I own a 99' TJ. It currently has a 4'' suspension lift on it with 31'' tires. I am planning on putting on 35'' tires. The engine I have in now is a 4.0L. I still drive on the HWY with it, but I top out at 85 usually. If I were to put 35'' on my Jeep with still the 4.0L will it hurt the axels, or transmission? The speed will be reduced, that is a given, but to what extent? I am thinking putting in a 350 engine in, to help the HWY speed, but I am still on sure on the axel wear, if you could help me out that would be awsome.

Since no one else has responded ... i'll throw my inexpert opinion in.

i think you could keep it stock, but upgrade the axel gearing.  i read an article recently that indicated that most people don't go low enough when re-gearing axels.

There is a formula that will tell you what gearing you need to be in the 'power-band' of the engine with the transmission you run and the tire size you want.  I'm sure you could find it on the weeb, or perhaps someone could post it here.

i'm not sure what the cheapest way is to get decent hwy performance, but i suspect that even with a 350 you'd still need to re-gear.

as for the axels being hurt ... i don't think the stock axels are up to 35's.  depends how you use it.

Pete

  I've got an 02 Wrangler with a 4.0, 4 inch lift, 33 inch BFG allterrains.  I have had the lift and tires for about 2 1/2 years now.  As you could imagine, the power drop was pretty bad, and I contemplated an engine swap also.  But before I went that far, I bought a K&N air injection kit, throttle body spacer, JET stage 1 chip, Borla header, and a cat back exhaust. All easy bolt on parts, and alot cheaper than an engine swap.  I went from about 8 mpg to about 15mpg, and the power gains have been great also.  I use my Jeep mostly as a daily driver on the interstate and normally cruise at 75 no problem.  I also had 4.56 gears installed and it was well worth the money also(except for the whining noise that i gotta get fixed) The gear change alone will make a difference. Hope this helps, you won't be making v8 power, but you'll get by alot cheaper.   

Sounds like a good plan to me, but I am still wondering about my axels and if i put 35's on it. I won't be doing to much extreme offroading, mostly some trails, and mud pits, I'm still thinking that the axels might snap, can someone respond please?  

Well my two cents are yes you will snap an axel with 35s.  One of my buddies broke an axel with 33s driving through a ditch.  If you stick to the road and dont be to hard on it it will most likely hold up fine.  I would change the gears to 4.56 or 4.88. That would give you a good power feel and make it drive good on the street.  Thats just my two cents.      

well, this will make four cents...

i agree w/him, 33's require 4.56's in the axle.  35's require 4.88's, and thats exactly what i would run.  for the axle strength though, the front Dana 30 will usually hold up just fine with 35's and mild use, but the dana 35 rear, probly not.  Look for a Dana 44 out of a Grand cherokee--direct bolt in (TJ) and disc brakes, or a ford 8.8" with disc brakes--close to direct for a YJ (perch width).  both of these axles have good strength for mild offroading and install pretty easily.  Rubicon Express sells perches for tj's and yj's so you can just weld them on.
ak

You don't need a new engine.

Regear your axles.

When you go to a bigger size tire it "effectively regears" your Jeep.  You need to regear just to get back to where you were.

The problem is just that you have "effectively regeared" with the taller tires.  Also a slightly narrower tire will sacrifice a lot less to the friction gods on the highway.  Most folks overtire their Jeep anyway.  For all the stories of broken axles when was the last time you read a post about someone complaining about spinning tires even with lockers?

The biggest question to ask yourself is do I really take the Jeep off-road?

If you know in your heart that you just own the jeep to convey an "active, outdoor, lifestyle" image, then rest confidently knowing the Dana 35s will hold up 35s just fine on the road and the occasional fire road and you'll have the look  you want.

The no-lift TJ in JP magazine is runnin' 35s on a D35.

However, if you do even moderate wheelin' then you asking for disaster with that flexy 35.  The Dana 35 is not a strong axle by any means, however most folks don't really take their Jeep off-road they just want to look like they do.  You would be amazed at how many people go obsessive-compulsive with the Jeep and then try to get half their money back out of it once they realize they don't like the way it drives and they don't like jeepin' that much anyway.

What is your current ratio?  The 4.0L almost never came with even 4.10s.  The Explorer 8.8 swap might be ideal for you.  You can find brand new 8.8 rear ends for about $1000-1500 with the brackets already welded on for a TJ. Or you can go to a boneyard and scrounge up your own 95+ (disc brakes) Explorer 8.8 rear for unbelievably cheap. Look for a 4.10 ratio and limited slip the tag would read 4L10 to indicate the limited slip.  Don't pay over $350 as this axle is a dime a dozen and don't let the boneyard convince you the axle has a locker, it doesn't, they just like to use the word locker for limited slip. These are so common that if the calipers, rotors, or for that matter anything is missing  move on!

4.10 was common for the Explorer 8.8 so you would only need to regear the front to match. Rear disc brakes, 31 spline 1.32" axle shafts, and monster 3.25" tubes.  Weld the tubes to the housing, but there is some debate about full circle welds or just tacks top, bottom, front, and back.

While I agree that with 35s regearing is necessary it isn't true that for a given tire size a "right" gear ratio exists.  Heck, my 4-cylinder comes with 4.10 stock and with 33s I want 4.88.  That would be WAY overgeared (in my mind) for your 4.0L with 35s.  Keep in mind the trade-off on gears in a Jeep.  It's power or gas mileage, with a compromise in the middle.

Your engine makes plenty of power, heck, if you decide to do the engine swap I'll buy the engine, computer, and harness from you. There are so many tricks to getting HP out of a Jeep engine:

Try an AEM intake, good platinum plugs, super-low (less than 400 ohm) resistance wires, a brass dist. cap and rotor, a good aftermarket coil (Quadratec sells a great DUI kit though I prefer the MSD wires), have your throttle body and intake manifold machined out to 62mm to eliminate restriction, a hi-flow cat, a good set of headers (Banks, Borla), a cat back exhaust, swap in an electric fan (not the Taurus), and roller rockers.  Do that and you will be astounded with your I-6.

You can also stroke the thing with parts from the 4.2L.  It's possible to get so much power from that I-6 that you'll have to upgrade the transfer case just to handle it.  Don't give up on your 4.0.  It's not the engine but the context (gearing), heck the old Army jeep engines put out what, 90 HP?

Also never underestimate the importance of Synthetics.  Running Mobil 1 synthetics in the crankcase, differentials, transfer case, and transmission can help you realize 1-2 Mpg improvement right there and eliminate unecessary parasitic drag.  

An often overlooked benefit of converting to manual hubs is the elimiinattion of unecessary drag from turning the whole front end up to the transfer case.  Mods like this give you flexibility on the trail (break an axle dial out the wheel to spin freely, with a front locker you can still wheel out on three powered wheels), increased strength, and frees up the horsepower you are making to send it where you need it, the rear wheels on the road.