Transmission line pressure

Kind · Mar 23, 2016

I've been fighting shifting issues and didn't know why. I've been adjusting shift firmness tables but it only helped so much... It still never helped engaging the gears, predominantly the 3-4 shift. Anything over 30% throttle and it would just flair and never engage unless I let off.

I have always been hesitant to adjust the line pressure tables because I had read that the shift firmness tables is what would help most and also read not to mess with the line pressure tables to much. But after seeing the maximum commanded pressure under the values tab set to 375 I figured I had room to tinker as the stock H&S trans tune was only commanding a little over 200 at full throttle. I asked Forrest what he sets his too and then felt more comfortable messing with the line pressures.

I initially bumped all the gears up 20%. Noticed it helped... So I did the only reasonable thing to do, add more. I've always been a fan of how the old Spa*tan 6.4 files shifted and was looking more for that, especially with the way this truck builds power. I added another 20% on top of the 20% I already added and that was much better.

So far I'm a lot happier with how it goes through the gears crisply and confidently. The roads up here are still very cold and slick so I haven't pushed to hard yet but it seems like these setting will work very well for me.

Stock H&S line pressure tables

My 40% increase tables

ckrueg · Jun 17, 2016

Kind said:
I've been fighting shifting issues and didn't know why. I've been adjusting shift firmness tables but it only helped so much... It still never helped engaging the gears, predominantly the 3-4 shift. Anything over 30% throttle and it would just flair and never engage unless I let off.

I have always been hesitant to adjust the line pressure tables because I had read that the shift firmness tables is what would help most and also read not to mess with the line pressure tables to much. But after seeing the maximum commanded pressure under the values tab set to 375 I figured I had room to tinker as the stock H&S trans tune was only commanding a little over 200 at full throttle. I asked Forrest what he sets his too and then felt more comfortable messing with the line pressures.

I initially bumped all the gears up 20%. Noticed it helped... So I did the only reasonable thing to do, add more. I've always been a fan of how the old Spa*tan 6.4 files shifted and was looking more for that, especially with the way this truck builds power. I added another 20% on top of the 20% I already added and that was much better.

So far I'm a lot happier with how it goes through the gears crisply and confidently. The roads up here are still very cold and slick so I haven't pushed to hard yet but it seems like these setting will work very well for me.

Stock H&S line pressure tables

My 40% increase tables

Do you know at all what the y axis values are referring to? One looks like it goes from -200 to 650 and the rest all go to 5900. I know they're supposedly torque values but where does the tcm get them from?

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Kind · Jun 17, 2016

ckrueg said:
Do you know at all what the y axis values are referring to? One looks like it goes from -200 to 650 and the rest all go to 5900. I know they're supposedly torque values but where does the tcm get them from?

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No I don't know.

ckrueg · Jun 17, 2016

Hmm I've been trying to figure out what those are. I did find a table in the engine file called estimated torque before tcm intervention and another one estimated torque with tcm intervention. They're based on comamded driver torque and boost pressure. I'm guessing that's the torque value used by the tcm to set line pressure, but I'm gonna test this weekend to try and find out.

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Kind · Jun 17, 2016

I'm curious now. Let us know how it works out for ya!

ckrueg · Jun 17, 2016

Kind said:
I'm curious now. Let us know how it works out for ya!

Will do, I'm working on changing it now

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ckrueg · Jun 23, 2016

well I changed the 2 tables in the engine file that I mentioned before and changed up my line pressure tables to keep the pressure similar to my previous tune. Now it seems like the torque values used by the line pressure tables are indeed the ones from the tables I changed in the engine file. Definitely makes adjusting pressure easier when I know what throttle position and rpms I am adjusting it at.

drunk on diesel · Jun 23, 2016

Great info

Kind · Jun 24, 2016

ckrueg said:
well I changed the 2 tables in the engine file that I mentioned before and changed up my line pressure tables to keep the pressure similar to my previous tune. Now it seems like the torque values used by the line pressure tables are indeed the ones from the tables I changed in the engine file. Definitely makes adjusting pressure easier when I know what throttle position and rpms I am adjusting it at.

How did you go about changing the tables in the engine file? What values did you change to what?

ckrueg · Jun 24, 2016

These are the two tables I changed in the engine file. They are basically the same values. I just changed them to a be more consistent with the engine torque.

I changed all my line pressure tables to be similar to this. Lowest pressure at zero torque and going up for negative torque which is in cases of engine braking. According the the previous tables I changed. Also most of the line pressure tables have bogus torque values but I just overlay the other tables with the 1-2 shift table and assume they should have been the same

This is what the stock and h&s base files had. My table is the first picture.

Also I changed this table in the transmission tune. The previous values were really odd. Not sure if this table did anything but I figured I change it to be smoother and go up similar to the pedal to torque table with 1020 being 100 percent pedal position.