Stall clutch fried? 6L80E

[G8V8]

I have an 08 G8GT. It has cam, heads, headers, FAST102. The transmission is a 6L80 built by Circle-D and the Stall is a 258mm, 2800 C2 also from circle-D. The trans and stall were installed 5-6 months ago.

A few days ago I started to notice what felt like a very slight "miss" when under a load. I'm due for plug change and wrote it off to that. It would come and go and seemed load dependent and would all but disappear when eng and tran were warmed up. (My trans temps are typically 165-175 when fully warmed up). The couple mornings ago, with cold engine and going up a slight incline, Dash Boss showing +/-0 Converter Slip RPM in 6th, I felt what almost felt like slight "trailering" that went away on level ground. It was a slightly different feel than the earlier described "miss". This happened a couple more times going to work that morning.

On the way home, the slight "miss" and "trailering' feelings were a little more pronounced and when I fed throttle to move around some slower traffic there was a deffinate shuddering or bucking. It felt like a serious "miss" with the bucking hitting about twice a second or so. I was doing mid-to-upper 40s in 6th with Converter Slip RPM showing "0". When I lifted, the shudder stopped. When I rolled in again, it returned. I pulled the shifter to Manual 6, the stall unlocked (Converter Slip RPM was not at or near zero) and when I fed throttle there was no shudder, bucking or "miss" feeling. I repeated this twice with the same results.

When I got home, I modified the tune to add more ramp pressure and regulator offset. Test drive produced the same or maybe even slightly worse results. I then changed the tune to prevent any lock-up in any gear, speed or throttle position. Dash boss confirmed Converter Slip RPM was greater than zero (up to a few hundred RPMs). Car drove 100% normally. No shudder, miss, bucking, etc.

I parked the car and have contacted circle-d who are totally great to work with. The guess is that the converter lock up clutch is toast for some reason. C-D will know for sure when they open it up.

Can any of you with expertise with aftermarket stalls and tuning, please look at the tune I've been running to see if the problem could have been caused by the TCC settings.

TIA,
Ed

[G8V8]

Anybody?

[bluegoat06]

What was the previous tcc offset psi ? your current tune shows 50psi, so i'd assume you were running stock offset before ? Do you have any current logs that show tcc pressure and slip rpm ? do you have another from previous weeks that shows the same with the old tcc offset ?

[G8V8]

The tune I provided IS the tune I was running for weeks, actually months, with the stall. I only changed it the day of the troubles to see if it got better or worse. It got better when it was commanded to never lock. It basically did not change when offsets were increased to 90.

With this stall, the tune I posted with 50 offsets and 1.0 instead of 1.5 is how it was for months and right up thru the shuddering and other problems. This is the tune I changed only AFTER the acceleration pulsing and shuddering and then the changes were just short lived to see if they changed anything.

[bluegoat06]

I wonder if 50psi then was too little pressure. i tested my tune with the stocker 2 days prior to switching to the Yank 3200 SS to gauge how the tune/verter were going to react before the Yank. with 50PSI, the slip was zero on flat roads, tcc pressure was about 49PSI in the logs, but going uphill under load, the slip was 12-15RPM, because of that, i did increase the offset to 90PSI, ad the slip went down to 2-3rpm, under that same load. tcc pressure on flat roads is 60PSI, and under load it increases to 90psi, it behaves the same with the Yank, so i keep the offset to 90PSI.

I guess the clutch was still slipping for you, or perhaps the clutch was weak ? In the logs, you should be able to see if the trans is applying more than 90psi of pressure which would perhaps indicate the clutch is gone, an the trans is trying to apply max pressure to keep it locked, i think max pressure is harcoded to 109psi in the TCM per GM specs.

[bluegoat06]

Forgot to add, in the logs you'll see what the verter is doing, it might not even be the verter having an issue, but your pcm tune and the cam. when the verter is not locked, the engine rpm is higher thus masking what could be the real issue, the engine might be bucking at low rpm/load, and the verter being locked is making the issue worst. that's why i asked you to post some logs with tcc line pressure, and tcc slip rpm. there was another guy having some shuddering issues with the stock verter not too long ago, he's got a stock verter, and the verter was fine, just locking/unlocking in some weird spots, more likely because how the tune was set for the cam he's got.

[G8V8]

Thanks Bluegoat. I'm not driving it untill we put the new stall in it. Maybe you are right about 50 not being enough. I will make a tune with 90 and log with that and the new stall. The original Circle-D stall and that tune felt great for 4 or 5 months and several thousand miles. Maybe it was slipping a little and I never saw it on my DashBoss. I monitor slip all the time I'm driving and when it was in a lock didn't see much slip. Maybe the BD was not fast enough to capture short slip times.

Thanks.

[G8V8]

Bluegoat and others,
Circle-D looked inside the stall that was not holding lock and said it had some, but overall, very little wear. The new stall seems to be working fine so time will tell. I have increased my regulator offset to 90 psi from 50 psi. Max pressure is set at 165. The apply ramp the exact same as bluegoat's, 90 at 0 rpm and higher and 89 ft-pounds and higher. My regulator gain is 1.0 but bluegoat's is 1.500. Should I change mine. What does that mean?
Also, my adapt min is 0 and adapt max is 100. bluegoats is at OE with -21.8 and 21.8 repectively. What does this do? What is the impact? Should i change mine?

[camaro1]

turn off wot tcc apply if it isnt already

[G8V8]

turn off wot tcc apply if it isnt already

Thanks, already off. just want to know the effect of regulator gain and adapt min and max.

[bluegoat06]

G8V8, i didn't see your question before, sorry, i found out about it today, because i was using this thread as a reference.

I don't know what max/min tcc adapt would do, but the regulator gain is the gain for the TCC pressure offset (or min Tcc pressure when the converter is applied initially).

Your initial TCC pressure (when apply is commanded) is referenced as TCC offset / Regulator gain. example, you had your offset at 50psi, with the gain at 1.5, you min tcc pressure would be 33.3 PSI. the way i have it, i'm saying my offset is 90 PSI, but the gain is the stock 1.5, my min tcc pressure would be 60psi (90/1.5) when applied. once the verter locking clutch is applied, that pressure would go up as needed to keep 0 slip, and according to some people, the TCM uses the apply ramp table to do so.

You can read about it here http://www.hptuners.com/forum/showthread.php?t=37626

If you need more than 60psi initial pressure, then lower the gain to 1, and increase the offset to 70 or 80 or 90 psi as needed. 90 psi offset with 1.0 regulator would yield 90psi min pressure when the verter is first applied.

[G8V8]

Thanks Bluegoat.

[IDRIVEAG8GT]

Can't really tell you because I'm not sure, but Chris is one of the best to work with on this stuff.