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Rear End Bang

Glava2876

By Glava2876
in Troubleshooting & Recalls

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Glava2876 Enthusiast

Glava2876

Posted
Posted

My new Denali 6.2 A8 started the 2-1 bang shift that can feel like you were rear ended.

I also have a 2015 Corvette with a M7, but the Corvette uses the same basic 8speed and I noticed some similar complaints about the A8 on the Corvette Forum -so I asked about it on one tread, letting them know it was in my GMC and got this response;

 

 

The 2-1 bang is a 0 pedal driver demand issue. The factory table has large negative torque demand at 0 pedal coming down in speed and when you get to 0 mph it demands 77 ft lbs (axle torque) from like -400.

I have been working with the driver demand table in the low speed / low (or zero) pedal areas as well as the downshift speeds/torque converter unlock speeds and have nearly eliminated the issue.

A large percentage (almost all) of the A8 issues are due to poor programming and don't need a transmission replacement. GM needs to crack some heads in their computer nerd dept and write some tunes that work better.

 

 

I am not the sharpest tool in the shed and it may not be right, but I thought I could try giving a little gas with my right foot while braking with the left to see if more than 0 demand made any difference. It did and depending on the amount that I pushed the accelerator while I braked, the bang was just barely perceptible or gone.

So is there a way to get a tune to do that?

pm26 Senior Enthusiast

pm26

Posted
Posted

Big bang for a big buck - sounds like something GM is getting good at.

 

I am quite sure a good tune can greatly mitigate this problem. I am disappointed that they even have issues like this with the new Corvette.

BuyAmericanIron Enthusiast

BuyAmericanIron

Posted
Posted

My truck does exactly the same thing. Our subdivision is on a road with curves and slight ups and downs. At times when cresting a slight incline at about 30 mph when you let off of the gas it feels like the trans tries to upshift and you get the "bang". First time it did this (with the 2nd transmission) my wife took a deep breath and looked at me and said "did someone just hit us?" All I could say was no, it is just the transmission clunk, again. I have gotten used to it now and just ignore it until the truck is gone. Damn shame with such a nice truck. My wife's ATS is smooth as silk. Why does the truck have to be so different?

Tattooo Senior Enthusiast

Tattooo

Posted
Posted

Mine has done that from day one but after 6 months it doesn't do it hardly at all....could've been the tranny learning & programming driving pattern but not sure

pm26 Senior Enthusiast

pm26

Posted
Posted

Add clamps on the leaf springs... it will help. Search for more info...

How would absence of such clamps cause a "bang"?

GMC-AT Senior Enthusiast

GMC-AT

Posted
Posted

I have no idea... I just know there is a long post about it helping a lot of the bang, rear end clunk, etc, etc... and even trans shifting. I installed on my truck after reading.. and does help. truck feels more planted in the rear as well.

Glava2876 Enthusiast

Glava2876

Posted
  • Author
Posted

dang, bud, can't you even give me credit when you copy/paste my material? :lol:

Sorry, I wanted to get the information on both sides, but wasn't sure if I should put your actual name on it.

So are you happy overall with the Corvette -mine is my all time favorite car!

Anyway, I'm bringing my Denali in Friday to see what the dealer comes up with and will share what they do -and other than the bang problem, I think that this truck is great.

Higgs Boson Enthusiast

Higgs Boson

Posted
Posted

Sorry, I wanted to get the information on both sides, but wasn't sure if I should put your actual name on it.

So are you happy overall with the Corvette -mine is my all time favorite car!

Anyway, I'm bringing my Denali in Friday to see what the dealer comes up with and will share what they do -and other than the bang problem, I think that this truck is great.

 

I am just kidding with you, I thought it is funny we are both on the same two forums with the same two cars.

 

yes, i like my C7, its a perpetual project..... :-)

i also am very happy with my truck!

scott19677 Senior Enthusiast

scott19677

Posted
Posted

 

I am just kidding with you, I thought it is funny we are both on the same two forums with the same two cars.

 

yes, i like my C7, its a perpetual project..... :-)

i also am very happy with my truck!

 

 

Hi. My second car is a Ford Focus and has a front end bang. You think I could join your guy's club. lol Ehh.... never mind I'm just jealous. New truck AND a Corvette! I should have stayed in school.

But on a serious note I did just call and make an appointment to have the "bang" issue checked out on my '14 Z71 and I was just wandering if you guys know where exactly the banging is occurring at? Is it the trans? The slop in the rearend? U joints? All of the above? I'm trying to get mine fixed before I get my tune.

Higgs Boson Enthusiast

Higgs Boson

Posted
Posted

 

 

Hi. My second car is a Ford Focus and has a front end bang. You think I could join your guy's club. lol Ehh.... never mind I'm just jealous. New truck AND a Corvette! I should have stayed in school.

But on a serious note I did just call and make an appointment to have the "bang" issue checked out on my '14 Z71 and I was just wandering if you guys know where exactly the banging is occurring at? Is it the trans? The slop in the rearend? U joints? All of the above? I'm trying to get mine fixed before I get my tune.

 

It's hard to tell where it is occurring mechanically.

ace ventura Enthusiast

ace ventura

Posted
Posted

I had the rear end bang and the dealer ended up finding two bolts in the trans were not at all tightened at the factory.

TxTruckMan Senior Enthusiast

TxTruckMan

Posted
Posted

When I saw the title of the thread I thought this was going to be about something more exciting!

 

Sorry, my mind lives in the gutter sometimes...

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