About Composite Leaf Springs on the 2019 Silverado and Sierra

Z06JPB · August 26, 2019

This has been an on-going research project of mine. I discovered when I inquired about having the Trail Boss (TB) factory lift kit (GM part# 84629787) added to my 2019 LT Z71, that I could not have the kit installed due to the secondary composite leaf springs on my truck. Upon further investigation, I found that ONLY the LT with 5.3L (and LT with 3.0 diesel and short box) had the composite leaf springs preventing the truck from having a TB lift added.

On the GMC side, I found out the Sierra Denali also uses the same leaf springs with composite secondary as the LT 5.3L.

My first impression was, “why the heck would GM do this?” Why wouldn’t the LTZ or High Country (HC) have the the composite leaf? Why would only the mid-level LT have it? The Sierra Denali has it and it’s a $60K+ truck. My LT averages around $45K. I might be a little upset as a LTZ or HC owner to find out my rear suspension is the same as on any Custom trim truck, or even, the base W/T model.

I’ve doing a lot of reading on composite leaf springs and there are more advantages to them than disadvantages. Though they are dimensionally bigger (thicker) than the steel counterpart, they weight a lot less, last longer, and offer better damping properties than steel. GM has had a good track record using composite leaf springs. The same technology has been used on the corvette since 1997 with the introduction of the C5.

Disadvantages are minimal, such as, they are more expensive to produce, can burn up in a fire, and in this case, can’t be further bent or altered out of original specification. This must be the reason GM won’t allow the lift to be added to vehicles with a composite leaf. I’m sure the leaf could take the additional stress, GM engineers just want to play it safer than sorry.

So with this, the Silverado LT 5.3L (and LT 3.0 diesel with short bed) and the Sierra Denali are the only trucks to use the composite leaf. Though I’m disappointed I won’t be able to get the TB lift added, I’m now pretty stoked to find out my LT has more mechanical innovation put into the suspension and I didn’t have to spend $15K+ more for a Sierra Denali to get it.

However with this, it seems that if someone is looking for a top-end truck, the Denali would be the better choice over the HC which lacks the particular composite leaf spring feature, if that mattered to the buyer.

For reference, attached here are the GM compatibility charts for the Silverado and Sierra to see if you can add the TB lift kit. Also here is a link to the previous discussion about the TB lift kit where you can find more detail about installation and issues surrounding the composite leaf springs.

bobboberton1 · January 30, 2020

Have you found out anymore information? Also surprised that my LT Z71 cannot accept GM official 2" lift. Did you end up installing another lift?

2020_Z-71 · August 13, 2020

Heck I’d just like Install better shocks, with soils and struts to level my truck. $50,000 PLUS dollars and I can’t even lift this POS truck, yea I’m friggen pissed. This is my first new Z71 and I’ll be damned it’s looking like my last one too!

AJMBLAZER · August 16, 2020

On 8/13/2020 at 2:23 AM, 2020_Z-71 said:

Heck I’d just like Install better shocks, with soils and struts to level my truck. $50,000 PLUS dollars and I can’t even lift this POS truck, yea I’m friggen pissed. This is my first new Z71 and I’ll be damned it’s looking like my last one too!

No reason you can’t. Blocks will go under them and standard rear springs will bolt in place of them.

bmdupont · September 15, 2020

My dealer quoted me the lift plus the steel sprigs as I have composite now. I’m sure someone else has pointed this out but just in case I’m posting.

Edited September 15, 2020 by bmdupont

Welder2014 · September 15, 2020

On 8/26/2019 at 2:40 PM, Z06JPB said:

This has been an on-going research project of mine. I discovered when I inquired about having the Trail Boss (TB) factory lift kit (GM part# 84629787) added to my 2019 LT Z71, that I could not have the kit installed due to the secondary composite leaf springs on my truck. Upon further investigation, I found that ONLY the LT with 5.3L (and LT with 3.0 diesel and short box) had the composite leaf springs preventing the truck from having a TB lift added.

On the GMC side, I found out the Sierra Denali also uses the same leaf springs with composite secondary as the LT 5.3L.

My first impression was, “why the heck would GM do this?” Why wouldn’t the LTZ or High Country (HC) have the the composite leaf? Why would only the mid-level LT have it? The Sierra Denali has it and it’s a $60K+ truck. My LT averages around $45K. I might be a little upset as a LTZ or HC owner to find out my rear suspension is the same as on any Custom trim truck, or even, the base W/T model.

I’ve doing a lot of reading on composite leaf springs and there are more advantages to them than disadvantages. Though they are dimensionally bigger (thicker) than the steel counterpart, they weight a lot less, last longer, and offer better damping properties than steel. GM has had a good track record using composite leaf springs. The same technology has been used on the corvette since 1997 with the introduction of the C5.

Disadvantages are minimal, such as, they are more expensive to produce, can burn up in a fire, and in this case, can’t be further bent or altered out of original specification. This must be the reason GM won’t allow the lift to be added to vehicles with a composite leaf. I’m sure the leaf could take the additional stress, GM engineers just want to play it safer than sorry.

So with this, the Silverado LT 5.3L (and LT 3.0 diesel with short bed) and the Sierra Denali are the only trucks to use the composite leaf. Though I’m disappointed I won’t be able to get the TB lift added, I’m now pretty stoked to find out my LT has more mechanical innovation put into the suspension and I didn’t have to spend $15K+ more for a Sierra Denali to get it.

However with this, it seems that if someone is looking for a top-end truck, the Denali would be the better choice over the HC which lacks the particular composite leaf spring feature, if that mattered to the buyer.

For reference, attached here are the GM compatibility charts for the Silverado and Sierra to see if you can add the TB lift kit. Also here is a link to the previous discussion about the TB lift kit where you can find more detail about installation and issues surrounding the composite leaf springs.

1981 Corvette first year using composite rear spring.

Gangly · September 15, 2020

My understanding from posts on this site and others is that most owners of trucks with composite leaf springs haven't changed anything about their rear suspension, other than blocks and shocks, and simply added the factory lift regardless with no issues at all. I'm not sure what the engineering behind the decision to not use a factory lift on composite leaf springs is, but I sure would be interested to know as I don't personally see an issue, but a materials expert/engineer should be able to explain it.

Duramax3oh · September 15, 2020

Well this is interesting that I was not aware of at all. So I have composite leaf springs in my ‘20 Silverado LT Z71? And that is a good thing right? Lol

In planning to order front coil overs shortly (1.5-2” front lift) I’m okay with adding 1-2” blocks in the rear? And/or add-a-leaf or Roadmasters RAS?

bmdupont · September 15, 2020

3 hours ago, Gangly said:

My understanding from posts on this site and others is that most owners of trucks with composite leaf springs haven't changed anything about their rear suspension, other than blocks and shocks, and simply added the factory lift regardless with no issues at all. I'm not sure what the engineering behind the decision to not use a factory lift on composite leaf springs is, but I sure would be interested to know as I don't personally see an issue, but a materials expert/engineer should be able to explain it.

I think you are right, 2 dealerships said it wasn’t needed and 1 said I would need to change the leaf springs. All have checked with VIN. I looked and I believe mine are composite. The one dealer who said new leaf springs would be needed must have old info.

Grumpy Bear · September 15, 2020

I use to have a parts man that knew every part for every car over a 40 year period. Today, if it isn't in the computer it can't be done. They don't ask why or why not. It just can't because.....it doesn't say that it can. Just say' n.