L39TLB Auto-Shifting Transmission

MikeinDewey

New member

Equipment
L39 TLB
Mar 19, 2016
10
0
1
Dewey, AZ
The GST transmission on my L39 suddenly started to auto-shift; that is, when placed in most any gear it suddenly decides to rapidly bounce around to plus or minus the selected gear, displaying the gear changes on the display panel and confusing the drivetrain (and the driver). Is there an intelligent path for troubleshooting this problem or knowing guesses as to the obvious cause? The tractor has just over 800 hours and the transmission fluid and filters were replaced roughly 30 hours ago. All other hydraulics work just fine. Previously, 1st and second gear would occasionally disappear but 3rd seemed to have become 1st, but the cause (hot or cold, forward or reverse, 2WD or 4WD) was not consistent and I simply worked around the annoyance. This escalation of what I assume to be part of the same problem is a little harder to ignore.
 

MikeinDewey

New member

Equipment
L39 TLB
Mar 19, 2016
10
0
1
Dewey, AZ
I took out the GST Lever Sensor and found some corrosion on the electrical pins. Also, the cable connector seemed to be loose. After cleaning the pins and using some electrical tape to secure the connector to the Sensor, the auto-shifting seems to have been cured. Occasionally loosing 1st and 2nd gear, with 3rd seemingly becoming 1st (or 2nd) is still an issue, for another day. Also, I don't often use gears 7-12, but just noticed that when I do, there's a pause and then a kick into gear that makes me think that I should be wearing chaps and a cowboy hat. If anyone happens to have an idea for dealing with either of those two issues, it'd be appreciated. I did go through the WSM and found squat and also went through the Electronic Instrument Panel diagnostics and found all the settings to be nominal with no stored error codes.