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Old 09-26-2013, 01:01 PM   #1
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How to confirm gear ratio?

It's not on my invoice. I can find conflicting info online. How do I confirm which gear ratio I have??

2013 Wrangler Unlimited Sport S with automatic transmission. I found the transfer case ratio of 2.72

I looked all over on the tags on the bottom and couldn't find the gear ratio. It's either 3.21 or 3.73, but I want to know what I have.

I have the trailer tow group (not max tow). I have the anti-spin rear differential axle. Nothing tells me which ratio I have though.

Thanks for any help!
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Old 09-26-2013, 01:06 PM   #2
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Jack the rear of the jeep up so the rear tires are off the ground. Turn the wheel one revolution. Count how many times the drive shaft turns. If it rotates 3.2 revolutions for one wheel turn, you have a 3.21, If it rotates 3.7 revolutions for one wheel turn you have a 3.73

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Old 09-26-2013, 01:08 PM   #3
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Log onto Jeep.com and enter your information....you can find out your build info on that site.
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Old 09-26-2013, 01:18 PM   #4
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Should be a line item on the invoice or window sticker if you have the 3.73s. Max tow would have made them an automatic but the Trailer Tow can be had w/ either gear set.
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Old 09-26-2013, 06:16 PM   #5
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I called Jeep and gave them my VIN and they told me my build is a 3.21 gear ratio.

So, is there any positive to 3.21? Better gas mileage perhaps?
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Old 09-26-2013, 06:43 PM   #6
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NOTHING wrong with the 3.21s unless you plan to run big rubber in the future. By big rubber, I would say anything bigger than a 33" as you have 32"s from the factory.

In fact, if you talk to any good mechanical engineer, they will tell you that the lower sustained rpms (like cruising on the interstate) the better for long life.
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Old 09-26-2013, 07:32 PM   #7
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Quote:
Originally Posted by Plasticpirogue View Post
NOTHING wrong with the 3.21s unless you plan to run big rubber in the future. By big rubber, I would say anything bigger than a 33" as you have 32"s from the factory.

In fact, if you talk to any good mechanical engineer, they will tell you that the lower sustained rpms (like cruising on the interstate) the better for long life.
Thanks for that!

For towing, I have a bicycle carry rack, a cargo rack, a motorcycle tow attachment and a ball for small trailers. I have zero need for the max tow package, so I think I'm better off with the 3.21 ratio gears for my needs. After thinking about it, I'm glad I have the 3.21 ratio.
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Old 09-27-2013, 07:30 AM   #8
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Quote:
Originally Posted by Plasticpirogue View Post

In fact, if you talk to any good mechanical engineer, they will tell you that the lower sustained rpms (like cruising on the interstate) the better for long life.
I would say this might be true if you don't try to regularly accelerate quickly or tow anything at all. Deeper gears make both of those MUCH easier on the engine and drivetrain and would far outway any increased wear from a small bump in rpm at a sustained rpm.

Personally I think the 3.21s are just Jeep's method of helping pull down the CAFE average but if using it more as a DD they work for a lot of people.
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Old 09-27-2013, 09:38 AM   #9
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3.55's would be great.
I debated between 3.21's and 3.73's. It all depends on where you live and how you use the Jeep. My only issue with 3.21's is that it limits the tow rating on the 4 door to 2000 pounds instead of 3500....outside of that, when I test drove both (back to back), I was fine with either.
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Old 09-27-2013, 11:47 AM   #10
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3.55s would have been a perfect ratio for JKs with stock tires. Sadly, no one makes them.

I went with 3.21 gears because I knew I was going to do a lot of modification to my Jeep. No sense paying for 3.73 gears when you're going to swap in lockers and regear for 35" tires anyway.
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Old 09-27-2013, 12:23 PM   #11
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For anyone staying with 33" and under tires 3:21 is a good ratio for mpg and yet it is still plenty zippy. Nothing wrong with it at all.
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Old 09-27-2013, 06:54 PM   #12
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mine came on the window sticker, said it like 12 times "3.73" this and 3.73 that. if its not marked, its probably a 3.21

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