Leaking gear boxes on mower decks

[TJP440]

My departed GR2120 ( bought a new one) had developed the leaking gearbox seal on the mower deck. In looking at it I noted the breather valve had a 5 stamped on it. Removing the valve I noted that is was spring loaded and would require X amount of pressure to open (5lbs?). That coupled with the small vent holes that always get covered with clippings dirt etc. got me to thinking.
So, I replaced the vent with a backwards facing filter and a 90 degree elbow on it. Mowed 3+ Acres 4 or 5 times with no signs of leakage. Thought I would post it here and possibly help someone with a leaky box. The fitting is 1/8 NPT and the P-clamp was secured to top rear bolt on the gear box.
The filter was oriented with the direction of flow towards the rear and the elbow was added for a bit more protection.

 

[TJP440]

Wanted to up date this. The above mod worked well on level ground but would still puke a bit of fluid going down STEEP hills and possibly when mowing with the R side of the deck substantially lower (mowing a hill sideways). I have devised what I believe will resolve the issue permanently but need to test it a bit more to be sure. Will update

 

[D2Cat]

Wanted to up date this. The above mod worked well on level ground but would still puke a bit of fluid going down STEEP hills and possibly when mowing with the R side of the deck substantially lower (mowing a hill sideways). I have devised what I believe will resolve the issue permanently but need to test it a bit more to be sure. Will update

Why not put the original check valve in the hose where you have the filter? Wouldn't that allow less dirt in?

 

[whitetiger]

Wanted to up date this. The above mod worked well on level ground but would still puke a bit of fluid going down STEEP hills and possibly when mowing with the R side of the deck substantially lower (mowing a hill sideways). I have devised what I believe will resolve the issue permanently but need to test it a bit more to be sure. Will update

Why not replace the leaking gearbox seal, reinstall the original vent back into the gearbox, and be done with it?????

 

[TheOldHokie]

Why not replace the leaking gearbox seal, reinstall the original vent back into the gearbox, and be done with it?????

Too simple.

Dan

 

[TJP440]

Too simple.

Dan

not quite
The seal isn't the issue, it's the flipping vent/breather.
I'm not sure if it's the hilly acreage or the poorly placed VB.
The hills are one issue. The other, if one looks at the placement of the breather, it is just to the R of the gearbox shaft which can/ will throw oil as it rotates. If enough oil get's into the opening for the V/B it will start pushing fluid out. Couple that with the suggested UDT2 foaming you now have wet fluid on top of the Gearbox collecting everything it can.
Then as the fluid cools back down it will draw debris into the tiny vent holes plugging them.
We now have a non vented gearbox that will eventually take the seal out. It's a bad design that Kubota has ignored correcting.

 

[TJP440]

Why not put the original check valve in the hose where you have the filter? Wouldn't that allow less dirt in?

Probably not as the filter was holding about an ounce of fluid and it the check valve will still be in the same dirty environment collecting debris. The other issue is the check valves vent holes get plugged rather quickly.

 

[JasonW]

That machine specs UDT2 for the gearbox? I haven’t seen that before. Ones I’ve dealt with called for gear oil or 10w-30 motor oil.

Since you mentioned a foaming issue with UDT2 have you thought about using gear oil instead? You know for a gear box?

 

[TJP440]

I'm running 75-140 Synthetic gear oil in it currently. And yes it calls for UD2 in the mower deck gearbox.

 

[Henro]

I'm running 75-140 Synthetic gear oil in it currently. And yes it calls for UD2 in the mower deck gearbox.

Curious. Calls for, or as an option along with gear oil?

 

[whitetiger]

Curious. Calls for, or as an option along with gear oil?

It is a standard Pearless (If I remember correctly) off-the-shelf gearbox. It calls for SUDT2 in the Kubota OPM.

 

[North Idaho Wolfman]

It's a bad design that Kubota has ignored correcting.

That's a pretty highly opinion based statement that lacks anything to back your claims.
There are 100's of thousands of these gearboxes in use and there are not 1000's of claims of leakage.
If the seal is leaking then the seal needs replaced, simple as that.
It doesn't require a space shuttle rework.

 

[TJP440]

That's a pretty highly opinion based statement that lacks anything to back your claims.
There are 100's of thousands of these gearboxes in use and there are not 1000's of claims of leakage.
If the seal is leaking then the seal needs replaced, simple as that.
It doesn't require a space shuttle rework.

There in is the problem. The seal was not leaking and still isn't. The oil is coming from the vent. Many may use these on flatter ground. I have a number of hills some are fairly steep. That is part of the reason I chose the GR is the AWD and well as glide steer.
The picture below is of a new unit at the 50 hour service. I unfortunately uncovered the vent before taking the pic, it was completely buried.
Standing the mower deck up overnight drained only 2 ounces of fluid. 1/2 of what should've be in there. Both of the small holes in the breather were plugged. Fluids expand when hot and contract while cooling down.
This is going to possibly create two issues.
1. Over pressurization of the gearbox when hot.
2. Drawing a vacuum as it cools
Either may cause the lower seal edges to flex leading to the failure of the seal and the recommended 400 hour replacement.
My first attempt to resolve the issue resulted in the filter holding a small amount of fluid in it's bottom and a dip or two on the deck.
That is when I realized the fluid may be more prone to escaping on the hills. especially when going downhill or when the mower deck is angled to the R.
My second version is still being evaluated but so far is as dry before use when new.
I realize there are many of these units out there but if one googles "Kubota mower gear box leaking" there are plenty of hits.
i spent 45 + years in engineering resolving random issues like this and other initially unexplained occurrences. Will keep all posted on the latest revision

 

[TJP440]

Curious. Calls for, or as an option along with gear oil?

Good question, UDT2 is spec'd in the manual with no mention of a subsstitute. I will email the dealer to see if there are any TSB's but am doubting it.

 

[JasonW]

Just looked at the owners manual for the GR2120. It says to replace the mower gear box seal every 2 years.
To check oil every 50H and change every 150H.

Just me but that amount of fluid I’ll change it every 50H or once a year on my ZD331.

 

[TJP440]

Curious. Calls for, or as an option along with gear oil?

Just looked at the owners manual for the GR2120. It says to replace the mower gear box seal every 2 years.
To check oil every 50H and change every 150H.

Just me but that amount of fluid I’ll change it every 50H or once a year on my ZD331.

Do youhave a GR or just looked at the manual?
IF you have one, What year is your unit and or what date was on the manual?
Interetsing that they've changed to 200 hours
Does it call for UDT2 and or any sub'stitutes?

 

[JasonW]

Do youhave a GR or just looked at the manual?
IF you have one, What year is your unit and or what date was on the manual?
Interetsing that they've changed to 200 hours
Does it call for UDT2 and or any sub'stitutes?

No I have a ZD331. Looked at the manual online. Date on the front says 2014.

Are you saying your manual states the gearbox oil change interval is 200H?