Is it better to use gear oil or trans fluid in front axle of FWA Kubotas?

[DennisArrow]

With my B7610, there was hydro fluid in the front axle/transfer case/differential when I got it a 400 hours......I kept that in there and topped it up after a few hours use, with more sud2. A slow weep developed around the left hand wheel hub/knuckle. Not enough to drip; but enough to notice that it was wet and collecting dirt...........

At 500 hours I changed out to 80/90 gear oil that one gets from tractor supply.........DRY as a bone for the last 200 hours over a couple of months......During that time I did some really heavy jobs involving LOTS of bucket work and 4wd........

One thing that the B series guys might note............

When I changed the fluid in the front axle, I filled the case up to the top of the dipstick fill mark.......All seemed OK.......Then, a few hours later, it was a quart low.....NO NO LEAKS........There is definately some kind of air space that doesn't just fill up when one is changing and adding fluid......I think even now I need to check it again........God bless......Dennis

 

[TomSeller]

Not a one-word answer, but my dad, a gearing engineer, designed the tools used to manufacture gears, including gears used in differentials. He said that the appropriate oil for meshing gears depends in part on how the gears are made. Differential gears are spiral bevel type, with more sliding contact than straight spur-type gears. If a gear is precision cut with multiple hardening and finishing operations, then lighter-viscosity oil will give adequate "float" to prevent most metal-to-metal contact. A heavier oil like 80W90 maintains more film thickness, allowing gears of slightly lower finishing specification to still give satisfactory life in service. Kub's manufacturing standards are pretty high - which may explain why either oil is ok with them for the front axle.

Good explanation. Curious with your knowledge which do you use?

 

[von-mil]

My B3030 originally had UDT in the front axle case. After almost every use I would notice a large drop forming on the underside of the "pumpkin". I have since switched to 80/90 gear oil and it has been leak-free ever since.

I also agree on the need to re-check the fluid level for a number of days after changing the front axle fluid.

 

[rbargeron]

Good explanation. Curious with your knowledge which do you use?

My knowledge is pretty limited - front axles get 80W90 or straight 90W gear oil, gear transmissions where the hydraulics use the same oil get regular ag hydraulic fluid/gear oil - including the ones with hydraulic clutch packs. The clutch disks are bronze and seem not to be prone to chatter.
HST transmissions get SUDT - I think the SUDT formulation has some additives to limit chatter as sliding surfaces come to a stop. Honda has worked on that issue a lot in cars - they have slightly different differential oil for several models.

 

[sixdogs]

,,,

........

One thing that the B series guys might note............

When I changed the fluid in the front axle, I filled the case up to the top of the dipstick fill mark.......All seemed OK.......Then, a few hours later, it was a quart low.....NO NO LEAKS........There is definately some kind of air space that doesn't just fill up when one is changing and adding fluid......I think even now I need to check it again........God bless......Dennis

This seems to be a common issue with all Kubotas. Check a NEW tractor after the first few hours of use and check after a gear oil change. They always need more oil. Beats me.

 

[SSdoxie]

One word answer = Either.

BabyGrand's statement was right on. "I think the manufacturers use the hydraulic fluid because it meets the requirements and they avoid the risk of "which oil goes where" mix ups at the factory and service facilities. One less lubricant to keep in inventory also reduces costs."

Bobcat engineers asked Daedong this question when rewriting the manuals. The response was just what was stated above. To avoid confusion in factory.

I chose to use 80W-90 because my use is primarily loader work and felt the higher viscosity would offer better protection during heavier loads on front axle.

 

[LD1]

I use The universal hydraulic oil stuff. Same thing that goes in the rear end/trans.

Not really any scientific or what one is better reasoning. My reasoning is more simple. The front axle holds 2 around 2.5 gallons IIRC. The trans and rear hold 7.5. So it works out perfect buying 2 5gal buckets. And filling. Gear oil is SLOOOOWWWW through a little hole and funnel.

And besides, there are lots of gears and stuff in the transmission and rear end, and its good enough for them, I am sure it is just fine in the front end.

 

[MHarryE]

It depends which tractor. The SCUTs and CUTs have standard gear drives and the best commonly available is synthetic 75W-90. The utilities with limited slip differentials have clutch facings with materials not comparable with most gear oils that will disintegrate. The answer is in the book. If it says to use either SUDT-2 or gear oil, go with the synthetic gear oil. If it says SUDT-2 only.

 

[deminin]

My Kubota B2910 came with the Super UDT in the front axle. It ran ok until it was well past the warranty....then, it spun a bearing, and cut a groove in the axle housing. I bought all the parts and rebuilt it myself...And Then, I put 80W90 in the axle, and it as been doing great for over 5 years now. Kubota says you can use either the UDT, or 80W90...from my experience, I will Stay with the heavier oil.

 

[varmint]

I know this off-target, but heck... I changed the transmission oil in my (manual 5 speed) Subaru and used the French Motul synthetic oil that the Subaru forum speed freaks love. Same weight, of course. I have noticed smoother shifting, especially when the weather is cold. Just seems to work better. If your tractor sees a lot of cold weather, the viscosity of synthetic might be a factor?