Hard down shift while coming to a complete stop - Chevy and GMC Duramax Diesel Forum
11-16 LML Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #1 of 34 (permalink) Old 11-03-2016, 08:35 AM Thread Starter
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Hard down shift while coming to a complete stop

Hey everyone,
I've searched a bit and can't find a thread on this issue. My 2016 Denali HD with Allison transmission is downshifting hard into 1st gear when coming to a complete stop (sorta feels like someone taps the rear end) This is happening is very intermittent and may only happen when the truck is in regen mode (not 100% certain though).

Has anyone else experienced this? Thanks in advance.

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post #2 of 34 (permalink) Old 11-03-2016, 08:53 AM
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Originally Posted by Kmagee View Post
Hey everyone,
I've searched a bit and can't find a thread on this issue. My 2016 Denali HD with Allison transmission is downshifting hard into 1st gear when coming to a complete stop (sorta feels like someone taps the rear end) This is happening is very intermittent and may only happen when the truck is in regen mode (not 100% certain though).

Has anyone else experienced this? Thanks in advance.
Good Morning Kmagee,

We understand that you are looking for some assistance from other forum members, so we would like to offer our help. If you this interests you, please private message us with your VIN, full contact information, current mileage, and preferred GM dealership. From here, we will be able to take a look at your situation on our end and hopefully reach a resolution on your behalf. Thank you and we look forward to working with you.

Philip J.
GM Customer Care
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post #3 of 34 (permalink) Old 11-03-2016, 09:44 AM
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Originally Posted by Kmagee View Post
Hey everyone,

I've searched a bit and can't find a thread on this issue. My 2016 Denali HD with Allison transmission is downshifting hard into 1st gear when coming to a complete stop (sorta feels like someone taps the rear end) This is happening is very intermittent and may only happen when the truck is in regen mode (not 100% certain though).



Has anyone else experienced this? Thanks in advance.


How new is it? The Allison is a smart transmission and takes sometime to learn. While it's learning you can feel hard shifts. When I do a re-learn on mine, it will do the same thing. So if the truck is new, I wouldn't worry about it too much for now. It should slowly go away as you drive it more.


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post #4 of 34 (permalink) Old 11-03-2016, 11:44 AM Thread Starter
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How new is it? The Allison is a smart transmission and takes sometime to learn. While it's learning you can feel hard shifts. When I do a re-learn on mine, it will do the same thing. So if the truck is new, I wouldn't worry about it too much for now. It should slowly go away as you drive it more.


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I have about 15k miles on it. Bought the truck new in May and I've experienced the issue about a dozen times since first noticing the problem mid October.

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post #5 of 34 (permalink) Old 11-03-2016, 11:59 AM Thread Starter
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Originally Posted by GMCustomerService View Post
Good Morning Kmagee,

We understand that you are looking for some assistance from other forum members, so we would like to offer our help. If you this interests you, please private message us with your VIN, full contact information, current mileage, and preferred GM dealership. From here, we will be able to take a look at your situation on our end and hopefully reach a resolution on your behalf. Thank you and we look forward to working with you.

Philip J.
GM Customer Care
Hi Philip,
I've tried PMing twice but they don't seem to be going thru. Could you try PMing me and I'll reply? Thanks in advance.

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post #6 of 34 (permalink) Old 11-03-2016, 01:56 PM
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Hi Philip,
I've tried PMing twice but they don't seem to be going thru. Could you try PMing me and I'll reply? Thanks in advance.
Good Afternoon Kmagee,

I would like you to know that we have received your private message and an adviser will be responding to you shortly. Thank you for your continued patience and we look forward to working with you.

Philip J.
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post #7 of 34 (permalink) Old 11-03-2016, 08:07 PM
 
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Kmagee: I have the same issue.. 2016 Duramax/Allison 12k on it. I have read here about it. Some chalk it up to "fuel slosh". It absolutely is not. I can't pinpoint it exactly, as far as what triggers it. But It never starts, right from a startup. It does happen, though exactly as you describe. Around 5MPH, when coming to a complete stop. It is a certain THUD, as if I get rear ended. The only thing that corrects it, is shutting the truck off. Usually after doing this, it goes away, for several hundred miles. I asked the dealer about it, they checked for bulletins, and they claim nothing, nor have they ever heard of it. They scanned my truck, but found nothing.. I am curious too, what this could be, and where this issue will be at 50/70/90k miles..
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post #8 of 34 (permalink) Old 11-04-2016, 01:20 PM
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I am betting it is just the allison shifting into 1st. do you feel the other downshifts when it slows down? actually feeling it shifting and slowing? I know most people (including myself) slow down harder now than in the winter for obvious reasons. I had an issue with my 04 when it downshifted the first time with snow on the ground...I ended up getting spun around because the back tires lost traction (stupid stock tires). Have you still felt this thud in the winter when you slow down differently than when it is dry?

Just throwing it out there, but I am betting it is fairly normal. My truck does it too and I think it is more pronounced during a regen.

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post #9 of 34 (permalink) Old 11-04-2016, 02:33 PM
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From time to time over the years I've followed Dmax related forums there have been a few who have reported shifting issues that ending up having parts (solenoid, valves...) in the transmission.

There have also bee some that have the similar/same symptom but it only occurs with the fuel tank level within a certain range, and even then it only occurs under certain drive/stop situations -- certain fuel level, certain rate of decel etc.

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post #10 of 34 (permalink) Old 11-06-2016, 02:32 PM
 
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The hard downshift into first when coming to a stop has happened on mine since day one, but only when the truck is in regen mode. The RPM increases by a about 300 RPM during regen and will affect the downshift into first when coming to a stop. Doesn't do it all the time while in regen but in my experience, if it happens, it is only when the truck is in regen and idle RPM is up. I assume this is not a fixable problem but let us know if it is a problem that can be fixed.

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