2018 8 Speed Truck - Shift Pressure Question - Normal or Bug?

[WS6FirebirdTA00]

I was looking through some shift pressure tables and noted several did not have similar rows while others did.

I am curious why some are the same and others are different. Mainly, I want to ensure that was right and not some sort of bug.

2nd, 4th and 7th were all the same "issue".

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Thanks

[WS6FirebirdTA00]

Just saw 5th gear was the same way.

My concern is I have not seen this in other calibration and want to make sure I should keep it this way.

[WS6FirebirdTA00]

FYI - support responded this is correct in the calibration

[cmitchell17a]

I really wish we could explain the reason why some tables are different in some place and the same in others and the other weird things in stock tunes. I'm guessing GM maybe didn't have the luxury of programming these tables with a nice graphical interface with nice smoothing tools, then again I don't see why they wouldn't. Some things you see in the stock tunes completely go against all logic. I also really believe a lot of these tables don't really do anything, and we are just effected by the placebo effect.

Also what operating system is your TCM on your truck? I just unlocked my TCM on my 17 camaro but I couldn't read out the stock tune and had to overwrite with a downloaded TCM tune and its missing a lot of parameters vs a 2017 TCM truck tune im looking at.

[DGS]

I wouldn't compare a Camaro trans tune with a Truck even though the transmissions/gear ratios may be the same. They can have different RPO's (M5U/M5X, MQE) . Their are different torque converters, Gross Vehicle Weights, and Gross Vehicle Weight Ratings for these vehicles. Truck have tow haul modes that passenger vehicles don't. Trucks can have AWD/4WD and limited passenger vehicles are AWD not ever including Camaro. All of these change torque requirements, ratings and pressures. Even some of the clutch disc counts are different giving them different torque ratings. These transmissions are GM/Ford joint venture. Like you stated, some of the weird values are probably never utilized. Possibly they are markers for hidden tables that we don't have access to.

[WS6FirebirdTA00]

My OS is 24291279, for a 2018 Sierra 8 speed.

Why I am concerned a little here is I have never seen the tables like that before in any tune. Granted, I haven't seen a lot of the new stuff, but still.

The 2017 truck I downloaded from the repository (24281243) has the tables I would expect to see. There is a lot different between the two, maybe the newer one is the update to deal with some of the concerns in previous models?

Either way, it looks weird how 2,4,5,7 are set up. There must be something internal to the transmission that would require this. That, or like some other tables there are weird steps that need to be corrected. I don't want to change it because I really don't know a lot about autos.

There are also some other tables I feel are missing. Granted, it is a 2018 so they may come in time.

[DGS]

There are cal updates to the 2018"s. Depending on what is in the repository, it may lack the updates. Send me your VIN and I can probably pull the current cals listed for it. I also send you the latest fluid flush with new fluid p/n bulletin published January 2019.

[WS6FirebirdTA00]

Sending you a PM

[DGS]

You should have both by now. Good luck.

[fifty]

Is that the new j-62120 atf fluid? I have he 8l90 in a 2015 Yukon and a 8l45 in my Colorado. Thebyukon has all of the issues, shuddering and 1st gear downshift clunk. I only have 20k on the clock but the Yukon is out of warranty so I want to flush the trans myself to see if the new fluid helps the shuddering at least.

It’s definitly got to be a tune issue since both transmissions share the same problems. My 8L45 has minor shuddering that got better with tuning, but it still has a hiccup when slowly coasting and then getting back on the gas. Like a clutch slipping.

I’m going to see if I can post the tsb for folks to read. I’m having a heck of a time trying to load it...

[WS6FirebirdTA00]

It is the M1 HP ATF. Not sure the J number

[chameleon]

Is that the new j-62120 atf fluid? I have he 8l90 in a 2015 Yukon and a 8l45 in my Colorado. Thebyukon has all of the issues, shuddering and 1st gear downshift clunk. I only have 20k on the clock but the Yukon is out of warranty so I want to flush the trans myself to see if the new fluid helps the shuddering at least.

It’s definitly got to be a tune issue since both transmissions share the same problems. My 8L45 has minor shuddering that got better with tuning, but it still has a hiccup when slowly coasting and then getting back on the gas. Like a clutch slipping.

I’m going to see if I can post the tsb for folks to read. I’m having a heck of a time trying to load it...

I too have a 2015 yukon but with 60k, we are not out of warranty, 2015 models are 100k and 6years or something (i looked it up) so your still covered bud.

[WS6FirebirdTA00]

Good point, I thought the drivetrains were like 60k/5yr or something like that

[cmitchell17a]

These transmissions are GM/Ford joint venture. Like you stated, some of the weird values are probably never utilized. Possibly they are markers for hidden tables that we don't have access to.

What do you mean by "markers", and yes I agree HP Tuners did the best they could to go through the code and give us the tables they thought were relevant and had the most control, however, I'm sure a lot of the stuff we need for good drivability is buried way down somewhere else.

[DGS]

Mobil 1 Synthetic LV ATF HP

19417577 (US)

20 qts flush