2014 - 2018 5.3 6 speed downshift jerks

chrispassas21 · October 25, 2019

Do you all think if I got the fluid changed out with that new Mobil one stuff it will help with this shudder/bucking? Thanks in advance

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slimjim2525 · October 26, 2019

So, my truck has the dreaded clunk when downshifting, especially noted when hard braking. Even my wife noticed, and she doesn't usually notice anything. I read somewhere to add lube guard red. I was a little hesitant because the truck is still under warranty with 27k miles. I couldn't take it anymore though, and added it. It made shifting, and especially downshifting 90% better. It did not eliminate it completely. but now way more often than not, it does not clunk.

Bob2C · October 26, 2019

So, my truck has the dreaded clunk when downshifting, especially noted when hard braking. Even my wife noticed, and she doesn't usually notice anything. I read somewhere to add lube guard red. I was a little hesitant because the truck is still under warranty with 27k miles. I couldn't take it anymore though, and added it. It made shifting, and especially downshifting 90% better. It did not eliminate it completely. but now way more often than not, it does not clunk.

How much did you add?

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slimjim2525 · October 26, 2019

A full bottle, 10 oz. It says 1oz per quart of tranny fluid. How much do our 6 speeds hold.

Bob2C · October 26, 2019

A full bottle, 10 oz. It says 1oz per quart of tranny fluid. How much do our 6 speeds hold.

Ok. Great. Holds 12 to 13 quarts

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nluchau · October 28, 2019

On 10/25/2019 at 12:48 AM, mmmikkke said:

My truck's tcc lockup by itself is not harsh or jerky. For my 2016 Silverado 4.3L V6, harsh or jerky describes the 3-2 and 2-1 downshifts as I come to a very gradual stop and the tcc has not yet unlocked. At zero throttle, decelerating to a gradual stop, my truck's tcc seems programmed to unlock after the 2-1 downshift, just in time to NOT lug the engine before shedding those final 2 or 3 mph. In other words, under the described conditions, tcc unlocks at the "last minute" so that engine RPM stays above or at 600 (idle) as the truck slows to 3, 2, 1, and finally 0 mph. I'm considering buying an hp tuner at hptuners.com just so I can play with the tcc minimum speed (minimum unlock speed while decelerating). It seems if I could raise tcc min speed to maybe 10 mph. then the 3-2 and 2-1 downshifts would occur while the tcc is unlocked, and so the torque converter's fluid coupling would absorb the 3-2 and 2-1 downshift harshness and all would be good.

My lockup isn't harsh or jerky either upon acceleration. The only issue is upon decel when it goes 4-3, 3-2, 2-1. There is a tie up sensation when it downshifts and what I've read and been told is TCC is engaged during decel and at each downshift it unlocks and locks again but yes I do feel the "let go" at almost stopped and it feels like someone bumped into you from behind. If the TCC wasn't locked up during decel I dont think I'd be bringing up this issue but apparently its just how it is. It's really hard for me to acknowledge this I guess.

nluchau · October 28, 2019

On 10/26/2019 at 8:22 AM, slimjim2525 said:

So, my truck has the dreaded clunk when downshifting, especially noted when hard braking. Even my wife noticed, and she doesn't usually notice anything. I read somewhere to add lube guard red. I was a little hesitant because the truck is still under warranty with 27k miles. I couldn't take it anymore though, and added it. It made shifting, and especially downshifting 90% better. It did not eliminate it completely. but now way more often than not, it does not clunk.

I've always wondered about this stuff and had heard good things. I just wanted warranty to work for me but it hasn't. Might be something I need to try.

nluchau · October 28, 2019

On 10/25/2019 at 4:59 AM, chrispassas21 said:

Do you all think if I got the fluid changed out with that new Mobil one stuff it will help with this shudder/bucking? Thanks in advance

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Good question, as far as I know the dealer was only replacing the fluid in the 8 speeds not the 6. If you switch it out on your 6 speed let us know if it works.

chrispassas21 · October 28, 2019

Good question, as far as I know the dealer was only replacing the fluid in the 8 speeds not the 6. If you switch it out on your 6 speed let us know if it works.

I don’t see what the difference would be? Both ATF but this is not my strong point.

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slimjim2525 · November 3, 2019

On 10/26/2019 at 9:22 AM, slimjim2525 said:

So, my truck has the dreaded clunk when downshifting, especially noted when hard braking. Even my wife noticed, and she doesn't usually notice anything. I read somewhere to add lube guard red. I was a little hesitant because the truck is still under warranty with 27k miles. I couldn't take it anymore though, and added it. It made shifting, and especially downshifting 90% better. It did not eliminate it completely. but now way more often than not, it does not clunk.

Well, not so fast. Got 3 quite harsh downshifts today. It's so random it's annoying. I go get a coffee every morning with my dog and drive around listening to the news. Some days it's perfect, some days it's shit. Thinking of changing out the fluid now that the lube guard did not take it away completely. It is better though.

nluchau · November 4, 2019

9 hours ago, slimjim2525 said:

Well, not so fast. Got 3 quite harsh downshifts today. It's so random it's annoying. I go get a coffee every morning with my dog and drive around listening to the news. Some days it's perfect, some days it's shit. Thinking of changing out the fluid now that the lube guard did not take it away completely. It is better though.

Thanks for the honest feedback on the product. I guess I won't be trying it. Funny thing is though, my downshift jerks aren't random as they occur all the time.

mmmikkke · November 4, 2019

The recently accumulating anecdotes suggest that the tcc is not unlocking, during deceleration to a stop. For my truck, this is an intermittent problem, but for @nluchau's truck, for example, the problem is chronic. @nluchau, when did you first notice this and did it begin as an intermittent malfunction and progress to a chronic one? I'm starting to think this is a defect in the design of the tcc and this problem might eventually affect all 6L80 trucks as they age and get past 50k miles.

nluchau · November 7, 2019

On 11/3/2019 at 11:01 PM, mmmikkke said:

The recently accumulating anecdotes suggest that the tcc is not unlocking, during deceleration to a stop. For my truck, this is an intermittent problem, but for @nluchau's truck, for example, the problem is chronic. @nluchau, when did you first notice this and did it begin as an intermittent malfunction and progress to a chronic one? I'm starting to think this is a defect in the design of the tcc and this problem might eventually affect all 6L80 trucks as they age and get past 50k miles.

I noticed this from day 1 of ownership (New truck). Now I have 39k miles. On my second transmission and it still does it but not as bad. Now I have an abrupt 4-5 shift under slow acceleration. It hits hard at slow throttle but if I'm heavy on the throttle it seems ok. At the moment that is now more irritating to me than the jerky downshifts.

Brian11275 · September 13, 2020

So basically this is not a malfunctioning transmission, I presume. This mild jerking sensation is normal, yes? If this is the case then I guess I can live with it. It’s just something I’ll have to get use to. As long as I know that there’s nothing actually wrong with the vehicle.

mmmikkke · January 23, 2021

Funny thing is, I had some work done on my Silverado at my local GMC dealer. They gave me a 2018 Sierra as a loaner. Velvety smooth--no jerking. Are there 2 or more plants that manufacture the 6L80s? Maybe depending on place of manufacture the tune is different with one optimizing fuel economy and one optimizing smoothness..

Anybody else have any thoughts? Bueller?