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Interesting... progress with odd trans behavior? (2015 6-speed)

OmniGLH

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Silver ice 6.2 Senior Enthusiast

Silver ice 6.2

Posted
Posted

My .02! well tried it this morning on my way to work. I have the 8 speed with the 3:42. Big improvement on shifting. I never had the so called clunk. So when I got off work I said the hell with it turn it off again along with traction control and stability trac. A lot faster truck.. and no (muddkatt) I didn't try to roast them. Wink wink

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Shu Enthusiast

Shu

Posted
Posted

I noticed more on my 30 mile drive home part city, some 70+ mph highway and then some 60+ mph two lanes. First the truck accelerates so much smoother through the gears. No gear change hesitations. My truck does not have a horrible vibration at all but I have always noticed my water bottle cap ring (left over after you break the cap off) rattles when the bottle is in the console cup holder. Well on my drive home with this deactivated I noticed that I wasn't hearing that rattle. So I watched carefully and the bottle was not vibrating as before. I also noticed that as I came off the highway from 63 mph up to a stop and left turn that the truck brakes much better. To me I feel prior to deactivating it, it felt like the torque converter was staying locked up and down shifts stalled later and the combination of those kept engine momentum making the brakes work harder. Also this would explain the transmission odd reaction to coast then back on the gas and getting the stall then reaction and then clunk or wrong gear.

Thomcat Senior Enthusiast

Thomcat

Posted
Posted

Thanks for the post :) ...wondered why the action of the tranny appeared to be "working backwards" when on my mountain roads and I couldn't get the grade brake to engage the way it did on my Avalanches......also why the mild 2-3 clunk.

 

My later year '12/'13 Avalanche trannys were also equipped with hill descent braking......although few owners really knew it existed or how it operated. The feature was "off" by default whether or not the shift lever button activated tranny was set in trailer towing mode......the feature turned on automatically only if the vehicle was decending a hill AND your foot remained on the brake holding it at a constant speed for more than 10 - 15 secs. - then the DIC would light up "Hill Braking On" keeping a constant speed until the you reached the bottom of the hill and then the DIC message would go out and the tranny's grade brake released back to the normal "off" mode.

 

Until reading this post, I wondered why the Silverado wouldn't engage hill braking when going downhill with foot on the brake at constant speed - now I know why....it's always on and you manually have to turn it off after every start!

 

Added: Played with it today and I see why and I'm glad it's on by default, at least in my mountain area, otherwise without the normal grade braking, even running an empty bed, it's a runaway going down steep mountain roads like the 1/2 mile long 7% grade on 230. So the normal grade braking on is welcome and can easily be turned off on long flat roads.....plus an additional more severe grade braking is activated when in trailer/town mode light is lit when in normal grade breaking..

Dunc Enthusiast

Dunc

Posted
Posted

Sorry if this is a dumb question, but if everyone is having such great results with this, why isn't the truck set up like this in the first place? Is there some kind of downside here?

Either GM is trying to achieve something by doing this (longer brake life, a change in MPG, or something) that we aren't aware of or the engineers simply didn't get the programming right. I'm leaning toward option 2 because why purposefully create something with poor shifting patterns and damage sales and/or a reputation. Either way I'm happy to finally have a truck that will turn a corner smoothly and not have a transmission that shifts like it's getting mixed signals. I just hope that GM reads this, takes notes, and investigates it to determine if they can release a programming update for us.

 

After trying this again yesterday and this morning I am convinced it's not in my head and the trans is shifting better. There were points yesterday in slow speed traffic where I knew it should be jerky and it was not. That proved it to me. I still get a clunk when shifting from R to D out of my driveway which is likely, but forward operation on the street is much better than before. The clunk when changing into R or D could be a simple programming change to reduce the harshness of engagement?

BIGDOGx Senior Enthusiast

BIGDOGx

Posted
Posted

Either GM is trying to achieve something by doing this (longer brake life, a change in MPG, or something) that we aren't aware of or the engineers simply didn't get the programming right. Either way I'm happy to finally have a truck that will turn a corner smoothly and not have a transmission that shifts like it's getting mixed signals.

 

After trying this again yesterday and this morning I am convinced it's not in my head and the trans is shifting better. There were points yesterday in slow speed traffic where I knew it should be jerky and it was not. That proved it to me. I still get a clunk when shifting from R to D out of my driveway which is likely, but forward operation on the street is much better than before. The clunk when changing into R or D could be a simple programming change to reduce the harshness of engagement?

Just makes too much sense for it not to fix the many issues we were having. The trans would constantly feel like it was trying engine brake and that's because it was. Maybe a good option when going down a hill towing something, but not driving on flat ground and trying to turn a corner! The setting is clearly not working as it should and needs to be programmed on the off position as a default as said previously.

 

Starting today i'm calling the 800-gm number everyday until they confirm they will be fixing this for good! I encourage everyone else to take ten minutes everyday to let gm know we are not forgetting this issue and they will be fixing it to OUR satisfaction not theirs!

The Mad Veteran Enthusiast

The Mad Veteran

Posted
Posted

Just makes too much sense for it not to fix the many issues we were having. The trans would constantly feel like it was trying engine brake and that's because it was. Maybe a good option when going down a hill towing something, but not driving on flat ground and trying to turn a corner! The setting is clearly not working as it should and needs to be programmed on the off position as a default as said previously.

 

Starting today i'm calling the 800-gm number everyday until they confirm they will be fixing this for good! I encourage everyone else to take ten minutes everyday to let gm know we are not forgetting this issue and they will be fixing it to OUR satisfaction not theirs!

 

I was just going to say something like this. But is there other ways too? Like send in complaints to GM about the issue or something.

zert100 Enthusiast

zert100

Posted
Posted

My '14 6.2 max tow has a very pronounced decel clunk that is most noticeable in 2nd & 3rd when letting off the gas. Of course the dealer and GM say its perfectly normal. I will give this a try today and report back. I'm hopeful, but not holding my breath...

Dunc Enthusiast

Dunc

Posted
Posted

The setting is clearly not working as it should and needs to be programmed on the off position as a default as said previously.

I'd be OK with a program design to have it as on, but only if the ange sensors detect and actual grade worthy of it. Going down a 0.5% angled road is not what I considering needing grade brake (which has turned mine on before). Now a 5-7% grade road then sure have it come on....otherwise it should be off completely and not doing something funky in the background while we think it's off.

 

EDIT: Didn't they say the trans was fixed on the 2017 models? If so they they clearly know what the problem was so why not send out the same fix for the cars under warranty still that were clearly not designed right? If they fixed it already then there is no additional R&D costs...only the cost of deploying the updates in the field. This also assumes their fix is programming and not mechanical.

tnchevy Senior Enthusiast

tnchevy

Posted
Posted

I read this post when it first started and got to try it out yesterday(only drive my truck 1 or 2 days a week). My truck did shift better and it also had less vibration on a short stint on the interstate. This isn't conclusive for me yet because my truck has always drove different on different days. My grade braking does come on quite often in my neck of the woods, mainly on long downhill stretches of highway and it actually does a decent job of holding the truck at a constant speed when gong down these long grades. I said decent because it is not perfect. The long grades that I regularly drive on are 55 mph speed limit and I stay close to that but the grade braking wants to hold the truck at 62 mph so I am still braking slightly. My old truck I was just used to these hills and would drop the truck to 3rd gear (4 speed tranny) to keep from hitting the brake so much. I will test it out more this weekend but I hope this is for real and just not an illusion.

Dunc Enthusiast

Dunc

Posted
Posted

Are any of you using cruise control with grade braking off? I think cruise control uses the same grade braking "technology".... still clunky feeling.

I am not, but that got me to thinking....I've notice that I can easily get better MPG without cruise control. I'm wondering now if the cruise control MPG might improve some.

piratepenguin Enthusiast

piratepenguin

Posted
Posted

I really didn't think that this would do anything, but i was amazed at the difference on my commute in to work today 30miles of stop and go city. The truck feels 500lbs lighter and shifts were so smooth i couldn't even feel them happening. It didn't stutter on finding any gears either. I'm honestly blown away at the difference this has made. Something is seriously screwed up from factory on these trucks.

Newell33 Enthusiast

Newell33

Posted
Posted

I got rid of my 2014 junker, but it always felt like there was a transbrake activating at times. I noticed it around corners like some, and then of course I had the horrible shifting characteristics and clunking. It was obvious that something in the programming wasn't right. I wonder now if this would have made any improvement. What baffles me though is that even with a custom tune, the truck exhibited some of this behavior. I'd be curious to hear how tuners are approaching this system, and if it's part of their programming. If they essentially leave the system intact and alone, then that would likely explain my truck's behavior.

kp52 Enthusiast

kp52

Posted
Posted

Been going back and forth (you can disable/enable while driving) and there certainly is a difference. Lot of hills where I live and my biggest complaint with this truck ('15 5.3/6sp/3.42) is the horrible shifting from the trans, it clunks, bangs, hesitates and never seems to be in the 'right' gear when passing. Turning off the grade braking helps quite a bit, especially for the horrible 'bang' when I slow down up a steep grade pulling into my driveway. The noise is so bad I drive 1/2 a mile out of my way so I can go downhill when turning into my driveway. No bang with the grade braking off, time will tell though, it may start to 'learn' if there is another table dedicated to the grade braking off and get worse over time. For now I'll turn it off and enjoy it.

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