I'm really impressed with the great feedback on this forum. The level of detail, and the overall wealth of information here is almost addicting.

I'm still trying to put an upgrade plan together for my 08 JK Rubicon 2-door. The more I read, the more questions I have to be answered.

I know the topic of re-gearing has been hit pretty hard here. There are a lot of different opinions. When I go to 35s, I'm still not sure what route I'll choose for the ratio.

I have an automatic, with 4.10 gearing. Because I'll be doing highway driving, I'm pretty certain that I won't be looking too close at 5.13s. I am considering 4.88s, or even 4.56s. But, as has been suggested in other threads, I will probably put some miles on it with the 35s and see how it feels to me.

That being said, I am preparing to re-gear. For those of you that have regeared, can anyone share their thoughts about the type of shop that did the work? (I understand that this isn't your typical DIY job.)

I live in Indianapolis, and am pleased with a transmission / rear end shop that has done differential work for me in the past. Should I be concerned about a shop that doesn't cater more to Jeep products? (I won't consider using them if they aren't familiar with the lockers.) Are there any set-up tools they might not have for Jeep work?

If not this type of shop, what's the best way to locate an experienced shop capable of doing the work? Should I stay away from the dealers? Anyone have experience around Indianapolis?

Thanks for any advice that can be shared.

Jeff

 

With an auto and 35's you will definitely want 5.13's, I've driven MANY highway miles with mine and definitely know 4.88's wouldnt be enough. You want loose any top end, I've easily cruised at 75-80mph running about 2600-2800rpm....4.56's would just be a complete waste of a lot of money to regear

I would definitely stay away from 99.99% of dealers for gear swap, they just dont have the experience.

 

Jeff,

You're still thinking old school on gears. You're thinking that lower rpm will mean better fuel economy. The JK wants to be between 2500 and 3000 cruising dn the freeway. I've got 5.13's and 35's and if I was doing it today I'd go with the 5.38's that are newly available. I'm at 2600 at 75 and would prefer to be at 2700-2800. 4.56's would be a complete waste of money. I've never encountered a person with 5.13's that wished they had gone with 4.88's instead. Virtually everybody I've talked to with 4.88's wishes they had went with 5.13's. Believe me, with an automatic 5.13's are a no-brainer. It's just about getting your cake and eating it too as you get the power and mileage. If you go with 4.56's or 4.88's you won't have the power and will get no better or less fuel economy.

 

GREAT INFO

so as of now you run 5.13, but if you had waited would have gone with 5.38? maybe these are what i will look at here in the near future when i get my 35's

 

There isn't anything special about doing a Dana rear end as opposed to a Ford or GM. The guys you trust are a better candidate than guys that specialize in Jeep stuff.

The right approach to gear selection is first rolling on what you already have. People who suggest you need 5.13s or 5.38s didn't listen to what you had to say and where you're from. A guy in Colorado will have more of a hill to deal with getting out of his driveway than you will find in the whole state of Indiana.

Where the JK likes to be RPM-wise is dependent on the rolling weight and what is sprung and unsprung weight. Heavier tires like the Toyo MTs are going to require a little more gear than some of the tire/wheel combinations that might weigh 20-25lbs less per corner. Bumpers, gear, winch, 2/4 door all will add weigh and with added weight a little more power/RPMs to keep it rolling efficiently.

Fuel efficiency wise, (2 door, 6 speed, long flat highway commute) my Jeep ran most effectively at 18-2000 RPMs before rolling on 35s. After the 35s I need an additional 2-300 RPMs to keep it happy, but again that's on the highway flats, without the big slam auto downshift going up Colorado grades. It's a different animal and rolling on your stock 4.10s for a while will tell you where you need to be way better than someone on the other side of the country.

One last thing. When the time does come to make the gear switch I would err on the steeper side. With all that you or anyone else does to their Jeeps there aren't many weight saving measures that will ever take place and it's not a job that you want to do twice. The primary detriment is a few hundred RPM and some fuel mileage but you'll never make up for the cost if you need to do it twice.

 

I could be completely wrong, but I'm thinking it wouldn't be the best idea to go with 5.38's with 35's simply 'cause once you get used to that combo, if you ever decide to step up to 37's you'll have nowhere to go gearwise to compensate for the extra tire size. If you go to 4.88's, then you'd have 2 levels to downgear to if you decide to step up in tire size and still one level to go if you opt for the 5.13's first.

Just my $.02 and you can take it for what it's worth.

 

Doing gears isn't a job I would want the expense of doing twice. There isn't any cost savings on doing it twice and if the ultimate goal is to run 37s when you have your gears installed get where you need to be the first time.

 

Sorry I'm new at all this. I have a 07 Unlimited. No tow package. Manual Transmission with 255/75R17 wheels and tire's. Im in Iraq so no access to my Vin. Wondering if anyone had a good Idea of what gearing I have? I have a Rock Krawler and 35's waiting for me.Wondering if I need to re gear. Thanks for any help you can give.

 

More than likely 3.73s or possibly 4.10s.

With the manual transmission the need for an immediate gear swap isn't as pressing as it is with an automatic. You'll probably lose 6th gear on anything other than the highway flats with 3.73s but not a big concern.

As mentioned in this thread and others, put a couple hundred miles on with the new wheels and tires before deciding on what gears to run. Again, the 6 speed is going to make a shallower gear set a lot more bearable in the short term.

 

The shop you want to use will be the one who tells you "it's not normal for gears to make noise. No how, no time, no where." ....and then back that up with a warranty against gear noise. Of course, if said customes does somethin stupid like get the Jeep in such a bind as to cause gear damage, then all bets are off. LOL