Gear Change 9.5" 12 bolt

rgiles675 · September 5, 2014

Check out eastcoastgears.com out of North Carolina. They have the parts to setup the rear end on the 2014's and claim to have done a handful in house. I just ordered the parts the other day and my truck is at the local shop now. They claim a new posi duratrack by Yukon, a 9.5" 14 bolt gear set, a yoke adapter kit, a diff cover spacer and their master install kit will get it done. The front end of our 4x4's are the same 8.25" reverse IFS gear set as previous years. Give them a call and hit option # 2. They know their stuff. Hopefully my shop here in Ohio will have everything together by this evening and I will let you know how the truck is. I went with the 410's to replace my 3.42's. 35" tires and a 6" lift is what I have too

Greatly Appreciated!

badchevy · September 5, 2014

Greatly Appreciated!

No problem. Keep in mind that I have heard the early round of '14 trucks had the '13 trucks 8.5" rear end. The later '14's have a 9.5" rear end. I found out the hard way and first ordered 8.5" gears before I talked to Eastcoast. The best way to find out is to count the bolts on your rear differential. The 8.5" set on the older style has 10 bolts and the newer style on most '14's 9.5" has 12 bolts hold on the diff cover. Someone else can chime in if I am wrong, but I believe this is correct.

Edited September 5, 2014 by badchevy

CAtaylor · September 5, 2014

Check out eastcoastgears.com out of North Carolina. They have the parts to setup the rear end on the 2014's and claim to have done a handful in house. I just ordered the parts the other day and my truck is at the local shop now. They claim a new posi duratrack by Yukon, a 9.5" 14 bolt gear set, a yoke adapter kit, a diff cover spacer and their master install kit will get it done. The front end of our 4x4's are the same 8.25" reverse IFS gear set as previous years. Give them a call and hit option # 2. They know their stuff. Hopefully my shop here in Ohio will have everything together by this evening and I will let you know how the truck is. I went with the 410's to replace my 3.42's. 35" tires and a 6" lift is what I have too

You got it man, hope the install goes good for you. I would have replied sooner but have been in England the past 6 days, their phone data service sucks over there if you have a US phone.

DCOX · October 28, 2014

Check out eastcoastgears.com out of North Carolina. They have the parts to setup the rear end on the 2014's and claim to have done a handful in house. I just ordered the parts the other day and my truck is at the local shop now. They claim a new posi duratrack by Yukon, a 9.5" 14 bolt gear set, a yoke adapter kit, a diff cover spacer and their master install kit will get it done. The front end of our 4x4's are the same 8.25" reverse IFS gear set as previous years. Give them a call and hit option # 2. They know their stuff. Hopefully my shop here in Ohio will have everything together by this evening and I will let you know how the truck is. I went with the 410's to replace my 3.42's. 35" tires and a 6" lift is what I have too

How'd the install go? Everything turn out ok? How do u like the 410?

badchevy · October 29, 2014

How'd the install go? Everything turn out ok? How do u like the 410?

I'm not quite happy with the front install, but that could be the shop who did the work. They are trying to tell me the front end is slightly different even though it still takes the 8.25" gear as the previous years. The crush sleeve didn't work with the install kit, so they used a solid spacer that was machined. No big deal as a lot of folks setup their pinion with a hard spacer and not the crush sleeve. I had the shop setup a new pattern after I drove the truck 500 miles with the first install. I am still hearing a faint whining noise and occasional rattle under acceleration from the front. It could be the gears, but I have a feeling it is the setup. It gets louder with 4 wheel drive engaged. I really like the feel of the rear end with the duratrack carrier and the adapter kit works really well.

Overall the 4.10 seems the way to go though. I kicked around the 4.56, but I didn't want to lose too much mpg on the highway. Right now when running 65-70 I am at 1900 rpms. I would rather be around 1700, but in town the mpg has seemed to improve. If I could have the best of both, 3.73 would be perfect for highway and something like a 4.56 would be good for in town. I guess the 4.10 is about the right median for mix driving.

Edited October 29, 2014 by badchevy

DCOX · October 29, 2014

I'm not quite happy with the front install, but that could be the shop who did the work. They are trying to tell me the front end is slightly different even though it still takes the 8.25" gear as the previous years. The crush sleeve didn't work with the install kit, so they used a solid spacer that was machined. No big deal as a lot of folks setup their pinion with a hard spacer and not the crush sleeve. I had the shop setup a new pattern after I drove the truck 500 miles with the first install. I am still hearing a faint whining noise and occasional rattle under acceleration from the front. It could be the gears, but I have a feeling it is the setup. It gets louder with 4 wheel drive engaged. I really like the feel of the rear end with the duratrack carrier and the adapter kit works really well.

Overall the 4.10 seems the way to go though. I kicked around the 4.56, but I didn't want to lose too much mpg on the highway. Right now when running 65-70 I am at 1900 rpms. I would rather be around 1700, but in town the mpg has seemed to improve. If I could have the best of both, 3.73 would be perfect for highway and something like a 4.56 would be good for in town. I guess the 4.10 is about the right median for mix driving.

Thanks for the info. It is pretty hard to get any regear info on these newer trucks. I plan to do my 4.10s around Christmas. Thanks again

Mike1220 · October 29, 2014

I'm not quite happy with the front install, but that could be the shop who did the work. They are trying to tell me the front end is slightly different even though it still takes the 8.25" gear as the previous years. The crush sleeve didn't work with the install kit, so they used a solid spacer that was machined. No big deal as a lot of folks setup their pinion with a hard spacer and not the crush sleeve. I had the shop setup a new pattern after I drove the truck 500 miles with the first install. I am still hearing a faint whining noise and occasional rattle under acceleration from the front. It could be the gears, but I have a feeling it is the setup. It gets louder with 4 wheel drive engaged. I really like the feel of the rear end with the duratrack carrier and the adapter kit works really well.

Overall the 4.10 seems the way to go though. I kicked around the 4.56, but I didn't want to lose too much mpg on the highway. Right now when running 65-70 I am at 1900 rpms. I would rather be around 1700, but in town the mpg has seemed to improve. If I could have the best of both, 3.73 would be perfect for highway and something like a 4.56 would be good for in town. I guess the 4.10 is about the right median for mix driving.

So for someone who does mostly highway driving you would recommend 3.73 gears? I'm not worried about in town mileage. How much 'get up and go' do you think would be lost by going to a 3.73 instead of a 4.10? Just curious. I plan to do this not long after (or at least as soon as I can) I put on bigger tires. Looking to put on some 34s and then 35.5s after those wear out.

badchevy · October 29, 2014

Well GM puts a bigger rear end with a 3.73 in some of the newer half tons when they do a high country with 6" pro comp lift and 33"-35" tires. If you are going from a 3.08 to 3.73 you will see a nice difference. 3.42 to 3.73 may yield minimal difference but still be a nice gain. I went from 3.42 to 4.10 to make sure I had enough. On the highway 3.73 would run the rpm a little lower than 4.10. Only a couple hundred but enough to make a difference. I can still get 16-17mpg avg on hwy with my 410s, 6"lift and 35 tires

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Mike1220 · October 29, 2014

any idea

Well GM puts a bigger rear end with a 3.73 in some of the newer half tons when they do a high country with 6" pro comp lift and 33"-35" tires. If you are going from a 3.08 to 3.73 you will see a nice difference. 3.42 to 3.73 may yield minimal difference but still be a nice gain. I went from 3.42 to 4.10 to make sure I had enough. On the highway 3.73 would run the rpm a little lower than 4.10. Only a couple hundred but enough to make a difference. I can still get 16-17mpg avg on hwy with my 410s, 6"lift and 35 tires

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any idea on how much higher that would be if you did the 3.73 instead? Also would I need to change to the larger rear end or just use the conversion kit? I currently have 3.42s and want to keep my highway mileage as high as I can. I am getting a Diablo tuner soon to help with that a little bit

badchevy · October 29, 2014

You can use the same conversion kit I used and run the 3.73. Swapping the whole rear end would be expensive as the one I mentioned on some of the high country's is a different axle with a different size differential. With the kit you can choose ratio size that is a 9.5" gear

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Edited October 29, 2014 by badchevy

badchevy · October 29, 2014

Thanks for the info. It is pretty hard to get any regear info on these newer trucks. I plan to do my 4.10s around Christmas. Thanks again

I know what you mean! I am learning a ton about these gears. I wish I had the tools to have done the setup and install myself instead of a shop.

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Mike1220 · October 29, 2014

You can use the same conversion kit I used and run the 3.73. Swapping the whole rear end would be expensive as the one I mentioned on some of the high country's is a different axle with a different size differential. With the kit you can choose ratio size gear that is a 9.5" gear

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That's what I thought and wanted to make sure. Do you know how much better the mileage would be? Also would the 4.10s be better in the long run incase if I ever take this truck off roading / mudding. I don't plan to go do anything hardcore so I would think the 3.73s would be good.

You can use the same conversion kit I used and run the 3.73. Swapping the whole rear end would be expensive as the one I mentioned on some of the high country's is a different axle with a different size differential. With the kit you can choose ratio size gear that is a 9.5" gear

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That's what I thought and wanted to make sure. Do you know how much better the mileage would be? Also would the 4.10s be better in the long run incase if I ever take this truck off roading / mudding. I don't plan to go do anything hardcore so I would think the 3.73s would be good.

badchevy · October 29, 2014

Also, when I had the stock 3.42s and my current setup I was running around 1300 rpms at 70mph. I tuned to match tire size with a Diablo Intuner. Since I am now at 1900 and the tuner adjusted for 4.10, I'd imagine 3.73 would be around 1500 or 1600 rpms which is close to stock with 3.42s running at 70

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Edited October 29, 2014 by badchevy

badchevy · October 29, 2014

That's what I thought and wanted to make sure. Do you know how much better the mileage would be? Also would the 4.10s be better in the long run incase if I ever take this truck off roading / mudding. I don't plan to go do anything hardcore so I would think the 3.73s would be good.

That's what I thought and wanted to make sure. Do you know how much better the mileage would be? Also would the 4.10s be better in the long run incase if I ever take this truck off roading / mudding. I don't plan to go do anything hardcore so I would think the 3.73s would be good.

I would imagine mpg could be 1-2 difference. 4.10 would definitely be better down low for off road. Shorter gears have a better crawl speed. The taller the gear the easier it is on the highway. I haven't driven a truck with 3.73s. If you are considering that ratio, I would check online for a dealer that has one of the lifted high country models with 3.73. Test drive to get a feel. Wish I had done that before my install

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