Gear swap from 3.08's

CenTex5.3 · February 29, 2016

So I got blessed with the 3.08 rear axle in my truck. I did a quick search and didn't find what I was looking for so, has anyone had experience going from 3.08 to 3.42 or 3.73's in our 14-15 trucks.

I'm wondering how much mpg variance there is between the two. I average 13mpg on E85 and 16-17mpg on 87, and about 20mpg on 87 on the highway.

Any input?

07Softail · March 2, 2016

If going from 3.08 to 3.42 you will have to change carriers and there are no 3.73's available for the 9.5's unless you go with a conversion hack job which uses old style 14 bolt carrier and ring and pinion set. Or do what I did and get a whole 9.76 axle with the 3.73's in it.

RT

CenTex5.3 · March 2, 2016

hmm, good to know. I searched complete rear axles and they aren't cheap. I have a set of gears out of an 04, but don't think they're interchangeable

So I was looking at these http://www.summitracing.com/parts/mgr-gm9-5-342/overview/. those won't go in without changing parts other than the install kit?

Dan1220 · March 2, 2016

Check out east coast gear supply. They have everything you need and they sell kits specifically for our trucks.

Many will tell you to go to 4.10 if you're spending the money to do it.

I am in the same boat with 3.08s. I am not ready to put an aftermarket tune in the truck though, due to warranty concerns

LongrangeLauber · March 2, 2016

hmm, good to know. I searched complete rear axles and they aren't cheap. I have a set of gears out of an 04, but don't think they're interchangeable

So I was looking at these http://www.summitracing.com/parts/mgr-gm9-5-342/overview/. those won't go in without changing parts other than the install kit?

Correct, they are for the 14 bolt. I did a write up about a year ago regarding regearing these new trucks. Nothing available for the 9.76" rear, and the 9.5" uses the older style 14 bolt gears and you have to get a new carrier, yoke, seal, bearing kit, etc in order to get steeper gears in these new rear ends.

I wish Yukon would just step up and make a direct replacement ring and pinion set for these trucks. A lot of people are lifting them so then they join a forum such as this one and start looking around for other mods and want to do a regear eventually. It only makes sense IMO

Georgia1911 · March 2, 2016

AAM offers a 4.10 (10/41) gear set for the 9.5" 12 bolt, but you will still need a new carrier.

http://www.demandaam.com/axle-results?vm=GM&q=9.5%22+12+Bolt+-+Rear+Axle

silveradosid · March 2, 2016

i looked at gm parts, if you want 3.42 it is a 1000 bucks for crown and pinion for front and back. i am thinking of this because i have 3.08's. just waiting to hear from dealership if it would void the warranty if i do this my self

TJay74 · March 2, 2016

Make sure to account for a custom ECM/TCM flash as well, speedo will be a ways off which will throw the shifting off as well since it is based on rpm's and speed to determine the shift points.

CenTex5.3 · March 2, 2016

Check out east coast gear supply. They have everything you need and they sell kits specifically for our trucks.

Many will tell you to go to 4.10 if you're spending the money to do it.

I am in the same boat with 3.08s. I am not ready to put an aftermarket tune in the truck though, due to warranty concerns

4.10 will be too much gear, I just want that little extra uumph at the drag strip and city driving. I'll reprogram with the Tech2 so warranty shouldn't be an issue, except for the gears themselves.

Correct, they are for the 14 bolt. I did a write up about a year ago regarding regearing these new trucks. Nothing available for the 9.76" rear, and the 9.5" uses the older style 14 bolt gears and you have to get a new carrier, yoke, seal, bearing kit, etc in order to get steeper gears in these new rear ends.

I wish Yukon would just step up and make a direct replacement ring and pinion set for these trucks. A lot of people are lifting them so then they join a forum such as this one and start looking around for other mods and want to do a regear eventually. It only makes sense IMO

Thanks for the info, do you have a link to the writeup? I didn't find it in a search.

So does anyone have a link to the carrier we need to go at least 3.42s? I've looked at several sites and they don't show anything on it.

07Softail · March 3, 2016

Go to the AAM website they have an exploded view of the axle assembly with GM Part numbers. FWIW the only difference in the 9.5 and the 9.76 is the pinion bearings are larger on the 9.76 that's it all of the other parts have the same exact part numbers.

RT

Dan1220 · March 3, 2016

Could you elaborate on the tech2 and not voiding the warranty? What is it?

CenTex5.3 · March 3, 2016

Could you elaborate on the tech2 and not voiding the warranty? What is it?

It's the factory scan tool. My shop has one, and a friend of mine is a tech at GM and told me that it's capable of reflashing the ECM to change the gear ratio to 3.42 or 3.73. I'll know for sure when the time comes though.

Go to the AAM website they have an exploded view of the axle assembly with GM Part numbers. FWIW the only difference in the 9.5 and the 9.76 is the pinion bearings are larger on the 9.76 that's it all of the other parts have the same exact part numbers.

RT

Ok I gotcha, I need the carrier from a 9.76 to get the steeper gear.

07Softail · March 3, 2016

The carriers are the same part number based on the break of the gear ratio 3.08 are different. 3.23-3.73 are the same part number carrier both 9.5 or 9.76

RT

CenTex5.3 · March 3, 2016

The carriers are the same part number based on the break of the gear ratio 3.08 are different. 3.23-3.73 are the same part number carrier both 9.5 or 9.76

RT

Thanks for the info in this post, I think I found what I need thanks to you.

TJay74 · March 4, 2016

It's the factory scan tool. My shop has one, and a friend of mine is a tech at GM and told me that it's capable of reflashing the ECM to change the gear ratio to 3.42 or 3.73. I'll know for sure when the time comes though.

Your buddy is wrong on this part, the K2xx trucks don't use the Tech II to flash the modules, they are done via a laptop by connecting to the GM global system. That system uses your VIN to find the calibration for the modules in your truck, it will only flash the modules with the current programming GM has on file for your VIN for those modules. The dealer can no longer make changes to gear ratios or tire sizes anymore, that loop hole was closed out when the 2014 (K2xx) trucks came on line.