2015 LTZ 6.2L Rear Axle Gearing Change

[txmuder]

OK so I did this on my 2012 with 6.2 and really enjoyed the difference by changing to 410 gears verses the OEM 342's. Yes lost MPG but considering I drive a company vehicle 5 days out of 7 it was not a big factor IMO.

I spoke with the same CO that did the work last time and was advised to go with 373's on this setup due to the 8 spd tranny gearing. Which from my research sounds right. Who if any one has done this and how did it turn out?

 

Also he quoted me right at $1000.00 with Tax included. (2012 cost was around $870,00)

[newdude]

Is it a max tow?

[blwright]

Is it a max tow?

if his stock gearing is 3.42, yes.

[newdude]

if his stock gearing is 3.42, yes.

 

Aware of that...was asking op if his truck is max tow or not but judging by the small mirrors in his profile pic, I am assuming that it is not a max tow.

[txmuder]

No Mine is not (323 gearing), looking to step up to 373 gearing. 1st gear is OK on take off but after that (esp when towing) seems to fall on its face. I guessing that with the 8spd tranny it still will be getting decent MPG esp if I put it back to AFM (4V mode) which I have disabled now and still am ranging combined City/Highway around 17.4. Highway on a 180 mile trip to East Texas was 22.6 with out 4V activated.

[Badass69]

No Mine is not (323 gearing), looking to step up to 373 gearing. 1st gear is OK on take off but after that (esp when towing) seems to fall on its face. I guessing that with the 8spd tranny it still will be getting decent MPG esp if I put it back to AFM (4V mode) which I have disabled now and still am ranging combined City/Highway around 17.4. Highway on a 180 mile trip to East Texas was 22.6 with out 4V activated.

Interested in this as well. I am not disappointed with my 3.23's in my double cab but I think a 3.73 gear set would be pretty fun on stock tires. I mean Ram still offers 3.92's in their 8 speed trucks and the zf's first gear is steeper than the 8L90E. The additional mechanical advantage while in any gear would be nice.

 

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[TxTruckMan]

Post pics of the rubber stripes on the road after your mod. You are going to burn through tires like crazy with those gears. Enjoy!

[robvas]

Yea, the truck is not "falling on it's face"

[Badass69]

Yea, the truck is not "falling on it's face"

With a load on its not that impressive either. I know where the op is coming from when he says that. I mean it's still strong but a deeper set of gears would really help the situation. The engine is impressive no doubt and feels tons more powerful than the old LS L92/L9H... especially for low end torque. Yes you can break the ratio down gear by gear and show it can drop 4 gears and Rev to the moon but at the end of the day it only still has 3.23's regardless of what gear it is in. Having 8 speeds really allows it to stay in the powerband but with 3.73 it would just be all that much stronger plus cruise at no different rpm than the 6 speed 3.73 trucks do now. As much of a gutless joke that they are the Hemi Rams really have it in that regard with the ZF and 3.92's... but those turds need all the help they can get too. I had around 8000 lbs behind mine and beyond the crazy vibration from the back of the truck it pulled okay. And really... mine falls on its face every single time it shifts into second the first time it shifts after a start.... Lol! Different issue though.

 

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[07Softail]

AAM which is the manufacturer of the axle assembly under your truck makes a 3:73 ratio for the 9.76, I think i'm going with 4:10's in my 2014 5.3 2wd RCSB.

 

RT

[robvas]

With a load on its not that impressive either. I know where the op is coming from when he says that. I mean it's still strong but a deeper set of gears would really help the situation. The engine is impressive no doubt and feels tons more powerful than the old LS L92/L9H... especially for low end torque. Yes you can break the ratio down gear by gear and show it can drop 4 gears and Rev to the moon but at the end of the day it only still has 3.23's regardless of what gear it is in. Having 8 speeds really allows it to stay in the powerband but with 3.73 it would just be all that much stronger plus cruise at no different rpm than the 6 speed 3.73 trucks do now. As much of a gutless joke that they are the Hemi Rams really have it in that regard with the ZF and 3.92's... but those turds need all the help they can get too. I had around 8000 lbs behind mine and beyond the crazy vibration from the back of the truck it pulled okay. And really... mine falls on its face every single time it shifts into second the first time it shifts after a start.... Lol! Different issue though.

 

Sent from my potato

A 8-speed with 3.23 is very, very close to a 6-speed with 3.73 gears. 2nd and 3rd are actually better ratios than the 6-speed.

 

PickupTrucks.com tested a 2015 Silverado with 3.23's against a 2015 Sierrra with the 3.42's and they performed almost identically in the Davis Dam hill climb and loaded 1/4 mile

 

 

 

[Badass69]

A 8-speed with 3.23 is very, very close to a 6-speed with 3.73 gears. 2nd and 3rd are actually better ratios than the 6-speed.

 

PickupTrucks.com tested a 2015 Silverado with 3.23's against a 2015 Sierrra with the 3.42's and they performed almost identically in the Davis Dam hill climb and loaded 1/4 mile

 

 

 

And if you read what you quoted I already said that with my break it down gear by gear comment.... lol. The truck would just be that much more impressive with the 8 speed and 3.73 gears, period. It doesn't really matter to me how it stacks up to prior model year trucks in performance. .. i want improvement not semi equality. Towing with 3.23's in this thing is pretty meh at best... it tows like a powerful engine handicapped by high rear end gearing. If you mat it so it drops into like third and of course it pulls but with a deeper rear end ratio it wouldn't automatically need all that rpm with torque this engine makes. I drove a max tow version too and decided that it really wasn't worth the money with only 3.42 gears and god awful looking mirrors so this route and possibly going 3.73 made more sense. I see myself doing a gear swap in the near future honestly but my hold out is the aftermarket and getting rid of the gov lock. I want a Detroit locker in this truck like my 05 has in it. If it takes too long i will just drop the old 9.5" carrier in it(I happen to have a new 9.5" Detroit on the shelf too) and be done with the gov lock and the gears. Not to mention the rpm it runs at in 8th really isn't necessary either considering the 6L80e has the same overdrive ratio as the 8 and the 3.73 gear 6 speeds do well for economy anyhow.

 

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[txmuder]

Ok, its done as of Friday 10-30-2015. Rear gears are changed from 3.23 to 3.73 ratio and I love it so far but since SE Texas has been hit with so much wind and rain starting that same Friday I dont have any actual performance figures other than I ate the lunch of a 2015 GMC CC with 6.2 and the towing package with 3.42 and 17" or 18" wheels setup. He also had a programmer and CAI. I walked off and left him on 3-4 different tries. He and I pulled over and he did not understand why he did not pull on me (he first thought I had a 5.3 and the Rally Edition due to my strips, LOL!!)

 

The change cost 1465.00 and the axle shop had to go with GM's 3.73 gears and limited slip unit as the OEM setup with 3.23 gears requires it all to be changed. Something like that ( I am not a mechanic so don't have great details).

 

My MPG has not really changed that much and actually it seems it remains in 4V easier due to the torque has increased while its in that mode and takes less effort to accelerate in 4V mode, so my average MPG has seemed to increase when cruising around (keeping my foot out of it) Got to work this morning and at 26 miles to work averaging 70 MPH the MPG shows 20.1 average and 20.6 best. 75 MPH RPM's are reading about 1900 rpms

 

When it dries out some I will play with it a little more and try and get more performance info, but it is a positive difference so far.

 

Jim

[TJay74]

Did the shop reprogram the ECM/TCM for the gearing change?

[txmuder]

No the shop only installed new gearing, I reprogrammed the ECM using my programmer I have installed and was able to change to 3.73 ratio from 3.23.