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!

 

[LSCALADE]

Here is a response from Chat GPT, I was hunting 6th gear shudder similar to the original post.

What that offset actually does​

• Offset is the baseline clamp once the TCC is in an apply state.
• The final commanded apply pressure is bounded by your Max TCC Pressure and your Desired Pressure (5672) lookup, then shaped by Gain and the Apply Ramp.
• So even if Offset is 90 psi, you’re still capped by Max (we set ~128–130 psi). You’re not forcing unlimited pressure.

When higher offset helps​

• Stock style (~26 psi offset, ~1.5 gain) is soft and reactive → it can hunt around 0 slip at light load.
• Raising Offset to ~88–90 psi gives a steady clamp so slip decays smoothly; lowering Gain to ~0.80 prevents “snap-lock.” This is exactly what quiets 6th-gear shudder.

When problems could occur​

If any of these are true, back it down a bit:

• Harsh/bangy applies at low RPM or on small grades → drop Gain to 0.75 first; if needed, lower Offset to ~85 psi.
• Converter already damaged/glazed → pressure can’t “fix” it; it may shudder regardless.
• Over-aggressive maps (Apply-Ramp right side maxed, very early 6th-gear lock) → you’ll feel lugging; ease those tables or delay 6th lock.
• Duty/pressure pegged but slip remains → indicates hardware leak/wear; don’t keep cranking pressure.

A cautious, stepwise approach​

1. Set Offset 85–90 psi, Gain 0.80, Max 128–130 psi.
2. Keep our balanced Apply Ramp (small left of 0, progressive right to ~90–100).
3. Use the scaled 5672 table we built (cruise band +30%, cap ≈ 6.5 psi).
4. Road-test and log: TCC Slip, Desired Slip, TCC Duty/Pressure, Line Pressure, Gear, TPS, RPM, TFT.
   • Target 0 to ±5 rpm slip at steady cruise.
   • Duty shouldn’t live >90% to hold lock; if it does, add a little desired pressure in the cruise band or +5 psi offset.
   • If applies feel sharp, reduce Gain to 0.75 or trim the +80…+200-rpm cells in Apply-Ramp ~10%.

Bottom line​

Within the 85–90 psi offset / 0.75–0.85 gain / ≤130 psi max window and with sensible tables, you’re in the range many tuners use precisely to eliminate shudder and cut heat. That’s more likely to extend converter life than harm it. If anything feels harsh in your truck, take one click off Gain or Offset and re-test.

 

[LSCALADE]

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.

Here is a simple answer from AI by pasting your graph and asking for corrections.

• Orange (TCC slip) spikes to ~10–30 rpm as engine load climbs and line pressure (blue) holds ~45–60.
• That’s classic: not enough clamp in the mid-load band and the ramp isn’t adding pressure fast enough once slip starts.

Here’s exactly what I’d change to kill that shudder without bringing back harshness:

---

1) Give it more ceiling where it’s slipping​

[TCM] 5672 – TCC Desired Pressure (Line kPa × PCA kPa)

• Rows (Line): 900, 1200, 1500 kPa
• Cols (PCA): 52.5 → 115.5 kPa → ×1.30 (add 30%)
• Cols (PCA): 126.0 → 168.0 kPa → ×1.15 (add 15%)
• Leave 300 & 600 kPa rows stock for light-throttle smoothness.
• Cap any cell at ~6.5 psi, then Smooth (rows once, columns once).

Why: That strip is exactly where your trace lives when slip rises in 6th; this lets the controller command more real clamp there.

---

2) Make the ramp pull slip down faster (but not snap)​

Apply Ramp vs Slip Error


Keep your softening near zero (to avoid tip-out jab), but add authority once slip grows:

• Do not change: negative side, 0 cell, +5 column (keep your comfort tweaks).
• Increase: +10, +20, +40, +60 rpm columns by +10–15% (for 6th only if you have per-gear; otherwise global).
• Leave: ≥+80 as-is (you already have enough there and pushing it risks harshness).

Why: Your shudder builds from small slip; these columns tighten the correction right where it starts.

---

3) Regulator dynamics (only if you’re still soft/reactive)​

You said earlier you were at 45 psi offset / 1.5 gain. That combo lets the clutch “float.”

• Move to Offset 80–90 psi, Gain 0.75–0.85.
• Max TCC: 125–130 psi, Min: 25–30 psi.

If you already tried ~88/0.80 and got a little tip-out harshness, keep Offset but drop Gain → 0.75 (don’t lower Offset first).

---

4) Scheduling guardrail (prevents lug-lock events)​

6th-gear Apply/Release vs TPS/Speed (the band where your trace sits):

• Apply TPS: add +3–5% in the 50–65 mph bins.
• Release TPS: add +2–3% so it lets go a touch sooner on light lift.
• Keep 2–3 mph hysteresis (apply higher than release).
• If AFM is on, set Desired Slip in 6th = 5–8 rpm; if AFM off, 0 rpm.

---

Quick “after” check on a repeat run (same road, 55–70 mph in 6th)​

Log: TCC Slip, Desired Slip, TCC Duty/Pressure, Line Pressure, Gear, TPS, RPM, Speed, TFT.

• Target: slip 0 to ±5 rpm steady (or 5–8 with AFM), no saw-tooth bands.
• Duty to hold: ideally <85–90%.
• If you still see 10–20 rpm oscillations right in mid-load: add another +10% to PCA 63–84 kPa at Line 1200–1500 kPa in 5672, re-cap 6.5 psi, and bump +20/+40 ramp cells another +5%.

This sequence directly addresses the part of the map your graph shows slipping (mid line, mid PCA) and tightens the ramp only where shudder forms—so you keep the smooth tip-out you worked on while erasing the residual buzz.

 

[MWD_CTSV]

I haven't had any issues at all with the TCC since it has broken in finally. It just works wonderfully. Either mine took over 3K miles to burnish in properly, or I possibly had a poor early break-in causing the slip-catch-slip-catch shudder. I had actually had though of reducing the min pressure, but either way I need to revisit this and get a graph of the TCC pressure again with my current settings.

 

[Marky Dissod]

haven't had any issues at all with the TCC since it has broken in finally. It just works wonderfully.
Either mine took over 3K miles to burnish in properly, or I possibly had a poor early break-in causing the slip-catch-slip-catch shudder.
I had actually thought of reducing the min pressure, but either way I need to revisit this and get a graph of the TCC pressure again with my current settings.

Reducing min pressure is not nearly as good an idea as addressing pulsewidth modulation of the TCC application & release,
because then you'd potentially be PWMing the TCC with even less pressure.
Prior to 1995, the TCC was either 'all on' or 'all off', and only the rate of application was adjustable.
Since 1995 GM has used PWM to address NVH (GM would prefer that you NOT feel the TCC or variable cylinder modes at all),
which leads to increased wear of the TCC over time.

 

[mikez71]

I thought apply ramp was faster with lower numbers? Is AI backwards, or am I?