8L90 Flare on the 2-1 downshift on C7 Corvette

[BuggyMasters]

Well the quick relearn procedure worked great on my car and the trans is doing fantastic with one nagging exception and that is when coming to a stop with foot on brake and no foot on the gas. More times than not, when you get to the stop sign it’s as if the car is between gears and you get a slight rev and then it pops into first. It’s enough that if you weren’t prepared for it and you had cars in front of you and you didn’t have your foot solid on the brakes you stand a chance of it lunging into a car in front of you. If using the paddles things work great.

There’s a trans tune on it (I didn’t do it). On the downshift scheduling I am only looking at the first column or so in this explanation since the throttle position coming to the stop is zero. The stock tune has the 3-2 and 2-1 matched at 6mph which to me means it would do a 3-1 downshift. The tune that’s in the car now has it doing a 3-2 at about 13 mph and then a 2-1 at 8mph. What I think is happening is it’s not even done with the 3-2 and the 2-1 gets commanded and that’s what’s causing the delay into 1st. I plan on putting the 3-1 shift back into it with a blending of the table so to speak.

To those of you who have a solid trans tune understanding: Any flaws in my proposed game plan that I am not considering? (Don’t know why this forum replaces apostrophes with question marks)

[BuggyMasters]

I’ll update my own: I retuned it putting the 3-1 back and the trans works perfectly now. Looks like my theory was correct! I don’t know the physical configuration of the clutches but it clearly like a 3-1 when coming to a stop way better than a 2-1. All good now.

[ssmotors]

I?ll update my own: I retuned it putting the 3-1 back and the trans works perfectly now. Looks like my theory was correct! I don?t know the physical configuration of the clutches but it clearly like a 3-1 when coming to a stop way better than a 2-1. All good now.

Thanks for the Info. I am having the same issue and this may very well be the fix i am looking for.

[VMoua]

I’ll update my own: I retuned it putting the 3-1 back and the trans works perfectly now. Looks like my theory was correct! I don’t know the physical configuration of the clutches but it clearly like a 3-1 when coming to a stop way better than a 2-1. All good now.

I too am having this 2-1 flare in my 2015 denali. With the 8l90. My local tuner couldn't understand why the factory tune from 3-2 and 2-1 was rpm matched. So he raised 3-2 shift to 8rpm and the 2-1 shift to 2mph.

I like your proven theory of tuning 3-1!

When I downshift in manual mode, it shifts great... I would downshsift to 3rd, just under 30mph, 2nd gear just under 20mph, and then to 1st gear just under 10mph. My question to you is, can I raise my downshift mph higher so that it has a cleaner/smoother/more time to downshift?

How is your 1-2 shift when cold? Mine feels like the tranny is going to fall off. But when it's warmed up, it shifts normal. Do you think it's possible to tune the 1-2 shift with a delay so it's not so harsh when cold?

Any help is greatly appreciated!

[Kapem23]

I too am having this 2-1 flare in my 2015 denali. With the 8l90. My local tuner couldn't understand why the factory tune from 3-2 and 2-1 was rpm matched. So he raised 3-2 shift to 8rpm and the 2-1 shift to 2mph.

I like your proven theory of tuning 3-1!

When I downshift in manual mode, it shifts great... I would downshsift to 3rd, just under 30mph, 2nd gear just under 20mph, and then to 1st gear just under 10mph. My question to you is, can I raise my downshift mph higher so that it has a cleaner/smoother/more time to downshift?

How is your 1-2 shift when cold? Mine feels like the tranny is going to fall off. But when it's warmed up, it shifts normal. Do you think it's possible to tune the 1-2 shift with a delay so it's not so harsh when cold?

Any help is greatly appreciated!

And to answer your question
1. If you were to match your TUTD downshift settings to your part throttle downshift tables ( normal, pattern A, Pattern B etc) this would give you the same feel as your manual mode. Otherwise yes you can change the downshifts speeds.

2. Do you know when your TCC commands lockup?
I only ask because if you are commanding lock up in second it could be the reason for the jolt you feel when it up shifts. If you changed the lock up to say 4th or 5th gear you will find much smoother shifts.
If lock up is not the issue and you do want a longer ?pause ? between 1-2 you can adjust the shift times trans>shift timing power 1-2, pattern A 1-2 (special 1) pattern b 1-2 (special 2).

If you want a uniform feel between patterns the tables will need to match , in your case especially in the 1-2 shift times