HST Power Loss on Kubota Grand L3940 HST+

[skelly132]

I have a L3940HST and have the same problem also with 320hrs. i need some help here. i PM Rocksprings but havent herd anything back. im at a loss here with this tractor can someone plz help me.

 

[Bluegill2]

I keep seeing these low or no power threads.

Always seems to involve a HST trans?

Never see this with gear drive?

Guess ya can always put a turbo on it!

 

[Grateful11]

No problem here "yet", knock on wood, and the L3940 is used about 1/2 an hour everyday of the year. It's got close 800 hours on it.

 

[The Fred]

Guess ya can always put a turbo on it!

Happy New Year you joker.

Fred

 

[Bluegill2]

Happy New Year you joker.

Fred

Happy New Year to you Turbo Wizard!

 

[kubotapop]

Hey this was getting interesting. But now its important as my l4740 hst+ is having these problems. Noticed when plowing snow. Could go down the hill in 3rd range in high, but could not come up the hill till I shifted down. Now its the same road I've been plowing with this tractor since it was new in 2009, and it used to come up the hill in 3rd high range a little slower but would do it. Now not at all with the plow up. The engine seems to keep the rpm's up but the machine slows down. No black smoke. All filters have been changed. Any ideas? I've had a bunch of Kubotas over the years 2250, 2900. l3710, l4330 and some would require a suction screen to be cleaned on the side of the tranny. Now that doesn't appear in the manuel. Although I never found a spec on the sreens. Any ideas? thanks Pop

 

[MessickFarmEqu]

9/10 times we see this issue in the shop its because someone used something other than SUDT for their HST fluid.

 

[stoyan79]

Was the damage permanent, or everything was back to normal, once switched back to SUDT?

Have you ever heard of problems with AMSOIL HST fluid? Now you got me worried ...

9/10 times we see this issue in the shop its because someone used something other than SUDT for their HST fluid.

 

[MHarryE]

Was the damage permanent, or everything was back to normal, once switched back to SUDT? Have you ever heard of problems with AMSOIL HST fluid? Now you got me worried ...

several years ago I got a bulletin published by Kubota showing the benefits of SUDT in cold operation. The bulletin didn't give specs like viscosity at various temperatures but it plotted several different parameters vs temperature got SUDT, standard UDT, and commercial grade hydraulic fluid that advertises meeting UDT specs. The SUDT was far superior in all cold operation tests.

Once again I gave not seen specs on SUDT2 so it is hard to make a positive statement but hydros have kind of a sweet spot operating between 9 and 16 cSt. Not knowing the Kubota spec you would want to look for a high viscosity index, probably in the 130 - 200 range. Your Amsoil probably has a high VI. Next would be to see if it maintains >9 cSt at 100 degrees C. Then the hardest part to find in specs is viscosity at your coldest temp. My best guess here is 1200 cSt at the coldest temp but I only see most oils stating viscosity at 40 degrees C. If I didn't use SUDT2 in my Kubota tractors I would probably find a suitable Amsoil or Mobil synthetic.

One key point to remember the Kubota CUTs with which I am familiar have inlet suction filters and cold, thick oil is like molasses through the filter so the system starves, pumps cavitate, all kinds of mean and nasty things. At Cat we avoided suction filters by having a first pump that could withstand fine particles (only wire mesh strainer on the inlet), then a pressure filter to make the entire remainder of the system have finely filtered oil. Problem? Rev the engine to high idle before the fluid is warm and blow the gasket out of the filter spraying everything. Solution - move to Hawaii where it is always between 70 and 85. Problem gone.

 

[rScotty]

9/10 times we see this issue in the shop its because someone used something other than SUDT for their HST fluid.

My Kubota dealer doesn't push for SUDT or SUDT2 over standard HST fluid. Like some other shops, they had problems with that first SUDT synthetic and are understandably gun shy about using the SUDT2 that replaced it. They will put in a synthetic if you ask for and want to pay the extra $$, but their recommendation is to use any top quality standard HST fluid and that's exactly what they use in their shop.

My own feeling is that my dealer is over-reacting to synthetics, but have to admit that they haven't had many trans/hydraulic issues to deal with in their shop. So what they say has proven over the years to work well for the Kubotas the sell, as well as being the same advice my owner's manual gives.....and has the extra advantage of being exactly the oil that Kubota's HST+ was designed to use.

Based on AMSOIL's good record in all kinds of systems, if I was going to go to a synthetic then AMSOIL would be my choice. I had a repair shop for years and can't recall a single instance where AMSOIL had a compatibility problem. It wouldn't be the first place I'd look.

rScotty