decoy5657

2012 JKU Sport. I have my build sheet and all I know is I have 3.21 rear gear ratio; I assume it's the same on the front...

Let's assume I want trutrac's front & rear (don't want to start a discussion about why, or what's better, or worse, etc)

I don't know the spline count?

This guy for the front:
Detroit Locker 912A584 - Detroit Trutrac by Eaton Performance Limited Slip Differential for 27 Spline Dana 30 with 3.54 and Numerically Lower Gear Ratio - Quadratec

This guy for the rear?
Detroit Trutrac by Eaton Performance Limited Slip Differential for 07-16 Jeep® Wrangler & Wrangler Unlimited JK with Dana 44 Rear Axle - Quadratec

ShutterBug

Your final drive ratio must be the same for the front and the rear.

I'm not going to answer your question, however.

Here's some advice that I am sure others will give you. If you are going to spend the money to have TruTrac's put in, then spend a little more and regear it to a lower (higher numerically) gear ratio. For a 2012, I would recommend 4.56. Aside from the cost of the ring gear and pinion, the labor cost remains pretty close to the same.

When a pinion and carrier are installed in your differentially, there are shims that get interred in either side of the pinion as well as on either side of the carrier in order to properly position everything in exactly the right spot. The tolerances are very tight, to the thousandth of an inch. So when your gear shop puts in the TruTrac, they'll have to redo a lot of that work anyway.

So swapping out the ring gear and pinion to a more suitable ratio only makes sense.

Call or start a chat with a place like Northridge 4x4, Krawl Off Road, River City Offload, etc. and tell them what you have and they'll give you a little education on what would work for you. Get multiple opinions and ask questions. Educate yourself on this so you can make a qualified and informed decision.

decoy5657

Appreciate the feedback. Why is 4.56 more suitable? - In my case it's a daily driver. We have a decent snow season and a lot of rain. I'm never going to be on rocks or have a wheel off the ground. This is my first Jeep and I've had it for 8 months or so. I'm very happy with it, even with two open diffs and 9 inches of snow.

nthinuf

D30 is 27 spline
D44 is 30 spline
(if it were a rubicon, it would be d44 30 spline front and d44 32 spline rear)

You are staying with 3.21's?

If so, that is the correct front truetrac. If you choose to regear to 3.73 or higher, you will want 912A585 up front. The rear will be the same for any jk ratio.

Also, if you are buying them yourself, check with Summit racing, they have lower prices. (wow, I take that back. Just checked and the front truetrac for 3.21's is way overpriced there.)

If you are installing yourself, pay attention to the bolt and bolt hole sizes. You may need to get the holes drilled out, and these use a hard metal, so paying a machine shop is common.

decoy5657

My vote is that the 3.21 stays unless someone provides incredibly compelling evidence to change.

Just curious, do you know why the fronts require specific kit for different ratios and the rear doesn't?

Probably won't do this one myself. First time doing anything this precise in my DD. I've done engine rebuilds and swaps but my background is all VW.

arjeeper

Drive a Jeep with 4.10s and you'll have your "incredibly compelling evidence". The 4.10 is the perfect gears for the Wrangler in factory configuration. Add bigger tires of any sort and 4.56 or bigger is in order.

Really, I think they only put 3.21s in Jeeps to boost federal fuel economy test numbers, not because they're the best for drivability.

There is no way I'd pay to have Trutracs installed and then leave the old 3.21s in place.

nthinuf

Don't know. After all these years of reading about JK gears and lockers, I don't think I've ever read a post explaining the reasoning for the d30 carrier break. Just that it is 3.21 'only', or all gears from 3.73-5.38.

What tire size?

As the others have mentioned, it might not be a bad idea to spend some time researching gear ratios before you decide to stay with 3.21 (not just the few replies you get here, do some searching, there about a gajillion regearing threads to read through for opinions. Check the charts, etc. ) You'll pay about the same labor whether it is installing gears or installing a truetrac, since the gears have to be set up again anyway, so it may be worth the added expense to slap new gears in at the same time. (depending on tire size and location and usage/needs and opinion/preference and ...)

Here is a decent gearing how-to. Worth a look if you are considering tackling the truetrac install yourself. (or might be just enough to convince you to pay someone else)

https://www.jk-forum.com/forums/jk-w...gearing-82262/

decoy5657

I'll definitely consider the 4.10 ratio. Stock size tires. I might end up with a set that is 275/70 but nothing big that requires a lift. I do too many highway trips to compromise ride quality in this one too much.

Thanks for the info and links. Absolutely digging into this as much as I can, as I have the flu and have been quarantined to my house for a few days, alone.

ShutterBug

Here's my take on this. Your mileage may vary.

Now that I have read through the responses and see that this is your first Jeep, this makes it a little more interesting. I, too, am driving my first Jeep, a 2014 Sport 2 door. I've had it for about 2 1/2 years. When I bought it, I had NO IDEA that I would be where I am today. After a few months of owning it, I bought 33" tires because I KNEW I would never go bigger than that. 6 months later and the 35s went on. LOL!

My point being, try to avoid saying "I will never take my jeep ...." because plans may change. If you haven't wheeled the Jeep much with a group of other Jeep owners, then I might suggest holding off on doing any kind of gear work.

I've been wheeling my Jeep on 3.21 gears with open diffs since I started wheeling it. I've been to some pretty nice off road parks. I prefer rocks and do just fine. My lift helps a LOT. You might find that the 3.21s, with some decent all terrain tires (Duratracs are what I have) will be OK for a while.

Personally, I want to do more than I can today - so I am swapping out the axle's with Rubicon axles, 4.88 gears and selectable lockers. If you would have told me that even a year ago I would be doing this I would have laughed at you!

As others have echoed, do some research. You might find it will take you months to figure out what you really want to do.

I suggested 4.56 (4.10 would be good, too) because they will work well with 33" and 35" tires, and give you a better crawl ratio for off road driving. The likelihood that you will want to put 33" or even 35" tires on your Jeep is really high, even though you may not know it today.

decoy5657

I totally hear you. I know myself well enough to know that this Jeep isn't ever going anywhere where's it's gonna get banged up, broken, scratched, etc. That's a hobby that's just too expensive for my taste and the closest offroad park is 2 hours away.

I've had cars that have been through what you described. Different beasts completely, but I've done the upgrades the amazing engines and tires and suspensions, etc. I end up hating what I've done because I spend too much time behind the wheel on a daily basis running around town and I've made the vehicle uncomfortable for daily use...

Having said all of that, I AM shopping for an older 2 door that I can go crazy with.