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2020 Silverado 6 speed issues

R J

By R J
in Troubleshooting, Warranty & Recalls

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Grumpy Bear Senior Enthusiast

Grumpy Bear

Posted
Posted
13 hours ago, flyingfool said:

i found it interesting and have no idea why, but by shifting to neutral  on a 1500 truck , I actually gained more "rear brake bias" durring a stop. I wish i knew more about the brake proportioning system on these truck, 'cause the nose dive brake effect is not ideal. i wish it could be modified somehow

When you hit the brakes the torque converter clutch unlocks and the truck is now pushing the motor adding braking to the back wheels (2wd) or all four (4wd). The speed logic in the TCM will downshift to the gear for the speed on it's own as if you were coasting to a stop. At some point below about 10 mph your so far below the converters minimum coupling speed it no longer matters. 

 

Some states, like the one I live in, there is actually a law against being out of gear while in traffic. Just say' n. 

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CamGTP
CamGTP

Are you sure it's transmission related??   The 6 speeds can have a downshift clunk or lurch feeling sometimes at slower speeds but there really isn't much you can do about that. Sometimes it

Grumpy Bear
Grumpy Bear

When braking hard. There is  your clue. Drivelines have some play. It's required. Ever hear a string of box cars string up stopping? Just taking out thy slack. 

CamGTP
CamGTP

The work trucks and custom trims can still get the 6 speed auto.

flyingfool Senior Enthusiast

flyingfool

Posted
Posted (edited)

that's what i would think, but coasting to stop, usually the idle speed is about 800-1000 rpm so it still has a push your braking against. i just cant figure why the brake bias changes when in neutral

Edited by flyingfool
Grumpy Bear Senior Enthusiast

Grumpy Bear

Posted
Posted
18 minutes ago, flyingfool said:

that's what i would think, but coasting to stop, usually the idle speed is about 800-1000 rpm so it still has a push your braking against. i just cant figure why the brake bias changes when in neutral

That is strange. Mine idles at 535 rpm. My converter stalls at 1635 and starts to couple around 750-800 rpm. 

swathdiver Senior Enthusiast

swathdiver

Posted
Posted
13 hours ago, Grumpy Bear said:

YIKES, I'm only 30K from issues? 

?

That's less than a year away!

As clean as you keep your fluid Marty, I doubt it.  Mine is almost there too.

1 hour ago, flyingfool said:

i would like to find out more info on this, is there a gm tech bulitin  or tech documentation?

 

not even considering panic stop but just regular daily stop and go action,  neutral shifting makes the truck feel effortless entering the stop and more relaxing, then when in  Drive and having the engine pushing the driveline

Never seen anything about it or how it works save for that explanation given to me once.  Just stumbled across it while exploring the Tech-2.

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Alexmorales0850 New Member

Alexmorales0850

Posted
Posted
8 hours ago, swathdiver said:

As clean as you keep your fluid Marty, I doubt it.  Mine is almost there too.

Never seen anything about it or how it works save for that explanation given to me once.  Just stumbled across it while exploring the Tech-2.

Sup bud, read most of you comments seem like you have great knowledge with these trucks. 
I have a 17 1500, with a 4.3 sadly. My gear ratio is 3.23. With a 6speed transmission.  I’m planning on lifting it to 9” and slapping on some 37s. What gear ratio do you recommend to keep similar rpms to stock. Yes I know 37s with a v6 is stupid but I just love that look. 

Grumpy Bear Senior Enthusiast

Grumpy Bear

Posted
Posted
19 minutes ago, Alexmorales0850 said:

Sup bud, read most of you comments seem like you have great knowledge with these trucks. 
I have a 17 1500, with a 4.3 sadly. My gear ratio is 3.23. With a 6speed transmission.  I’m planning on lifting it to 9” and slapping on some 37s. What gear ratio do you recommend to keep similar rpms to stock. Yes I know 37s with a v6 is stupid but I just love that look. 

4.10 and 37's = 31 (stock) and 3.23. 

4.30 would be close to a 3.42

4.56 about the same as 3.73

4.88 close to 4.10

If you run in M5 on your current 31's that will give you a feel for rpm in top gear with the 4.10 on 31 or 4.88 on 37.

Frankielozano214 Senior Enthusiast

Frankielozano214

Posted
Posted
17 minutes ago, Grumpy Bear said:

4.10 and 37's = 31 (stock) and 3.23. 

4.30 would be close to a 3.42

4.56 about the same as 3.73

4.88 close to 4.10

If you run in M5 on your current 31's that will give you a feel for rpm in top gear with the 4.10 on 31 or 4.88 on 37.

Would this also be same for my truck? 2014 Silverado 5.3 2wd with 3.42 right now already lifted on 37s though but looking to regear soon but I drive on the highway a lot so would 4.10 be the best?

Grumpy Bear Senior Enthusiast

Grumpy Bear

Posted
Posted
1 minute ago, Frankielozano214 said:

Would this also be same for my truck? 2014 Silverado 5.3 2wd with 3.42 right now already lifted on 37s though but looking to regear soon but I drive on the highway a lot so would 4.10 be the best?

If you wish to keep the 3.42 to stock relationship; then 4.30. There is a small fly in the ointment however. Roll out distance is NOT Pi of the diameter and this reference treats it as if it were. That is a 31" tire will have a rollout of something less but how much? Some places like Tire Rack will have that information for a specific tire. 

 

That said even if off by an inch or so the rpm will be pretty darn close for the ratios I've given. 

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CamGTP Senior Enthusiast

CamGTP

Posted
Posted

Use a rpm/gear ratio calculator to see where your RPM's will end up.

 

I think with 4.10's on those size tires you'd be around 1750-1800rpm at 70mph.

 

Right now it's probably around 1500 at 70mph if I had to guess.

 

 

Alexmorales0850 New Member

Alexmorales0850

Posted
Posted
54 minutes ago, Grumpy Bear said:

4.10 and 37's = 31 (stock) and 3.23. 

4.30 would be close to a 3.42

4.56 about the same as 3.73

4.88 close to 4.10

If you run in M5 on your current 31's that will give you a feel for rpm in top gear with the 4.10 on 31 or 4.88 on 37.

Great info brother. Something I forgot to ask. How will the truck perform with overdrive on those gears. 

Alexmorales0850 New Member

Alexmorales0850

Posted
Posted
25 minutes ago, CamGTP said:

Use a rpm/gear ratio calculator to see where your RPM's will end up.

 

I think with 4.10's on those size tires you'd be around 1750-1800rpm at 70mph.

 

Right now it's probably around 1500 at 70mph if I had to guess.

 

 

I’d have to drive it to be sure. But it sounds about right. Just worried about how re gearing will affect overdrive 

Frankielozano214 Senior Enthusiast

Frankielozano214

Posted
Posted
37 minutes ago, Grumpy Bear said:

If you wish to keep the 3.42 to stock relationship; then 4.30. There is a small fly in the ointment however. Roll out distance is NOT Pi of the diameter and this reference treats it as if it were. That is a 31" tire will have a rollout of something less but how much? Some places like Tire Rack will have that information for a specific tire. 

 

That said even if off by an inch or so the rpm will be pretty darn close for the ratios I've given. 

Ok kinda get it I’ll definitely have to read more on this to make sure I get the right gears for my truck

CamGTP Senior Enthusiast

CamGTP

Posted
Posted

A tune is required when changing gears and tire size. So whoever does the tune should be able to get it shifting good.

 

I think the computer/ABS may freak out if you actually put 37's into the tune though, I forget if they can put 35's in the calibration have it be fine and just deal with a slightly off speedo.

Frankielozano214 Senior Enthusiast

Frankielozano214

Posted
Posted (edited)
4 minutes ago, CamGTP said:

A tune is required when changing gears and tire size. So whoever does the tune should be able to get it shifting good.

 

I think the computer/ABS may freak out if you actually put 37's into the tune though, I forget if they can put 35's in the calibration have it be fine and just deal with a slightly off speedo.

Got my truck tuned already, and tires size calibrated already but needa regear and get another tune after I install my exhaust since I’ve done a cold air intake.

Edited by Frankielozano214

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