Power Loss L3940 HST

[SHC]

Hey guys, hope you can help me out. Our Kubota has about 580 hrs on it and we have experienced a loss of power when trying to drive up grades. We are not loosing engine speed. The first time I noticed it was pulling out of the barn after hooking up the bush hog. It felt like I was pulling against the brakes! I double checked and they were in the off position and I checked the bush hog as well to make sure nothing was hanging up. I started the tractor again and released the brakes and raised the BH and pulled out. I felt a slight loss of power again and again it felt like I was pulled against the brakes. I stopped and backed up and pulled up several times and then everything felt ok. I drove up into the orchard and cut for about 2 hours. I headed up to our upper fields and the trail is fairly steep and no problems. Stopped for lunch and tried to finish cutting and there it was again. I could NOT drive up into the orchard area. The PTO was off and deck was raised. I had the Range Shift Selector in L and 4 wheel drive engaged and double checked brakes etc.

I did not want to force the issue so I drove down to the barn and checked what I could. Everything seemed normal, HST oil was changed in early April as was all filters. Next day it ran OK most of the day then it acted up again!
I normally use the Auto/HDS/ Stall guard setting in high. It will adjust to load as you work.

I am pretty sure that we have the wet disc brakes and they are in the HST Box. Trying to figure if the problem is related to the HST portion of the system. I did not experience any loss of PTO RPM, but one of our guys did when using the Rotor Tiller. It is my guess that its not the engine power but the HST transmission at fault. Any suggestions or remarks will be more than appreciated.

 

[lugbolt]

Try turning stall guard off. Does it help?

Does low gear seem to make any difference?

Are you running in 4x4 all the time? If so, adjust the tire pressures if you haven't already. If they're off front to rear (out of spec), it'll feel like the brakes are on all the time. Similarly, if the fronts are worn and the rears aren't, it'll do the same thing.

Yes you have wet brakes but they aren't in the HST. They're in the rear axle housings. If you think you have an issue with the brakes jack up a rear tire and then spin the tire (neutral/4x4 OFF). Does it spin free? IF yes, you don't have a brake issue on that side UNLESS it's a cabin model and the cab mounts are worn, which can cause the brakes to be partially engaged when the cabin shifts a little on the worn/loose/broken mount(s). Normally the pedals have enough free travel in them that it's not an issue. OH...try this...unlock the brake pedals and move them independently. Does the left pedal go further down toward the floor than the right? They should be pretty well equal in their travel. If you have one that's "tight" (doesn't go down very far), then it may be worth adjusting them.

HST issues are rare on these and because of that, going into HST diagnosis would be a last resort. What kinda fluid are you using? What kinda filter(s)?

 

[SHC]

Thanks for your response.
We always operate with Range Selector in L per the dealer’s instructions, and also the HST in Auto H-DS mode. I did move the lever from L to M several times just to make sure I was in L. I tried various HST modes including stall guard to see if somehow it had defaulted to a less than desirable setting. As noted I turned off the PTO to get rid of the load on the tractor but it made no difference on the power loss. We also keep it in 4WD when working or moving in dirt or grass. The tire pressure is set at 22 front and 20 rears. I did notice when I parked it that the RF looked a little low and I will check that with a gauge on my next trip up.

I will definitely jack up and check for brake release on both sides. We do not have a cab on our application. Appreciate the clarification on the location of the brake pac. We use the UDT oil in the HST. The dealer did not have our filters in stock when we stopped so we installed after brand filters that he recommended. There were no problems after the oil and filter change in April.

I did take note that the emergency brake was not “holding” as well as it did originally on grades and it is on my bucket list of things to do post haste. It’s a three hour ride so it’s always a race against time to get things done. I will check on items you listed and let you know.

The 3940 has been a great addition for us, the ole Ford 8N (1953) just flat got tired of trying to maintain 200 acres of fields and woods. We sold it to a collector that was glad to get it.

Thanks again and will let you know what I find!

 

[MilkyWay]

Hi SHC and welcome to the forum. I am quite the noob myself but there is plenty of talent here to help you. Clear, thoughtful descriptions are a must if a simple resolution is to be found. When you say power loss, do you have to rev the engine higher to maintain speed when the problem occurs? Also, one thing I might suggest; if you have the good fortune to be on hilly/sloped terrain, see how much slope is needed for your machine to roll on it's own, if you can do that with hst tranny's. Like I said, I am a noob, also my L5450 is not hst. point being is if you can test brake drag under seemingly "normal" and then "draggy" (is that a word?) circumstances.

 

[SHC]

Thanks for the response Milky Way!

Engine speed does not appear to be effected during the power loss. We have several operators including myself and only three of us have experienced this loss at one time or another. The problem is intermentant and as a retired Hvy truck mechanic and service manager those are the worst. As stated prior if running attachments (bush hogs, tillers etc) the loss of power does not effect the engine RPM but it does effect the ability of the tractor to maintain desired road speed especially if you direction of travel is upgrade or in plowed ground. Any increase in throttle will NOT overcome the loss. It happens very quickly so its tough to get a good "feel" as to what the heck is going on. My first thought process was that somehow the brakes had applied. Example if you failed to release the EB and tried to pull out, you can attempt to overcome it by applying more throttle (engine speed) but you KNOW something is not right and hence the search for the problem. I am headed up tomorrow so we shall see what "evil lurks"............... stay tuned! And thanks for the follow up.

 

[kevinj]

Thanks for the response Milky Way!

Engine speed does not appear to be effected during the power loss. We have several operators including myself and only three of us have experienced this loss at one time or another. The problem is intermentant and as a retired Hvy truck mechanic and service manager those are the worst. As stated prior if running attachments (bush hogs, tillers etc) the loss of power does not effect the engine RPM but it does effect the ability of the tractor to maintain desired road speed especially if you direction of travel is upgrade or in plowed ground. Any increase in throttle will NOT overcome the loss. It happens very quickly so its tough to get a good "feel" as to what the heck is going on. My first thought process was that somehow the brakes had applied. Example if you failed to release the EB and tried to pull out, you can attempt to overcome it by applying more throttle (engine speed) but you KNOW something is not right and hence the search for the problem. I am headed up tomorrow so we shall see what "evil lurks"............... stay tuned! And thanks for the follow up.

Does it affect the PTO speed also?

You may have oil on the main clutch.

 

[lugbolt]

Could be main clutch issue. Does the clutch pedal have about an inch of freeplay? If not it should. Adjust as necessary and try again.

Could be a filter issue.

Could be fluid issue. UDT is good fluid. Super UDT is better.

My suggestion? Remove right side filter (suction) and look at the magnet. If it's full of metal, I mean a LOT of metal, there may be damage inside the HST although I would certainly consider that as a rarity. Almost 3 decades of fiddling with Kubota and only ONE HST failure on a tractor. Couple small mowers but just the one tractor (L4330HST-C as I recall). I do not ever want to see that tractor again

 

[SHC]

Well go figure!

As posted earlier we gave the 3940 a real work out last week. Whatever the problem was it did not show up at all! Ran like a "bear" no power complaints no issues at all. I cant help but wonder if one of the HST modes got locked in (stall guard) but the dash indicators showed another mode? So you cant fix what is not busted! As stated ran great for three days under all kinds of loads and conditions.

So all we can do at this point is wait and see............

Thanks for those of you that weighed in!