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4L80/85E Transmissions. 6L90 Transmission Discuss the 4L80/85E transmissions found in the 6.2/6.5L equipped vehicles and Duramax equipped vans. 6L90 discussion.

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Old 02-19-2019, 04:49 PM   #11 (permalink)
DAVe3283
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If you lose power after a downshift, the engine is not healthy. My 1982 6.2L would behave like that when the injection pump was failing. Put a new pump on, and it makes good power all the way to redline.


I would think you should be able to hold 80+ MPH even in that truck with a healthy 6.5L. I've pushed my squarebody to 105+ MPH and it was still pulling, and those are pretty bad aerodynamically too.


When my last pump was going out, I had the truck dynoed, and it was making 62 HP at the rear wheels. That's less than half the rating of the engine, and the 6.5L is rated more still. I bet you're down on power for some reason, and that is your root problem. A downshift should never result in LESS acceleration.

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Old 02-19-2019, 08:32 PM   #12 (permalink)
Still Bill
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I think I'm not explaining it well. After thinking about it, when it kicks down, it does pick-up, but I think I'm hesitant to let it rev that high and I let off the pedal. This causes it to up-shift and then I try to give it a little more and cycle repeats.


I don't think anything is "wrong". I can't imagine doing 100mph, or that it was designed for that. I need to get it weighed. Fully-loaded, I have 50 gallons of water, three motorcycles, two persons (including my own 270lbs). Generator, 15 gallons of gasoline, lots of tools, big cooler full of food, beer, and ice.....


Is your 105+ turbo? Mine is NA. Dually, of course. Windows and wing vents open. Don't recall ever getting passed by UPS, Fed-Ex, or bread trucks ever in my life. Not sure they can go that fast.



Also, We "think" I have a lowered compression Marine engine.


80 if my personal speed limit, I don't feel safe over that. Afraid that big flat windshield is going to pop out and hit me in the face.



ANYHOW - My original question is still unanswered - regardless of whether or not my truck is running at optimum - Is is possible to make the passing gear less sensitive?



As I may have mentioned, when I had a code 22 (no passing gear, but no TC lock), I sort of liked it - up to a point. A middle ground would be perfect.

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Last edited by Still Bill; 02-19-2019 at 08:54 PM.
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Old 02-28-2019, 12:37 PM   #13 (permalink)
DAVe3283
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I am not familiar with the factory controls on the early 4L80E with the 6.5. I know on the gas motors, you can reprogram the computer to have it shift however you want. In your case, you might have to switch to an aftermarket transmission controller, which is expensive, but will do what you want.


I recommend you look into what tuning is available for the 6.5 controller, and have it tuned if possible. If not, look into aftermarket transmission computers.


My 6.2L is naturally aspirated, but it is not a dually. 105 MPH is sketchy, which is why I called it quits. It would do more, but I didn't feel safe, even in the middle of nowhere with no one else on the road. But it did have the power for it. Yours sure has some weight to haul around, but the weight only means it gets to top speed slower. The top speed is when the engine power can't overcome the air resistance. I still think yours should be able to do 80 MPH without drafting.


I wouldn't personally be afraid to let it downshift and rev out for a while, especially if it is just now and then (hills, short highway sections). I understand not wanting to have it redlined for hours on end, as that does shorten the lifespan of the engine and is just unpleasant to listen to on a long trip. But if you can't tune the stock computer, you have to decide if the cost and complexity of an aftermarket transmission controller is worth it vs. just letting it rev out now and again.
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2003 GMC Sierra 2500HD LB7 Duramax 4WD Crew Cab SB
310k miles. 8,260 lbs empty. Built motor, and still slow.
2003 Chevy Suburban 2500 LB7 Duramax AWD Quadrasteer
135k miles. 6-speed Allison conversion. Quadrasteer 4-wheel steering.

1982 Chevy C10 Silverado 6.2L Diesel RWD Single Cab LB

115k miles. Built 700R4 automatic, 4.11 gears.

Cheap bastage -- guilty as charged.
~~ TheBac
If you try Pee in the urea tank, Ur ine for big problems. ~~ heymccall
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Old 02-28-2019, 02:00 PM   #14 (permalink)
johnH123
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The control sector of the computer should be the same for the gas and diesel, so a tune should work for you.
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Old 03-07-2019, 01:10 PM   #15 (permalink)
Still Bill
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I wish I could just install a switch to lock-out the passing gear when it isn't wanted. I'm sure that is possible, but don't know how to hook it up.
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Old 03-07-2019, 01:58 PM   #16 (permalink)
johnH123
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It's not unless you have a special controller and a tune...
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A few mods: 3" straight pipe, Bosch boost gauge, Bosch glow plugs.


Gone but not forgotten: 2001 silverado 2500hd CC/SB, 4x4, 6.0 vortec, 229k miles when I traded it.
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Old 04-03-2019, 05:40 PM   #17 (permalink)
updatelee
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Its pretty easy to change in tuner pro. get yourself a programmer and change it yourself I personally really hated the stock shift patterns so I changed them all, I found it willing to downshift so incredibly easily, and I live in the parries ! tuner pro will let you completely change all the shift points
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Old 06-11-2019, 06:19 AM   #18 (permalink)
funtoy
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It can be made to work as you would like it.

Just keep plugging at it.
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Old 11-13-2019, 09:08 AM   #19 (permalink)
Still Bill
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UPDATE:
Well, I did nothing, but eventually it got better on it's own. Runs great now. I can cruise at 75-80 and still get passing gear only when I want, or come to a hill, etc. Maybe the computer had to "learn"? Or, maybe some loose connection fixed itself?
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