How To: Reduction Gear Oil Change

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jaap said:
So, I went back to the dealer this morning. There was oil leakage again and when opening the side plug, oil came out, even though they opened it last time too. So the leakage wasn't caused by over-filling, that's for sure. The leakage seems to come from the little tube, but also the dealer doesn't know why. It remains an unsolved mystery.
It's an EV, just isn't much to go wrong with it on the mechanical side. It's either the tube system as others have already said or some major manufacturing defect in the gear box that just is allowing the fluid to leak out, which would be a first here as I've never read about anything like that happening before. You would be the first. Before jumping to extremes though, my gut feeling says it's simple and the dealership is just over-thinking the issue. This issue can be reproduced, it's easy to remove that air shield at the bottom to see everything. I'm at a loss as to why they can't figure this out. :?
 
Might be easy enough to just replace the breather tube, it's a cheap part. Or at least inspect the old one, looking for plugging up.
 
To continue the tale of the leaking leaf...

I went back to the dealer this Monday. They kept the car for two days.

The workshop manager was a bit less helpful then his colleague last time. He talked more about the end of my 3-year warranty (this week) and how doing your own maintenance might be a contract breach then about what they actually researched or found.

According to his story, there was still too much oil in the reduction gearbox (even though they already opened it twice and I did not refill anything in between). They replaced the oil with 1.35 liter of genuine Nissan oil. They also replaced one part: number 290T7X (BRUSH ASSY) because Nissan told them to do so. That is not the breather itself (part 38322M) but it's close. They gave me this printout from the workshop manual:
gearbox.png

gearboxpartlist.png

Next episode: In two weeks I will bring the car to the dealer again so they can check if it's still leaking. The workshop manager made me promise not to touch anything in between (I think he suspects me of secretly overfilling the gearbox at night).

To be continued...
 
Looking at the FSM it appears that the breather is for the earth brush housing and not the gearbox.

So there should not be any oil in the earth brush housing unless the seal on the main gear shaft is leaking. If it is leaking then oil can get pumped into the housing with no way to return to the gearbox. The leaked oil fills the brush housing and then pushes up into the breather tube, then blows the tube off the breather as the oil pressure increases.

The caution notes in the FSM mentions that there should be no oil on the brush surface and not to even touch the brush,
• Degrease shaft surface (brush contact surface) (A), and verify
that there is no dust or other substance on it, then install the earth brush.
• Degrease brush surface, and verify that there is no dust or
other substance on it, then install the earth brush.
• Never reuse O-ring.
• Never apply oil to O-ring. Verify that there is no oil on it, then install O-ring.
• Never touch brush area.
• When substances such as oil and dust are adherent to the
shaft surface (brush contact surface), remove them and
degrease the shaft surface to install brush.
• When there is corrosion on shaft surface, remove corrosion
to install brush.
When reusing with original parts, never allow oil to contact brush area.
 
jaap said:
...
Next episode: In two weeks I will bring the car to the dealer again so they can check if it's still leaking. The workshop manager made me promise not to touch anything in between (I think he suspects me of secretly overfilling the gearbox at night).
...

Seeing as how any excess simply leaks out of the fill hole, you'd have to be fairly dedicated to the task to pull this off. :lol:
 
LeftieBiker said:
I think he's also parking the car on the side of a hill, with the fill hole(s) on the uphill side. ;)

Well we covered that. I think this dealership is either clueless or uninterested judging by their reliance on incantations ("save us, oh Genuine Nissan Oil") and their readiness to blame it on the customer.
Anyway I think nlspace nails it. It's an air breather and there shouldn't be any oil in the space it communicates with (brush housing).
 
From looking at the exploded view and reading the service manual, it is clear that the intermediate shaft extends into the brush housing so that the brush rubs directly on the shaft. Either there is a shaft seal between the brush housing and the main gear case or it is normal for oil to get into the brush housing. Even though the manual discusses degreasing the shaft surface, I suspect there is no seal and the vent tube on the brush cover is truly a vent for the whole gear case. If so, then replacing the O-ring, brush cover, breather hose, and breather should eliminate the oil leakage.
 
Ben Nelson dismantled a gearbox and there was no oil in the brush housing when he removed the cover (seen at 2:09). Electric brushes won't work well with an oil film on the contact patch of the shaft. The internal rubber seal can be seen at 6:28.

Also you can see the oil ports and channels in the housing for lubrication of the bearings. If the return port was blocked then that might be another reason for oil to get pumped past the seal into the brush housing.

https://youtu.be/L5WhB7uQLzY?t=129

https://youtu.be/L5WhB7uQLzY
 
It is interesting that neither the Nissan online parts catalog nor the exploded views in the service manual show the oil seal on the intermediate shaft. Also, the text of the service manual does not discuss that oil seal. I wonder how the main part of the gearcase is vented.
 
GerryAZ said:
It is interesting that neither the Nissan online parts catalog nor the exploded views in the service manual show the oil seal on the intermediate shaft. Also, the text of the service manual does not discuss that oil seal. I wonder how the main part of the gearcase is vented.

Perhaps because Nissan deems opening/overhaul of the case to be beyond the scope of their dealer service. (i.e. replaced as an assembly).

Just speculating but it seems reasonable the breather is in fact there to prevent any pressure differential between the TM case and the small enclosed space of the brush housing, so as to not drive seepage past the oil seal into the housing. The rest of the case may be vented by other means.
 
Nubo said:
GerryAZ said:
It is interesting that neither the Nissan online parts catalog nor the exploded views in the service manual show the oil seal on the intermediate shaft. Also, the text of the service manual does not discuss that oil seal. I wonder how the main part of the gearcase is vented.

Perhaps because Nissan deems opening/overhaul of the case to be beyond the scope of their dealer service. (i.e. replaced as an assembly).

Just speculating but it seems reasonable the breather is in fact there to prevent any pressure differential between the TM case and the small enclosed space of the brush housing, so as to not drive seepage past the oil seal into the housing. The rest of the case may be vented by other means.
Since the video posted by Nlspace clearly shows a seal on the intermediate shaft and there is no replacement seal shown in the parts catalog, a new gearcase should fix the oil leak. Nubo probably has the right analysis--dealer cannot replace seal so replace the whole assembly.
 
If it's under warranty and on them, then replace the "automatic transmission" ; if not, then get a real mechanic to dismantle the gearbox and replace the seal.

Nissan Parts,
Automatic Transmission
Part Number: 32010-3NF0B
Supersession(s): 32010-3NF0A; 320103NF0B; 320B0-3NF0A; 320B0-3NF0B
MSRP: $1710. doesn't appear to include the breather cover, brushes, hose or breather.
 
When I wrote my first post in this thread, I never expected to hijack it with so many posts about leaking oil. But the story continues :(

Two weeks ago the Nissan dealer filled the reduction gearbox with "genuine Nissan oil" and replaced the brush assembly that grounds the moving parts in the gearbox. None of this had anything to do with fixing a leak, of course.

Today they checked the gearbox again. Their first conclusion was the leakage was "fixed" because there was no oil spilling out of the gearbox. I told them to open the casing that holds the brush assembly, and for sure, there was at least 200ml oil in there (it should have been dry).

So finally they agree that it's probably necessary to replace the oil seal in the gearbox. As mentioned by GerryAZ, the prescribed way of doing this is by replacing the whole gearbox. So the dealer is going to contact Nissan and hopefully I will get a new gearbox some time soon. Wether it comes free remains to be seen, they never fail to mention that by now, my warranty has run out. Of course, my reply is that I would not have minded if they fixed it within the remaining warranty time, when they still could have ;-)
 
As long as the issue was reported and verified (that something was wrong, anyway), the warranty should cover it. They don't get to run out the clock and then charge for the work.
 
jaap said:
there was at least 200ml oil in there (it should have been dry).
That is a lot for that small space. Looks like nlspace & GerryAZ etc. on here nailed it. If you go to the BenjaminNelson youtube video cited above, at the 5:06 point, the offending inner seal is visible at the bottom of your screen. On the brush side, it's just a metal c-ring & washer, not a seal.

Agreed, as long as the dealership was made aware of the problem happening before the warranty expired, OR it can be reasonably assumed the problem has existed for a long time, then Nissan "should" honor the warranty on it. New transmission or will they somehow get the inner seal and pop it on to the old disassembled unit? Given the possible damage to everything in there from very-low oil levels, I'm hoping they'll just replace the whole thing with a new unit that should last 200,000 to 500,000 miles or so.
 
i notice that the gearbox is using spiral-cut gears with radial contact bearings. This is a poor combination because of the axial load imparted to the intermediate shaft by the gears, and the low axial load capacity of radial bearings.

Straight-cut gears wouldn't have this problem, but they tend to make noise. Preloaded angular contact bearings would solve the axial load problem, but they tend to cost a bit more.

But the net result of the axial load was likely to wear out that internal seal. Its interesting that the leakage in 2 weeks was greater than the amount of oil left in the gearbox that started this discussion. i would guess that with the worn out seal it would be empty and leaking again after about 10 weeks or so.
 
nlspace said:
But the net result of the axial load was likely to wear out that internal seal.

If that's true, I would have expected other Leafs having the same problem. There are enough people on this forum that at least one of them should have had leaking oil before?

My guess (and hope) is that it's just a rare factory assembly error.
 
Could be an assembly error, or a stack up of tolerances for the shaft, bearings and seal, or damage such as a scratch or nick in the sealing surface.

An interesting measurement with the car on a lift or front jacked would be to put a dial indicator on the end of the intermediate shaft and then exercise the gearbox in forward and reverse by rotating the wheel to backdrive it thru the differential. That might eliminate my axial load theory if the shaft has no axial travel.

Then it would need inspection and measurement of the shaft surface and seal for diameter and bore, etc. to get clues for the failure.
 
nlspace said:
i notice that the gearbox is using spiral-cut gears with radial contact bearings. This is a poor combination because of the axial load imparted to the intermediate shaft by the gears, and the low axial load capacity of radial bearings.
It's the same design as the Hyundai Kona Electric gearbox. Helical-cut sideload is a minor issue on the input shaft because of the low level of torque relative to the bearing size. On the intermediate shaft it's mostly balanced between the torque going in and torque going out.
The final shaft has tapered rollers. Job done.
 
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