So I got a new jeep (well 1998 new to me ;p) and was trying to confirm what i've found out so far. It has 30's in the front and 35 dana's in the back? Correct? 27 splined in the back? (coming from a toyota background so may be a little rusty here, heh). I'm looking to get a locker for it soon and was looking at this http://www.northridge4x4.com/proddetail.php?prod=EATON-TRUETRAC
But then I read that the rear-end is actually weak and should be replaced with dana 66, so would it be better to wait to a new end? Also from what I read my gear ratio is 3.73? or is it a 4.10? Thanks for your time and patience for a new jeep guy =)

Congrats!<img src="/forums/images/graemlins/kewl.gif" alt="" /> What model Jeep? I'll assume Wrangler. Stock gear ratio depends on which engine for one thing, A 4 cyl should have 4.10 stock, a 4.0 six should be 3.07 stock. These are the most common gears anyway. I never heard of a Dana 66, A dana 60 is overkill. A nice Dana 44 or Ford 8.8 or 9" are popular swaps, you are not likely to need anything stronger unless you plan on replacing the Front axle also and going Monster Jeep or something. How large of tires do you plan to run? What kind of Wheeling? These are the factors that determine if you might enjoy a locker in a D35 or be sentencing it to death by installing one. <img src="/forums/images/graemlins/cheers.gif" alt="" />

... just want to add, assuming your new Jeep is a Wrangler, that not all Wranglers came with a dana 35 for the rear axle. My 98 Wrangler Sahara has a dana 44 rear axle, and bigger R&P gears (7.37:1).

98 Wrangler 4.0L Sport Edition. And thanks i'm loving it so far. My main wheeling will be nothing like huge rock crawl's and such like that, but some mild occasionally. At the moment i've been reading alot on what people do after they break rear end and such (replace with the ford r new dana 44). Dana 66 (probably me not fully reading what web page i was on most likely..heh). I got about 1500 or so to spend on some upgrades, it has what I like to call stock (radial a/t's) that look to just be street tires. I want to get a lift and tires but that's a little out of the budget. So i've been reading up on northridge4x4.com and pirate along with here to get idea's. I'm unfortunately wouldn't say mechanic savy but learning. I also live currently in an area i cant' work on it so will be having to need to get the work done or i think i could squeeze both in (maybe) if i bought them myself, but the other half say's she want's it done professionally too. Any idea if i could get 31 or 32" tires under the stock and survive and still wheel till i get the lift or is it to cramped? Guy today said it would be rubbing up front and also said that i could still use my stock rims for the new tires..which really surprised me that it would fit. Any personal opinions would be greatly appercaited =). It also only had 69k miles on it when I got it, and the undercarriage looked like no one even took it over a blade of grass =)

I also seem to be getting mabye 15mpg..is that average or maybe I need to check something out everything seem's to be running in the correct ranges and it sounds like a new wrangler off the lot heh. I'll know for sure after I fill it up again tomorrow.

Of course gas mileage depends a good bit on driving habits. Based on your 15 mpg estimate, I'm guessing it's an automatic transmission. If so, 15 mpg is normal for city driving. The EPA estimate is 15-17 for the automatic, 17-20 for the manual. If you have the manual transmission, there is either something wrong or you drive like a maniac (or your estimate is wrong) <img src="/forums/images/graemlins/smile.gif" alt="" /> . it would be a good idea to check everything included in normal scheduled maintenance list like all fluids, filters, etc. Even though it may run like a new one, it's not, and who knows what has been done to it or where it's been. Chrysler says change the fluid and filter in automatic transmissions regularly, I have a service manual for your Jeep around here if you want details but unless you have solid documentation that proper maintenance has been done, you should do it. I would change the oil in EVERYTHING if it were mine. And be sure to use the right fluids when you refill. Proper air pressure in tires can help with mileage also. Check it if you haven't. I think you can fit 31 or 32 inch tires with a 2" budget boost lift. Check into them. don't expect larger tires to help with MPG though. Again, a lot depends on how you drive, running 32" tires on my CJ didn't hurt my mileage a bit (stock 3.31 gears, man. trans.) I drive like the old Grandpa I am though. Your results may vary! <img src="/forums/images/graemlins/lol.gif" alt="" />

One thing here Pete. You are driving around in a one to one final gear.. So your milage is not hurt as much when installing a slightly taller tire.
BUT the newer trannys with the overdrive gear start lugging when a taller tire is installed.. so milage is affected more in the newer Jeeps than the older ones.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Jim I had a T5 with overdrive. I used 5th gear anytime I was going over 50. There are other reasons the 258 in the old CJ does so well, it's not stock by any means. <img src="/forums/images/graemlins/cheers.gif" alt="" />

Yeah i'll know my estimate by this evening when I go to fill up, the records that i recieved showed everything was serviced when it should have been so that's a plus =). It's a manual and I dont drive like a maniac but I dont put around either.

Got 15mpg, half of it was probably city driving, not sure how much that effects..heh

You may have discovered why the last owner got rid of it! <img src="/forums/images/graemlins/lol.gif" alt="" /> I owned a 91 Wrangler (sold it too my brother), 4.0, 5 spd manual, 3.07 gears with 100k miles on it. I checked the mileage several times. 18-19 around town, 20-21 hwy. It's wearing 30" tires. Two things Jeeps are famous for are poor mileage and wide variations in mpg, I guess it's possible you have a lower gear ratio and that might explain less MPG and if that is the case you might gain mpg by going to taller tires. Other than that all I can think of to suggest is: Get used to it! <img src="/forums/images/graemlins/shiner.gif" alt="" /> <img src="/forums/images/graemlins/cheers.gif" alt="" />