High Country 9.76" differential gear swap from 3.23 to...

Darksky · November 1, 2016

Has anyone with a 9.76 inch rear end done a gear swap? The High Country with a 6.2 liter engine is only available with the 3.23 . That gear gets knocked down considerably when going to taller tires.

East Coast Gear Supply shows a 4.10 set for this diff which requires different bearings (which are included in their kit). Has anyone bought these gears and installed them on their truck?

I know that 3.73 is an option that is readily available as well. How many of you have done this on the 9.76 differential?

Darksky · November 2, 2016

I thought I might add a few things. The following contains some of my research and a little of my math. Buyer beware on both.

My truck: 2015 Chevrolet Silverado 1500 High Country edition 6.2 liter (L86) engine coupled with the 8L90 eight speed transmission, driving the 9.76" rear diff with 3.23 gearing. Lifted six inches with a FabTech lift kit including their Uniball upper control arms and Dirt Logic 2.5 coilovers (Eibach Springs are on the coilovers). Rear shocks are Dirt Logic 2.5 non reservoir. I added one custom leaf to the rear packs, a full length leaf with the correct Spring rate to stiffen the packs somewhat without altering the arch.

I exchanged the the factory wheels and tires for 305/64/R18 BFG TA KO2 tires on Rockstar 18x9 wheels with 0 offset/5" BS (as per FabTech reccomendation)

Factory Tires: P275/55R20 31.9 inches tall 10.8 wide 632 revolutions per mile

Currently: 305/65/R18 33.5 inches tall 12.2 wide 619 revolutions per mile

Reference: 325/65/R18 34.6 inches tall 13 wide 601 revolutions per mile

Reference: 34x12.5/R18 33.5 inches tall 12.5 wide 621 revolutions per mile

Reference: 35x12.5/R18 34.5 inches tall 12.5 wide 602 revolutions per mile

I am not running the larger tires because they do not fit on the truck when you allow for suspension compression and turning lock to lock. FabTech's website states a 35 will fit with some trimming. You would have to remove any and all mud flaps, cut out the fender liners and pursuade the steel slightly. I am not willing to do that. I live on a long gravel/dirt road and use my truck as a ranch vehicle as well as my primary highway vehicle. I don't think it is prudent to drive a truck whose suspension travel is limited by rubbing tires. (Maybe this is a discussion for another time).

Gearing versus net Gearing compared to factory tire size:

3.23- 33.5" tire / 3.07 - 34.5" tire / 2.98 - 34.6" tire / 2.94

3.73- 33.5" tire / 3.54 - 34.5" tire / 3.44 - 34.6" tire / 3.40

4.10- 33.5" tire / 3.89 - 34.5" tire / 3.78 - 34.6" tire / 3.74

It is also important to think of the additional weight of the larger tires. My current tires weigh 62.8 pounds each, the heaviest of these weigh 67.6 pounds each.

Edited for spacing

wuznme · November 2, 2016

Haven't done it yet, when I do them going to 3.73's and a TrueTrac. Think the 4.10's with Whipple will be too much.

truckguy82 · November 2, 2016

The problem with the differential gears is you need two of them, and they aren't cheap.

With these trucks it's more cost effective to add power than it is to change the gears.

wuznme · November 2, 2016

The problem with the differential gears is you need two of them, and they aren't cheap.

With these trucks it's more cost effective to add power than it is to change the gears.

The fronts aren't too bad it's the rears which are about double, then the TrueTrac cost.

Also in my eyes its cheaper to change gears than turn up the boost anymore, since the upgrades for fueling is costly! Plus the gears will give a better overall daily driving experience.

Donstar · November 2, 2016

It sounds to me like you have a very nice truck. I know the 4.10's will enhance your available power, but I'm curious as to what are the shortfalls of your current setup? I picture your truck already having neck snapping power!

truckguy82 · November 2, 2016

The fronts aren't too bad it's the rears which are about double, then the TrueTrac cost.

Also in my eyes its cheaper to change gears than turn up the boost anymore, since the upgrades for fueling is costly! Plus the gears will give a better overall daily driving experience.

I probably should have specified "most of the time" it doesn't make sense.

If your considerably modified already yeah gears certainly make sense at some point.

wuznme · November 2, 2016

It sounds to me like you have a very nice truck. I know the 4.10's will enhance your available power, but I'm curious as to what are the shortfalls of your current setup? I picture your truck already having neck snapping power!

Nothing short, just want the little bit extra. LOL

newdude · November 4, 2016

Why not try a good tune (Blackbear Performance) before swapping gears?

Darksky · November 5, 2016

I have a tuner sitting in my shop, I want to make my decision about gearing before sending it back for programming. I am trying to suppress a strong urge for headers as well.

In all reality, gears are needed. The increased tire height has knocked it down too far, especially considering that the High Country started out with only 3.23. My truck rarely sees eighth gear unless I am on the interstate. I can keep it in manual and drop it down one gear and most of the time it brings it right to the bottom of the pwerband. Many times it seems that the mileage picks up slightly.

Often when tooling along at 50ish, it seems like it is almost lugging (to me)

MrNasty · November 8, 2016

Im planning on adding headers and doing a regear very soon. I have looked around on a lot of forums and I plan to go 3.73. They will help keep the low end torque with the headers and make the truck quicker even without headers. I think it will make a better daily driver than the 410's but I know some will disagree. I also plan to add the whipple in the very near future.

Sent from my iPhone using Tapatalk Pro

07Softail · November 8, 2016

3.73's are perfect for my 6l80 and 32" tires. if going 35's or so 4.10 would be it.

RT

powerhaulic · November 8, 2016

4.10 just do it

Darksky · November 9, 2016

Spoke with a rep from East Cost Gear Supply. The 4.10 gears they offer for the 9.76 are actually gears for a 9.5. You have to purchase a bearing set which allows you to place them in the bigger housing. The gears either 3.73 or 4.10 are $385 from them. However, the bearing set for the 4.10 is an additional $300. That raises the price for the 4.10 to $685.00 for just the parts ft the rear differential.

wuznme · November 9, 2016

I can get the 3.73 or 4.10 for same price, was already looking to put the guts of the 9.5 in my 9.76 so I could get a real posi or true trac and ditch g80. None of the aftermarket is making a replacement for the g80 in the 9.76

Got quoted $3000 for front and rear, the parts are $1900