Hydrostat Transmission Shifting to Neutral Downhill

[mljenkins]

I have a Farmtrac HST390. Sometimes the hydrostatic transmission shifter (Low, Neutral, Medium, High) actually moves from low to neutral when going downhill. This has happened while in 4WD with my cutter on the back. It has happened with and without the PTO running. It has happened at low engine speed and at high engine speeds (PTO engaged running brush hog).

I have a FEL but nothing in it and it is close to the ground. I am glad I have at least been taught safety precautions from other operators so that the outcome of my situation has been positive, other giving me a brief surprise. I was able to nail the brakes the times it has happened to stop it from taking off (luckily I keep the brakes locked going down steep hills so I didn't accidentally just hit one brake and roll it).

Has anyone else ever experienced this? At first I thought my leg was hitting the shifter. I tried to reproduce this by tapping on the shifter while going downhill and could not. The couple times it happened to me yesterday I am 95% sure I did not hit the shifter.

Does anyone have any idea what could be causing this? Could it be something simple like a spring that has lost tension, or something more serious like gears that are worn? The tractor has about 380 hours on it currently, and about 50 of those I have put on it. It has done this since I purchased it last year from a local tractor dealer.

Thanks for your input.

 

[beenthere]

Sounds like either a worn gear or some adjustment is not right.

I'd discuss it with the dealer where you bought it. It is not right, and could be considered dangerous (as momentarily, you are out of control until you gain control and get it stopped).

 

[mljenkins]

Well, I purchased it from a Kubota dealer. The nearest Farmtrac dealer is in the next state from here. I'm not sure whether they can fix it or not. It seems every time I take anything anywhere, they keep it for weeks and then it never gets fixed right.

I agree it is very dangerous. I think the previous owner probably experienced the issue, JMO. The reason I think this is after a while I noticed down around the shifter the sheet metal has a small indentation where the shifter has been pushed forward into the sheet metal.

I am not sure what responsibility, if any, the dealer I purchased the tractor from would have in fixing the issue. The salesman said they would cover any repair costs 50% for a year, but my concern is whether they can fix the issue without messing something else up. I wish I at least had a clue what it was so I knew how much to expect for a repair bill.

 

[mljenkins]

Well, interesting enough today on the same hill (which I should add it has never done this before on this hill) I tried 3 times down the same hill at different engine speeds and never could reproduce the issue. One thing I was very careful about was keeping my leg away from the shifter. I'm starting to wonder if this is operator error. The only other explanation is that somehow I am not engaging the low gear good enough, or there is something odd at a certain point of engagement. I really think it has to be operator error. If that is the case, I think it would be prevented if the shifter would have been about 3 inches shorter. If I do find it is operator error, I'll probably end up cutting the top of the shifter rod off and rethreading it for the knob to go back on.

 

[trac]

How easy does the gear shift move when shifting between speeds when stopped?

 

[mljenkins]

Pretty easy. I mean it's not like pinky finger easy, but a simple hand movement will change the gears.

 

[trac]

We had a few tractors doing this when they first came out. Talked to the service department back then, and they felt by increasing the detent spring pressure, this would make shifting the range level alot stiffer. Seemed to work for the problems we had. I believe, I had to remove the left platform to get at the dentent plug. I'll look at a 390 in our yard to tell you which one it is. Trac

 

[mljenkins]

Thanks for the info. I went through my parts and service manual yesterday night when I got in from work and was trying to find which spring you were talking about. I couldn't see it in the pictures, but was pretty tired. Sounds like that could help. When you say left platform you mean the floor platform?