Post New Transmission: Infamous Clunks

B-train said:

I'd be curious to see what the new shift programming from GM is. I compared my 2008 Denali with the 6 speed to my friend's 2014 Denali and found 2 completely different shift patterns. I don't recall the names right off hand, but maybe the rebuilt transmissions require the newer shift pattern? Could a pattern for a different year/transmission cause weirdness? Just a random thought for someone who may know more than I on shift patterns.

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tkdgirl said:

But wouldn't the vehicle not work properly if it went back to the default tune? I mean I told the transmission guy that he could not flash

Nick, thank you. Here is the history:

July 2023: Engine rebuilt due to lifters, deleted, custom tune optimized for towing.
July 2024: Transmission blows while towing. New GM transmission installed by local (ohio) mechanic where my car died. Taken to a GM dealership to program.
Last week: Transmission clucking begins.

It actually did a bit of clunking when I was towing before the transmission blew.

I don't think the local mechanic did any of those things you mentioned above. The rear main seal was replaced when the engine was rebuilt.

My local mechanic, who has the Denali right now, said the transmission was 'programmed' to act the way it is.

I have no idea what's going, just that the clunking is not normal and I don't want it to blow another transmission.

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NickTransmissions said:

You're welcome...I would definitely have the mechanic go over the vehicle with a fine tooth comb to rule in or out causes and sources of your clunking. Even a worn rear transmission mount can causr those or similar symptoms.

Not sure i like his explanation about the shifting but maybe that is simply the extent of his knowledge. Shift strategy logic is programmed to the TEHCM based on OS variant which is driven by a number of factors including model/sub-model, installed powertrain package, variant of valve body (they changed a few times over the years in the 6L80s and 90s) and more.

Keep us posted.

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tkdgirl said:

As I posted here last month, my transmission blew and was replaced with a GM OEM one.

Since then, I am having a terrible time with 2-3 clunks when stopping. It did happen with the old transmission but only when towing. Now, it's everyday driving. I have a custom tune so not sure where to start on this. The dealer programmed the transmission only because of the custom tune.

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Geotrash said:

This matches what I experience with my '07 and '12 XL Denali's. The shift points and patterns are noticeably different between the two. It's especially noticeable in tow/haul mode. The '07 is much more prone to downshifting earlier when slowing down and revs higher before upshifting.

Side note: Interestingly, Blackbear said they couldn't tune the tow/haul mode in my '07 for me, and I didn't ask them about it for my '12, though both have Blackbear tunes and I love them. Not sure whether it was a technical limitation of their platform or not wanting to mess with those tables. It makes me wonder if I could use HP Tuners to adjust the tow/haul shift points.

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Foggy said:

My 14 with HPTuners lets me program shift points, TCC lockup, etc separately
as 2 diff tables between TOW mode and Reg Drive mode.
The adapts and all that stuff in the general settings are the same
I put my shift points in the Drive mode to more what the Tow mode was from
the factory as my personal preference

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tkdgirl said:

So far, not a single GM dealership has returned my call.

@NickTransmissions because I have a custom tune, are they going to give me the runaround, and, ultimately void any warranty?

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j91z28d1 said:

I'm curious who tuned the tranmission?

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Foggy said:

My guess is that the new trans is just the stock calibrations.. And that whomever tuned
the vehicle last year did some of the normal mods thru HPTuners that makes the
6L80E a "nice" transmission to have. (personally imo the factory settings suck!)

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