NX55 HST Jerky Transmission at Low Speed

[TN8Man]

Anyone have an issue like this?

While using my PTO stump grinder in low gear where I need to be able to move slowly the transmission is jerky.

 

[seville009]

Check the hydraulic fluid level

 

[TN8Man]

I did, it is within range.

 

[MinnesotaEric]

I have that issue and it goes away as the fluid heats up. Im thinking it is some
Pressure regulating issue—maybe even a dirty hydro filter (as my machine is very close to the servicing time of the hydraulics and transmission).

 

[TN8Man]

I agree it might be a hydro flow issue. I just changed both hydro filters about 30 hours ago so I think I'm good filter wise. I did notice a lag in pedal to movement where it seems I have to press the pedal further to get the tractor to move.

 

[DieselBound]

I'm sure you've already checked, but make sure you don't have any hydraulics dead-heading. Usually one can hear this happening.

 

[Eagle1]

Check for play in the linkage between petals and actual swash plate. On my LS the heim joints like to come loose.

 

[dusty3030]

Check for play in the linkage between petals and actual swash plate. On my LS the heim joints like to come loose.

Fly by wire, no linkage on OP's tractor.

My NX can be jerky as hell usually on medium range pedal to the floor and it's when the fluid has warmed up. I can set cruise and it stops and travels smoothly. I've figured out a bunch on my tractor but not this one yet.

 

[TN8Man]

Fly by wire, no linkage on OP's tractor.

My NX can be jerky as hell usually on medium range pedal to the floor and it's when the fluid has warmed up. I can set cruise and it stops and travels smoothly. I've figured out a bunch on my tractor but not this one yet.

I have also (in the past) experienced jerky response after several hours cutting grass on a hot day on my hilly property. When I got out of the cab I could feel the heat radiating from under the tractor. So this experience is possibly linked to hot fluid. After the tractor cools down some it runs fine. If I'm not running the PTO on hilly terrain it run's fine all day long. I changed the method I mow which seems to help. I now mow in low gear and the pattern is strictly straight up/down the hillside where I would mow horizontal before in medium gear.

The problem I have now is jerky movement while creeping forward in low gear with the PTO stump grinder running. This occurred on the first stump on flat ground so I don't think the fluid temp is a factor.

 

[MinnesotaEric]

Cross posted from a different forum:

Back in June of this year I had issues with my 2014 NX4510HST. It has 900 hours on it now. Regardless of the gear that I was in it showed L in all 3 speeds. The N worked in neutral. I took apart every connector on my tractor and plugged them back in. I looked for branches stuck up under the tractor. There were none to be found. The Calibration light was on and my tractor did not move. It took many times of running the calibration sequence before it finally took and I had my tractor moving again. This happened again on Saturday to me. This time the H light was lit in all positions including the nuetral. After many times of reseting the calibration sequence I was up and running again for a short period of time. I must have run that program 40 times yesterday to get my work done. Now I have a flashing Cal. light. The tractor will run in this mode but is very jerky to start off. Anyone have any ideas on this before I bring it to the dealer. I also should mention that while the H light is on I also have a dim L light on and no N light in nuetral. To start my tractor I have to jump the solenoid.

I also have a 2014, a very early NX6010 HST with a cab. My machine has 775ish hours and is approaching the 800 hour service. When cold it has frequently surged on the transmission but the issue immediately cleared itself up or I traveled slow enough so as to not trigger the issue until there was a tiny bit of heat in the trans/hydro oil at which point the issue always cleared itself up. This late summer, the issue became stupid. The HST surges in all ranges sometimes with the CEL flashing and sometime not until the trans/hydro oil is fully warmed up. It acts like the charging pump is trying to go out, but then works fine.

I brought the tractor back to my level 2 trauma center to lift my side by side that I need to weld on. Checking the hydro fluid when cold, the dipstick said it was low. But then fluid came pouring out moments later. The next day the dipstick again said low, but with the dipstick out, the build level came back up to full. I'm hoping my issue is something really stupid, so I popped off the trans breather (the candy cane looking thing to the left of the remote valve stack on the back of the tractor) and although it appeared to not be clogged, I blew out a big chunk of cogging whatever it was. I kind of doubt case vacuum or pressure is the cause, but malfunctioning breather can do all kinds of weird things in other transmissions. I haven't bothered firing up my tractor to see if clearing the breather helped or not as I'm waiting for my wireless microphone to charge up (YouTube stuff).

Since I'm orphaned without a dealer who knows about NX's, I put in a call to a long established dealer in TN to learn if there are any updates or software flashes I've missed out on as well as if updates can be applied by sending off the ECU rather than the entire tractor or if the mothership could add any color to our HST surging problem.

As I understand it the newer NXes had a battery ground strap between the trans hand the frame issue and there are two different transmission programs floating around.

EDIT: jumping the solenoid wise, be sure your midpoint PTO isn't on. It has happened to me twice. Also, I think your gear position switch is shorting out on itself.

 

[TN8Man]

Fly by wire, no linkage on OP's tractor.

My NX can be jerky as hell usually on medium range pedal to the floor and it's when the fluid has warmed up. I can set cruise and it stops and travels smoothly. I've figured out a bunch on my tractor but not this one yet.

My jerky motion also only seems to occur when the hydro fluid is hot. Normally the hydro fluid only gets that hot when I'm using the PTO for an extended period of time.

In my manual section 4.7 HST CONTROL SYSTEM (HST MODEL) it shows a oil temp sensor. I want to find out how to get the transmission oil temp sensor data to a dash mount readout.

Anyone have any ideas?

 

[MinnesotaEric]

Locate the sensor. If a single wire, it works by grounding and you can tab a temp gauge into it.

 

[TN8Man]

I'm going to look for it but the diagram shows a iron core inductor symbol instead of the usual resistor type temp sensor. I did a internet search for a Kioti oil temp sensor part but can't find anything.

 

[MinnesotaEric]

I'm going to look for it but the diagram shows a iron core inductor symbol instead of the usual resistor type temp sensor. I did a internet search for a Kioti oil temp sensor part but can't find anything.

If it is a two-wire, then one wire is the signal, and the other wire is the reference voltage. You want to tap into the signal which will be a lower voltage than the reference voltage. Reference voltage comes out of the ECU, and is modified by the sensor. The reference voltage may be battery volage, maybe 12v or something less.

 

[justman777]

I've experienced both trans surging, and the jerkiness the OP mentioned. For surging, it's always with the forward pedal depressed almost to the floor. Seems like there's a "sweet" spot that causes it to switch between surging and not surging. For jerkiness, it's always when I depress the reverse pedal just a bit, usually backing up to an implement. I theorized the potentiometers in the pedals were sending "odd" or intermittent voltages to the TCU, causing the surging or jerkiness. It made sense to me, because the surging happens very near the high end range of the forward pedal, and the jerkiness happens at very near the low end range of the reverse pedal. It'd be interesting to probe the wires to see what the voltages look like across the range of the pedal movement, because they should be pretty linear across the entire range. If the voltages increase linerally, and then at some point increases (or decrease, depending on how the potentiometer works) abrubtly, that would cause the TCU to surge. If the voltage is intermittent (on/off), that could cause the TCU to turn on and off and subsequently cause the trans to jerk. Of course, it could also be the programming in the TCU that commands a sudden power increase (surging) For instance, a reference voltage of 2 volts (notional) is your "stopped" setting for the TCU. As you depress the pedal, the voltage gradully increases from the pedal potentiometer, causing a commensurate power setting in the TCU. At some point, however, the TCU programming interprets a particular voltage from the potentiometer at around 90% of pedal travel to actually be the 100% power setting, causing the trans to surge. All this is theory though. I'm away from my tractor right now, and don't really have a means to test.

 

[Eat Your Veggies]

Anyone have an issue like this?

While using my PTO stump grinder in low gear where I need to be able to move slowly the transmission is jerky.

It might not be the same issue, but have you had the dealer do the NX update that came available in May (I think) of this year? The dealership in my area had a “stop sale” order for the recent in-stock NX series from 2020 forward pending release of the update. It was due to operational issues much like you describe.

Specific details are sketchy, but from chatting with my dealer, it involved several new grounding straps and a software tweak. Supposedly, this fix applied to the NX series a fair bit older than my 2020.

 

[justman777]

It might not be the same issue, but have you had the dealer do the NX update that came available in May (I think) of this year? The dealership in my area had a “stop sale” order for the recent in-stock NX series from 2020 forward pending release of the update. It was due to operational issues much like you describe.

Specific details are sketchy, but from chatting with my dealer, it involved several new grounding straps and a software tweak. Supposedly, this fix applied to the NX series a fair bit older than my 2020.

Did your dealer happen to mention an update number or reference source? It'd be sweet if a software update and a few grounding straps fixed the issue(s).

 

[TN8Man]

Thanks for the info!
I have not had my tractor in the shop this year, I do my own regular maintenance. I'll have to call the shop about this. I bought my tractor new in mid 2019.

 

[Eat Your Veggies]

Did your dealer happen to mention an update number or reference source? It'd be sweet if a software update and a few grounding straps fixed the issue(s).

Not that I recall, but I’ll contact them for a reference and post it here. I’ve only put 30 hours on the tractor - mostly moving snow- but have had none of the heretofore mentioned transmission issues so far.

 

[Eat Your Veggies]

I emailed my dealer for the info regarding the issue. Heres their reply:

“The Stop Sale Bulletin is DOCUMENT NUMBER: US/CA-020922 and the Mandatory Service Bulletin is DOCUMENT NUMBER: MSB050322UC. If the dealer recently got the tractor, Kioti would have taken care of it already. If it was a tractor received at the dealership before February 2022, then it might potentially still be affected, but I'm sure most, if not all, of the affected units have been repaired and sold.”

There were delays getting the parts necessary for the fix, so I had to wait longer than anticipated. The speculation for the delay was that Kioti prioritized issuing the kit to dealers for ‘recall’ tractors already sold and in use before sending it to Stop Sale units. In retrospect, the delay could have been supply chain or other reasons.

It doesn’t seem like there are many significant changes from year to year in most Kioti models. If I had an NX that was less than 5-6 years old AND had jerky transmission or other quirks, I’d contact my dealer.