re-gearing for 37's ??

[Byrds8]

That is about what I figured but wasn't sure.

[Txgunslinger]

Glad I found this thread as I have been hunting for 3.73 gears for the front and begun exploring factory GM options. I am determined to find a 3.73 (I’m running 37’s on my stock 3.23 setup and running tow/haul mode continuously) gear set and will also report back when I have found something. Stay tuned… r

[Txgunslinger]

On 5/12/2022 at 8:39 PM, barr8888 said:

I haven't taken the cover off my front axle to verify anything personally yet.  But finding reliable information and/or parts to change the front axle ratio has been much more of a challenge than I was expecting, so far.

Just curious, if I actually get the gumption to pull the cover off my front diff, what am I looking to confirm once I’m in there? Some kind of manufacturer stamp/mark? Size marks? Dots? I really want to regear my truck. Tow/haul is fine with the 37’s for now, but there’s a trailer in my future (albeit the lightest all-aluminum enclosed hauler I can find), so I need to prepare.

 

Assuming I pull some useful information out once I’m in, take that to the dealership and cross reference it? Someone here also mentioned ‘pictures to prove it’… any links to where those might be? If this wasn’t so frustrating it almost feels like a quest - YOU SHALL NOT PASS 3.23 GEARS!

[AJMBLAZER]

Yeah, you can tell everything you need to know from the RPO codes. Gear ratios and which axles you have, GM or AAM Co. 

 

Then you need to dig through the parts diagrams and find the part numbers for the gears you want. 
 

You could try to find a VIN for a truck with the gears you want and the parts dept could look this up. 

[AJMBLAZER]

https://www.gmpartsdirect.com/v-2020-chevrolet-silverado-1500--lt--5-3l-v8-gas/driveline-and-axles--differential

https://www.gmpartsdirect.com/v-2020-chevrolet-silverado-1500--lt--5-3l-v8-gas/universals-and-rear-axle--rear-axle

 

https://www.gmpartsdirect.com/v-2020-chevrolet-silverado-1500--lt--3-0l-l6-diesel/driveline-and-axles--differential

 

https://www.gmpartsdirect.com/v-2020-chevrolet-silverado-1500--lt--3-0l-l6-diesel/universals-and-rear-axle--rear-axle

Edited August 6, 2023 by AJMBLAZER

[offroadman83]

How does that help.... says not for sale

[Txgunslinger]

I’m gonna check in with my local driveline shop when I get back home and see what he says. He quoted me last year but he may not have realized what I was asking for. Or he did and has an inside line I don’t know about. I’ll post back after I talk to him. Twisted Axles in SA

Edited August 6, 2023 by Txgunslinger
Bad grammar

[AJMBLAZER]

6 hours ago, offroadman83 said:

How does that help.... says not for sale

Gets him parts numbers. It’s a start. 
 

www.car-part.com

Edited August 6, 2023 by AJMBLAZER

[barr8888]

On 8/5/2023 at 7:56 PM, Txgunslinger said:

Just curious, if I actually get the gumption to pull the cover off my front diff, what am I looking to confirm once I’m in there? Some kind of manufacturer stamp/mark? Size marks? Dots?

As has been stated, there's really nothing to be gained from removing the front cover that you can't more easily determine from your RPO build codes and VIN.  My thoughts back then were related to some apparent rumors/misinformation related to the front ring gear having been attached to the front carrier by GM in such a way that the entire carrier would need to be replaced to change the gearing, instead of just changing the ring and pinion gears themselves, as one would expect.

 

I went around to some driveline and performance shops at the time and no one had any definitive information (including supposedly knowledgeable GM industry contacts) on what, if anything, was available for the front axle in '19+ GM trucks.  The rear axle (RPO codes listed further below) apparently has aftermarket gear sets available, regardless of axle manufacturer (AAM or GM).  It's the front axle where all the difficulty comes into play, as I'm sure you know.  I basically gave up back then and decided to wait until the pandemic's effects on industry were a little further behind us. 

 

(As a side note, I still intend to replace the rear OEM limited-slip carrier in the rear with an Eaton TrueTrac, as there's no better time to do it than during a gear set change.  I believe the TrueTrac will be more robust/reliable than the OEM solution, especially with the increased mass and leverage of the larger tires).

 

The ideal (and likely most cost-effective) solution is an aftermarket gear set for the front axle, but this depends on whether or not any are available.  If not, then this is where RPO build codes and VINs could come into play.  First, you need to know which front axle you have, an AAM or a GM (mine is a GM, RPO=SU5).  Then, you need to determine what ratios GM uses (or used) in that front axle.  If they used a 3.73 in some truck combination, then you might be able to order GM parts that will accomplish what you need, if the parts are available, and if you can definitively determine the correct part numbers (this is where the VIN from a truck that has the front axle and ratio you need can prove invaluable).  From my research back then, it looks like the 3.0 Duramax diesel 4x4 truck was available with 3.73 gearing.  What I was never able to determine, though, was which front axle GM uses (or used) in that truck.  That's where my own research into a potential OEM 3.73 solution stalled, so I never got to the part about whether these parts are available/backordered/cost/etc.  

 

'22-Limited GMC AT4
Front axle:  SU5=GM, SU4=AAM

Rear axle:  SU8=GM, SU7=AAM

 

Do keep us informed of any progress you make.  It's probably time for me to resume my own research, too.  The 6.2L, 10-spd trans, and tow/haul do a good job of masking the gearing issue with my ~5k trailer, but I can still tell it's not ideal.  And even in no-trailer highway cruising scenarios (w/out tow/haul engaged) the slight surge/sluggishness at times is definitely noticeable, as the trans ratios were never designed for an (effectively) 3.08 axle ratio.

[Txgunslinger]

Phenomenal update, thanks. I tried scanning the upc code for my rpo list of options but for some reason it would only show me a partial list and then cut off, so I gave up. Guess I’ll pursue that further and save my knuckles for a different job. Like I said earlier, I’m going to visit the axle shop in town when I get back at the end of august and report back then.

[barr8888]

8 hours ago, Txgunslinger said:

I tried scanning the upc code for my rpo list of options but for some reason it would only show me a partial list and then cut off,

Mine cut off, too.  I presume they all do that, for whatever reason.  Ask your dealer's service dept. (any dealer should be able to do it) to send you a copy of your truck's build sheet.  All they should need is your VIN, which your own dealer may already have on file.  The build sheet will list all of your RPO codes (mine is 6 pages long) and a brief description for each. 

[barr8888]

(digging up an older thread here) This is likely not news to anyone that’s been searching, but the latest information I have (this time from East Coast Gear Supply in NC) is that re-gearing options are still not available for the front differential in these trucks.  The reason cited was once again related to how the OEM ring gear is attached to the carrier (I’ll avoid using the term “welded” this time, though I’ve now heard it described that way from multiple sources).

 

If anyone has had better luck, do chime in.  2022 Limited AT4 here, with SU5 GM front axle / SU7 AAM rear axle.

Edited April 19, 2024 by barr8888

[lmcfad01]

Trying to do the same thing on a 19 Z71 with 3.23 diff. These are the parts I got from a dealer for stock assembly with 3.73 gears. The catch is that since they can't match to your VIN, there's no returning if it doesn't work. Now who has the balls ($$$) to give it a shot! 

 

https://www.gmpartsbin.com/p/Chevrolet_2019_Silverado-1500-LT-Extended-Cab-Pickup-Fleetside-53L-EcoTec3-V8-AT-4WD/Differential-Housing-Front/75803041/84446296.html

 

https://www.gmpartsbin.com/p/74589573/84496944.html