Sorry if this is a subject often beat to death but I couldn't really find what I wanted to know so.......right now I have stock axles with factory gearing. I am running 31" tires. All the charts I can find seem to point to a 4.11 gearing as optimum for my set up. How hard is this to do? Do the axles have to be swapped out to 44's? What is the general cost? How big a difference is this going to make with my little 4 banger? Please tell me everything you can think of about this subject. I have lots of time to read so write me some novels. BTW I don't really get to do much off-roading right now but will in the future. I don't really think I will be going any bigger than the 31"s right now. It is also my DD. Thanks guys.
What gear ratio came in your rig now? Do you feel with the 31's that your 4cyl is lagging power? The carrier break is at 3.73 an up (numerically) on the D30. So if you have 3.55s you have to replace the carrier as well (in the D30 not the 35 rear). Which begs the question: While I'm in here should I replace the carrier with a locker/limited slip? The answer to that question would be a resounding YES! Even though you said that you don't do much driving offroad, when you need both front wheels to turn; i.e. stuck in mud, one wheel off pavement, whatever, you would benefit from having at least a limited slip or lunchbox ( ex: Lock-right) type carrier.
Disclaimer: Never install a locker in a stock D35. Always upgrade the D35 to handle the extra stress from running a lockable/HD limited slip type carrier!
So assuming you have the proper carrier now for the gear change to 4.11s, you should consider the upgrade to the locking capabilities of your front end. Now as far as the proper gearing ratio goes, the charts give you the ratios for tire size to put you into the correct RPM range for your motor and driving style. You would ultimately want to be in the RPM range that you would balance performance with mileage. Or at least get back to stock performance. Not only for longevity of all the drivetrain components, but also for your driving pleasure and frustration reduction.
Some people go to the higher rpm range for the chart so that if they want to go slightly larger tires in the future they can. Also so they can get up into the power output range if they drive a lot of hills. This is all very subject to your area, driving style, percentage of offroad/pavement driving, etc. etc.
When you go to change the gears, I would have a professional install them that will offer you a warranty on their work and will give you proper break in procedure to follow. Typically these installers/shops have more confidence in the work and care that you get the best experience from your purchase. Installing gears, if you haven't done it and aren't comfortable with it, as mentione above, is risky and can very well get expensive on a learning curve basis. Since you said this is your daily driver, I wouldn't take the chance on doing it myself or let a friend do it that hasn't done many of them before. Most quality shops charge around $300 per axle and maybe less if you buy the gears etc from them. Call around, ask a lot of questions. Make a list of questions before you call so you can compare the answers you receive.
As far as the axles having to be switched out to 44s, the answer is no. there is no reason I can see, from what you posted, that should need to go to 44s. If in the future you desire to get into some more serious wheeling, then consider 44s. Now if you can find a Rubicon 44 front that someone is swapping out for a D60 for a reasonable price, go for that, Barring the quality of the axles condition, trustworthiness of the seller, possibly having a shop look at it, budget, etc etc. Obviously you have to take into consideration that both axle gears have to be changed at once.
Changing gears to make the final drive ratio correct for all the above reasons is one of the most "bang for the buck" upgrades you can do, especially after changing tires to larger dia. You will get your performance and mileage back.
Plan, think, ask question, plan! Do it once for your current and future driving needs.
I can sell you 4.11s f/r with install kits for $490 plus applicable taxes and shipping. These are 8620 heat treated alloy gears with 2 yr warranty. Call around for pricing. Ask questions again and compare.
Good luck on your build.
Allen
