Rear Diff/Gears Help

g0ats3cks · March 7, 2019

My truck is a 2014 Silverado 1500 LTZ

RPO Codes related to this are GU4 and G80 (let me know if you need additional info).

I'm lifting my truck 3.5 inches and putting 33's on it. Unfortunately, my truck came with the 3.08 gears and I'm wanting something that's going to make it more responsive and better for towing. I asked my local truck shop about swapping out to 3.73 or 4.10 gears and I was told I need to replace something (I didn't quite understand what they were talking about, I think he said the housing) or use an adapter. They recommended not using the adapter and replacing instead. So, it seems this is more complicated than just swapping out the ring and pinion and requires additional parts and labor. Can anyone shed some light on this for me?

Also, when I'm looking for parts online, there are all different size ring and pinions (Ex. 8.5, 8.6, 9.5, and 9.75) and for different bolt rear ends (Ex. 10, 12, and 14), all listed under 2014-2018 Silverado 1500s. How do I find out what's on my truck? The only thing I can find through the RPO Code is the gear ratio (GU4 - 3.08) and G80 (Limited Slip Differential).

Any help is appreciated, thanks.

FlipZ71 · March 7, 2019

On top of the rear housing us a set of ##

This will tell you the size...

What the shop has told you is correct ...

The Carrier in your housing that runs the 3.08 gears can not be used to run the 4.10

The carrier is the assembly the ring gear is mounted on ....

g0ats3cks · March 7, 2019

Thanks for the info.

Are they also correct that using the spacer is ill-advised in a daily driver? The truck is not used for off-roading or towing heavy loads consistently, just the occasional trip to the boat ramp. Should I spend the extra money on the carrier swap or would I be ok with using the spacer?

FlipZ71 · March 7, 2019

Honestly I dont know...

All I know concerning the spacer is the same as what you were told....

g0ats3cks · March 7, 2019

Ok, thanks for the info.

aseibel · March 7, 2019

I don't know if you really NEED 3.73 gears to drive on 33's. Now if you wanted to go up to 35's that would be a much bigger difference from stock tire size.

If you are dead set on swapping gears for improved response, I think you may be able to put 3.42 in your current housing with the same carrier, for less money? I'm not an expert on gears, maybe someone can chime in with what gears you could stick in with your existing carrier.

But if you're willing to pay the $2,000+ for the work, you can get whatever axle ratio you want.

Edited March 7, 2019 by aseibel

g0ats3cks · March 7, 2019

Thanks for the input. Just going on the bit of research I've been able to do since my initial post, it seems most people with 33's recommend 3.73 or 4.10 gears. 3.73 if you want to retain some good fuel economy, or the 4.10 if you want the extra performance. Another response I saw said that running 3.73 with 33's would perform roughly the same as 3.23 gears with stock tires and that running 4.10 with 33's would perform roughly the same as 3.73 with stock tires. I was quoted $1500 for the swap.

Some info I got from East Coast Gear Supply says that if you have 3.08 gears, you must use the ring gear spacer or swap carriers to change to any other gear ratio, the way I understand it. Here is the info:

https://eastcoastgearsupply.com/files/PDF Files/gm9-5-12-bolt.pdf

Edited March 7, 2019 by g0ats3cks

aseibel · March 7, 2019

maybe my math is off, but here's my thoughts:

going from oem tires, which I'm assuming are 31.5" to 33" is an increase of about 10% in circumference

Going from 3.08 gear to 3.73 is a change of 21%, or more than double the difference.

3.42 gears with 33s would maintain roughly your same ground speed to axle speed as your OEM truck/tires.

So if you want your truck to drive like a OEM one with 3.42, I guess you do need to switch to 3.73. haha, I hope no one could follow that logic.

g0ats3cks · March 7, 2019

Yeah, I follow you there. I'm not very good with this gear ratio thing, and only going off what I see others have done, said, or told me. Overall, it is more complicated than I initially thought (just swapping the ring and pinion). Maybe I'll just get a tune first and see how the truck reacts to that before I shell out a grand or more on new gears.

swathdiver · March 7, 2019

The 3.08 ring and pinion uses a different sized carrier. Don't cheap out with the spacer, you'll only pay for it later, get the larger center section and 3.73s will be fine. For less money, you might look for a complete axle swap that already has a 3.42 or 3.73 gear in it. Especially if it's a 9.5" RPO AXN semi-floater. Much stronger than the 8.6".