TCC line pressure (vs load) causes TCC slip

[MWD_CTSV]

I discovered this on my 2011 Yukon 6L80 awhile back and forgot to share it.
This is primarily TCC engaged in 5th gear (or possibly 6th) in the sub 2000 rpm range, with desired TCC slip of '0' (programmed not stock).

At low load, the TCC line pressure has a lower threshold, effectively the initial pressure offset or minimum effective pressure.
As load is increasing (positive derivative) the TCC line pressure ramps up as it anticipates higher load and is trying to get ahead.
However, at steady load, the TCC line pressure continually decays back to the minimum, which allows for slip to occur. It is almost as if there is a separate desired TCC slip factor which is occurring inside the PID loop, allowing for the pressure drop. In any case, as you can see a steady low rpm load like going up a steady incline will not hold the pressure very high above the minimum.

Keep in mind, there isn't a TCC line pressure sensor. The computer is only estimating the line pressure, but you can still see that it is trying to decrease the pressure. So the only way to compensate for this in a tune is to increase the offset pressure and/or the gain so that the minimum is high enough to maintain zero slip under high load low rpm.

 

[Geotrash]

View attachment 425749

I discovered this on my 2011 Yukon 6L80 awhile back and forgot to share it.
This is primarily TCC engaged in 5th gear (or possibly 6th) in the sub 2000 rpm range, with desired TCC slip of '0' (programmed not stock).

At low load, the TCC line pressure has a lower threshold, effectively the initial pressure offset or minimum effective pressure.
As load is increasing (positive derivative) the TCC line pressure ramps up as it anticipates higher load and is trying to get ahead.
However, at steady load, the TCC line pressure continually decays back to the minimum, which allows for slip to occur. It is almost as if there is a separate desired TCC slip factor which is occurring inside the PID loop, allowing for the pressure drop. In any case, as you can see a steady low rpm load like going up a steady incline will not hold the pressure very high above the minimum.

Keep in mind, there isn't a TCC line pressure sensor. The computer is only estimating the line pressure, but you can still see that it is trying to decrease the pressure. So the only way to compensate for this in a tune is to increase the offset pressure and/or the gain so that the minimum is high enough to maintain zero slip under high load low rpm.

Neat - thanks for sharing. Significant implications for towing as well, I suspect. I wonder if a TC with a stronger lockup clutch has an easier time maintaining its hold with the decaying line pressure.

 

[MWD_CTSV]

Neat - thanks for sharing. Significant implications for towing as well, I suspect. I wonder if a TC with a stronger lockup clutch has an easier time maintaining its hold with the decaying line pressure.

I am certain that the 2020 dual clutch is stronger (high torque holding) is a much better choice for towing. It should also work better at the same line pressure vs a single.

It seems that the factory clutch material has the highest coefficient of friction in the 2% or less slip range. The slip doesn't run away as the pressure drops, so in effect this has to be true.

 

[Marky Dissod]

I discovered this on my 2011 Yukon 6L80 awhile back and forgot to share it.
This is primarily TCC engaged in 5th gear (or possibly 6th) in the sub 2000 RpM range, with desired TCC slip of '0' (programmed not stock).

At low load, the TCC line pressure has a lower threshold, effectively the initial pressure offset or minimum effective pressure.
As load is increasing (positive derivative) the TCC line pressure ramps up as it anticipates higher load and is trying to get ahead.
However, at steady load, the TCC line pressure continually decays back to the minimum, which allows for slip to occur.
It is almost as if there is a separate desired TCC slip factor which is occurring inside the PID loop, allowing for the pressure drop.
In any case, as you can see a steady low RpM load like going up a steady incline will not hold the pressure very high above the minimum.

Keep in mind, there isn't a TCC line pressure sensor.
The computer is only estimating the line pressure, but you can still see that it is trying to decrease the pressure.

So the only way to compensate for this in a tune is to increase the offset pressure and/or the gain,
so that the minimum is high enough to maintain zero slip under high load low RpM.

This is another one of those posts where I wish that the 'Helpful Check Mark' was available;
'Love' is too imprecise.

This is yet another reason why those who have not yet gotten tuned missing out.

 

[mikez71]

This guy has some nice videos..

That video deals with the regulator offset, gain, apply ramp etc. He actually did tap into the valve body to get actual pressures.
BUT, what is discouraging, is he can't really tell a difference with most of the changes he makes! Sounds like the slip tables are the main method to reduce slip.

I've noticed our generation has the TCC unlock at higher throttle%/speeds, usually unlocking a couple mph before downshifting.
The newer 2015+ tunes have mostly one lock/unlock speed for the higher gears. It won't unlock before downshifting. I believe I like the feel of the 2015+ tcc, in that it stays "locked" versus unlocking and revving up.

I've got a fair amount of slip, but I have not zero'ed the tables. I plan to keep some slip. I tried the 2015+ slip values (TCC desired slip AC off)
No discernable difference. I also changed the torque axis to match the values of the 2015+. (0.00, 0.09, 36.88, etc)


Here's a snapshot of a log I took recently. cursor line is showing mid shift 4 to 5. I think that's why the slip flares a little there..

 

[Foggy]

I saw an article related to this topic
It stated that the actual OE clutch material "require" some slip to lubricate
it.. It's a wet style material..
I have set mine to Zero slip most of the time, but I have a stock core TQ built
with a larger aftermarket clutch... I don't really know for sure what it's made of,
but I suspect it's a diff material than OE
Maybe someone can confirm or deny ???

 

[mikez71]

@Foggy - Have you logged the slip and did you have to change any other settings?

@MWD_CTSV - I wonder if the "TCC desired pressure" map is affecting your lowered pressures? Might try turning off TCC adapts.
It appears to be off in the 2015 tahoe and 2018 silverado tunes. (By setting max speed below min speed)


Here's some changes compared to the 2018 silverado tune. shift times, inertia tables and closed throttle downshift.
The gray '7' cells were 8's and 9's in my stock 2012 tahoe tune.
The red shift time cells are that much slower compared to the 2018 silverado. The blue cells are that much faster compared to the '18 silverado.
TCC adapt settings at the right..

 

[Foggy]

@Foggy - Have you logged the slip and did you have to change any other settings?

@MWD_CTSV - I wonder if the "TCC desired pressure" map is affecting your lowered pressures? Might try turning off TCC adapts.
It appears to be off in the 2015 tahoe and 2018 silverado tunes. (By setting max speed below min speed)


Here's some changes compared to the 2018 silverado tune. shift times, inertia tables and closed throttle downshift.
The gray '7' cells were 8's and 9's in my stock 2012 tahoe tune.
The red shift time cells are that much slower compared to the 2018 silverado. The blue cells are that much faster compared to the '18 silverado.
TCC adapt settings at the right..

View attachment 425793

I did the basic changes with slip. And NO tcc in 1-3 gears.. only 4th over 44 mph.
5 & 6 gears... My shift tables are way UP in mph.. stock sucks.. I don't even command
6th until 64 mph...
I also have the circle D highest stage parts in mine and they recommend NOT changing
pressures, etc too much from stock as the parts already do it. (it was over 3K in just
hard parts, plus my converter)

I have not logged slip to any extent other than just watching it live at certain
times to make sure it is behaving the way I want..
The 2015 + years are a bit different than my 2014 operating system

 

[mikez71]

Yup, the 2015+ are different, and some values are very different..

Some are close enough I'm fairly confident they are used the same way. Some have the same values in cells despite the axis rpm value being different. It is minor scaling change instead of going to 6250 rpm, the 15+ seem to go to 6000 rpm in some maps. But I am considering the shift time decreases.

So far very happy changing to more of the 15+ shift maps. Definately need to dial in my 5,6 gears thanks for your points of reference!