re-gearing for 37's ??

Alfred Padula · November 4, 2021

People !!! Front gear ratio change is not available for 2021 Silverado 1500 4X4. So do not change rear ratio because you cannot change the front !!!. I learned the hard way after having my rear end done to 4:56 . We have contacted many axle rear end shops and they say " NOT AVAILABLE" NOBODY KNOWS WHEN GEAR SET WILL BE AVAILABLE.. . My rear end is already geared to 4:56 so I am stuck driving truck with out front drive line while waiting for someone to manufacture front 4:56 gear ratio... My tires are 36"

Alfred Padula · November 4, 2021

Just now, Alfred Padula said:

People !!! Front gear ratio change is not available for 2021 Silverado 1500 4X4. So do not change rear ratio because you cannot change the front !!!. I learned the hard way after having my rear end done to 4:56 . We have contacted many axle rear end shops and they say " NOT AVAILABLE" NOBODY KNOWS WHEN GEAR SET WILL BE AVAILABLE.. . My rear end is already geared to 4:56 so I am stuck driving truck with out front drive line while waiting for someone to manufacture front 4:56 gear ratio... My tires are 36"

Any help would be greatly appreciated !!!

Rayo1025 · December 13, 2021

I'm on the same boat, I've been looking at re-gearing since I'm running 37", no luck finding front gears or lockers, any one has any solutions for this new stile Silverado, I have a trail boss edition

Alfred Padula · December 13, 2021

Rayo, there is no front gearing available as of yet. Rear gears are available but when my 4x4 shop installed them and a Hypertech speedo calibrator for the 4:56 rear gears my truck computer would not accept this change. there is no fix as of yet....I drive my truck in Tow/Haul mode all the time which really helps out but this is not a permanent fix.

M1ck3y · December 15, 2021

I believe with the front its not a simple ring/pinion swap you have to replace the whole diff. I don't know if the front diff is different on T1's or not, but with the k2's you can go up to 3.73.

For some reason I'm thinking the ~~3.0 diesel has 3.73s~~, so you should be able to.

Edited December 16, 2021 by M1ck3y

AJMBLAZER · December 15, 2021

1 hour ago, M1ck3y said:

I believe with the front its not a simple ring/pinion swap you have to replace the whole diff. I don't know if the front diff is different on T1's or not, but with the k2's you can go up to 3.73.

For some reason I'm thinking the 3.0 diesel has 3.73s, so you should be able to.

Take a look at your front diff. About ten years ago GM went from the split diff style front IFS diffs they had been using to a more conventional (looks like a rear diff with a removable cover) diff. I believe the ring gear changed then as well.

Starting in 2019, after the AAM Co rear axle vibration issue the 14-18 trucks suffered from, GM has started making their own axles again as well as using some AAM Co axles. That's where the change is.

These axles can be regeared just like any other axle. The aftermarket just hasn't started making gears for the front yet. The rear axles are pretty much the same internally since 2014.

M1ck3y · December 15, 2021

32 minutes ago, AJMBLAZER said:

Take a look at your front diff. About ten years ago GM went from the split diff style front IFS diffs they had been using to a more conventional (looks like a rear diff with a removable cover) diff. I believe the ring gear changed then as well.

Starting in 2019, after the AAM Co rear axle vibration issue the 14-18 trucks suffered from, GM has started making their own axles again as well as using some AAM Co axles. That's where the change is.

These axles can be regeared just like any other axle. The aftermarket just hasn't started making gears for the front yet. The rear axles are pretty much the same internally since 2014.

Good info, thanks. So your saying the T1's use the same front diff as the k2's?

AJMBLAZER · December 15, 2021

I can't confirm that. I do think that they must have changed something internally on the AAM Co made front axles since it seems like the ring and pinion from the 14-18 trucks won't work.

The new GM front axles are not supported by the aftermarket yet.

jpfanner · May 12, 2022

I know this is an old post but since GM offers the 3.0 Duramax with 3.73's and someone like me who has a 6.2 with 3.42's and has gone up to 35's, going to 3.73's would make up for the tire size difference. (weight and wind resistance is a different story) but at least when towing my 10,000lb toy hauler I'd be slightly better off than where I am today. I'd rather go all the way to a 4.10 but with 3.73's my speedo would be extremely close and I could ditch the Hypertech inline corrector. Thoughts?

AJMBLAZER · May 12, 2022

Deeper is better.

barr8888 · May 12, 2022

4 hours ago, jpfanner said:

I know this is an old post but since GM offers the 3.0 Duramax with 3.73's and someone like me who has a 6.2 with 3.42's and has gone up to 35's, going to 3.73's would make up for the tire size difference. (weight and wind resistance is a different story) but at least when towing my 10,000lb toy hauler I'd be slightly better off than where I am today. I'd rather go all the way to a 4.10 but with 3.73's my speedo would be extremely close and I could ditch the Hypertech inline corrector. Thoughts?

I'm in basically the same boat. See this post in a different thread:

I'm actually in slightly worse shape, since my AT4 has factory 3.23 gearing. I'm at (effectively) a 3.08 gear right now with 35" tires and the stock 3.23's. The 6.2L and 10-speed trans DO make up for a lot, but 3.73's would get me pretty close to (effectively) stock 3.42 gearing, which is the same thing you're after (and should be perfect for my needs).

While I'm pretty sure rear axle ring/pinion sets are available aftermarket (my rear axle is an SU7; an AAM axle. SU8 is the GM rear axle)... the big questions revolve around the front axle.

Rumor has it that GM may be welding (or otherwise permanently attaching) the ring gear to the carrier in the front axles on these trucks. If that's true (and I've heard it from more than one source) then that may be part of the reason the aftermarket doesn't seem to have any ring/pinion sets available (yet, anyway).

Now I'm not opposed to purchasing a whole front carrier (w/ring) and pinion directly from GM in 3.73 if that's the only way to do it right now, but that brings additional questions into play. GM is using two different front axles on these trucks. The SU5 (what I have) is a GM front axle. And there's also an SU4, an AAM front axle.

So, if the 3.73 front ratio is only available with the 3.0L Duramax diesel, which front axle are they putting in those trucks?... and/or... are the internals (ring/pinion/carrier) interchangeable between the AAM and GM axle? Because if ALL of the Duramax diesel 3.73 geared 4x4 trucks have AAM axles... and the internals are not interchangeable... then even trying to buy 3.73 front gearing direct from GM won't work for me (and my GM front axle).

Just food for thought. If you come up with a workable solution, please do come back and post it here (I'll do the same).

Edited May 12, 2022 by barr8888

AJMBLAZER · May 12, 2022

The front gears are not “welded to” the front carrier. That’s been disproven many times. There’s pictures around here to prove it.

barr8888 · May 13, 2022

5 hours ago, AJMBLAZER said:

The front gears are not “welded to” the front carrier. That’s been disproven many times. There’s pictures around here to prove it.

It's not my intent to spread misinformation... I'm only citing what I've personally been told by a GM dealership parts person... and have also read elsewhere.

I acknowledge that it doesn't sound like something that makes any sense to me. I don't see how the hardness of the ring gear itself could be maintained if any attempt was made to weld it, for one.

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.

Edited May 13, 2022 by barr8888