6L80 Tune (2-> 1 downshift questions)

[67Steven]

New to the tuning world and I have been reading what I can, but I would like to address this one issue now if possible.

I am having an issue with the 2nd to 1st downshift- I basically need to bring the truck to a stop or nearly so before it shifts down.

It's terrible if you are rolling into a red light and it turns green. The transmission will either stay in second and lug, or lurch into first usually at or below 2 mph.

I have not changed a thing from the tuner I had do the original work. From looking at other 6l80 tunes, most 2->1 shifts (in Normal) are 7-9 mph @ 0% throttle, where mine is at 20 mph and doesn't occur until 1-2 mph. Am I reading that correctly? Should I look elsewhere for downshift properties?

Any pointers would be appreciated.

Well, I can't attach the file as it is too large (sheesh!)

http://www.filedropper.com/1972blazer

[aknovaman]

Lower the settings to 7 mph and it will be fine.

[67Steven]

Originally Posted by aknovaman

Lower the settings to 7 mph and it will be fine.

I will give it a try, thanks.

I would like to know the 'why' behind the 'do' part if you or anyone could briefly explain- I like to learn this stuff for future use!

[BR3W CITY]

Originally Posted by 67Steven

I will give it a try, thanks.

I would like to know the 'why' behind the 'do' part if you or anyone could briefly explain- I like to learn this stuff for future use!

Afaik, its because there isn't the same capacity for overrun that the 4speeds had, due to the design of the internals. The 6l80e's are clutch-to-clutch, and setting too high of a downshift speed would cause more slip between clutches then allowed, and it would probably want to try and shift right back up.

Thats how I understand it from the reading. 6l80e's confuse the crap out of my because the Truck,car,and 'vette's were all setup and programmed a little differently.

[67Steven]

Originally Posted by BR3W CITY

Afaik, its because there isn't the same capacity for overrun that the 4speeds had, due to the design of the internals. The 6l80e's are clutch-to-clutch, and setting too high of a downshift speed would cause more slip between clutches then allowed, and it would probably want to try and shift right back up.

Thats how I understand it from the reading. 6l80e's confuse the crap out of my because the Truck,car,and 'vette's were all setup and programmed a little differently.

Thanks for the information. I thought it might have something to do with wanting to up-shift or the the TCM saves itself from destruction by not allowing the downshift at too high of speed.

It makes me wonder what else is wrong in the tune...

[Hart_Rod]

Originally Posted by 67Steven

Thanks for the information. I thought it might have something to do with wanting to up-shift or the the TCM saves itself from destruction by not allowing the downshift at too high of speed.

It makes me wonder what else is wrong in the tune...

Steven,

email me a copy of your tune and I will take a look at it, r.

R

Edit: just noticed you posted the tune above.

[Hart_Rod]

Steven,

I downloaded your tune and then downloaded a factory 2008 GMC Sierra 6.2/6L80 tune and then did a compare between the two. It looks like the guy that did your tune has some stuff jacked up in the auto shift sections of the tranny tune.

[Hart_Rod]

Steven,

Make these changes to your tune and let me know what you think.

R/

[67Steven]

Originally Posted by Hart_Rod

Steven,

Make these changes to your tune and let me know what you think.

R/

Sweet, thanks! I just got back in town, and I will load it and try it out. I will let you know!

[67Steven]

Just went for a short test drive and it is a night and day difference, thanks!

No more 1st gear 5000 rpm shifts at 3/4 throttle!!

It seems to go around corners in the correct gear now, too.

I would like to stay in first just a hair longer, and second seems to drop off fast. Should i change the 1->2 and 2->3 shifts to a higher number on the throttle % chart?

Thanks again for your help.