6L80E - Sloppy 6 to 3 WOT Downshift

[Aaron407]

While continuing to refine the tune on my supercharged G8 GT, I noticed that my WOT 6-3 downshifts are still fairly "sloppy." In stock form, they were absolutely horrible due to torque management, but I've tuned that out to a reasonable extent with TM set to use only timing control and a minimum TM spark of -3. This reduced the jerky motion, but the shift still takes a long, long time while it's pulling about 200 ft.lbs. through timing reductions. In the attached log at 4:01, there is a wide open throttle shift from 6 to 3. You can see that there is clutch control torque management being commanded by the transmission for nearly a full second while the shift completes. After this, it hits into gear nicely, but I'm looking for a way to reduce this shift time.

6-3 TM.png

Unfortunately, there are no shift time tables for 6-3 power downshifts, so I'm trying to sort out the shift sequence to see how I can help the issue. Although the current gear PID shows it briefly cycling from 6-5-4-3 in the blink of an eye, I'm fairly certain that it doesn't run through each gear. I have reduced my 5-3 and 4-3 shift times in case they are an intermediate step, but haven't noticed any difference. It's worth noting that power downshifts from 6-2, 5-2, and 5-3 feel perfect, with 6-3 being the only problem child.

Can anyone suggest anything else that I could try?

EDIT: If it matters, I have reset the transmission adapts and fast adapts while at operating temperature, but it had effect on this issue.

[Aaron407]

I'd love to hear any thoughts on this, unless I'm the only one fighting with the issue

[5FDP]

With no tables to look at or change, I don't see how you'll be able to do anything.

[Aaron407]

I got it sorted. I ran through the fast adapt relearn process to reset the shift adapts (I don't think the standalone reset buttons actually do anything as they didn't help previously). After a short drive, the 6-3 shifts are quick and firm. I wonder if this will also fix my harsh cold garage shift issue.

[Aaron407]

Now it has started to degrade again in terms of shift quality. It was shifting nicely after the adapts were relearned, but are getting closer again to how they were before. It's too bad that there are no 6-3 downshift tables to play with.

EDIT: I have read that the 6L80E cannot shift directly from 6 to 3, and instead shifts to another gear first, likely 5, and then down to 3. I'm trying a reduction of the 6-5 shift time to see if it feels better.

[Aaron407]

Can anyone offer any insight into the shift process? Does it indeed shift from 6-5 then 5-3 in the 6L80E on a WOT 6-3 downshift? Without knowing what's going on in terms of shift staging and without 6-3 tables, it's kind of a shot in the dark.

[5FDP]

Don't quote me on any of this but because GM did away with the one way clutches and switched to a clutch to clutch shifting process, that is the reason for feeling each downshift sometimes depending on what gear you are in. Perhaps the way the clutches are put together or the way it's designed to shift out of 6th gear being a double overdrive in a way. I don't have a book on how it works or taken them apart to know much more.

[Aaron407]

I'd like to resurrect my old post in case anyone else has fought with and beaten this issue.

As mentioned, I can relearn the adaptive shifting, and the 6-3 works well for a short period of time, but degrades again after awhile. What I'm wondering is if I may be able to monitor specific transmission PIDs to determine what is changing over time as a result of the adaptive relearning and possibly compensate. I'm also trying to figure out if I'm the only one who hates the way it shifts, or if I'm just the only one picky enough to try to fix it...

[Tre-Cool]

with a blown 6lt why are you even going back to 3rd from 6th?

i always make 4th gear the lowest you can go back to. you simply dont need the rpm in 3rd gear with a blown car with a heap more torque available.

[Aaron407]

I'm mostly looking to get from 6th to 3rd for highway passing around 60 mph. 3rd gear at around 60 mph is close to my peak torque, whereas it bogs down a bit in 4th.