Very weird shift behavior by a 6L80e

[Tick]

I'm tuning a customers a G8 with a 1900 Maggie and am having a very weird issue that occurs at the end of a wot pull. Basically, the car will complete the 3 to 4 shift just fine. A few moments later once the throttle is released the car holds itself in 4th gear according to the log, then after about two seconds of what seems to be a normal amount of engine braking something strange happens as if the car downshifts or the converter locks. RPM's jump up from about 3000 to 5000 instantly and it is so violent that the rear tires drag on the pavement a bit. After another second or two I pushed the shifter into neutral to give the engine a break, but the log still shows the trans to be in 4th gear.

On the log, the transmission remains in 4th gear during this entire event. According to the status bit the converter does not lock up. This has happened twice and both times it seems to jump the rpm up at 102 mph. The throttle is completely released.....

Also, when logging "Trans TqMgt Type" their is a brief moment during the initial coast down that will register "clutch control" on the log. When the rpm jumps up, this just registers "none". Torque converter clutch slip jumps up to about 600 rpms when the rpm jumps up so I know the converter isn't locked or locking.

Why wouldn't this car just shift into 5th and 6th once the throttle is released? I don't see anything wrong with my shift mph tables....but 5th is commanded at wot right at about the same mph we are letting off and 5th to 4th is commanded at 102 at wot where my weird issue seems to happen, but on the log 5th gear was never even commanded and it happens at 20% throttle (completely closed).

What are "safety shifts" and could that have something to do with it? I would continue to test theories, but everything is so violent i feel like something is going to break.

[Tick]

The WOT pull starts at about frame 3450.

I kinda feel like it the rpm jump might be something mechanical with the transmission or torque converter... When the rpms jump it goes to about 5000 rpms and 99 mph which is about the same readings that are logging when wot in 4th gear.

Still doesn't explain why it wouldn't just go into 5th gear once the throttle is released instead of dragging the engine down like it does.

[hivoltagedriver]

I've never seen anyone zero out all of the shift times like in that tune. I know the 6L80E is REALLY picky about the transmission tune. I'm not a pro by any means, but it looks like you have changed a LOT of tranny tables, and I think less is more with this transmission.

[Tick]

That transmission tune is straight out of "The Tuning Schools" training manual. Yes, a lot of stuff is changed...mainly just leaves you with one place to concentrate on shift times... I've tune quite a few 6L80e cars with the tips and procedures from that manual with great results.

From what I've found with the 6L80e, when 200+ hp is added the less is more approach goes out the window. Getting these higher hp cars to shift is my biggest weakness when it comes to tuning in general.

[realcanuk]

Sounds like something similar to what mine did just before the 4/5/6 clutch pack fused to together completely. Hopefully it is something else in your case.

[snowvette]

Maybe something here can help.
http://forum.grrrr8.net/showthread.php?t=27179

[vectorbundle]

I'm tuning a customers a G8 with a 1900 Maggie and am having a very weird issue that occurs at the end of a wot pull. Basically, the car will complete the 3 to 4 shift just fine. A few moments later once the throttle is released the car holds itself in 4th gear according to the log, then after about two seconds of what seems to be a normal amount of engine braking something strange happens as if the car downshifts or the converter locks. RPM's jump up from about 3000 to 5000 instantly and it is so violent that the rear tires drag on the pavement a bit. After another second or two I pushed the shifter into neutral to give the engine a break, but the log still shows the trans to be in 4th gear.

On the log, the transmission remains in 4th gear during this entire event. According to the status bit the converter does not lock up. This has happened twice and both times it seems to jump the rpm up at 102 mph. The throttle is completely released.....

Also, when logging "Trans TqMgt Type" their is a brief moment during the initial coast down that will register "clutch control" on the log. When the rpm jumps up, this just registers "none". Torque converter clutch slip jumps up to about 600 rpms when the rpm jumps up so I know the converter isn't locked or locking.

Why wouldn't this car just shift into 5th and 6th once the throttle is released? I don't see anything wrong with my shift mph tables....but 5th is commanded at wot right at about the same mph we are letting off and 5th to 4th is commanded at 102 at wot where my weird issue seems to happen, but on the log 5th gear was never even commanded and it happens at 20% throttle (completely closed).

What are "safety shifts" and could that have something to do with it? I would continue to test theories, but everything is so violent i feel like something is going to break.

would you mind telling how you resolved this?

thanks.