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I have a 2012 JKU Sport with auto. My build sheet says 3.21 rear end and lists auto farther down the sheet under options. I've read in several places that the autos only come with at least a 3.73. I check what's stamped on the diff cover and it doesn't match anything to do with either. Anyone know how to tell for sure? Just curious for towing purposes. Dealer says I'm good up to 2,000 lbs. but Chrysler charts say 1,000 lbs. with 3.21 rear end.
 

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Why would you not trust your build sheet? The build sheet is correct.
 

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Are you sure you have a build sheet? The window sticker lists all the standard features and then the specific optional equipment on the Jeep.

But, my build sheet, and I think all build sheets from Chrysler do not refer to "options" in any way. It just lists everything that went into building the Jeep.

If you are relying on the window sticker, they can be confusing. They list the standard equipment (manual tranny, soft top, 3.21 gears, etc.) But, all of that is overridden by the options listed in the right hand column.

IF you have the build sheet, you can rely on what it says you have.
 

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in a sport you can get auto with either 3.21 or 3.73 with or without tow package. An easy way to check is just lock it in a certain gear and compare your rpms to your mph.
 

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From what I understood 2012 autos only came with 3.21's unless you got the tow package then you get 3.73
I believe this is correct, except you could also add just 3.73 axles (DME) for $95 in the JKU Sport without the tow package.
 

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All pre-2012, non-Rubi auto's came with 3.73's.

You have a 2012.

The standard axle ratio for non-Rubi's became 3.21 for 2012.

Your tow rating is 2000 pounds...but the Chrysler info on this is a mess...and could say nearly anything (or nothing) depending on the source.
 

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jadmt said:
in a sport you can get auto with either 3.21 or 3.73 with or without tow package. An easy way to check is just lock it in a certain gear and compare your rpms to your mph.
Or jack her up and spin the drive shaft.
Count how many turns of the shaft to make the wheel go around once.
 
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