L5p down shifts hard - Chevy and GMC Duramax Diesel Forum
2017-19 GM T-K2 Platform Performance Parts Discussion Discussion of Performance Parts For the '17 and up L5P Duramax Trucks No Advertising

 
LinkBack Thread Tools Display Modes
post #1 of 10 (permalink) Old 07-15-2019, 09:45 AM Thread Starter
Junior Member
 
1lunger's Avatar
 
Join Date: Mar 2019
Location: 06002
Posts: 70
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.


Sent from my iPhone using Tapatalk

Last edited by 1lunger; 07-15-2019 at 11:12 AM.
1lunger is offline  
Sponsored Links
Advertisement
 
post #2 of 10 (permalink) Old 07-15-2019, 12:07 PM
Junior Member
 
miller11386's Avatar
 
Join Date: Sep 2013
Posts: 66
Garage
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.

Miller's Youtube Channel

2018 Silverado Duramax High Country in Deep Ocean Blue Metallic CCSB/SRW 4x4 L5P
Purchased 8-11-2018 - All stock


1993 Toyota Supra - Renaissance Red - 1000+hp
miller11386 is offline  
post #3 of 10 (permalink) Old 07-15-2019, 02:13 PM
DuramaxForum Fanatic
 
redwngr's Avatar
 
Join Date: Feb 2011
Location: SW Ont
Posts: 5,633
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.

2018 GMC 2500 L5P CCSB 4x4 Denali - Mineral Metallic; previous '11 LML, '10 LMM and 04.5 LLY
redwngr is online now  
Sponsored Links
Advertisement
 
post #4 of 10 (permalink) Old 07-15-2019, 04:16 PM
Junior Member
 
Join Date: Feb 2019
Posts: 27
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.
Southern Duramax is offline  
post #5 of 10 (permalink) Old 07-15-2019, 04:45 PM Thread Starter
Junior Member
 
1lunger's Avatar
 
Join Date: Mar 2019
Location: 06002
Posts: 70
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!


Sent from my iPhone using Tapatalk
1lunger is offline  
post #6 of 10 (permalink) Old 07-15-2019, 10:05 PM
Junior Member
 
Join Date: Aug 2017
Posts: 44
Mine does it too usually when braking hard or in regen. Its occuring less frequently over time. I'm at 11k miles.

2019 L5P 3500HD LTZ Z71
pullin15 is offline  
post #7 of 10 (permalink) Old 07-16-2019, 05:42 AM
Duramax Lifetime Supporter
 
markhuntsville's Avatar
 
Join Date: Mar 2010
Location: Huntsville, AL
Posts: 102
Garage
2017 25K miles here - noticed same thing during regen and hard braking... also noticed some when towing and hard braking.

2017 Silverado 2500HD High Country L5P CCSB
Deep Ocean Blue Metallic
Cocoa Interior
Heartland LED Headlights/Fogs
Edge Insight CTS2
Bak Revolver X2 Tonneau Cover
GM OEM LED Bed Lighting
Weather Tech Floor Liners
B&W Turnover GN
Air Lift LoadLifter 5000 Air Bags
markhuntsville is offline  
post #8 of 10 (permalink) Old 07-16-2019, 06:49 PM
Duramax Lifetime Supporter
 
monkeyman's Avatar
 
Join Date: Nov 2016
Location: Grays Lake,IL
Posts: 555
Send a message via AIM to monkeyman
To me once the truck learns your driving pattern trans shifts smoother, I love the way it shifts almost like a manual!

To many vehicles to little time! New LP5 owner first 2017 GMC Denali Duramax
monkeyman is offline  
post #9 of 10 (permalink) Old 09-07-2019, 07:01 AM
 
Daveflis33's Avatar
 
Join Date: Sep 2019
Posts: 3
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!
Daveflis33 is offline  
post #10 of 10 (permalink) Old 09-07-2019, 11:37 AM
 
BVRCWolf's Avatar
 
Join Date: Jul 2017
Posts: 7
Garage
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.

2019 3500 hd SLT crew cab
BVRCWolf is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Chevy and GMC Duramax Diesel Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome