L35 Harsh shifting GST

mpaavola · Nov 3, 2018

Good afternoon everyone. I have an 2004 L35 that when I shift gears it has a very fast and harsh engagement. The problem is most pronounced when I shift to 2nd then third then fourth. It gets better as I go up the gears. The problem seems to have come about when I changed from whatever hydraulic fluid the service company was using to the super UDT fluid. My understanding is there is an adjustment on the trans to change the speed of engagement. If so I have not found it yet. Does anyone know where on the trans this adjustment might be or can direct me to the service manual that will have this info. I don't have a problem buying the manual if I need it but I don't know which one is appropriate. Any help will be appreciated.

Thanks
Mark

rbargeron · Nov 4, 2018

The L35's GST is a gear-type with hydraulic actuators to do the shifting. Travel is by hydraulic clutch pack. When a gear is selected, shifting gears and re-applying the clutch are automatic. There are two general designs so getting the manual for your specific tractor is best.

Testing and troubleshooting GST function involves measuring pressures at several points on the unit's left side. GST units include a modulating valve that softens clutch engagement by timing the clutch pack pressure rise after the gear is engaged. The WSM describes various operating conditions, and shows the orifice in the modulating valve. The WSM I have covers the early model GST but doesn't get into how to adjust the shifting.

Changing to a lower-viscosity oil might affect shifting, and/or the clutch pack could be getting grabby. The later-version GST's are specifically designed to shift quickly in the upper gears - maybe yours is shifting in the fast mode all the time? Sorry I don't have a direct answer.

There is some general info in this TBN thread. Search for more here and on OTT. At OTT North Idaho Wolfman knows the GST. Good luck, Dick B

mpaavola · Nov 5, 2018

Dick, Thanks for the help. This will give me a good starting point to start troubleshooting the issue. Does anybody know which particular service manual will show me the GST transmission troubleshooting?

Thanks
Mark

rbargeron · Nov 6, 2018

Mark - See my reply about GST variations at your other thread on OTT. Lots of good help available there too - tech questions often show up in both places.

mpaavola · Dec 18, 2018

Here is where I am at in the troubleshooting process. I have also posted on the other forum to cast a wider net.
I checked all the pressures and here are the results.

Original Adjusted
Relief Valve 410 425
GST Press 330 365
Pilot 360 N/A
Clutch Pack 365 N/A

The numbers above do not line up but the first number is the original and the second number is the adjusted. Pilot and clutch pack did not need adjustment.

So all of the pressures are normal but no change in operation. I did not expect any but I needed to check for a baseline. I now belief it is an issue with the Modulate valve and/or the accumulator valve. I took a look inside the modulate valve but there didn't appear to be any adjustments.
There is a graph in the manual that shows the operation of the circuits based on time but it does not provide any time values So I cannot see if the rate of engagement is correct.
So at this point of time I am going to replace the springs in the modulate valve and the accumulator unless anyone has any better ideas.

mpaavola · Dec 27, 2018

Well based on the lack of responses I am going to guess that nobody is a wizard with the inner workings of the GST transmission. I will try some things and get back to everyone if I find a solution.

David_Kb7uns · Dec 27, 2018

Have a L3130 GST controlled with a ECU, always use Super UDT but there is a setting in the Intellipanel for the lockup time on the hydraullic clutch pack solenoid and it will pulse it to make locking up smoother. Not sure how they did it before.

David

mpaavola · Dec 28, 2018

David, If it was only that easy. On the earlier models there are not any computers. It is all hydraulics and various mechanical adjustments.

rScotty · Dec 29, 2018

mpaavola said:
David, If it was only that easy. On the earlier models there are not any computers. It is all hydraulics and various mechanical adjustments.

Just wanted to let you know that I'm following along on this. I find the hydraulic GST and shuttle type transmissions interesting and like to hear about them.
rScotty