L5p down shifts hard - Chevy and GMC Duramax Diesel Forum
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post #1 of 10 (permalink) Old 07-15-2019, 09:45 AM Thread Starter
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L5p down shifts hard

So itís not all the time, but I noticed my 2019 seems to want to hit each gear down shifting when coming to a stop and it seems to be a noticeable down shift. Almost like when in hill decent mode. Only 13k miles on the truck. Havenít pull much of anything with the truck, a couple bobcats or minis a few times is all. Iíve changed the screw on filter once at 8k.

Edit: seems to be during regen, which makes sense I guess.

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Last edited by 1lunger; 07-15-2019 at 11:12 AM.
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post #2 of 10 (permalink) Old 07-15-2019, 12:07 PM
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I noticed some aggressive downshifting in my first 10k miles. It takes time for the trans/TCM to learn your driving style, however the most aggressive downshifts I've experienced were when I started braking hard, then let up on the pedal some.

I will say they are a bit alarming until you realize its just the transmission guessing incorrectly on a downshift.

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post #3 of 10 (permalink) Old 07-15-2019, 02:13 PM
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Torque converter programming changes (on L5P gen) to lock TC in lower gears seems to make the shifts more noticeable.

My LML was definitely a smoother shifter, both up and down, than this one.

And every once in awhile it gives a particularly harsh one -- that I've not be able to reproduce.

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post #4 of 10 (permalink) Old 07-15-2019, 04:16 PM
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I am glad I ran across this. I am at almost 15,000 miles. I have noticed when hard braking, I get hard downshifts. Guess it is everyone. Good to know.
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post #5 of 10 (permalink) Old 07-15-2019, 04:45 PM Thread Starter
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I find it also happens under hard braking and letting off. I was trying to get it to do it today, but Iím not in regen right now. Glad to know Iím not the only one. Lol!

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post #6 of 10 (permalink) Old 07-15-2019, 10:05 PM
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Mine does it too usually when braking hard or in regen. Its occuring less frequently over time. I'm at 11k miles.

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post #7 of 10 (permalink) Old 07-16-2019, 05:42 AM
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2017 25K miles here - noticed same thing during regen and hard braking... also noticed some when towing and hard braking.

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post #8 of 10 (permalink) Old 07-16-2019, 06:49 PM
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To me once the truck learns your driving pattern trans shifts smoother, I love the way it shifts almost like a manual!

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post #9 of 10 (permalink) Old 09-07-2019, 07:01 AM
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I have a 2019 with 13k on it now, experienced hard downshift into first gear when braking hard and a not “smooth as butter” shift from 3-4 like all the other gears normally shift. took to dealership they claim normal operation, its a heavy duty tranny so you will feel stuff like that. Ok? So i have a 60k + truck that feels like the tranny is falling out of it. Great! My buddys father has a 02 low mileage single cab and had a few hard shifts occasionally and he said to try driving in tow haul mode once in a while, the trannys are ever learning so from my understanding if you throw different shift points and patterns at it which is what tow haul mode does, it will learn those shifts and forget the bad ones? I have noticed smoother shifts across the board and the hard downshift is gone, even though i get nervous coming to a stop light from 40-60 mph in fear of the infamous boom that is called first gear. Hope this helps, it worked for me!
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post #10 of 10 (permalink) Old 09-07-2019, 11:37 AM
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There are a few good articles online that describes what is happening and why. After I had a not so good talk with the Shop Foreman from the local Stealership where he told me he has never seen a Allison transmission fail, which made me angry and I went online and searched for articles and blogs.

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