HST Issue - Jerky Motion - SOLVED

[ve9aa]

I don't know for certain how "fast" you need to see these changes in PWM (or intermittent electrical) , but if you can't afford an oscilloscope don't overlook the possibility of using a good ol' analog voltmeter (physical needle).

Anytime I am diagnosing a rapid intermittent in electrical ccts, I dig out one of my 30 or 40 year old biggie analog meters and can usually "see" what's happening much clearer than even my best Fluke digital multimeter can show.

YMMV

 

[mcmxi]

I hate to replace parts without identifying something wrong, but at this point I’m not certain what to do next ....

... but hate to spend approximately $500 just to try something.

Look forward to any suggestions someone might have. Thanks in advance!

All I can suggest is the possibility of paying a Kubota dealership for a couple of hours of diagnostic work. The local dealer charges $150/hour or thereabouts. Obviously the tractor isn't under warranty but perhaps they'll be able to point you in the right direction and you'll be able to fix the issue yourself if it's a case of swapping out parts.

It seems like you've put in a lot of work but are no closer to a resolution. Maybe it's time to get a second opinion.

 

[North Idaho Wolfman]

Look on the last page of your WSM and see if it matches this P/N:
9Y111-03693

 

[200mph]

Look on the last page of your WSM and see if it matches this P/N:
9Y111-03693

It's an older version based on the last four digits. Bought it a while back.

 

[rbargeron]

I think I have a theory about what's going on with the OP's L4740HSTC-3

In my L48's HST, the servo regulator establishes a "desired" position for the swashplate and the hydraulic piston moves it there. But Kubota's newer control features provide some independence of engine rpm, hydraulic attachment speed (a loader) and tractor travel speed. For that to happen there are provisions for electronic controls to enhance what in older designs were fixed relationships.

This excellent video from Neil at Messick's demonstrates several of the new HST features - specifically HDS (Hydraulic Dual Speed), which can be set in manual OR automatic mode in one of the Intellipanel's menus.

If I'm not mistaken, the OP's L4740HSTC-3 may be going into dual-speed, either by the left-side steering column lever or, if set to automatic, doing by itself in response to the apparent workload. If this system is acting up, unexpected speed changes could certainly result.

 

[ruger1980]

After reading that this model has what Kubota labels as Hydro Dual-Speed, which I am going to assume is a 2 speed motor in the hydrostatic transmission. This could definitely be is causing the complaint.
Can you duplicate the issue easily or is it very sporadic? Do you see any common theme on when and what is happening at the time the complaint occurs?

 

[200mph]

I think I have a theory about what's going on with the OP's L4740HSTC-3

In my L48's HST, the servo regulator establishes a "desired" position for the swashplate and the hydraulic piston moves it there. But Kubota's newer control features provide some independence of engine rpm, hydraulic attachment speed (a loader) and tractor travel speed. For that to happen there are provisions for electronic controls to enhance what in older designs were fixed relationships.

This excellent video from Neil at Messick's demonstrates several of the new HST features - specifically HDS (Hydraulic Dual Speed), which can be set in manual OR automatic mode in one of the Intellipanel's menus.

If I'm not mistaken, the OP's L4740HSTC-3 may be going into dual-speed, either by the left-side steering column lever or, if set to automatic, doing by itself in response to the apparent workload. If this system is acting up, unexpected speed changes could certainly result.

Just a statement: The L48 I believe uses the same proportional valves to establish "desired" position.

The only reason I don't suspect the dual range selector (electronic switch) is I would expect the Intellepanel display to alternate between turtle and hare icons like it does when operator selects hi/lo. When manually selecting hi/lo there is a noticeable delay compared to fast how the speed is changing.

Won't rule out the possibility something may be happening with this part of the circuit.

I'll watch the videos you suggested as they may aid in brainstorming. Maybe Neil can come to my house and explain firsthand. It would be a short trip.

Ruger: I have not been able to replicate the problem and it is random.

To those who may have contributed but didn't get a direct reply, I apologize, but I am reading everything and considering all.

 

[rbargeron]

" Just a statement: The L48 I believe uses the same proportional valves to establish "desired" position" The L48's HST regulator is quite different - no electronic controls at all. Its all mechanical linkage - even uses an external 2-way strut damper to prevent hydraulic shock from abrupt F-R shifts.

In his videos Neil seems like an involved and very lucid guy. If you called him and described the symptoms he might take an interest in it. Its a subtle enough problem that most dealers would simply start replacing whatever speed-control components now comprise the former all-mechanical servo regulator. But that would be no fun - and could really damage your checkbook. I'll bet Neil could get the attention of the factory rep to involve the design group - who might really understand how the symptoms line up with their design. Best luck, Dick B

 

[GBJeffOH]

I am hoping members can help with a situation I’m having with an L4740HSTC-3 tractor.

Issue: Ground speed can be very erratic and jerky while HST pedal held in constant position. It can act properly and then start acting up.

Background Info:

It doesn’t do it all the time, but it can act erratically when moving forward and may not respond to HST pedal input. I first noticed it in the summertime when mowing a very uneven trail. It almost felt like the tires were slipping and then catching in the dry grass. When snow blowing I was unable to maintain constant ground speed. Sometimes it becomes very jerky like moving the HST pedal very rapidly. It hasn’t gotten any worse, but there are times when it is OK. I don’t trust it when maneuvering close to something of value or that motion control can be assumed.

What I have done so far, but not necessarily in order.

• Verified fluid level OK (Super UDT2, about 120 hours on it with Kubota filters). Fluid is clean.
• Cut both HST and hydraulic filters apart and they were clean. Replaced with Kubota filters.
• No codes stored in the Intellipanel
• Checked HST Pedal sensor for dead spots while rotating. Checked 20+ times on multiple days just to be certain. Resistance changed as it should and never dropped out or spiked. Tested in both directions and both sides of the sensor. (One side increase with rotation and the other side decrease)
• Removed and reattached electrical connectors to most of the input sensors. Nothing looked corroded or was not fully attached.
• Checked sensor outputs and ranges in using diagnostic options in Intellipanel. Everything was in range. Even went through the resetting process of all sensors, just in case something got hammered in memory.
• Monitored sensor range while tractor was acting up. Inputs were all steady while ground speed was oscillating (jerky). I’m not convinced the values showing in the panel react fast enough to show dead spots. IE: Intellipanel responds too slowly to compared to sensor fluctuations.
• Since the servo sensor output was fluctuating around, I replace the sensor with new. It was a long shot, but it didn’t resolve the issue. Old sensor tested good during bench testing but thought something needed to tried.
• Inspected pressure relief valves – Looked brand new with no wear, scaring marks, broken springs, etc…
• Have NOT checked pressured as I don’t have gauges high enough or certain of the correct fitting(s).
• It acts up using Cruise Control, which leads me to believe the HST pedal sensor is not bad. Cruise and HST use same sensor but have not tried swapping them. (I’m 50/50 if I’m remembering this correctly)
• Removed Forward and Reverse Proportional valves today. I really thought one of these would be the problem based on how the tractor is behaving and expected to find the spool valves damaged or binding. Unfortunately, the spools will move using mechanical means. The valve does not appear to come apart. I tried removing the 24mm nut from the coil side, but that didn’t do anything to allow disassembly.
• F/R Proportional valve coils resistance valves value published in WSM.
• Tractor can act up when transmission is cold or warm.
• PTO, Steering, FEL and 3pt hydraulics working as they should.

I hate to replace parts without identifying something wrong, but at this point I’m not certain what to do next.

• Does anyone know what the input voltage is to the F/R Proportioning valves? I’d like to bench test while they are removed from the tractor. Want to verify they are stroking the same and returning home position with every cycle.
• How does the proportioning valve work to maintain constant ground speed? Does CPU provide constant voltage or is it pulsed off/on? I could not find any info in WSM on supply voltage or logic (steady on or pulsing).
• Can anyone confirm the correct threads for the pressure ports to test pressures? The WSM calls out 3/8 BPS, but it’s been known to be wrong. I assume BPS is British pipe threads. They look to be straight threads.

I have read a few threads about others with Grand L 40’s and 60’s loosing forward and reverse and replacing at least one of the proportion valves to solve the issue. But nobody stated if the valve passed or failed bench testing prior to replacing. Another user mentioned corrosion, but never stated where this corrosion was. I’m not certain how corrosion would impact the valve unless it was with the electrical connections. Mine are clean inside where the spool valve resides, but outside by the coil retaining nut (24mm) there was corrosion. Electrical connector looks clean. Given the electrical coil seems locked onto the valve, I’m not certain why the 24mm nut is needed.

Without any guidance from the community, I’m thinking about replacing the HST pedal sensor and one of the proportional valves, but hate to spend approximately $500 just to try something.

For reference:

HST sensor: TD170-52302 (servo position feedback sensor)
F/R Proportional Valves: TD170-59310
HST Pedal Sensor: TD160-32303 (Same p/n used on cruise control)

Look forward to any suggestions someone might have. Thanks in advance!

Does it do it while the cruise is on?

 

[200mph]

With respect to "Does it happen when cruise is on"

I'm not 100% certain, so reluctant to answer... I remember trying cruise lever when it acted up and thought that it continued to be jerky. But it was a while ago and perhaps I'm not remembering correctly. What's your thoughts if acting up with cruise engaged or not?

At one time I was able to video the dash display when acting up and it was moving forward (jerky) without HST or cruise being engaged. (Intent of video - hoping to see a flash of an error message or slight illumination of one of the system lights (hi/lo, pto, error message...)

I don't know when I'll be able to work on it again, but I did buy a HST pedal sensor. They are known to fail. Hated to buy, but wanted to try something, even if not backed by sound diagnostics with low probability of success.

 

[200mph]

Finally, some time to work on the tractor.

Installed the new HST Pedal Sensor.

Next step is to fine adjustment for the sensors following the procedure outlined in the manual. (See below)

Short story: Error 73 during step 1 of calibration process which is for swash plate sensor. Theses errors generally indicate a sensor is not in the correct initial position to allow fine adjustment (calibration) to occur.

No error codes are stored in memory. Mode "H"

Hypothesisizing only one servo proportional valve is working (reverse) and has caused the servo to move to a position not favorable to allow calibration to take place.

The manual does not indicate what to do if an error occurs during the calibration process.

Generally, these errors indicate the inputs (throttle, HST, HST Response, Cruise, etc...) are not in the correct initial position requiring user to do so, before proceeding.

Full Background:
In mode "K", Set cruise to off, HST Sensitivity to middle and HST Pedal to Neutral (no foot on pedal).
Step 1 All OK
Next step Cruise at max, Max Fast on HST Response Dial and HST fwd fully depressed After a few second all OK
Next step cruise off Max Slow on HST Response Dial and HST reverse fully depressed. Never got the approval to pass this step after many seconds (waited much longer than in the previous steps)

Shutoff and repeat steps this time it goes throught all the steps without issue.

Shutoff to exit calibration, restart and tractor wants to creep in reverse with no input to HST Pedal. Full FWD on HST pedal - nothing, Reverse works.

Shut off and try to mode K.

This time in step 1 of calibration process it is giving error 73 for swashplate sensor error.

Disconnect and reconnect electrical sensors several times in case bad connection at swash plate sensor and servo proportional solenoid valves (FWD and REV)

Repeat mode K with same results of error 73.

What is strange is that when I go into mode "H" to check for stored errors, all is OK - NO ERRORS present.

Enter mode "D" to clear codes anyway.

Repeat to Mode K and still have error 73.

I did remove the proportional valves prior to all this to see if something was stuck in the spool causing it to hang up. Both fwd and rev spools moved easily. Reinstalled on tractor.

I'm thinking 'only one proportional valve is working and has caused the servo to move into non-neutral position so now it can't start the calibration mode because it isn't in the correct position to start the test. Sensor is good or would store code. This sensor (swashplate) is new also and old sensor yields same result.

Thoughts????

 

[200mph]

Part II

Current State: Tractor moves rearward with no HST pedal input

Swapped the proportional valves: Tractor moves forward with no HST pedal input

Swap back to original position: Tractor moves rearward without HST pedal input.


Coils on the proportional valves read the same resistance. The WSM has no other information on how to diagnosis further. At least in my older copy.

All o-rings on the proportional valve look to be in good shape.

I'd love to disassemble the proportional valve, but don't understand how it is possible.

Guess I'll be buying a $300+ proportional valve this week. Fingers crossed it will resolve all issues.
1) Allow fine adjustment to take place in the CPU
2) Resolve the jerky motion

 

[Russell King]

It's an older version based on the last four digits. Bought it a while back.

I noticed that @North Idaho Wolfman asked what specific part number manual you have and that your answer was NOT specific in providing the information.

NIW probably has several manuals and would likely have read through them to find out if they have any information on how to resolve your issue. Please respond with your specific number manual and see if that can get his attention.

NIW or @whitetiger are the most likely candidates to have the latest version manual on how to diagnose the problem. You may want to contact them directly with a private message if they don’t respond to your thread

 

[Russell King]

I also think you asked about the pipe thread and mentioned BSP….but I can’t find that post now…

I would assume that that is straight pipe thread and requires a sealing washer and that 3/8 is just a size designation that has li to do with the physical size of the opening.

Straight thread is normally described by BSPP and there is a tapered version but on my old Kubota all have been straight threads for the ports into the tractor.

sorry if this isn’t relevant to the thread but I didn’t see any other reply to your question

 

[200mph]

Problem appears to be solved by replacing both Proportional servo valves for Forward and Reverse. Ran it for 10 minutes and it operated smoothly in forward and reverse.

This was very frustrating to diagnose as both coils read within specification and their spools moved freely. What can't be checked is how the electromagnetic coil moves the internal components of the spool valve.

One proportional valve had some corrosion on the 22mm nut, but this seems irrelevant at this point. I may try to take one of the valves apart to better understand why they failed. Disassembly of the valve will be destructive in nature.

Proof problem is solved will require longer run times, but at this point I'm feeling somewhat comfortable the problem is resolved.

For those who have the intellipanel, it's worth knowing how to navigate the various diagnostic screens. There is a good bit of information available.

Thanks to all who participated or followed along.

For those not familiar with the Grand L's 40's and 60's most operator inputs are by wire using potentiometers. Linkages for the most part don't exist for cruise, throttle, pedal, etc...

 

[Nicksacco]

I love a happy ending.
May the tractoring force be with you!

Personally I'd like to see the innards of that control valve if you care to post.

 

[200mph]

I plan on posting pictures, but it could be a while.

During this endeavor, never found any pictures posted on the web. Other than poor operation, there is no evidence they are not functioning as intended.

 

[ROBERTL45]

I plan on posting pictures, but it could be a while.

During this endeavor, never found any pictures posted on the web. Other than poor operation, there is no evidence they are not functioning as intended.

 

[ROBERTL45]

Please forgive me if my post is redundant or not applicable but I have an L45 that moves rearward with pedal in neutral detent position. If I rotate the pedal forwards the tractor will never move forward but will stop. While stopped if I turn key off it will lurch rearward. Any ideas?

 

[200mph]

If your tractor uses proportional valves to control movement, both proportional valves are needed to maintain Swashplate piston position (for forward and reverse speed). With only one PV functioning only one direction will be possible and unpredictable. So if first statement is true, it sounds like the PV is the issue.

If you swap valve positions, it will likely move in the opposite direction. In hindsight, I would recommend just buying both and moving on if you can afford the approximate $340/each. Keep in mind the new Grand L tractors use electronic controls and there are no linkages for HST control.

If your equipment has the ability enter diagnostic mode, it's possible to see the swashplate position output. I could see mine was at far end of travel when one of the PV died completely.

Hope this helps