HST Issue - Jerky Motion - SOLVED

[ROBERTL45]

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...

I have the same problem and the Intellipanel I think on my L45. Where can I learn how to get into the diagnostic mode on that panel? I just bought the tractor last week and after losing forward I'd let it sit overnight and I'd have forward for a little bit then lose it again. Now no forward at all and moves rearward with the pedal in the neutral detent. If I rotate the pedal forward to stop the rearward motion and then turn the key off it will surge rearward.

 

[ROBERTL45]

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

I assume since it is controlled by a pot on the HST pedal and I believe it has the intellipanel that it uses PVs I just don't know where they are. Waiting for parts and service manual to come in. Sounds like my L45 is the same setup as yours.

 

[ROBERTL45]

I have the same problem and the Intellipanel I think on my L45. Where can I learn how to get into the diagnostic mode on that panel? I just bought the tractor last week and after losing forward I'd let it sit overnight and I'd have forward for a little bit then lose it again. Now no forward at all and moves rearward with the pedal in the neutral detent. If I rotate the pedal forward to stop the rearward motion and then turn the key off it will surge rearward.

 

[200mph]

FYI...
RobertL45 and I spoke about his symptoms in detail via phone and text. After replacing both proportional valves his issues seems to be resolved.

It's frustrating there isn't a definitive diagnosis when these proportional valves go bad. Continuity tests on the coil can be within specs and no error codes present in the display. Internally the spool can move freely, but something goes wrong with them. I've yet to find time to dissect the proportional valve and coil, but it is on the agenda.