915JKU

So I bought my first Jeep Wrangler JKU in October and so far love the damn. Bought it base model Sport with manual everything, so it came with 16's and stock 3.21 gears

Got really tired of wheeling and every time get thorns in the stock tires, and have to get them repaired every week almost. So I bought 5 BFG KO2's(33's) to beef that up a bit.

Crappy thing is that I commute 196 miles everyday to work, so gas mileage is kind of a big thing as this is my daily driver for now, and my MPG went from 21 to about 14, this is with the 6 Speed Manual.

The poor thing drives like a dog, 6th gear is pretty much useless especially going up hill so Im saving up for a regear.

As of now I am completely satisfied with my 33's (32.8's actually) and dont plan on going to 35's, but MAY consider doing so down the road so will 4.10's be a good gear for both tire sizes?

My question is, does anyone out there have 4.10s installed on their manual JKU and drive long distances like I do? Would you recommend another ratio? I'd like to drive at a speed of 80 mph without killing my gas budget so are 4.10s are good gear for my application? I really just want to get the acceleration back as well as some MPG's to make this work, as I do plan on installing a 2.5 lift and know that will also effect my MPG.

If they are a good choice, what exactly will I need to complete the install? New Carriers? I plan on doing it myself and want to know what to get with budget in mind. I know they have those kits that come with new bearings and all the fancy hardware, but honeslty im pretty sure I shouldnt need those kits as the Jeep only has 20k miles on it. Let me know what you guys think.

shabbernigdo

i have 4.10s on my 2012 2 door and plan on going to 4.56. 4.10 isint bad but dont feel that great with 35s. i spend more time in 5th then i do 6th gear.

Gman*2007

Welcome to the forum 915JKU

nthinuf

The stock tires were 29"? And you did 'not' recalibrate the speedo for the new 33's, correct? So in addition to the speedo and odo being off, the mpg's are also reading lower than what you are actually getting?

Assuming that is the case, you might start with a programmer to set the proper tire size, (using the actual measured height, not what the tire mfg lists in the specs!), and gear ratio. Or a tuner which will also give you a minor hp/tq boost.

A d30 with 3.21's will need a new open carrier, or a full case limited slip or locker. (the rear d44 carrier is fine.) I think the d30 open carrier is around $90. A Detroit trutrac is the lowest priced traction device I am aware of, a bit under $400 at Summit. Most everyone is going to tell you to get master kits and new bearings, but that's totally up to you.

915JKU

Thanks bud!

915JKU

Thats exactly what I was afraid of, thats what im having now and its just with 33s.

915JKU

Had no idea a tuner was necessary for 33s, I mean I knew mph was going to be off but not by much that was going to make me go buy one you know? But the MPGs are calculated by hand, I learned to not trust the built in one once you get new tires unless you use a tuner.

But what kind of carrier does the D30 have right now? Is it something like the Trutrac or is it just an open carrier? Sorry about the questions, Im new to differentials. Pretty much I was just trying to have a similar setup to stock, eventually once the D30 dies on me, thats when I'll upgrade. Thanks for your information reply btw, is there a special brand you guys would recommend for the Ring and pinions? Any brands to stay away from? Thanks!

RFL83-13

As far as gear ratio is concerned, Rubicon's come stock with 4.10's. They have 32" mud terrains and they do fine. That being said, the rpm difference between 4:10 and 4:56 is less than 300. I have known people to run 4:10's on 35's and others who run 4:56's. In my opinion, I would run 4:56 if you plan on going to a 35" tire. Even if that's a year or two from now. It's a big and expensive job so you only want to do it once.
With 20k miles I would not worry about master kits, however I would look into shim kits for both front and rear axles. With the right tools you can transfer the inner pinion bearings and Dana 30 carrier bearings without damaging them. You will also need new crush sleeves for both front and rear axles. You may need to change your pinion shim for the new gears so having some fresh crush sleeves will be a good idea. I would also get new pinion seals for both axles. You could do some damage to the old ones while installing the new pinion. Also, on the front axle you will most likely have to remove the pinion seal in order to get the crush sleeve out. Behind the inner pinion race is an oil deflector and it tends to keep you from removing the stock crush sleeve. Once you remove the pinion seal and outer bearing you can retrieve the original crush sleeve.
I recommend Yukon or G2 gears. Good price and warrantee and well cut gears. Cheaper brands can potentially be harder to set up. Trust me, I know.
One more thing. When your transferring the spider gears on the stock Dana 30 carrier to the new carrier you will notice that the thrust washers behind the side gears are tapered. They put a little bit of pressure on the spider gears. It's due to poor machining of the carrier(called Dana to find that out). Ideally you can get flat thrust washers for a Dana30 and eliminate the tapered ones. A local diff shop or supply house should have some in stock. Used ones will work as well.
Take your time and be patient. Make sure your patterns are perfect and it will pay off in the end.

RFL83-13

Dana 30 has an open carrier stock. Personally I would stay away from Dana SVL, Motive, Richmond Excell, or any black box special.
Oh yeah, Nitro Gear in another good brand.

kmrtnsn

You should really be looking at 4.56.