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Old 11-01-2016, 08:00 PM   #1
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Rear Axle Ratio

So, I just purchased a used 2016 RAM 1500 4X4, Quad Cab, Express on Saturday and I feel pretty lucky I got the majority of the options I wanted. One was the 8HP70 Transmission, what little I've driven it so far, this transmission feels very smooth.

Since I bought it used I didn't have the window sticker and I was a little fuzzy on all the other options. But I believe there is nothing that is not not he internet and after a little searching yesterday I was able to find the window sticker for my VIN and downloaded a copy.

While I was happy to see the Anti-Spin Differential Rear Axle was added, I don't see the 3.92 Rear Axle Ratio listed, so I can only assume it has the stock 3.21 Rear Axle Ratio? Am I correct in my assumption?

If this is the case, how can I upgraded to the 3.92 Rear Axle gears? How much might it cost? It is my understanding with that rear axle ratio, I can pick up a couple more MPGs and another ton of tow weight capacity. Again, am I off base here? Any ideas, comments, or suggestions are welcome.

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Old 11-01-2016, 08:46 PM   #2
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There will be a sticker on the bottom of the rear driver side axle tube that will tell you what gear ratio you have. Being an 8sp, it will either say 3.21 or 3.92.
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Old 11-02-2016, 08:49 AM   #3
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Quote:
Originally Posted by SoloScuba View Post
So, I just purchased a used 2016 RAM 1500 4X4, Quad Cab, Express on Saturday and I feel pretty lucky I got the majority of the options I wanted. One was the 8HP70 Transmission, what little I've driven it so far, this transmission feels very smooth.

Since I bought it used I didn't have the window sticker and I was a little fuzzy on all the other options. But I believe there is nothing that is not not he internet and after a little searching yesterday I was able to find the window sticker for my VIN and downloaded a copy.

While I was happy to see the Anti-Spin Differential Rear Axle was added, I don't see the 3.92 Rear Axle Ratio listed, so I can only assume it has the stock 3.21 Rear Axle Ratio? Am I correct in my assumption?

If this is the case, how can I upgraded to the 3.92 Rear Axle gears? How much might it cost? It is my understanding with that rear axle ratio, I can pick up a couple more MPGs and another ton of tow weight capacity. Again, am I off base here? Any ideas, comments, or suggestions are welcome.
---------------------------------
If you find that you need to upgrade...go 4:56 IMO
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Old 11-02-2016, 08:53 AM   #4
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---------------------------------
If you find that you need to upgrade...go 4:56 IMO
For a 5sp or 6sp truck, I'm 4.56's all the way. With how the 8sp transmission is geared though, 4.56's are WAY too much gear. 3.92's have shown to be more than enough gear, even for the guys that are at the track every weekend.
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1/8 - 6.91 @ 102.83MPH
1/4 - 10.95 @ 125.63MPH
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Old 11-02-2016, 10:31 AM   #5
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Originally Posted by mjfikac View Post
For a 5sp or 6sp truck, I'm 4.56's all the way. With how the 8sp transmission is geared though, 4.56's are WAY too much gear. 3.92's have shown to be more than enough gear, even for the guys that are at the track every weekend.
--------------------------------------------
Would that still be applicable for a lifted truck running an overall diameter of 35" or more .

Thanks

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Old 11-02-2016, 02:38 PM   #6
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Maybe if your running 44s
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Old 11-04-2016, 07:46 AM   #7
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Rear Axle Ratio - Follow Up

mjfikac - Thanks, I crawled under the truck yester day and sure enough it's a 3.21.

I'm okay with that, this is a 4X4 and daily driver so I'm going more for MPGs and I'm happy with the factory HP and Torque.

I drive like there's an egg on the gas pedal now and the Fuel Economy Gauge is telling me I'm getting 20 MPG average. We'll see when I fill up and do the math, gas vehicles usually read high.

Any ideas on how I can continue to up the MPGs would be appreciated. I'm already a hyper miler, yep I'm that guy. But I'm okay with it, this beast is smooth and it's like riding in a Lay-Z-Boy.
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Old 11-12-2016, 09:41 PM   #8
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Quote:
Originally Posted by mjfikac View Post
There will be a sticker on the bottom of the rear driver side axle tube that will tell you what gear ratio you have. Being an 8sp, it will either say 3.21 or 3.92.
So I have an 09 and the sticker has been worn off or whatever.....any tips on telling what it is? I know they were a 3.55 or 3.92 in 09 right?
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Old 11-13-2016, 10:14 AM   #9
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So I have an 09 and the sticker has been worn off or whatever.....any tips on telling what it is? I know they were a 3.55 or 3.92 in 09 right?
A couple of easy ways is to locate the data sticker in your glove box. If not there, go to mopar website and order your build sheet by using your VIN. Another way is to jack up the rear end, chock it, throw it in neutral, rotate a rear tire by hand and figure the ratio by how many times the drive shaft rotates compared to a rotation of the tire.
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Old 11-13-2016, 10:49 AM   #10
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Yes as mentioned, mark the driveshaft and tire. Turning the tire will give you 3-1/2 turns = 3:55, 4 turns will be 3:92...


I simple looked at the box they came in, it's marked on the end of the box.... lol
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