Is it possible to rebuild a HST damper?

[oldnslo]

An HST will shift towards neutral by design but typically will return completely to neutral without some external centering device.

On your tractor the blue spring package is meant to return to neutral and the orange damper controls how fast it returns to neutral. They work in conjunction with each other.

Can you measure the blue spring package to insure that is returning to the same length repeatedly from both directions of movement. Not sure what tolerance of repeatability is acceptable but doubt more than plus or minus 1/32 inch

 

[4lane]

An HST will shift towards neutral by design but typically will return completely to neutral without some external centering device.

On your tractor the blue spring package is meant to return to neutral and the orange damper controls how fast it returns to neutral. They work in conjunction with each other.

Can you measure the blue spring package to insure that is returning to the same length repeatedly from both directions of movement. Not sure what tolerance of repeatability is acceptable but doubt more than plus or minus 1/32 inch

I do not think I can accurately measure the blue spring dampers return length. Now that I have had a closer look, I should go back to the original plan of seeing if the HST brings it to neutral without either the orange or blue damper, or both. I would be interested to see if the HST brings it to neutral or not to even see if one of these is the culprit or not.

 

[s219]

Be careful, it may return to neutral abruptly and violently without the dampers hooked up. So put it in low gear and don't go too fast.

 

[4lane]

An HST will shift towards neutral by design but typically will return completely to neutral without some external centering device.

On your tractor the blue spring package is meant to return to neutral and the orange damper controls how fast it returns to neutral. They work in conjunction with each other.

Can you measure the blue spring package to insure that is returning to the same length repeatedly from both directions of movement. Not sure what tolerance of repeatability is acceptable but doubt more than plus or minus 1/32 inch

So I had some time to do my tests and here is what I found:

1. Both Blue centering spring and orange damper removed:
The HST does not return to center in any way. Press forward and it just stays there. Press reverse and it stays there there. Because there is absolutely no feeling the HST has any responsibility for returning to center I am assuming this is the design. When the transmission is engaged more, such as going up a hill the pedal is more firmly in the fwd position and it takes more effort to push it back to neutral than when unloaded as in on a flat. This is consistent with the experience when everything is hooked up - snaps back to neutral on flat but creeps when going uphill like the damper is not strong enough to pull it back to center.

2. With Blue centering spring removed but with orange damper attached:
If you put the pedal to reverse and release the damper pushes the pedal to the forward position. This seems odd. Since the pedal just flops fwd/reverse when there is no damper I would expect the damper to just keep the pedal at whatever position you put it in and just gives the pedal some resistance when doing so. I found this odd and potentially wrong.

I am still leaning toward the orange damper being weak and needing replacement. Especially since the HST provides zero return to center action.The only strange thing is when the transmission is under load so the pedal needs stronger effort to get it back to neutral. I do not see how the system of the blue centering spring and orange damper work together to handle this situation. Unless the damper pulls harder when fully compressed/extended and is progressive in that way...

 

[oldnslo]

So I had some time to do my tests and here is what I found:

1. Both Blue centering spring and orange damper removed:
The HST does not return to center in any way. Press forward and it just stays there. Press reverse and it stays there there. Because there is absolutely no feeling the HST has any responsibility for returning to center I am assuming this is the design. When the transmission is engaged more, such as going up a hill the pedal is more firmly in the fwd position and it takes more effort to push it back to neutral than when unloaded as in on a flat. This is consistent with the experience when everything is hooked up - snaps back to neutral on flat but creeps when going uphill like the damper is not strong enough to pull it back to center.

2. With Blue centering spring removed but with orange damper attached:
If you put the pedal to reverse and release the damper pushes the pedal to the forward position. This seems odd. Since the pedal just flops fwd/reverse when there is no damper I would expect the damper to just keep the pedal at whatever position you put it in and just gives the pedal some resistance when doing so. I found this odd and potentially wrong.

I am still leaning toward the orange damper being weak and needing replacement. Especially since the HST provides zero return to center action.The only strange thing is when the transmission is under load so the pedal needs stronger effort to get it back to neutral. I do not see how the system of the blue centering spring and orange damper work together to handle this situation. Unless the damper pulls harder when fully compressed/extended and is progressive in that way...

4lane,
not questioning your results but this does not sound like a typical HST control system. By best guess is that Kioti has some form of control linkage that reduces the tendency for HST to return to neutral. I know my Branson and BX Kubota both required more pedal effort to drive under load. If fact my BX 1850 was one of the models that stopped to suddenly.

wish you the best in resolving this problem.

 

[4lane]

4lane,
not questioning your results but this does not sound like a typical HST control system. By best guess is that Kioti has some form of control linkage that reduces the tendency for HST to return to neutral. I know my Branson and BX Kubota both required more pedal effort to drive under load. If fact my BX 1850 was one of the models that stopped to suddenly.

wish you the best in resolving this problem.

I did email with a Kioti dealer and got a good response (see below). Still nothing to direct me toward but helpful in eliminating the HST from the equation. That leaves me back to my tests where I added a third test and was able to stop the creep by removing the orange damper but keeping the blue centering spring attached.

3. Removed the orange damper, but kept the blue centering spring attached:
Snaps back to neutral on flat ground. On a hill, it takes a few seconds for it to pull it out of it "loaded" state, as the pedal is slowly pulled from this position to center. If you take your foot off from full fwrd, you can watch the pedal slowly return to center. It does not do this quick enough (4sec), but once it does, it's in neutral, and does not creep. This seemed like a good sign.

It's like the centering spring is not strong enough to overcome the damper. I would jump at rebuilding the centering spring by replacing the springs but you can't just buy the springs, unlike what the parts breakdown suggests. So...still grasping at straws here.


<---- Kioti dealer ---->

"As hst tractors get older this Creep becomes something that most customers live with. We find a laundry list of things that can contribute to creep. Most likely is not the hst system as it is a swash plate and does not have effect on centering. Most often we find linkage issues, like worn parts and bushings are the cause. Dempers and spring issues are not unheard of and the hst lever bolt on connection at the swash plate shaft is also common. It could be spring tension related also. Lastly yes the resistance of the pistons in the swash plate area (or lack of ) in an older unit could in theory contribute to a limited amount of stiffness to this system."