Machinist]

For whatever reason the shaft is not protruding far enough out of the bearing for the nut to have full thread engagement.

 

[tranas]

Yeah, that's because the PTO shaft is working its way out of the case and the gear/bearing stack.
Everything is supposed to be clamped together between the output bearing shoulder and the nut.

Once the nut fell off, the only thing stopping that blessed event was the rear seal. The bearing shoulder on the shaft (directly behind and shoving on the seal) is apparently what ejected the seal from the case. The failure would have been catastrophic in very short order. Kubota warranty got lucky.

 

[Fedup]

What about the possibility of undue stress on said nut? As in an implement PTO driveshaft that wouldn't/couldn't telescope as it should and during operation was pushing and pulling on the tractor shaft. If enough effort was applied the threads in the nut gave out as the weakest link in the chain.

Would you concede that as a possibility?

Hard to imagine an improperly installed nut in that spot holding fast for 1000 hours of use then failing for little or no reason, but yes, strange things do happen.

 

[dgtvrpepair]

I would look closely at the pro shaft on your implement. It should slide in and out easily. Also check to see if the shaft is too long when raising and lowering the implement. If it is too long and needs to be cut it will put extreme forces on the tractor pro when it bottoms out.

 

[GreensvilleJay]

Sure looks like it was cross threaded during the factory install. Nothing the owner could have done could cause that damage(imp PTO shafts are telescoping, no real load on the tractor PTO shaft. As for the 'why failed at 1000hrs'... tractor probably hasn't had PTO RUNNING for 1000hrs ! Heck my BX23S has 1225hrs on the clock, and ZERO using the PTO.
The repair is simple, new nut, shaft, seal..should be good to go in an hour.

 

[tranas]

Sure looks like it was cross threaded during the factory install. Nothing the owner could have done could cause that damage(imp PTO shafts are telescoping, no real load on the tractor PTO shaft. As for the 'why failed at 1000hrs'... tractor probably hasn't had PTO RUNNING for 1000hrs ! Heck my BX23S has 1225hrs on the clock, and ZERO using the PTO.
The repair is simple, new nut, shaft, seal..should be good to go in an hour.

Once again, I appreciate all of the responses. The dealer is fully into "the implement PTO could be at fault" scenario, for obvious reasons - but all repairs thus far have been done under warranty.

Couple of observations as to the implement PTO shaft:

1. PTO shaft is virtually new - Walterscheid OEM - and was properly sized at installation as to length for implement/tractor PTO distance.
2. The mulcher PTO has approximately 200 hrs max of operation and the implement PTO shaft has no visible signs of distress on the joints or the overload clutch - the spline tube moves freely.
3. Mulcher is properly sized for the tractor - rated for 90-120 CV (89-118 hp). Claims of overload of the tractor PTO are doubtful, as the tractor would simply bog and shut down from lack of horsepower.
4. The tractor PTO is obviously engineered to handle the full tractor horsepower - 114.8. (am aware output PTO hp is lower than engine rated hp). Loaded at maximum is what the PTO should be theoretically designed to endure without any issues.

However, GreensvilleJay's observations and evaluation of the repair procedure are likely correct. Doubt there was any issue other than lousy initial assembly. Cross-threading is the most likely scenario. Assembler simply jacked up the torque until the nut was flat with the washer and then staked the nut.

The observation that there is no real 'load' on the tractor PTO shaft is also correct - that's why Kubota does not use thrust bearings anywhere in the tractor PTO output gear box. Had there been some huge inappropriate thrust load, the bearing(s) would have shown heat and would have smoked far earlier than the threaded shaft nut would have been pressed off of the output shaft. Bearing condition is clearly visible - and the warranty repair replaced no parts other than the seal/shaft/nut. The helical cut gears show no evidence of heat whatsoever. The simple fact that the output seal and bearing race friction were able to keep the output shaft in the case after nut failure says the shaft 'overload' theory has no merit.

However, not all is well with the repair.

Once re-assembled, the tractor started and the PTO engaged with no load at idle (500 or 1000 rpm PTO speed selected) - the PTO box has a death rattle. Same volume and frequency at both PTO output speed settings, so that would indicate that the noise originates at the point of power input. The clatter is louder at idle than the tractor's engine. Disengage the PTO and you just hear the tractor's engine noise. Turn off the engine and spin the output shaft by hand - you still have the same noise. You can feel the noise in your hand as you turn the shaft. Conclusion - source is in the PTO box and it's not 'rattling' gears due to clearance. Once again - these are helical cut gears not straight cut ones - and there is no way to adjust gear backlash. The bearing cap is aligned and fixed by two dowels so movement or misalignment theoretically cannot be the cause. Audio of the PTO box noise attached.

Any input anyone might have as to the cause of the rattle would be appreciated.

 

[GreensvilleJay]

sigh, something is WRONG in the repair, quick return to dealer. Any 'in/out' of shaft ?
Maybe the 'sequence of parts on the shaft is wrong ? #050 and 080 look similar but could they have been swapped ? I didn't look them up but different numbers usually means different parts.
Noise when hand turning the PTO shaft indicates it IS in the PTO output shaft, not what is powering it.
Man I do feel for you, grass grows faster when tractors down !
Perhaps dealer will loan you a tractor ?

 

[Shadetree605]

Once again, I appreciate all of the responses. The dealer is fully into "the implement PTO could be at fault" scenario, for obvious reasons - but all repairs thus far have been done under warranty.

Couple of observations as to the implement PTO shaft:

1. PTO shaft is virtually new - Walterscheid OEM - and was properly sized at installation as to length for implement/tractor PTO distance.
2. The mulcher PTO has approximately 200 hrs max of operation and the implement PTO shaft has no visible signs of distress on the joints or the overload clutch - the spline tube moves freely.
3. Mulcher is properly sized for the tractor - rated for 90-120 CV (89-118 hp). Claims of overload of the tractor PTO are doubtful, as the tractor would simply bog and shut down from lack of horsepower.
4. The tractor PTO is obviously engineered to handle the full tractor horsepower - 114.8. (am aware output PTO hp is lower than engine rated hp). Loaded at maximum is what the PTO should be theoretically designed to endure without any issues.

However, GreensvilleJay's observations and evaluation of the repair procedure are likely correct. Doubt there was any issue other than lousy initial assembly. Cross-threading is the most likely scenario. Assembler simply jacked up the torque until the nut was flat with the washer and then staked the nut.

The observation that there is no real 'load' on the tractor PTO shaft is also correct - that's why Kubota does not use thrust bearings anywhere in the tractor PTO output gear box. Had there been some huge inappropriate thrust load, the bearing(s) would have shown heat and would have smoked far earlier than the threaded shaft nut would have been pressed off of the output shaft. Bearing condition is clearly visible - and the warranty repair replaced no parts other than the seal/shaft/nut. The helical cut gears show no evidence of heat whatsoever. The simple fact that the output seal and bearing race friction were able to keep the output shaft in the case after nut failure says the shaft 'overload' theory has no merit.

However, not all is well with the repair.

Once re-assembled, the tractor started and the PTO engaged with no load at idle (500 or 1000 rpm PTO speed selected) - the PTO box has a death rattle. Same volume and frequency at both PTO output speed settings, so that would indicate that the noise originates at the point of power input. The clatter is louder at idle than the tractor's engine. Disengage the PTO and you just hear the tractor's engine noise. Turn off the engine and spin the output shaft by hand - you still have the same noise. You can feel the noise in your hand as you turn the shaft. Conclusion - source is in the PTO box and it's not 'rattling' gears due to clearance. Once again - these are helical cut gears not straight cut ones - and there is no way to adjust gear backlash. The bearing cap is aligned and fixed by two dowels so movement or misalignment theoretically cannot be the cause. Audio of the PTO box noise attached.

Any input anyone might have as to the cause of the rattle would be appreciated.

sounds like pto shaft backlash to me ?. i hear, feel, see, this all the time when i am working on a rear diff on a atv.