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4L80E 4-2 downshift??

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Old 02-21-2013, 11:48 AM
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Alright guys, thanks for confirming what I already suspected.

The transmission is fresh & has a shift kit. It downshifts quickly & firm. He is just used to his old 60E, and the way this one acts was different and he was alarmed. Asked me if I could change it. I didn't want to be wrong when I told him it was normal.
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Old 02-21-2013, 11:53 AM
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Originally Posted by oakley6575
Definitely not the way it should be. Have you logged the truck when it happens. I'm sure you can log commanded gear and see if it commands third then second.
Yes, I have datalogged the commands, and the PCM is commanding it to go to third, then to second.
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Old 02-21-2013, 12:30 PM
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Originally Posted by gamble686
Sounds like an issue with the shift tables. What changes from stock did you make?
Lots of changes, trans is built & has shift kit and a Pro Yank.

Did you only adjust WOT shift speeds/RPMs or the partial as well?
I made several adjustments to all of the tables, and it still acted the same.

Also have you logged the truck while doing this? What does the TPS% look like during these shifts?
Yes, the datalog shows the PCM commanding the shifts in this manner. TPS at 100%.

Is this a DBC or DBW truck? Also what does your TPS enable full throttle % look like?
It's an early DBC (GMC C3). Full throttle enable at 85%. Tried lowering it just for ***** & giggles, didn't change anything.

Something seems very odd here.
Looks like it's normal actually.

I didn't want to ignore your post, so I answered your questions above, in red.
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Old 02-21-2013, 12:31 PM
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Thanks Jake, Tim, and Blake! Your help is much appreciated!!
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Old 02-21-2013, 01:02 PM
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Originally Posted by chevrolet all the way
Thats what i did nonnie. also good for brake boosting

Shhhhh... dont be telling all the secrets!
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Old 02-21-2013, 04:26 PM
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Interesting... something to look out for/be prepped for when i do my swap. Does this also happen on the 3-1 shift? Or the 4-1 shift? With the tight ratios of the 80e I would imagine a 4-1 shift isnt that uncommon with a heavy foot.
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Old 02-21-2013, 04:41 PM
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I haven't tried a skip-shift into first gear. But I'd suspect (since the tune file has no settings for it) that it will not skip ANY gear.
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Old 02-21-2013, 05:26 PM
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This has never even crossed my mind. In retrospect, my 4-2 may be a tad slow but there's no way I feel one downshift and then another.
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Old 02-21-2013, 06:44 PM
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Originally Posted by AKlowriderZ71
I haven't tried a skip-shift into first gear. But I'd suspect (since the tune file has no settings for it) that it will not skip ANY gear.
that would be a real bummer if there is no skip shift... doesnt really sound right to me. I feel like it would have come up before.
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Old 02-21-2013, 06:49 PM
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Originally Posted by GMCtrk
This has never even crossed my mind. In retrospect, my 4-2 may be a tad slow but there's no way I feel one downshift and then another.
This 4-3-2 shift is not slow. It's quick, and crisp. Maybe that's why it's more noticable? It is a brand new built trans with a shift kit and a Yank.

Why don't you datalog yours, and see if the trans commands 3rd before it commands second, and report back?
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