question LEAKING Gearbox/Hydraulic Oil

After changing the old Gearbox/Hydraulic oil to the new Gearbox/Hydraulic oil
(Ultra1Plus SAE 75W-90 Synthetic Gear Oil, API GL-4)
it is leaking from a bottom rear right side hole.

I did over fill a little, which other post said was OK to do when operating on side hills.
When I received the Zetor 3340 back February 2024, there was no leaking with the old Gearbox/Hydraulic oil,
which was just touching the bottom of the dipstick (very low).

The oil leaking from this back hole looks to be from where the brake compartment is.
This oil leaking seems to increase more when driving down hill,
then when Zetor 3340 is diving up hill.
Not sure why this seem to be happening yet, maybe oil is collecting in the brake compartment
and exit out of the hole more when going down hill.

Could this be a seal has failed on the right side and if so, what is the part number for it ?

Click on picture to see more:

If it drips out there, the shaft seal to the differential is usually leaking.
It is less common for it to be the actual paper seal or liquid seal on the bowl-shaped cover to the differential.
Unless it is brake fluid and not oil, because then the wheel brake cylinder would be leaking.

Unfortunately, to fix this, the portal has to be removed.
Very roughly:

• Jack up the tractor, remove the wheel, separate the cabin bearing and support the rear of the cabin,
• separate the side stabilizer,
• unscrew the push rod from the disc brake automatic,
  
• then remove the portal (pallet truck or workshop crane, definitely on firm, level ground otherwise it won't work).
  
• It seems to be the right side - so also release the differential lock actuation first.
  
• Then you can get to the possibly leaking spot...
  
  

And are you sure it is not coming from above? Because if the pressure pipe is leaking, it can damage the hydraulic cover seal (top) and then oil can run from above into the brake and then out again from below... you should clarify this first.

Best time to check the brakes and repair them if necessary.

Hi Joachim,
Thank you for your very good reply.
1) Brake Fluid or Gearbox/Hydraulic oil ?: the Brake Fluid reservoir is still full, so that is good.
2) I pumped out some of the Gearbox/Hydraulic oil so that it is now about 1/4th of the dipstick.
I will do a test to see if the leaking stops and/or is much less.
3) So I am not sure where the leaking is coming from yet.
Thank you for informing me about that it could be leaking from a top pressure pipe (the hydraulic cover seal (top).
I am not sure where this pressure pipe is yet on top.
4) I have a Vevor Endoscope Camera and so able to view up through the hole.
So far I did not see any evidence of where the Gearbox/Hydraulic oil leaking.
I will try this again and because of the pictures you posted on what is inside, I hope I will be able to see better
to where this leakage is coming from.
With these Vevor Endoscope pictures I was not always knowing what I was looking at, but you may see something in them that I missed.

Robertzetor3340 said:

1) Brake Fluid or Gearbox/Hydraulic oil ?: the Brake Fluid reservoir is still full, so that is good.

Click to expand...

Brake fluid is slightly sticky when rubbed between your fingers. This is an easy way to test it.

Robertzetor3340 said:

2) I pumped out some of the Gearbox/Hydraulic oil so that it is now about 1/4th of the dipstick.
I will do a test to see if the leaking stops and/or is much less.

Click to expand...

You can do that, but you shouldn't drive with 1/4 of the normal oil level all the time.

Robertzetor3340 said:

So I am not sure where the leaking is coming from yet.
Thank you for informing me about that it could be leaking from a top pressure pipe (the hydraulic cover seal (top).
I am not sure where this pressure pipe is yet on top.

Click to expand...

Just look if its dry or not on top like the arrow views...

Robertzetor3340 said:

4) I have a Vevor Endoscope Camera and so able to view up through the hole.
So far I did not see any evidence of where the Gearbox/Hydraulic oil leaking.
I will try this again and because of the pictures you posted on what is inside, I hope I will be able to see better
to where this leakage is coming from.

Click to expand...

4 possible washers/seals(red. green, blue) and the shaft seal (yellow) they can be wet and drop oil. Mostly its blue or yellow.

3) Not leaking from a top pressure pipe (the hydraulic cover seal (top). Also the 3 Point Hitch is working properly.

2) After lowing the oil level so that it is between the Low and High oil marks, the
Gearbox/Hydraulic oil is not to low to operate as the oil level is still between the Low and High oil level marks.

UNLESS ..... Zetor has the Gearbox/Hydraulic oil Dipstick Low Oil Mark NOT located in the proper place ?

When oil was over the Gearbox/Hydraulic oil Dipstick's High Fill Oil Mark it had a slow leak when not running the Zetor engine.
So this is a little good news.
Next I will drive the Zetor up and down hills and observe this oil leakage, as this leak may stop like when the old Gearbox/Hydraulic oil level was at the dipstick’s low oil mark.
I am leaning toward the right side axle shaft seal needs to be replaced.

As long as you are working on flat ground, it will be fine for now. But if it is as you describe, the shaft seal is definitely leaking - and it will stay that way.

If you are also working on a slope or with a tractor at an angle, you will not be able to avoid having it repaired.
Back then, shaft seals made of NBR (black, classic) were used, but Zetor later switched to MVQ (brown with a metal ring), which have a significantly longer service life and remain soft even in very cold temperatures, sealing well.

But remember - every centimeter less oil also means less good lubrication and potentially hotter oil because it then goes through the pump once a minute and not 0.6 times a minute when the gearbox is filled to the max.

Robertzetor3340 said:

I am leaning toward the right side axle shaft seal needs to be replaced.

Click to expand...

I think so too.

Little update:
With the Gearbox/Hydraulic oil level on the dipstick being above 1/4th the low oil mark,
there is still some oil leaking when Zetor 3340 is setting on level ground.
But is less then when the Gearbox/Hydraulic oil was filled over the high dipstick oil mark.
When I purchased this Zetor 3340 (Feb 2024), it was not leaking any oil anywhere and also did not leak when operating.
After purchase, checking oil level, the Gearbox/Hydraulic oil dipstick showed it was at the low oil mark.
I just do not have time to do the oil seal replacement at this time and hope to be able to do it in the summer.
I believe it is OK for now, as I will be using it mostly on flat ground.

I may try to do both axle shaft seals when I am able to do it.
They are not low cost; I need to do some shopping around for better prices.
I do not have the part number for these axle shaft seals yet.

Then it will definitely be the shaft seal ring or rings.