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Old 08-03-2019, 05:35 PM   #1 (permalink)
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6L80/90 question for the transmission experts

I have a 6l90 out of a '15 2500 Silverado I'm slapping in my jeep.

Shift arm on the side of the trans goes through 7 detents. I bought a Winters shifter that does PRN4321 so it can hit all the detents. I guess the Silverado shifter only cycles through 5. So, PRND and then low or sport or whatever.

I've read that the last two detents can be used, say, to start out in second gear, a tow/haul type mode and a few other things.

Then I've read that the last two detents won't do anything at all.

These transmissions are put in all kinds of different vehicles, I can't understand GM taking the expense to add the extra two spots and have them not do anything

So, what say Pirate? Can anyone tell me what the last two detent positions do?
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Old 08-03-2019, 06:02 PM   #2 (permalink)
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It is all in the programming. The switch in the tranny is all electronic other than the park pawl. The factory truck setup is PRNDM

The last two unused gates can be programmed to do other things, but it depends heavily on the who is doing the tuning. I don't believe any of the factory GM tunes had those gates active.
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Old 08-03-2019, 08:04 PM   #3 (permalink)
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Can you not program it for Tap Shift ?

My 6l80 has Tap shift programmed. Winters has a shifter for it.
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Old 08-03-2019, 10:39 PM   #4 (permalink)
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My 6L80E only has 5 detents. PRNDM.

I have a corvette tune on my engine which allows a non-BCM tap shifter to be used, while in M. Works great.
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Old 08-04-2019, 12:56 PM   #5 (permalink)
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Originally Posted by Mieser View Post
It is all in the programming. The switch in the tranny is all electronic other than the park pawl. The factory truck setup is PRNDM

The last two unused gates can be programmed to do other things, but it depends heavily on the who is doing the tuning. I don't believe any of the factory GM tunes had those gates active.
That's been my thinking the whole time, that it's electronic and not mechanical. I'm a ways away from driving this thing so I guess I'll start my search for a tuner with experience doing this kind of thing.



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Can you not program it for Tap Shift ?

My 6l80 has Tap shift programmed. Winters has a shifter for it.
My plan does include tap shift, but that will be the #3 position on my Winters shifter. My PSI stand alone harness was built for it and I have a RF paddle shifter setup for that.

It's those last two detents (which is positions #2 and #1 on the shifter) that I want to bring into play.



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Originally Posted by jpmassey View Post
My 6L80E only has 5 detents. PRNDM.

I have a corvette tune on my engine which allows a non-BCM tap shifter to be used, while in M. Works great.

Thanks for that. That tells me that GM didn't just slap one set of parts in all the transmissions going in all the different vehicles. If some have 5 detents and some have 7 detents, then those last two should do something.



For the record, I'm running an LS3 crate engine with a stand alone PSI harness. E38 ECU (that is brand new, never been programed). No BCM, chassis wiring is from Painless, so it's basically wired like a hotrod. And as said earlier, I have the Winters shifter that has PRN4321.
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Old 08-04-2019, 04:46 PM   #6 (permalink)
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That's been my thinking the whole time, that it's electronic and not mechanical.
Correct, the 6L80/90 trannies use a potentiometer in the valve body that measures the position of the lever. Other than P, everything is electronic. I found this out the hard way when I forgot to attach the pot to the arm. Every position other than P (including R) was just normal D.
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Old 08-04-2019, 04:50 PM   #7 (permalink)
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For the record, I'm running an LS3 crate engine with a stand alone PSI harness. E38 ECU (that is brand new, never been programed).
Just an FYI, PSI doesn't know how to program the ECU/TCM to make the non-BCM tap shifter work. (Or they just want people to buy their special paddle shifter). I had to go to Speartech for it.
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Old 08-04-2019, 06:13 PM   #8 (permalink)
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Just an FYI, PSI doesn't know how to program the ECU/TCM to make the non-BCM tap shifter work. (Or they just want people to buy their special paddle shifter). I had to go to Speartech for it.
When I bought the harness from PSI, I told them I had a Twist Machine paddle shifter. Psi just said that the wires that need to be connected for tap shift are in the harness. I never talked to them about programing.

I hope I can find someone who can do the initial programing AND dyno tune it under one roof. Hell, I'm more than willing to drag my junk half way across the country to have it done right.
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Old 08-05-2019, 08:23 AM   #9 (permalink)
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Old 08-05-2019, 08:55 AM   #10 (permalink)
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Also you'll want gauges that will show what gear you're in for TUTD shifting, or you can get an gear indicator which shows what gear as you tap through it. You can use it with out it but way less to thing about when you can glance and see what gear you're in. Speartech had gauges that show TUTD gear.
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Old 08-05-2019, 12:08 PM   #11 (permalink)
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I've always heard good thing about John. Just figured he was neck deep in doing the Motech LS JK swaps.

Granted, I have a JK and it has a LS, but that's where the similarities end. I don't have a single piece of the Jeep wiring or electronics left.

Do you know if John has a dyno?


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Also you'll want gauges that will show what gear you're in for TUTD shifting, or you can get an gear indicator which shows what gear as you tap through it. You can use it with out it but way less to thing about when you can glance and see what gear you're in. Speartech had gauges that show TUTD gear.
I have a AEM digital dash display that runs off the GM OBDII port. It displays what gear you're in.
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Old 08-05-2019, 01:23 PM   #12 (permalink)
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So, what say Pirate? Can anyone tell me what the last two detent positions do?
My last 2 detents controlled 1st and 2nd gear.
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Old 08-05-2019, 02:11 PM   #13 (permalink)
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My last 2 detents controlled 1st and 2nd gear.
Awesome to hear. I'll be hitting you up when tuning time comes, I believe you had someone that was "one the ball".
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Old 08-05-2019, 02:17 PM   #14 (permalink)
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Awesome to hear. I'll be hitting you up when tuning time comes, I believe you had someone that was "one the ball".
Jim at Zero Gravity Performance. I don't know if he has a dyno shop but what he did for my 6L80 was amazing.

Performance 4L80e 6L80E 6L90E Transmissions
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Old 08-05-2019, 03:41 PM   #15 (permalink)
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Thank you kind Sir.
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Old 08-06-2019, 07:10 AM   #16 (permalink)
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Quote:
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Jim at Zero Gravity Performance. I don't know if he has a dyno shop but what he did for my 6L80 was amazing.

Performance 4L80e 6L80E 6L90E Transmissions
I also used Jim. Trailered my rig 6 hours each way. He wired up the tap shaft and dropped programming in it. He did great work on my trans. There's so many thing you can do with the programming on these.

Mine is P, R, N, D1, D2. D1 is normal drive and what I use 95% of the time. D2 is sport shift and enables tap shift mode. Tap shift is really handy when crawling or with hills on the highway. The trans shifts A LOT, but it's super smooth. The sport mode he put in there originally was unbelievable hard/fast. It was barking 40s on 1-2 and 2-3 shifts. I later had it update it because it was too aggressive for a street-driven rig on 40s (IMO). Rev-matched downshifts are awesome. Engine braking is an option. He can tune how touchy it is to downshift. The first program he put in was too laggy on sand climbs and would let the engine bog out before downshifting, then I was stuck. His second tunes were spot on and I'm still loving it.
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Old 11-03-2019, 05:33 PM   #17 (permalink)
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How reliable have these 6L80/90 swaps been? I have a 4BT in my M715/J300 hybrid, with an NV4500 and I'm tired of the jumps between gears and the loss of boost/speed during shifts. But I do like that the truck is as simple as a hammer and nothing in it is going to fail without giving me warning. Thanks.
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Old 11-04-2019, 12:20 PM   #18 (permalink)
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I have yet to drive mine under it's own power. But, a 6l80 is rated to 550lb/ft of torque. Lots of street folks putting way more than that through them but, that's what GM rates them at.

From my research, they do not like to get hot, so a proper cooler setup is important.

Sorry that was no help whatsoever.
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Old 11-04-2019, 09:24 PM   #19 (permalink)
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How reliable have these 6L80/90 swaps been? I have a 4BT in my M715/J300 hybrid, with an NV4500 and I'm tired of the jumps between gears and the loss of boost/speed during shifts. But I do like that the truck is as simple as a hammer and nothing in it is going to fail without giving me warning. Thanks.
I put 12000 miles on mine in the last year.
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Old 11-06-2019, 02:27 PM   #20 (permalink)
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Thank you guys.

Mieser, how do you like yours?
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Old 11-06-2019, 02:32 PM   #21 (permalink)
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The 6L80 is still going strong in my old TJ. Out of all of the things I've done in Jeeps I miss that transmission the most.
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Old Yesterday, 07:24 PM   #22 (permalink)
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GM just released a performance 6L80E at SEMA. I doubt many saw it. It is a stand alone unit that can go behind most anything. It also has a 2400 stall and a 3000 stall. They could not give me pricing at the time but there is a part number. They also made it beefier with more clutches to handle a higher power rating. I think the number was 35-40% more.
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